I'm planning on finishing my basement in the next month or so and am absolutely amazed at the variety and volume of complete contradictory information regarding insulation.
My plan is to use 1.5 inches of EPS (R7.7) with unfaced fiberglass (R6ish) insulation and 1/2" gyp. bd. Does this seem about right? I've been looking at finehomebuilding and Green Building Advisor, this wall section is either the way to go or a terrible idea...
Not sure about what you are finding on finehomebuilding or Green Building Advisor. I'd recommend going here for information. It probably will contradict a lot of what you've read before, but the difference is that it will be right and the science will back it up. I recommend the article "Understanding Basements" to begin with.
I framed my 2x4 studs .5" from the basement wall and insulated with with R-13. Worked out perfect for me. I don't see why your proposed solution would not work. Why are too concerned about this?
I would use 1-5/8" galv. metal studs with rigid insulation. Maybe a vapor barrier on the side that faces the basement wall and raised subflooring panels.
The OP's proposed construction seems right to me, as long as I'm understanding right that the EPS is continuous and the studs are installed inside that layer.
I like open-cell spray foam in this location because it doesn't allow mold growth like fiberglass batts, if you can afford it...
I hope your clients aren't getting the same kind of advice you're all giving the OP.
poop876, it is a concern so you don't get mold growing in your basement ... you must live in a relatively warm, dry climate. Anob, your vapor retarder is on the wrong side of the insulation ... unless the OP's basement is being used as a freezer. Andrew.Circle, you've given better advice, but if the OP is in a cold enough climate, open-cell spray foam is going to allow too much vapor diffusion and you'll get condensation on the cold basement walls (especially with all the warm, moist air a kitchenette and/or bathroom with a shower will produce).
Again, I would highly recommend the article "Understanding Basements" to begin with. Good luck.
I did read the link, and I liked that it basically agreed with my proposed wall section. The hybrid wall is intended to save some cash, glad to see there is basically the exact detail I was planning on the link.
It's amazing how wildly different opinions are on this subject.
No plans to raise the floor, just carpet and padding
When I finished my basement, I used 1.5" XPS attached directly against the concrete foundation wall top to bottom (all seams taped). Then 1" airspace and 2x4 wood studs at 24" o.c.. R-13 fiberglass (unfaced) stapled to the studs. 5/8" moisture resistant gyp board.
The main reason I went with XPS is because it's more moisture resistant that EPS. My basement doesn't leak (knock-on-wood), but better to be safe than sorry.
And don't use a poly vapor barrier. The rigid acts as one
Sounds to me like your EPS is acting as the vapor barrier. If so, aren't you trapping vapor between EPS and concrete wall? How does it breath? Also, you have batts between the room and the EPS, which means the vapor barrier is on the cold side. I may be missing something, but I don't like the sound of this.
The rigid board is a vapor barrier and is on the colder side, but it's also enough insulation that the dew point is not an issue, particularly since the delta t is only 10 - 15 degrees. It may be more of an issue at the upper portion of the wall, I'll have to look into that. I prefer to use the same section for the entire wall, it's only 9ft tall after all.
I wonder if it makes more sense to just use all mineral wool, no vapor barrier, and green board?
What's the situation on the exterior of your foundation? That should help inform your path. For example, is there damp proofing or water proofing in place?
The reason there's so many opinions and options is because basement insulation is highly dependent on climate, soil, existing building conditions, presence of air conditioning in summer, etc.
For my money, in my cold climate, I put up continuous EPS (enough to act as VB), then frame out. Mineral wool is optional but shouldn't be more than 66% of the R-value of your entire assembly. No poly needed.
foundation walls are cip concrete, there has been minor leakage in one area which was resolved with an interior french drain. The basement at one time had pretty severe cracking, so much that 4" steel columns were put all around the perimeter and the cracks epoxy grouted. Likely cause was expansive clay and poor grading.
The previous owner also sprayed the walls with gunite, which I have to assume was to control moisture/humidity through the walls.
I had several people take a look before buying, all agreed that the foundation should be pretty bulletproof at this point. The potential for water is why I like the rigid (EPS) and rock wool idea.
I don't know what is on the exterior, but will be digging a window well real soon and will have that answered.
Not sure if i said here before, but this is detroit area, zone 5, so R15 is required.
EPS gets a bit of a bad rep because people confuse it with bead board or fast food packaging. EPS outperforms XPS in every way over the long term including R-value and moisture absorption.
To geezertect - when you sandwich the foam directly against the concrete, the vapour profile moves to the interior face of the foam. In other words, if you apply a vapour retarder to the inside face of your batt, you're creating a double vapour retarder. No good, usually, depending on the type (type 2 is ok because it's more permeable - aka MemBrain or latex paint).
