My friend who's finishing up his first passivhaus used mineral wool sheathing and plenty of cellulose. No foam that I can remember seeing/discussing.  

I agree, I'm a little skeptical of tape and foam for long-term durability.  Not sure how it holds up versus other systems in life cycle assessments, which would seem to be the name of the game for passivhaus and the like.

I'm no expert in passivhaus, but as I understand it, it is simply a performance-based standard when you boil it down to its essence. How one might achieve the performance required by the standard is up to them (obviously within current markets, technology, and products ... or invention of new technology, products, etc.).

Foam plastic insulation might be one easy, effective way of achieving the standard, but other techniques could achieve it as well. It might take some ingenuity and clever design, but probably not outside the realm of possibility for a designer who can come up with clever solutions.

Off topic in terms of the longevity of PH ... I thought this was an interesting article about Passivhaus in the US; The House that could Save the World (settle in, it's a longer read).

I was under the assumption it's performance based as well (using something like 90% less energy in heating and cooling than conventional build ).

I thought this was mostly achieved through a high thermal mass (massiv holzbau etc...)  rather than air tight construction?

My understanding is that in addition to thermal mass there are strict air infiltration tests and everything is extensively sealed - no gaps. But what concerns me is all of the images I've seen tend to show contractors taping up around windows or at joints between panels. i know for sure that the tape's lifespan is shorter than mine...

Yeah, I think air tightness is one of the more important concepts in Passivehaus. A contractor in a nearby town is building Passivehauses and I think they are most concerned with airtightness. If you are trying to limit the air exchanges down to the minimum for fresh air, then they have to be super-tight envelopes.

I think one important thing that isn't discussed enough is the idea of placing all of the exterior insulation outboard of the structure (including foundations walls). If this is done successfully with few thermal bridges, the structure will be kept at a constant temperature and a constant humidity. That would extend the life of weather membranes, tapes, and foam products since the building would move a lot less vs. a more typical batt in cavity wall construction. The weather control membranes may be inside the freeze-thaw 'envelope' and not subjected to temperature swings either depending on the wall section. Doesn't really answer the original question, but it's a thought. Sealants are another issue at openings, etc. Those don't last for 100 years, and would need periodic resealing I guess.

The oldest Passivehaus was built in 1991, so it isn't even 30 years old yet. Not sure if the newer membrane tapes in the US were around in Germany in 1991. Would be interested to see how those early projects are holding up, and whether any newer projects have failed or not.

That's a good point, Andrew, about the more susceptible materials being placed where they won't see much freeze-thaw or movement.

I'm not at all opposed to the idea of maintenance on buildings, in fact I think understanding and employing good maintenance is a beautiful idea (please ignore the decaying fascia board on my garage at home, haven't gotten around to repairing it yet. I'm talking about the Sudanese mud buildings with climbing sticks for re-stuccoing, or re-thatching a thatched roof - it's a very romantic notion, I know.). So re-caulking every couple years or whatever is to me a way of living in a sort of connected symbiosis with your house - dwelling in it. But my fear is that the tape covering seams are all at inaccessible places, so how does one know if the tape has deteriorated away in ten years?

"a way of living in a sort of connected symbiosis with your house"

This is a trait I fear most humans, even most architects, have lost. The overwhelming mentality that's arisen in the past couple generations is that your home is a bubble to keep the natural world out, rather than a vessel to harness the natural world for your comfort.

Bit of a digression, but I think movements like passivhaus, LBC, and some fringe off-grid concepts such as Earthships start to reawaken people to the fact that they need to live *with* their house as much as in it.

Great thread!

Well said, tduds.

Code up here, as a minimum, is effective R27 walls. Our commercial projects all start with a baseline of 4" of outboard rigid, though we're learning to fine tune pretty quickly.

For PH you're looking at wrapping your entire house in blueskin (or similar) from the top of the footings, right up to the peak of the roof. It's actually a very simple set of details. If you place most of your insulation outboard, you typically don't need a vapour retarder (so no sealing of electrical boxes, foam sill gaskets, etc).  But you do need an HRV for mechanical ventilation to get enough air changes. Anybody remember sick building syndrome?

