I’m working on a home design and wanted to ask for any constructive comments the community might have. We are looking to build a very well-insulated envelope with a straightforward process that most building crews could implement. Cost is not the primary factor, insulation-value and durability is. This is in climate zone 5.
I’ve attached my first pass at a shingle roof (RF-1) and stucco wall (PL-1). The basic concept I am working with is that the exterior Zip sheathing on walls/roof is our weather barrier that will dry to the exterior. The interior side of sheathing and framing would be coated in a generous pass of closed-cell spray foam, creating an impermeable air layer. This prevents the condensation issue of interior vapor reaching the exterior sheathing. Extra space in the cavity would be filled with readily available batt insulation.
Walls get Zip R12-Sheathing for the thermal break. The roof gets a layer of rigid foam on the interior side for a thermal break. I looked at options for applying foam to the roof exterior (Nailbase, for ex.) but I thought it would be simple to detail and construct a continuous weather barrier between the Zip R wall sheathing and Zip roof sheathing if I kept it exposed. Would it also be problematic to layer additional rigid insulation on the exterior roof sheathing as it might inhibit drying of the Zip sheathing underneath?
I’ve attached some detail drawings showing what I currently have.
Thanks for any comments. I read another similar thread recently and thought I would throw my hat in the ring for constructive comments.
Non Sequitur
Mar 21, 21 7:48 am
6” of spray-foam is the lazy answer to wall construction IMO. Also, how is that sheathing fastened to the studs through 2” spray? Anyways, stucco is also a bad choice, ditto if cost is not a concern.
b3tadine[sutures]
Mar 21, 21 8:54 am
Why the hate on the stucco? I mean as long as it's not synthetic.
Non Sequitur
Mar 21, 21 9:13 am
The 7/8 thickness seems to me to be a problem. It’s going to need careful detailing to avoid cracks and I’m not sure the sheathing is strong enough substrate since it’s not directly fastened to studs.
kjpn
Mar 21, 21 6:27 pm
Hi NS, the details show 4" of cc spf on interior side of walls and roof sheathing, which could be layered in a single pass of foam. The 2" on exterior side of wall sheathing is rigid foam (look up Zip R-sheathing). You use longer 4" fasteners to nail through the 2.5" product to the studs, so sheathing is secured directly to structure. I also questioned if Zip R-sheathing was compatible with stucco given the weight of the finish and somewhat distended attachment of sheathing to studs. Sure enough, there are details on Hubers technical library showing traditional hardcoat stucco on their Zip R-sheathing.
kjpn
Mar 21, 21 6:37 pm
Also to clarify behind the layer of cc spf would be mineral wool or fiberglass batt in the remainder of the cavity
spanky82
Mar 22, 21 12:51 am
What is lateral system for the building?
kjpn
Mar 22, 21 1:35 am
Zip R-sheathing (walls) and Zip sheathing (roofs). The engineer will have to check that the Zip R is going to work for walls as in some cases additional bracing is requ
ired.
Non Sequitur
Mar 22, 21 8:06 am
So did your office get a lunch & learn presentation from zip before you made these? I know what the system is but never used it myself.
spanky82
Mar 22, 21 9:06 am
RE: lateral system and your walls. Ok, well, I haven’t seen insulation between OSB sheathing and wood studs in a shear wall. What do you mean by “additional bracing”?
kjpn
Mar 22, 21 11:12 am
Stud walls with diagonal bracing?
Apparently Zip R sheathing has a different shear wall aspect ratio than directly attached sheathing, so if it's within an acceptable range in this application we would not need additional lateral bracing.
b3tadine[sutures]
Mar 21, 21 8:58 am
I'm curious. Why would the stucco system need a drainage plane?
This seems like a rather expensive system, when I'm pretty sure it's not required. You could do a calculated U value. I say that because you end up finishing the roof with asphalt shingles??
Non Sequitur
Mar 21, 21 9:16 am
We do our share of stucco assemblies and they are always treated as rainscreens or with a system that provides draining behind the foam sub. Better to provide moisture control redundancies than rely on a face-sealed system.
Yes, I would like to have used slate tiles but the shingles were deemed easier to maintain and less expensive. Check out Delta Dry for an example of the product type I had in mind.
Chad Miller
Mar 22, 21 10:23 am
NS and b3t - one thing we've found that that a three part stucco system with metal lath needs two (2) layers of building wrap as the first layer is destroyed by the stucco after about 5 years.
b3tadine[sutures]
Mar 22, 21 10:47 am
I'm asking because my house is going to hit the century mark on six years, and the system seems to be doing well, in minnesota.
Non Sequitur
Mar 22, 21 10:54 am
^perhaps things were done differently/better 100 years ago? Do you have deep overhangs that shield most of the rain from the walls?
b3tadine[sutures]
Mar 22, 21 1:40 pm
I've got a craftsman with exposed rafters, about 18"-24" deep. I definitely think things were different, my house isn't clad with plywood, or osb, I think that has a lot to do with the situation.
Chad Miller
Mar 22, 21 1:55 pm
I think it's because of of a couple of factors b3ta. First the stucco used 100 years ago was different today. It was nearly impermeable whereas today stucco is permeable. Second, back then the weather barriers used where typically asphalt paper that was installed two layers thick with staggered joints. The stucco destroyed the first layer of weather barrier which leaves a slight gap between the stucco and the second layer of weather barrier. This acts as a drainage plain.
BlazeFoley
Mar 23, 21 2:25 pm
Consider a product like Kingspan GreenGuard DC14
Drainage Mat behind the Stucco assembly. Stucco only acts as a rainscreen.
BlazeFoley
Mar 23, 21 2:40 pm
Also consider using screws for attaching Zip R instead of nail fastener's.....to mitigate the offset of structural anchoring.