If you're wondering how the concrete itself dries out, it doesn't. But it doesn't need to. Concrete is very happy to be wet (concrete poured underwater for bridge footings is much stronger than the same concrete cast above ground). If your basement leaks, that's more a function of soil type(s), grading, and hydrostatic pressure.
I would consider using steel z channel studs and rigid closed cell insulation on the outer walls, mold and water vapor can be a problem avoiding organic (wood) items and or items that might absorb and hold moisture in the event of a flood or just day to day seepage can cost more upfront but would hold up better in the long run. Also if you can afford the space I would keep the furring off the wall 2-3" like an air space in brick cavity walls so moisture that may seep through the foundation walls can evaporate and to accommodate the uneven gunite application which will probably be thicker at waist height than at the top or bottom.
You're being required to fireblock inside your own personal residence? What's considered as a fireblock in this case? I must be missing something or mis-remembering what you're doing.
Walls are roughly 9'6
Unless I'm not reading the code correctly, req. is cont. blocking along the top and a vertical piece of blocking running vert. every 10 ft.
I'm using 1/2 gyp. bd.
Are you interpreting that as a requirement or did plan review call for it? I'd be surprised to see that required and/or enforced on a remodel. Its not new construction.
Are you coping studs to the gunite or ?
I think that about covers it. I recommend rock wool instead of EPS, just much more simple construction. That and it avoids a long conversation every time someone new walks down there and sees it.
Unless your basement is waterproofed on the exterior (not just damp-proofed) and has an excellent capillary break under the slab and over the footing, guaranteeing your concrete walls will stay perfectly dry, you don't want any insulation that can pass water vapor, including mineral wool, and you don't want to add any vapor barriers. Closed cell spray foam or any rigid foam will work, but EPS is the most environmentally benign and it won't absorb an appreciable amount of water.
If you use a vapor permeable insulation, such as open cell spray foam, fiberglass or mineral wool, warm indoor air will condense on the concrete and provide a moisture source for mold.
You could check with your AHJ about whether or not firestopping is required.
You say you don't want any insulation that can pass water vapor. So, we're wanting a vapor barrier. But then say you don't want to add a vapor barrier. And then say to use closed cell spray foam, which acts as a vapor barrier.
If the dampproofing on the exterior isn't good, the wall needs to be able to dry to the interior. Water is going to get in, and it has to go somewhere. Vapor permeable sounds like the best option if dampproofing is an issue. The hydrophobic properties of mineral wool would probably be a plus. And no latex paint.
the variety of opinions of basement insulation is astounding.
Buildingscience.com actually built several different wall types and tested them over a period of time, I'm going with their recommendations, anything else is just a plausible theory. I've seen and heard of so many basement disasters that i want my basement to be bulletproof. That is partially why I didn't bother to ask the inspectors about horizontal fireproofing, I knew that I wanted to do it. I take great pride in my work and want it to be the best.
senjohnblutarsky, I should have been more clear about "adding vapor barriers." I meant dedicated class 1 vapor barriers, not insulation products that are themselves vapor barriers.
Foundations don't need to dry to the interior. In fact you don't want them to dry to the interior; there is no harm in them staying damp. Mineral wool is somewhat hygrophobic but throw it in a bucket of water, it absorbs some, which then supports mold growth.
As an industry we have only just figured out how to build insulated above-grade walls that don't grow mold, and we are still working on foundations. Even the folks at BSC, and Bill Rose, the noted architect and building scientist, admit that foundations and basements are complex and that every situation is different. Vapor impermeable rigid foam is the safest choice.
wd. guy - I was about to write something about the "drying to interior" being in direct opposition to Lstiburek, but instead I came across an interview in which he basically says that he was wrong!
furred out basement
I'm planning on finishing my basement in the next month or so and am absolutely amazed at the variety and volume of complete contradictory information regarding insulation.
My plan is to use 1.5 inches of EPS (R7.7) with unfaced fiberglass (R6ish) insulation and 1/2" gyp. bd. Does this seem about right? I've been looking at finehomebuilding and Green Building Advisor, this wall section is either the way to go or a terrible idea...
sorry, will bump up the batt to get a total of R15
What are you trying to accomplish?
Insulated living space, a bedroom, play areas, and kitchenette. Will eventually also have a bathroom
Not sure about what you are finding on finehomebuilding or Green Building Advisor. I'd recommend going here for information. It probably will contradict a lot of what you've read before, but the difference is that it will be right and the science will back it up. I recommend the article "Understanding Basements" to begin with.
I framed my 2x4 studs .5" from the basement wall and insulated with with R-13. Worked out perfect for me. I don't see why your proposed solution would not work. Why are too concerned about this?
I would use 1-5/8" galv. metal studs with rigid insulation. Maybe a vapor barrier on the side that faces the basement wall and raised subflooring panels.