I think you are right to be concerned about the tapes and other newer methods of sealing joints and penetrations, especially when they are behind cladding. I get nervous about the open joint cladding with any form of outboard insulation. It seems like if anything is going to destroy the newer materials faster than freeze/thaw, it is UV exposure.

I went on a Passivehaus tour with a group of about 20 people a couple years ago. After about 10 minutes standing around talking about the details, the air started to get thick and humid, and breathing wasn't quite as easy. The owner said, oh wait, I forgot to adjust the ventilation. He did, and about 10 minutes later the air felt more 'normal'. It was pretty amazing because rarely are you reminded that you breathe oxygen and exhale carbon dioxide; I take it for granted. In a regular house it doesn't matter, but the house was so air tight that 20 people affected the air quality in 10 minutes. The owner said it would probably take a day or so to get the house back to its normal, energy efficient state, and that the tour probably cost him $5 or so, of a $100 / year energy bill. Pretty amazing.

Yeah, I mean, a $100 annual heating bill is really super appealing, especially since I'm looking at building in northern Michigan.

I just have an immediate distaste for lots of foam and adhesive and vinyl...basically all of what I consider crappy, short term materials.  I also don't want a house that's smarter than I am, so I have no interest in fancy technologies for regulating fresh air from an iPad or whatever.  As tduds said, I want to live *with* the house. Or as my friend and architect Tim Gray said, I like the idea of using dumb technology, but in very smart ways. So a big dumb hunk of "real" material like concrete or timber that provides thermal mass is far more interesting to me than a thinner wall with lots of bells and whistles.

Minimize size. Less volume requires less energy

Mineral wool insulation. Very different from fiberglass, more efficient, tighter seal, less toxic. Supertight is problematic from a health PoV without toxic construction materials and dependence on mechanical air exchange is retarded. 

Passive solar. Use overhangs/vegeatation to control exposure, slab on grade with dark stone for thermal mass. Properly done a good wood stove is all the backup heat you'll ever need, and wood is a natural part of the carbon cycle (or would be if we properly maintained the resource). Aside from that, anyone ever wear a sweater? Designing for a stupid lifestyle has stupid consequences (high energy consumption). 

Another interesting article I read recently that touches on a lot of things we are discussing here (passive solar, thermal mass, fireplaces, tight construction, etc.) in terms of getting to net zero. I know it isn't the focus of the thread, but interesting from the point of view that really tight construction makes you think about things that normally we take for granted ... like a range hood, clothes dryer, or fireplace that works.

Also brings in the earlier article I posted about the house that could save the world because of the difference of opinions when it comes to passive house standards and Joe Lstiburek. 

Zeroing In from BSC.

Miles Jaffe, you can make breathable passivehaus-thickness wall using twin studs and cellulose wool.

On a related note, earlier this year 475 High Performance Building Supply drops some knowledge

"tapes have confirmed 100yr durability in rapid age tests & 20+in use"

Just attended a lecture by one of our country's most credible building scientists, he mentioned that in investigating houses he's found that the tape has held up better than he'd expected - that it was a little brittle but if you get 30 years out of a tape, that's what we expect from more durable materials. Also I want to address Miles point above - exterior stone wool definitely doesn't make a tighter envelope, it makes a more open envelope, which makes it really great for a lot of assemblies.

I can't find the text online, but Zumthor has an awesome description of solid timber construction in one of his books. He talks about how solid wood regulates the temperature and humidity, and it feels very comfortable. Obviously he is more poetic than me.

The projects use solid timber, and I don't think there is any insulation? Maybe someone can add to that with some more complete information. Definitely no tape for sealing joints though. The timber is the exterior and interior finish, so the wall looks about as simple as it gets. There are radiators for heat. I wonder if it is comfortable despite the large openings in all directions.