As for your nearly 100-year old home, I think it mostly comes down to one thing ... energy movement through the walls. I'd bet money that your nearly 100-year old walls aren't exactly over insulated, nor air tight. This means that a lot of energy moves through your walls. As it does that, it ends up taking a lot of that water stored in the reservoir cladding with it. As long as the drying exceeds wetting, you'll be fine, especially since is sounds like you don't have a lot of chopped up bits of wood that the mold and fungus likes to eat when it's wet (i.e. OSB). Now if you were to go crazy with the caulk (remember to post pics to the "show us your caulk" thread) and start sealing up all your walls making them air tight, and maybe even adding R-value in some way without messing with the cladding ... you might start to run into issues (hard to say for sure without knowing about the wetting of your assembly) because you'd be decreasing the ability for energy to move through the assembly and thereby dry out. For the sake of continuing this hypothetical, you could also decrease the wetting by maintaining a paint film on your stucco or extending overhands or something if you needed to rebalance the wetting and drying equation.
I mentioned in TC the other day that I want to better seal up and insulate my exterior walls in my home at some point. I'll be replacing the cladding during that process but my current cladding is also a reservoir cladding (wood siding). If I use wood siding on my walls after I better seal and insulate them, I'll be sure to use a drainage space behind the siding increasing the ventilation and it's ability to dry. Of course, I'd also be painting the wood thereby slowing the wetting as well.
b3tadine[sutures]
Mar 23, 21 5:50 pm
Oh, I've seen the "insulation" in my walls. Original to the home. So is the lath and plaster. Yet, my energy bills are not outrageous. I suspect a couple of things are at play. My roof, is awful. Same horrible insulation. Summers and winters suck. My saving grace is my gigantic oak, with tree canopy shading the bulk of my roof on the south west, and the neighbors oak on the north east side of my home.
mightyaa
Mar 23, 21 7:04 pm
And the ZIP system has an issue. Penetrations in it leak and there is no redundancy with a zip system like flashings being shingled behind the drainage plane. Once water get past the face, it is behind all your flashing. But with the drainage plane and felt layer (required by ZIP with stucco) it will help mitigate a lot of that. The flashings and weeps can be integrated behind that felt and the drainage plane will encourage moisture transport instead of allowing saturated conditions around those penetrations.
kjpn
Mar 21, 21 6:37 pm
I just realized that the image upload really butchered the JPG quality so no one can see the image. Here is a better version hopefully.
Chad Miller
Mar 22, 21 10:19 am
Still rather small to read.
natematt
Jul 15, 22 9:08 pm
Am I the only one who thinks it's odd to just apply paint as the standard condition for stucco rather than an integral color?
Chad Miller
Mar 22, 21 10:31 am
One thing I'll mention is that you really need to calculate the dew point in those wall and roof assemblies.
Right now you've got three unseparated types of insulation, rigid, ccf spray, and fiberglass batt. Each of these have varying R-values and perm ratings.
With the assemblies you've shown you have a high chance of having issues with condensation occurring inside the wall / roof assembly.
Non Sequitur
Mar 22, 21 10:52 am
Not to mention that it's quite a bit of coordination for what is at the end of the day a regular stucco and asphalt finish. I do question the OP's understanding of spray-foam when they claim 4" can be done in a single pass. In my exp, that depth requires 2 at least but we've also distanced ourselves from using spray as a main insulator so perhaps things are different today?
Side point, is there a 6mil poly vapour retarder in those details? I can't really them.
kjpn
Mar 22, 21 11:06 am
(
Chad see below)
NS, I am looking at this product for spray foam. Check out the product details... and no, I don't have a vapor retarder shown as the cc spf is a vapor barrier.
kjpn - I'm aware that CC spray foam can act as a vapor BARRIER. For example - I'm in climate zone 5 just like you. We did a project where we did extensive energy modeling and dew point calculations. We found that using continuous R-15 POLYISO insulation and R-3 CC spray foam on the inside of the studs worked very well. The closed cell foam was only used to seal the exterior wall penetration's and act as vapor RETARDER (NOT a vapor BARRIER). This only worked because we had no blanket insulation in the wall cavity and the continuous POLYISO's dew point occurred outside of the exterior wall sheathing. In the details you have shown you're going to get a dew point INSIDE your exterior envelope.
The product you linked acts as an air barrier and vapor barrier. Not a vapor retarder.
kjpn
Mar 22, 21 1:18 pm
Hey Chad, doing a 'flash' layer with cc spf will create a retarder not a barrier which is what you're explaining, I think. I think your wall assembly functions quite differently for that reason. Would love to see a detail to understand your design's
rationale further.
Chad Miller
Mar 22, 21 1:33 pm
I understand that kjpn. What I'm trying to say is the product you're using is a vapor barrier and so will the continuous insulation you're using. The wall system you have shown will have a really hard time drying out.
Chad Miller
Mar 22, 21 1:37 pm
Here are the wall system that you wanted to see . .
A few things to point out.
1. No exterior sheathing - the rigid insul and mtl strapping are providing the diaphragm needed.
2. The spray foam is acting as a vapor retarder.
3. No insulation in the stud cavity other than mineral wood to serve as req'd fire blocking and prevent energy loss at the edge of the roof insul.
4. These assemblies ARE NOT PERFECT. However they will perform at least as good as what you've shown and won't have any water vapor issues.
.
kjpn
Mar 22, 21 11:06 am
Hi Chad, thank you it would be educational for me to go through that process; I'll do that.
But my understanding is that if properly installed, the closed cell spray foam will negate the risk of condensation inside the wall cavity as well as at the exterior sheathing as it is a total vapor barrier and will not permit cold air or warm air through it. The exterior sheathing is distanced from any interior vapor doubly so by the layer of R-sheathing foam. And there is nothing cold on the interior side of the spray foam to generate condensation. The would studs will be kept warm enough via the spray foam and exterior R-sheathing foam.
Chad Miller
Mar 22, 21 11:53 am
It depends. The interior of you building will produce water vapor.
Wood Guy
Mar 23, 21 3:07 pm
For roofs in climate zone 5, you need at least 40% of the total R-value to be in the exterior, impermeable layer for the IRC to allow only a class 3 vapor retarder on the interior--meaning it's relatively safe from moisture accumulation.