The OP's proposed construction seems right to me, as long as I'm understanding right that the EPS is continuous and the studs are installed inside that layer.
I like open-cell spray foam in this location because it doesn't allow mold growth like fiberglass batts, if you can afford it...
I hope your clients aren't getting the same kind of advice you're all giving the OP.
poop876, it is a concern so you don't get mold growing in your basement ... you must live in a relatively warm, dry climate. Anob, your vapor retarder is on the wrong side of the insulation ... unless the OP's basement is being used as a freezer. Andrew.Circle, you've given better advice, but if the OP is in a cold enough climate, open-cell spray foam is going to allow too much vapor diffusion and you'll get condensation on the cold basement walls (especially with all the warm, moist air a kitchenette and/or bathroom with a shower will produce).
Again, I would highly recommend the article "Understanding Basements" to begin with. Good luck.
I did read the link, and I liked that it basically agreed with my proposed wall section. The hybrid wall is intended to save some cash, glad to see there is basically the exact detail I was planning on the link. It's amazing how wildly different opinions are on this subject. No plans to raise the floor, just carpet and padding
When I finished my basement, I used 1.5" XPS attached directly against the concrete foundation wall top to bottom (all seams taped). Then 1" airspace and 2x4 wood studs at 24" o.c.. R-13 fiberglass (unfaced) stapled to the studs. 5/8" moisture resistant gyp board.
Brug-G, was there a strong reason to use XPS over EPS?
The main reason I went with XPS is because it's more moisture resistant that EPS. My basement doesn't leak (knock-on-wood), but better to be safe than sorry.
And don't use a poly vapor barrier. The rigid acts as one
Sounds to me like your EPS is acting as the vapor barrier. If so, aren't you trapping vapor between EPS and concrete wall? How does it breath? Also, you have batts between the room and the EPS, which means the vapor barrier is on the cold side. I may be missing something, but I don't like the sound of this.
furred out basement
Is it just me, or does this thread title sound a little dirty?
The rigid board is a vapor barrier and is on the colder side, but it's also enough insulation that the dew point is not an issue, particularly since the delta t is only 10 - 15 degrees. It may be more of an issue at the upper portion of the wall, I'll have to look into that. I prefer to use the same section for the entire wall, it's only 9ft tall after all. I wonder if it makes more sense to just use all mineral wool, no vapor barrier, and green board?
here's a good read, testing reports on a variety of possible wall sections, i'm thinking rigid w/ rock wool is the way to go now
http://file:///C:/Users/mike/Downloads/BA-1003_BA_HighR_Foundations_Report.pdf
What's the situation on the exterior of your foundation? That should help inform your path. For example, is there damp proofing or water proofing in place? The reason there's so many opinions and options is because basement insulation is highly dependent on climate, soil, existing building conditions, presence of air conditioning in summer, etc. For my money, in my cold climate, I put up continuous EPS (enough to act as VB), then frame out. Mineral wool is optional but shouldn't be more than 66% of the R-value of your entire assembly. No poly needed.
foundation walls are cip concrete, there has been minor leakage in one area which was resolved with an interior french drain. The basement at one time had pretty severe cracking, so much that 4" steel columns were put all around the perimeter and the cracks epoxy grouted. Likely cause was expansive clay and poor grading.
The previous owner also sprayed the walls with gunite, which I have to assume was to control moisture/humidity through the walls.
I had several people take a look before buying, all agreed that the foundation should be pretty bulletproof at this point. The potential for water is why I like the rigid (EPS) and rock wool idea.
I don't know what is on the exterior, but will be digging a window well real soon and will have that answered.
Not sure if i said here before, but this is detroit area, zone 5, so R15 is required.
EPS gets a bit of a bad rep because people confuse it with bead board or fast food packaging. EPS outperforms XPS in every way over the long term including R-value and moisture absorption.
To geezertect - when you sandwich the foam directly against the concrete, the vapour profile moves to the interior face of the foam. In other words, if you apply a vapour retarder to the inside face of your batt, you're creating a double vapour retarder. No good, usually, depending on the type (type 2 is ok because it's more permeable - aka MemBrain or latex paint).
If you're wondering how the concrete itself dries out, it doesn't. But it doesn't need to. Concrete is very happy to be wet (concrete poured underwater for bridge footings is much stronger than the same concrete cast above ground). If your basement leaks, that's more a function of soil type(s), grading, and hydrostatic pressure.
I would consider using steel z channel studs and rigid closed cell insulation on the outer walls, mold and water vapor can be a problem avoiding organic (wood) items and or items that might absorb and hold moisture in the event of a flood or just day to day seepage can cost more upfront but would hold up better in the long run. Also if you can afford the space I would keep the furring off the wall 2-3" like an air space in brick cavity walls so moisture that may seep through the foundation walls can evaporate and to accommodate the uneven gunite application which will probably be thicker at waist height than at the top or bottom.