Here are some decent images of the guest houses he did:http://www.dailyicon.net/2009/04/leis-house-by-peter-zumthor/

Anyways, this project sprung to mind when Donna was talking about living 'with' the house, in a simpler, less technological way. Seems really appealing.

well, I don't know about the U.S, but in the middle east passivehaus design relies exclusively on techniques of cooling and ventilation using local materials..

one good example of traditional affordable passivehaus system is Hassan Fathy work in the 60's .. great techniques, you should look it up if you're interested .. there is also this amazing book "Stay Cool: A Design Guide for the Built Environment in Hot Climates".. there also this book "sun wind & light architectural design strategies"by Mark DeKay, and G. Z. Brown .. very interesting one..

... and the topic is so wide to explain! in cold climates I think they use mineral wool for insulation, compacted spaces, large insulated glass openings to let the sun in, the correct orientation towards sun,etc.... as Miles just explained

Sorry my studies focused more on hot-arid and hot-humid climates, but I'll look it up (I should)!.. still I like the idea of the electrical fireplace :p 

there is also this book  "your Home: Australia's guide to environmentally sustainable homes" written for different climate zones in Australia including cold climates..

It's a lot easier to do passivhaus in warm/hot climates (provide shade and ventilation) of course. I think assume folks above don't quite understand the intent of PH. Try designing for areas with 6000+ heating degree days.

bowling_ball     just for your infos, almost 60% of the energy consumed in my country goes on air conditioning. try to design a house in a climate where temperature reaches 58 C degree in the summer and 30 C in the winter surviving  without any air conditioner!!   ... stop making assumptions that is not based on any facts and can never been supported! in my opinion, creating a thermal mass that store heat in cold climates is much easier than creating a mass that store cool air in hot climates because heat can radiated, transmitted, and reflected from any object (including a human body).. PH is not exclusively limited to cold climates, and I can say it started with vernacular design in hot climates! 

See, Zaina, this is part of my problem: I grew up in Arizona and went to an architecture school that taught us vernacular responses to our weather conditions. We had a lot of students there rom the Middle East (and Malaysia) to learn about hot climate design. So for me dealing with a very cold climate is really something I'm not formally educated in!

People lived in hot climes for millennia without mechanical air conditioning. Many still do.

Sorry Zaina, it's nothing personal. But nobody "needs" air conditioning - heat can be addressed with shading and air movement. Good luck living without heat north of the 45th parallel. And heat means an envelope of some kind, to increase effectiveness and efficiency. It's absolutely a different approach than dealing with a hot climate.

Trombe walls were just mentioned in my lecture.. good idea!

Is the lower image supposed to be a trombe wall, or a solar chimney? If the former, the interior wall should be mass, not insulation.

I though the solar chimney is for ventilation..( particularly for outdoor bathrooms?)? don't you think a specific kind of insulation can do the work of the mass if it does not permit air  in or transmit temperature? .. I mean, why a mass not an insulation?

Mass is generally not a good insulator because the insulating element in any insulation system is trapped gas (air). The denser the material, the fewer air pockets and therefore the less resistance to thermal transfer. 

To think of it another way, typical insulation materials resist the absorption of energy, while typical 'mass' materials absorb, retain, and release that energy over a 24 hour cycle according to the availability of solar energy.  

Who hasn't seen a trombe wall with trees planted in front of it?

Happens every time. 

Vegetation can be used to provide effective seasonal shading.  

The trombe wall itself is stupid, just use a floor slab as thermal mass. Then you get to enjoy the light and view.

Zaina, the intention of the trombe wall is for the exterior glazed area to heat the mass wall on the interior, so that the wall will radiate heat to the interior throughout the day and night, and help maintain a more consistent temperature in the occupied portion of the building.

 Substituting insulation for mass in this case wouldn't have the same benefit - insulation by design prevents the migration of heat.  And in a trombe wall, that migration is exactly what you are trying to achieve.

In all but a few rare cases (maybe a weekend home in a cold climate?) mass needs to go on the inside of the envelope, and insulation on the outside.

And as Miles starts to suggest, trombe walls make less sense now than they did thirty years ago. With selective surface glazing and high performing IGUs, it's a lot easier to get adequate thermal resistance AND insolation when desired in a glazed wall - it just costs a lot of money. 

I've been lurking for a while but this discussion prompted me to sign up and post. Great forum.