I can't read the values you used on your images but since this is a moisture issue and not just a "let's get a permit" issue, I use the aged R-values: 4" of closed-cell foam is about R-24, 5.5" of fiberglass is about R-19 and 2" of XPS is about R-9, leaving you with about 45% of the R-value in the exterior layer. (I know it's a flash layer and not exterior insulation, but the calculations are the same.) So in theory, even if moist, indoor air gets into the fiberglass, the interior surface of the spray foam SHOULD be warm enough to prevent condensation. But it's much safer to allow drying to either the interior or exterior, and preferably both.
You are also using complicated assemblies with very high carbon emissions--XPS is about the worst product you can use for climate change. If you switch to the much more benign EPS, you will get some drying to the interior, and similar R-values--EPS remains R-4/in while XPS ages to about R-4.3/in.
My personal opinion is that having to resort to foam when building new, above grade, is a failure of design--there is always a way to insulate safely that will perform as well as foam with lower emissions. But that's another argument.
kjpn
Mar 23, 21 6:51 pm
Thanks for your comments Woodguy. Yes because of the depth of sprayfoam I'm showing there should not be condensation risks.Thank you for pointing out the difference between XPS and EPS, I'll look further into it as I would like to lower the embodied carbon of the assembly as much as possible.
As for the emissions of spray foam, I am specifying a product called Gaco One Pass that is Greenguard gold certified and does not cause greenhouse gas emissions when blown. The foam itself is manufactured from recycled and renewable materials.
Wood Guy
Mar 23, 21 7:20 pm
Kjpn, you have to be very careful with foam marketing--they are consistent about obfuscation, diversion and misinformation.
Gaco OnePass is advertised as having zero ozone depleting potential, which just means that it meets a law that has been in place for over a decade for all foam we use in construction. It has a conventional HFC blowing agent which is only outdone by the blowing agents in XPS in terms of negative climate impact. It's great that they replaced some of the resin with naturally derived resin but it's a drop in the bucket compared to the blowing agent impact.
Wood Guy, fantastic article. It is the most thorough and clear explanation of the dynamics behind condensation and using spray foam that I have found (and I've been doing a lot of digging lately).
Archinect needs to create content and resources like this pertaining to building science. It's a huge gap and opportunity imo.
kjpn
Mar 22, 21 1:07 pm
Hi Chad, I used WUFI light to model the wall assembly to doublecheck my rationale. Attached is a readout showing the moisture content in the wall assembly across a calendar year. Also there's a second readout showing potential for mold growth.
This shows a very stable wall assembly with no risk for condensation (no intersection of RH and temperature, ie dew point). The moisture content shown in the OSB is hovering at about 15-16% (within acceptable range). The whole home is humidified and air conditioned as well which is factored into the model.
I will play around with other options now, however - this software is very cool.
Chad Miller
Mar 22, 21 1:22 pm
That's great. I get what you're trying to do however there are several assemblies that are much simpler to install that will perform just as good or better. What you've proposed is an overly complex assembly with multiple failure points that requires the coordination of several trades that will be working literally on top of each other. If one of those trades dose anything incorrect then the entire assembly will fail.
Again I applaud you for wanting to create a high performance assembly and doing all this work. I just caution you that it needs to be easily built without relying on everything being installed perfectly.
EDIT:
Also be sure to run those calculations through your wall and roof framing. They will probably be OK however you need to make sure as a large presentence of exterior area will be at a framing member.
Jay1122
Mar 22, 21 3:20 pm
Ha, Look at you guys dueling it out. The 4" closed cell spray is less than 1 perm so it will be a vapor retarder. The Zip sheathing system will likely be another kind of air vapor retarder. What you want to avoid is trapping moistures in between them. Dew point analysis will help to know where it occurs. High perm assembly allows vapor to escape back out. Assuming vapor barrier is perfect is not a good practice. The small amount of vapor may still pass through the wood stud, or poor workmanship during installation. Whether this assembly will work, I do not know. Probably will.
What I don't get is why introduce 3 types of insulations. Isn't the point of zip sheathing all in one system being faster installation and less labor saving $$. It is serving as AWB, sheathing, CI. I would just use mineral wool batt inside the cavity. Apply vapor barrier/retarder as required by code and standard practice in that climate, whether class 1,2 or 3. I think it is inside the face of wall for cold climate.
Chad Miller
Mar 22, 21 3:32 pm
Actually Jay, the spray foam has a perm rating of less than 0.1 so it's a vapor barrier.
Jay1122
Mar 22, 21 3:36 pm
quick google gives me "Closed cell foam typically has a perm rating less than 1 perm for 2” of depth." Anyway, you guys continue.
Chad Miller
Mar 22, 21 4:34 pm
Your point?
kjpn
Mar 22, 21 7:04 pm
Jay, thank you for your commentary. You raise an important and accurate point about the WATER VAPOR permeability of cc spf which appears to be 1.7 perm-in. I had it wrong, and was confusing it with the AIR permeability of cc spf which is 0.01. In summary it is an air barrier not a water vapor barrier. And of course that is consistent with the moisture modeling I did earlier today. It is showing the moisture penetrating the cc spf over time. Appreciate the
comments!
kjpn
Mar 22, 21 11:30 pm
Actually, I wanted to add a correction to my reply for posterity's benefit. The water vapor permeability changes as the depth of the cc spf increases. the product I am specifying (Gaco Onepass) has the following values (.44" = 1.0 p, 1.0" = .44 p, 2" = .22 p, 3" = .15 p, and 4" = .11 perms). So 4+" is about as permeable as a class II vapor retarder
Chad Miller
Mar 23, 21 10:43 am
Nice catch about the VR of the spray foam kjpn! I'm sorry that I misread the product data sheet and thought it was a VB.