These guys have a simple system that is pretty much what Peter describes: quiktherm.com
thanks for all the advice - will submit for permit and start digging real soon.
Wife is going to flip when she finds out the permit is going to be at least $700!
basement insulation is about half complete - 4 in of EPS.
Found out that fireblocking is a major pain. No big deal at the top of the wall, but every 10' horz. sucks.
You're being required to fireblock inside your own personal residence? What's considered as a fireblock in this case? I must be missing something or mis-remembering what you're doing.
Fireblocking is required per IRC R302.11. Not sure why it being OP's personal residence would make it exempt.
10'-0" OC, HORIZONTALLY - How tall are your foundation walls?
Walls are roughly 9'6 Unless I'm not reading the code correctly, req. is cont. blocking along the top and a vertical piece of blocking running vert. every 10 ft. I'm using 1/2 gyp. bd.
Are you interpreting that as a requirement or did plan review call for it? I'd be surprised to see that required and/or enforced on a remodel. Its not new construction. Are you coping studs to the gunite or ?
The code requires blocking at the ceiling and floor levels, and 10' max horizontally. Required at furring , soffits, etc. as well.
^^ meaning, your wall plate at 9'-6" provides sufficient cavity blocking.
You're not reading it right...
Yes, the wall plate provides the blocking for the vertical. But blocking is also required at 10' max horizontal intervals.
^^ What am I missing in this convo? Seems thread seems way more complicated that it has to be...
I think that about covers it. I recommend rock wool instead of EPS, just much more simple construction. That and it avoids a long conversation every time someone new walks down there and sees it.
Unless your basement is waterproofed on the exterior (not just damp-proofed) and has an excellent capillary break under the slab and over the footing, guaranteeing your concrete walls will stay perfectly dry, you don't want any insulation that can pass water vapor, including mineral wool, and you don't want to add any vapor barriers. Closed cell spray foam or any rigid foam will work, but EPS is the most environmentally benign and it won't absorb an appreciable amount of water.
If you use a vapor permeable insulation, such as open cell spray foam, fiberglass or mineral wool, warm indoor air will condense on the concrete and provide a moisture source for mold.
You could check with your AHJ about whether or not firestopping is required.
^^ ??
You say you don't want any insulation that can pass water vapor. So, we're wanting a vapor barrier. But then say you don't want to add a vapor barrier. And then say to use closed cell spray foam, which acts as a vapor barrier.
If the dampproofing on the exterior isn't good, the wall needs to be able to dry to the interior. Water is going to get in, and it has to go somewhere. Vapor permeable sounds like the best option if dampproofing is an issue. The hydrophobic properties of mineral wool would probably be a plus. And no latex paint.
the variety of opinions of basement insulation is astounding.
Buildingscience.com actually built several different wall types and tested them over a period of time, I'm going with their recommendations, anything else is just a plausible theory. I've seen and heard of so many basement disasters that i want my basement to be bulletproof. That is partially why I didn't bother to ask the inspectors about horizontal fireproofing, I knew that I wanted to do it. I take great pride in my work and want it to be the best.
senjohnblutarsky, I should have been more clear about "adding vapor barriers." I meant dedicated class 1 vapor barriers, not insulation products that are themselves vapor barriers.
Martin Holladay, who manages Green Building Advisor (a subsidiary of Taunton Press and formerly also of Building Green) says it all more eloquently than I can: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall. Skip down about halfway if you're in a hurry.
BSC is a great source of information; I try to read everything they publish, have been to several of their trainings and hope to make it to their summer conference this year. They clearly don't like fibrous insulation with a separate vapor barrier: http://buildingscience.com/documents/enclosures-that-work/high-r-value-wall-assemblies/high-r-foundation-3-r13-fiberglass-batt-2x4-framed-wall.
And they only recommend open-cell foam with caveats. Caveats make me worry: http://buildingscience.com/documents/enclosures-that-work/high-r-value-wall-assemblies/high-r-foundation-7-open-cell-spray-foam.
Foundations don't need to dry to the interior. In fact you don't want them to dry to the interior; there is no harm in them staying damp. Mineral wool is somewhat hygrophobic but throw it in a bucket of water, it absorbs some, which then supports mold growth.
As an industry we have only just figured out how to build insulated above-grade walls that don't grow mold, and we are still working on foundations. Even the folks at BSC, and Bill Rose, the noted architect and building scientist, admit that foundations and basements are complex and that every situation is different. Vapor impermeable rigid foam is the safest choice.
wd. guy - I was about to write something about the "drying to interior" being in direct opposition to Lstiburek, but instead I came across an interview in which he basically says that he was wrong!
http://www.greenbuildingadvisor.com/blogs/dept/musings/joe-lstiburek-discusses-basement-insulation-and-vapor-retarders
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