A few years ago I thought Passive House went too far, used too many materials, too much foam, too reliant on mechanical ventilation and tapes, etc. I wrote a couple of blog posts on Green Building Advisor about an alternative concept called the Pretty Good House, which in many ways is a reaction against Passive House excess.

In the meantime, I helped a friend start a business building nearly foam-free Passive Houses that are panelized in a shop setting and erected quickly on site. I learned a lot in the process, and wrote content for their website explaining the basics: http://www.ecocor.us/. (I am now self-employed.)

In short, not every Passive House is a good house. Some builders, such as Ecocor, put a lot of effort into the long-term durability of the envelope, provide service cavities so mechanical equipment (which will eventually fail) can be repaired or replaced, build vapor-open assemblies so no moisture is trapped, and use only the highest quality materials such as the Pro Clima products sold exclusively by 475 in Brooklyn. As someone posted, their acrylic-based, zero-voc tapes have gone through accelerated age testing and should be good for over 100 years. Maybe not forever, but much longer than most building assemblies are expected to last.

We found that the lowest-cost way to build a Passive House is on a thick foam raft slab. We used the most environmentally friendly, durable foam, borate treated type 9 EPS, which has enough compressive strength to go under footings and thickened-edge slabs. It is not necessary to use foam, however. You can use Foamglas (an Owens-Corning product), which Ecocor is using on a current project, with mineral wool or (more expensive) Foamglas under the non-structural portions of the slab. (Here's an article I wrote about mineral wool: http://www.finehomebuilding.com/tool-guide/articles/mineral-wool-comeback.aspx). Or you can build on piers, with thick insulation in the floor system, which Ecocor is doing on another project, which as far as we know is the first time this has been done but hopefully won't be the last.

There are many other low-energy ways to build besides Passive House, and I'm not convinced it makes sense in warm climates. Thermal mass (in the form of floor systems, Trombe walls or other) can be effective in cooling-dominated climates, but they aren't very effective in heating climates, where building to the Passive House energy standard can work very well.

Good stuff. I like the 'pretty good house' concept, very balanced.

I've read your article on the pretty good house when doing some research a few months ago and I really like that take on it. As I get ready to renovate my own home, I'm hoping to use some of the techniques and lessons outlined. Thanks for sharing.

Thanks guys. I didn't mean to distract the conversation from Donna's original questions, "What is the longevity of the super-tight envelope? If I want to build a house that will last 100 years, is Passivhaus at all reliable, or will I end up with a fifty year old junky and separating foam box?"

I would say the longevity can be much longer than average, if one keeps air and water vapor from getting into the envelope, but it is inevitable that at least some of it will, so plan for it. 

• The more separate the control layers (WRB, Air barrier, Thermal barrier) are, and the more independent they are from the building's structure and mechanical systems, the easier it will be to repair or replace components when they fail or during renovations.
• The tighter the envelope is to air flow, the better protected it is.
• The envelope should be able to dry easily, most of the year at least.
• If a component fails, there should be another line of defense. For example, if the air barrier tape loses adhesion, but it is sandwiched between a rigid air barrier and a thick layer of dense-packed cellulose, it won't greatly affect performance. If the WRB tape fails, but the WRB is shingle-lapped AND whatever is behind it won't turn to mush if it gets hit with a little water occasionally.

The more insulated and air-tight the envelope, the more risk it is from mistakes of design or construction. In other words, the architect or designer needs to be diligent in spec'ing and detailing the envelope, and the contractor needs to be diligent in executing the details. If either party fails, then yes, you will end up with a pile of junk. 

Which is another reason why supertight is problematic. Or any non-standard construction. Design to build within the reasonable capabilities of the people performing the work.

But building higher quality buildings is NOT difficult, it's just a new skill set. The standard of construction has changed many times. At the moment in residential construction, we're seeing the inherent problems of stick-framed construction, which was developed over the last century to work very well in drafty, thin assemblies, but that is not forgiving of increasing levels of interior comfort and energy performance.

In my previous life as a carpenter/contractor I tore apart many old homes, and virtually every one built after 1950 had some level of mold and moisture issues. The worst are the ones built in the 1980's and 90's, with plywood or osb, fiberglass insulation and poly vapor barriers, flanged windows nailed to the face of the housewrap without flashing--the ones built "sort of tight" but without concern for what would happen once moisture found its way into the envelope. 