Keep in mind that:
</= to 0.1 perm is vapor barrier
> 0.1 through 1.0 perm is class II vapor retarder (semi permeable)
> 1.0 - 10 perms is a class II vapor retarder (permeable)
Chad Miller
Mar 23, 21 10:59 am
Jay - you do realize that everything you posted was already said in the posts above you?
Jay1122
Mar 22, 21 4:13 pm
Why is there 2" XPS rigid insulation under roof framing? If you want CI shouldn't it be on top. Serving as another backup protection. I know it all works. But why would someone doing shingle roof spend extra $$ and complicate things. I would use that extra $$ and do standing seam metal roof, looks much better and much more durable.
kjpn
Mar 22, 21 7:06 pm
Jay, I avoided the insulation on top primarily for moisture concerns. I thought that layering rigid insul on top of this sheathing, with cc spf behind it, would be trapping moisture in the sheathing and not allowing it to dry out to either side. I began the whole assembly design with cc spf as a premise so if that is removed I think more options present themselves..
Jay1122
Mar 23, 21 10:37 am
I feel its just overcomplicating things. Its just a simple shingle roof. What I would do is probably Batt insulation in stud cavity. Then 4" Rigid insulation on top of sheathing. Then Cover board on top of rigid insulation. There is also the Polyiso with built in cover board for sale. Then roof membrane and shingle/metal panel. Who spends that money for shingle roof is beyond me. I would do low slope roof with that money.
The insulation values are pretty much passive house standards. Do you have your HRV/ERV system ready. This seems like a rather high performance house. Why do you not want some better curb view appeals to help with resale value? Shingle roof+Stucco screams cheap 2x4 stick to me.
JLC-1
Mar 22, 21 6:31 pm
I have a similar problem that we have not been able to address because of the lack of testing of fire rated assemblies with zip panels; 2x6 wall, r-20 for cavity, r-5 for continuous, 1 hr rated, wood siding.
The fire rating threw a wrench on this last year, but until we try to change the ordinance, there's no listed assembly we can use.
very stupid in my opinion to add this fire rating to sfr where most have to be completely sprinkled.
bobbray
Jul 15, 22 3:48 pm
We're building a new home and in a couple of weeks and Zip-R12 sheathing will be installed. My question is around window openings. Would it be better to leave the insulated sheathing short of the jack (trimmer) studs and use 2-7/16 x 1-1/2" furring boards on top of the jack studs so the window nailing flanges have solid wood to nail to or just nail though the 2-7/16" thick sheathing into the jack studs using 4" nails?
I'm concerned that the framers might not get the R-12 sheathing up tight to the furring boards and leave gaps that will need to be foamed before using Zip tape. Huber says it's OK to nail through with 4" long nails around windows but my builder is concerned that the windows might not adhere long term to the wall and could move with any movements of the sheathing due to 2" of foam sandwiched between. With furring boards, I'd lose the exterior insulation over the jack studs and top/bottom around all windows. My builder doesn't think that's a big deal. It's my call, of course. My windows are very large with some 132" x 72" high.
What are people's thoughts on this?
proto
Jul 15, 22 4:21 pm
your architect is the best resource for your project
Wood Guy
Jul 17, 22 11:04 am
I don't like using Zip-R sheathing for several reasons and this is one of them. I have several different details, depending on the situation, but even being very conscious of energy performance, I prioritize long-term building durability.
With conventionally-sized windows I would be fine with nailing through the Zip-R, but for oversized windows like yours I would probably use solid blocking. I say "probably" because there are several other variables: are you using a rain screen, what are the interior and exterior trim details, what are the flashing details, how much do you trust your builder, is your builder familiar with fastening Zip-R12 with 4" gun nails without setting the nails too deeply, what are the window frames made of, etc..
Generally speaking, the other commenters are right; this is a forum for design pros, not for homeowners to ask questions, and your question is absolutely something a competent architect should be able to answer. But Zip-R is not well understood by the vast majority of residential architects (and builders) I know. You might try searching or asking at greenbuildingadvisor.com where this type of question is common.
bobbray
Jul 16, 22 5:48 pm
proto, an architect is not the place to ask this question. Huber is and I'm looking for those who have used Zip-R12 on what they did, as it can be done either way. Home architects design stuff but rely on structural engineers for loads and stress, as I've needed to use them for concrete walls and roof trusses in questionable areas.
Thanks for your awesome help though...POS
proto
Jul 16, 22 7:28 pm
lol
Richard Balkins
Jul 16, 22 10:49 pm
Consult your architect, and the construction contractor. Asking us who are not in contract with you is a waste of time. We aren't going to give you free professional advice beyond consulting the professionals you have. If they can't provide meaningful advice on the matter they should bring in a consultant. If they still can't provide meaningful advice then replace them with more qualified professionals.
Richard Balkins
Jul 16, 22 11:04 pm
The stuff above before you came along here is inter-dialogue between professionals. You are a client seeking for free the professional advice we bill clients for. Understand the business of architecture. We don't give for free to clients what we charge them for. You're not an architect, are you? You sound like a home owner who is trying to bypass consulting the professionals they have. Giving you advice directly to your project is placing liability on us to whom we are not getting paid. The OP of this thread is a professional so he/she's already bears liability to that project and would assume any responsibility for his/her decision. Any professional advice we give you for free.... specifically to what you are asking for, means we can be sued by you if there is issues associated to it because you are relying on our professional advice to you. You are not compensating any of us for professional liability insurance coverage for the next 10-20 or more years (for the duration of the statutes of limitations and statutes of repose) for your project. Now, I want my 5-cents.
Richard Balkins
Jul 16, 22 11:05 pm
For context of reference about the "5-cents":
Richard Balkins
Jul 16, 22 11:12 pm
5 cents a word, I would be rich.... especially with epic walls of text.
natematt
Jul 17, 22 11:13 am
"proto, an architect is not the place to ask this question." ... Why was this asked on Archinect then?
proto
Jul 17, 22 11:39 am
Exactly…lotta attitude/arrogance brought out from a pretty simple response. Guessing guy doesn’t actually have an architect on the project & apparently doesn’t know what an architect does. Always fun when owners are trying to figure out problems during construction that could have been figured out during design had they been willing to put a minimal amount of project fee to professional services.
Richard Balkins
Jul 18, 22 7:41 pm
I agree with you and nate. There's even professional building designers who (even if not a licensed architect) should be able to resolve this issue had the person consulted the professional they have, already, supposedly. Now it appears that "Huber" that is referenced in not an architect who's last name is Huber but the product manufacturer (Huber Engineered Wood). This means that they probably have an engineer on staff much like truss manufacturers and other engineered product manufacturers. In this case, the manufacturer's engineer on staff with a license should be the one to send his/her question to.
“Now it appears that "Huber" that is referenced in not an architect who's last name is Huber but the product manufacturer (Huber Engineered Wood).“
Balkins, I try not to be unnecessarily mean to people on here, but you really are out of your depth here. It is seriously cringey to witness how oblivious you are to it too, especially with the number of words you’ve pushed onto this page pretending to be an expert of some kind and speaking for architects. You’ve added nothing to this particular discussion.
Hello,
I’m working on a home design and wanted to ask for any constructive comments the community might have. We are looking to build a very well-insulated envelope with a straightforward process that most building crews could implement. Cost is not the primary factor, insulation-value and durability is. This is in climate zone 5.
I’ve attached my first pass at a shingle roof (RF-1) and stucco wall (PL-1). The basic concept I am working with is that the exterior Zip sheathing on walls/roof is our weather barrier that will dry to the exterior. The interior side of sheathing and framing would be coated in a generous pass of closed-cell spray foam, creating an impermeable air layer. This prevents the condensation issue of interior vapor reaching the exterior sheathing. Extra space in the cavity would be filled with readily available batt insulation.
Walls get Zip R12-Sheathing for the thermal break. The roof gets a layer of rigid foam on the interior side for a thermal break. I looked at options for applying foam to the roof exterior (Nailbase, for ex.) but I thought it would be simple to detail and construct a continuous weather barrier between the Zip R wall sheathing and Zip roof sheathing if I kept it exposed. Would it also be problematic to layer additional rigid insulation on the exterior roof sheathing as it might inhibit drying of the Zip sheathing underneath?
I’ve attached some detail drawings showing what I currently have.
Thanks for any comments. I read another similar thread recently and thought I would throw my hat in the ring for constructive comments.
6” of spray-foam is the lazy answer to wall construction IMO. Also, how is that sheathing fastened to the studs through 2” spray? Anyways, stucco is also a bad choice, ditto if cost is not a concern.
Why the hate on the stucco? I mean as long as it's not synthetic.
The 7/8 thickness seems to me to be a problem. It’s going to need careful detailing to avoid cracks and I’m not sure the sheathing is strong enough substrate since it’s not directly fastened to studs.
Hi NS, the details show 4" of cc spf on interior side of walls and roof sheathing, which could be layered in a single pass of foam. The 2" on exterior side of wall sheathing is rigid foam (look up Zip R-sheathing). You use longer 4" fasteners to nail through the 2.5" product to the studs, so sheathing is secured directly to structure. I also questioned if Zip R-sheathing was compatible with stucco given the weight of the finish and somewhat distended attachment of sheathing to studs. Sure enough, there are details on Hubers technical library showing traditional hardcoat stucco on their Zip R-sheathing.
Also to clarify behind the layer of cc spf would be mineral wool or fiberglass batt in the remainder of the cavity
What is lateral system for the building?
Zip R-sheathing (walls) and Zip sheathing (roofs). The engineer will have to check that the Zip R is going to work for walls as in some cases additional bracing is requ ired.
So did your office get a lunch & learn presentation from zip before you made these? I know what the system is but never used it myself.
RE: lateral system and your walls. Ok, well, I haven’t seen insulation between OSB sheathing and wood studs in a shear wall. What do you mean by “additional bracing”?
Stud walls with diagonal bracing? Apparently Zip R sheathing has a different shear wall aspect ratio than directly attached sheathing, so if it's within an acceptable range in this application we would not need additional lateral bracing.
I'm curious. Why would the stucco system need a drainage plane?
This seems like a rather expensive system, when I'm pretty sure it's not required. You could do a calculated U value. I say that because you end up finishing the roof with asphalt shingles??
We do our share of stucco assemblies and they are always treated as rainscreens or with a system that provides draining behind the foam sub. Better to provide moisture control redundancies than rely on a face-sealed system.
B3, this is why: https://www.buildingscience.com/documents/building-science-insights/bsi-112-drain-rainon-planethe-drainage-plane
Yes, I would like to have used slate tiles but the shingles were deemed easier to maintain and less expensive. Check out Delta Dry for an example of the product type I had in mind.
NS and b3t - one thing we've found that that a three part stucco system with metal lath needs two (2) layers of building wrap as the first layer is destroyed by the stucco after about 5 years.
I'm asking because my house is going to hit the century mark on six years, and the system seems to be doing well, in minnesota.
^perhaps things were done differently/better 100 years ago? Do you have deep overhangs that shield most of the rain from the walls?
I've got a craftsman with exposed rafters, about 18"-24" deep. I definitely think things were different, my house isn't clad with plywood, or osb, I think that has a lot to do with the situation.
I think it's because of of a couple of factors b3ta. First the stucco used 100 years ago was different today. It was nearly impermeable whereas today stucco is permeable. Second, back then the weather barriers used where typically asphalt paper that was installed two layers thick with staggered joints. The stucco destroyed the first layer of weather barrier which leaves a slight gap between the stucco and the second layer of weather barrier. This acts as a drainage plain.
Consider a product like Kingspan GreenGuard DC14 Drainage Mat behind the Stucco assembly. Stucco only acts as a rainscreen.
Also consider using screws for attaching Zip R instead of nail fastener's.....to mitigate the offset of structural anchoring.