The best were the un-insulated timber-framed buildings from the 19th century, such as my own 1830 home. The wall sills,window sills and other parts would eventually rot but were relatively easily replaced. But living in an uninsulated, drafty home does not meet modern comfort standards. Believe me, my wife reminds me regularly.

When timber framed/heavy timber construction changed to stick-framed construction, there was a different paradigm shift, which required education, adapting to new technologies (power tools) and materials (thin framing members). The status quo changes over time. 

I have seen many carpenters', contractors', and owner-builders' eyes light up once they see how simple the concepts are and how easy to execute, and the significance of building to a higher level. Plus is gives them something to be competitive about. 

Fast, cheap or nice.

Pick ONE.
 

have you explored the idea of a cordwood passive house?  In cordwood there is no vapor barrier and you can make the walls as wide as you want for insulation needs.  

Shirley, as cool as alternative building techniques can be, one of the central tenets of the Passive House standard is a very low level of air leakage: no more than 0.6 air changes per hour at -50 pascals of pressure (ACH50). Typical construction is in the range of 3.0 to 7.0 ACH50, or more.

Cordwood shrinks and swells with the seasons so you would never be able to reach the airtightness numbers, and therefor the low levels of energy use. I doubt you would even be below 7.0 ACH50 after a season or two of heating, cooling and the associated humidity swings.

Typical levels of insulation in the walls of a Passive House are usually at least R-30 but usually in the R-40 to R-60 range. Wood has an insulating value of 1.0 to 1.25 per inch, so your walls would have to be quite thick, in the range of 3-4 feet or more. Not impossible, but it would make window wells challenging. 

Of course I'm assuming you're talking about the Passive House building energy standard, either the original, international one developed in Germany, or the U.S. copycat with the same name but slightly different requirements. If you're simply talking about passive solar design, of course any building methodology can work, but a lot of experimenting has shown that for the lowest energy use buildings, an airtight and heavily insulated building envelope is the way to go.

Wood Guy,

good points! I was thinking more along the lines of passive solar design.  I've just started learning about the certified passive house standard from germany, there are so many factors to consider.  Now that I know about the passive house standard I'm excited to learn more about the techniques used to achieve that standard. 

Hello All, I am just finding this thread while searching for some posts about building longevity and resiliency.

I read the whole thing, and the points of view, technical information, and call-outs to real life projects somehow blend in so well that you can read this as a small article or blog post about good building construction practice in different places.

The one point I think is missing on the PH in cold vs hot climate is the humidity control. If you are in a hot and humid climate, PH standard principles can really be a game changer. Applying an airtight envelope, and mechanical ventilation, though HRV or ERVs, you are conditioning the interior space not only for temperature, but most importantly, humidity control; which translates into comfort and health. In the end, heat and cold can be easier to manage when humidity is kept in check.

FYI: I am taking from experience and some papers I wrote when I was in Grad School, so it wont be 100% from a scientific perspective, please expand/correct on this part if you can :)

Hot and Humid is almost impossible to cool down without de-humidification (for that you need A/C units and de humidification products), and the air you breathe can be suffocating; Hot and Dry is easier to cool down with cross ventilation, but it can get uncomfortable because the dry air takes moisture from skin and makes it itchy, and it can cause respiratory problems like asthma. In contrast cold and humid climate is bone chilling and difficult to heat-up without active means to dry it out and warm it up; and Dry Cold is equally bad for the same reason dry and hot is bad (skin problems, and respiratory problems).

SO,

With and airtight envelope and controlled ventilation, all of the issues above are regulated, and you end up with a more comfortable, healthy and a lower energy bill because you take out the need for A/C units in hot places, and heaters in cool ones.

Final thing to consider is that, even if the power is out and the mechanical systems are down, the indoor space will remain regulated for some time (I worked on a passive house that lasted 3 days with no power, in mid-winter, in Pennsilvania, and they said to have comfortable temperature and air throughout), and the people can use more modest (maybe passive) means to control the indoor climate.