Thank you, good suggestions
b3ta, here's another to add to your reading list of why you want a drainage plane for stucco claddings: https://www.buildingscience.com/documents/information-sheets/reservoir-claddings.
As for your nearly 100-year old home, I think it mostly comes down to one thing ... energy movement through the walls. I'd bet money that your nearly 100-year old walls aren't exactly over insulated, nor air tight. This means that a lot of energy moves through your walls. As it does that, it ends up taking a lot of that water stored in the reservoir cladding with it. As long as the drying exceeds wetting, you'll be fine, especially since is sounds like you don't have a lot of chopped up bits of wood that the mold and fungus likes to eat when it's wet (i.e. OSB). Now if you were to go crazy with the caulk (remember to post pics to the "show us your caulk" thread) and start sealing up all your walls making them air tight, and maybe even adding R-value in some way without messing with the cladding ... you might start to run into issues (hard to say for sure without knowing about the wetting of your assembly) because you'd be decreasing the ability for energy to move through the assembly and thereby dry out. For the sake of continuing this hypothetical, you could also decrease the wetting by maintaining a paint film on your stucco or extending overhands or something if you needed to rebalance the wetting and drying equation.
I mentioned in TC the other day that I want to better seal up and insulate my exterior walls in my home at some point. I'll be replacing the cladding during that process but my current cladding is also a reservoir cladding (wood siding). If I use wood siding on my walls after I better seal and insulate them, I'll be sure to use a drainage space behind the siding increasing the ventilation and it's ability to dry. Of course, I'd also be painting the wood thereby slowing the wetting as well.
Oh, I've seen the "insulation" in my walls. Original to the home. So is the lath and plaster. Yet, my energy bills are not outrageous. I suspect a couple of things are at play. My roof, is awful. Same horrible insulation. Summers and winters suck. My saving grace is my gigantic oak, with tree canopy shading the bulk of my roof on the south west, and the neighbors oak on the north east side of my home.
And the ZIP system has an issue. Penetrations in it leak and there is no redundancy with a zip system like flashings being shingled behind the drainage plane. Once water get past the face, it is behind all your flashing. But with the drainage plane and felt layer (required by ZIP with stucco) it will help mitigate a lot of that. The flashings and weeps can be integrated behind that felt and the drainage plane will encourage moisture transport instead of allowing saturated conditions around those penetrations.
I just realized that the image upload really butchered the JPG quality so no one can see the image. Here is a better version hopefully.
Still rather small to read.
Am I the only one who thinks it's odd to just apply paint as the standard condition for stucco rather than an integral color?
One thing I'll mention is that you really need to calculate the dew point in those wall and roof assemblies.
Right now you've got three unseparated types of insulation, rigid, ccf spray, and fiberglass batt. Each of these have varying R-values and perm ratings.
With the assemblies you've shown you have a high chance of having issues with condensation occurring inside the wall / roof assembly.
Not to mention that it's quite a bit of coordination for what is at the end of the day a regular stucco and asphalt finish. I do question the OP's understanding of spray-foam when they claim 4" can be done in a single pass. In my exp, that depth requires 2 at least but we've also distanced ourselves from using spray as a main insulator so perhaps things are different today?
Side point, is there a 6mil poly vapour retarder in those details? I can't really them.
( Chad see below)
NS, I am looking at this product for spray foam. Check out the product details... and no, I don't have a vapor retarder shown as the cc spf is a vapor barrier.
https://gaco.com/product/gacoo...
kjpn - I'm aware that CC spray foam can act as a vapor BARRIER. For example - I'm in climate zone 5 just like you. We did a project where we did extensive energy modeling and dew point calculations. We found that using continuous R-15 POLYISO insulation and R-3 CC spray foam on the inside of the studs worked very well. The closed cell foam was only used to seal the exterior wall penetration's and act as vapor RETARDER (NOT a vapor BARRIER). This only worked because we had no blanket insulation in the wall cavity and the continuous POLYISO's dew point occurred outside of the exterior wall sheathing. In the details you have shown you're going to get a dew point INSIDE your exterior envelope.
The product you linked acts as an air barrier and vapor barrier. Not a vapor retarder.
Hey Chad, doing a 'flash' layer with cc spf will create a retarder not a barrier which is what you're explaining, I think. I think your wall assembly functions quite differently for that reason. Would love to see a detail to understand your design's rationale further.
I understand that kjpn. What I'm trying to say is the product you're using is a vapor barrier and so will the continuous insulation you're using. The wall system you have shown will have a really hard time drying out.
Here are the wall system that you wanted to see . .
A few things to point out.
1. No exterior sheathing - the rigid insul and mtl strapping are providing the diaphragm needed.
2. The spray foam is acting as a vapor retarder.
3. No insulation in the stud cavity other than mineral wood to serve as req'd fire blocking and prevent energy loss at the edge of the roof insul.
4. These assemblies ARE NOT PERFECT. However they will perform at least as good as what you've shown and won't have any water vapor issues.
.
Hi Chad, thank you it would be educational for me to go through that process; I'll do that.
But my understanding is that if properly installed, the closed cell spray foam will negate the risk of condensation inside the wall cavity as well as at the exterior sheathing as it is a total vapor barrier and will not permit cold air or warm air through it. The exterior sheathing is distanced from any interior vapor doubly so by the layer of R-sheathing foam. And there is nothing cold on the interior side of the spray foam to generate condensation. The would studs will be kept warm enough via the spray foam and exterior R-sheathing foam.
It depends. The interior of you building will produce water vapor.
For roofs in climate zone 5, you need at least 40% of the total R-value to be in the exterior, impermeable layer for the IRC to allow only a class 3 vapor retarder on the interior--meaning it's relatively safe from moisture accumulation.
I can't read the values you used on your images but since this is a moisture issue and not just a "let's get a permit" issue, I use the aged R-values: 4" of closed-cell foam is about R-24, 5.5" of fiberglass is about R-19 and 2" of XPS is about R-9, leaving you with about 45% of the R-value in the exterior layer. (I know it's a flash layer and not exterior insulation, but the calculations are the same.) So in theory, even if moist, indoor air gets into the fiberglass, the interior surface of the spray foam SHOULD be warm enough to prevent condensation. But it's much safer to allow drying to either the interior or exterior, and preferably both.
You are also using complicated assemblies with very high carbon emissions--XPS is about the worst product you can use for climate change. If you switch to the much more benign EPS, you will get some drying to the interior, and similar R-values--EPS remains R-4/in while XPS ages to about R-4.3/in.
My personal opinion is that having to resort to foam when building new, above grade, is a failure of design--there is always a way to insulate safely that will perform as well as foam with lower emissions. But that's another argument.
Thanks for your comments Woodguy. Yes because of the depth of sprayfoam I'm showing there should not be condensation risks.Thank you for pointing out the difference between XPS and EPS, I'll look further into it as I would like to lower the embodied carbon of the assembly as much as possible.
As for the emissions of spray foam, I am specifying a product called Gaco One Pass that is Greenguard gold certified and does not cause greenhouse gas emissions when blown. The foam itself is manufactured from recycled and renewable materials.
Kjpn, you have to be very careful with foam marketing--they are consistent about obfuscation, diversion and misinformation.
Gaco OnePass is advertised as having zero ozone depleting potential, which just means that it meets a law that has been in place for over a decade for all foam we use in construction. It has a conventional HFC blowing agent which is only outdone by the blowing agents in XPS in terms of negative climate impact. It's great that they replaced some of the resin with naturally derived resin but it's a drop in the bucket compared to the blowing agent impact.
I've written about this topic: https://www.finehomebuilding.com/2021/01/15/is-there-environmentally-friendly-spray-foam-insulation, and https://www.finehomebuilding.com/2018/11/07/h280-is-using-closed-cell-foam-worth-the-trade-offs. (Be sure to click "read pdf" to get the important part.)
Wood Guy, fantastic article. It is the most thorough and clear explanation of the dynamics behind condensation and using spray foam that I have found (and I've been doing a lot of digging lately).
Archinect needs to create content and resources like this pertaining to building science. It's a huge gap and opportunity imo.
Hi Chad, I used WUFI light to model the wall assembly to doublecheck my rationale. Attached is a readout showing the moisture content in the wall assembly across a calendar year. Also there's a second readout showing potential for mold growth.
This shows a very stable wall assembly with no risk for condensation (no intersection of RH and temperature, ie dew point). The moisture content shown in the OSB is hovering at about 15-16% (within acceptable range). The whole home is humidified and air conditioned as well which is factored into the model.
I will play around with other options now, however - this software is very cool.
That's great. I get what you're trying to do however there are several assemblies that are much simpler to install that will perform just as good or better. What you've proposed is an overly complex assembly with multiple failure points that requires the coordination of several trades that will be working literally on top of each other. If one of those trades dose anything incorrect then the entire assembly will fail.
Again I applaud you for wanting to create a high performance assembly and doing all this work. I just caution you that it needs to be easily built without relying on everything being installed perfectly.
EDIT:
Also be sure to run those calculations through your wall and roof framing. They will probably be OK however you need to make sure as a large presentence of exterior area will be at a framing member.
Ha, Look at you guys dueling it out. The 4" closed cell spray is less than 1 perm so it will be a vapor retarder. The Zip sheathing system will likely be another kind of air vapor retarder. What you want to avoid is trapping moistures in between them. Dew point analysis will help to know where it occurs. High perm assembly allows vapor to escape back out. Assuming vapor barrier is perfect is not a good practice. The small amount of vapor may still pass through the wood stud, or poor workmanship during installation. Whether this assembly will work, I do not know. Probably will.
What I don't get is why introduce 3 types of insulations. Isn't the point of zip sheathing all in one system being faster installation and less labor saving $$. It is serving as AWB, sheathing, CI. I would just use mineral wool batt inside the cavity. Apply vapor barrier/retarder as required by code and standard practice in that climate, whether class 1,2 or 3. I think it is inside the face of wall for cold climate.
Actually Jay, the spray foam has a perm rating of less than 0.1 so it's a vapor barrier.
quick google gives me "Closed cell foam typically has a perm rating less than 1 perm for 2” of depth." Anyway, you guys continue.
Your point?
Jay, thank you for your commentary. You raise an important and accurate point about the WATER VAPOR permeability of cc spf which appears to be 1.7 perm-in. I had it wrong, and was confusing it with the AIR permeability of cc spf which is 0.01. In summary it is an air barrier not a water vapor barrier. And of course that is consistent with the moisture modeling I did earlier today. It is showing the moisture penetrating the cc spf over time. Appreciate the comments!
Actually, I wanted to add a correction to my reply for posterity's benefit. The water vapor permeability changes as the depth of the cc spf increases. the product I am specifying (Gaco Onepass) has the following values (.44" = 1.0 p, 1.0" = .44 p, 2" = .22 p, 3" = .15 p, and 4" = .11 perms). So 4+" is about as permeable as a class II vapor retarder
Nice catch about the VR of the spray foam kjpn! I'm sorry that I misread the product data sheet and thought it was a VB.
Keep in mind that:
</= to 0.1 perm is vapor barrier
> 0.1 through 1.0 perm is class II vapor retarder (semi permeable)
> 1.0 - 10 perms is a class II vapor retarder (permeable)
Jay - you do realize that everything you posted was already said in the posts above you?
Why is there 2" XPS rigid insulation under roof framing? If you want CI shouldn't it be on top. Serving as another backup protection. I know it all works. But why would someone doing shingle roof spend extra $$ and complicate things. I would use that extra $$ and do standing seam metal roof, looks much better and much more durable.
Jay, I avoided the insulation on top primarily for moisture concerns. I thought that layering rigid insul on top of this sheathing, with cc spf behind it, would be trapping moisture in the sheathing and not allowing it to dry out to either side. I began the whole assembly design with cc spf as a premise so if that is removed I think more options present themselves..
I feel its just overcomplicating things. Its just a simple shingle roof. What I would do is probably Batt insulation in stud cavity. Then 4" Rigid insulation on top of sheathing. Then Cover board on top of rigid insulation. There is also the Polyiso with built in cover board for sale. Then roof membrane and shingle/metal panel. Who spends that money for shingle roof is beyond me. I would do low slope roof with that money.
The insulation values are pretty much passive house standards. Do you have your HRV/ERV system ready. This seems like a rather high performance house. Why do you not want some better curb view appeals to help with resale value? Shingle roof+Stucco screams cheap 2x4 stick to me.
I have a similar problem that we have not been able to address because of the lack of testing of fire rated assemblies with zip panels; 2x6 wall, r-20 for cavity, r-5 for continuous, 1 hr rated, wood siding.
The fire rating threw a wrench on this last year, but until we try to change the ordinance, there's no listed assembly we can use.
very stupid in my opinion to add this fire rating to sfr where most have to be completely sprinkled.
We're building a new home and in a couple of weeks and Zip-R12 sheathing will be installed. My question is around window openings. Would it be better to leave the insulated sheathing short of the jack (trimmer) studs and use 2-7/16 x 1-1/2" furring boards on top of the jack studs so the window nailing flanges have solid wood to nail to or just nail though the 2-7/16" thick sheathing into the jack studs using 4" nails?
I'm concerned that the framers might not get the R-12 sheathing up tight to the furring boards and leave gaps that will need to be foamed before using Zip tape. Huber says it's OK to nail through with 4" long nails around windows but my builder is concerned that the windows might not adhere long term to the wall and could move with any movements of the sheathing due to 2" of foam sandwiched between. With furring boards, I'd lose the exterior insulation over the jack studs and top/bottom around all windows. My builder doesn't think that's a big deal. It's my call, of course. My windows are very large with some 132" x 72" high.
What are people's thoughts on this?
your architect is the best resource for your project
I don't like using Zip-R sheathing for several reasons and this is one of them. I have several different details, depending on the situation, but even being very conscious of energy performance, I prioritize long-term building durability.
With conventionally-sized windows I would be fine with nailing through the Zip-R, but for oversized windows like yours I would probably use solid blocking. I say "probably" because there are several other variables: are you using a rain screen, what are the interior and exterior trim details, what are the flashing details, how much do you trust your builder, is your builder familiar with fastening Zip-R12 with 4" gun nails without setting the nails too deeply, what are the window frames made of, etc..
Generally speaking, the other commenters are right; this is a forum for design pros, not for homeowners to ask questions, and your question is absolutely something a competent architect should be able to answer. But Zip-R is not well understood by the vast majority of residential architects (and builders) I know. You might try searching or asking at greenbuildingadvisor.com where this type of question is common.
proto, an architect is not the place to ask this question. Huber is and I'm looking for those who have used Zip-R12 on what they did, as it can be done either way. Home architects design stuff but rely on structural engineers for loads and stress, as I've needed to use them for concrete walls and roof trusses in questionable areas.
Thanks for your awesome help though...POS
lol
Consult your architect, and the construction contractor. Asking us who are not in contract with you is a waste of time. We aren't going to give you free professional advice beyond consulting the professionals you have. If they can't provide meaningful advice on the matter they should bring in a consultant. If they still can't provide meaningful advice then replace them with more qualified professionals.
The stuff above before you came along here is inter-dialogue between professionals. You are a client seeking for free the professional advice we bill clients for. Understand the business of architecture. We don't give for free to clients what we charge them for. You're not an architect, are you? You sound like a home owner who is trying to bypass consulting the professionals they have. Giving you advice directly to your project is placing liability on us to whom we are not getting paid. The OP of this thread is a professional so he/she's already bears liability to that project and would assume any responsibility for his/her decision. Any professional advice we give you for free.... specifically to what you are asking for, means we can be sued by you if there is issues associated to it because you are relying on our professional advice to you. You are not compensating any of us for professional liability insurance coverage for the next 10-20 or more years (for the duration of the statutes of limitations and statutes of repose) for your project. Now, I want my 5-cents.
For context of reference about the "5-cents":
5 cents a word, I would be rich.... especially with epic walls of text.
"proto, an architect is not the place to ask this question." ... Why was this asked on Archinect then?
Exactly…lotta attitude/arrogance brought out from a pretty simple response. Guessing guy doesn’t actually have an architect on the project & apparently doesn’t know what an architect does. Always fun when owners are trying to figure out problems during construction that could have been figured out during design had they been willing to put a minimal amount of project fee to professional services.
I agree with you and nate. There's even professional building designers who (even if not a licensed architect) should be able to resolve this issue had the person consulted the professional they have, already, supposedly. Now it appears that "Huber" that is referenced in not an architect who's last name is Huber but the product manufacturer (Huber Engineered Wood). This means that they probably have an engineer on staff much like truss manufacturers and other engineered product manufacturers. In this case, the manufacturer's engineer on staff with a license should be the one to send his/her question to.
bobbray, are you following the installation instruction and any special nailing schedule that your engineer requires for shear panels for stuff like wind and seismic brace wall requirements? Here's the manufacturer's documents for this system: https://www.huberwood.com/zip-system/insulated-r-sheathing?gclid=Cj0KCQjwidSWBhDdARIsAIoTVb0tzKv0OIvm4woip6E0iqFGNWdX_vnaQhF93XD99W9ZvX_YUuRsjocaAv3OEALw_wcB
“Now it appears that "Huber" that is referenced in not an architect who's last name is Huber but the product manufacturer (Huber Engineered Wood).“
Balkins, I try not to be unnecessarily mean to people on here, but you really are out of your depth here. It is seriously cringey to witness how oblivious you are to it too, especially with the number of words you’ve pushed onto this page pretending to be an expert of some kind and speaking for architects. You’ve added nothing to this particular discussion.
I assumed huber meant husband.