Best wall system for a 200+ year home?
Hi I am still in the planning phases of designing a home in zone 6. I was recently looking at building a ~R50 double stud wall with a 3/4″ rain screen gap clad in fiber cement siding.
I am 27 years old and plan to live in this house for hopefully 50+ years. I would like assistance determining if I am better off with a low maintenance lifetime siding like brick. Since I’m still fairly young does the added initial expense of brick have a favorable return on investment over 50 years or more when passed on into future generations?
I feel sustainable design should be low maintenance and that the future users of the house need not understand the science behind its design. I also think the system should be able to withstand prolonged periods of no maintenance if future users are ignorant of maintenance.
What wall system is best to use in a forever house?
With thoughts of making a house that can be passed from generation to generation please consider this wall system…
From exterior to interior:
Brick, air gap, WRB, insulation, masonry structural wall, service cavity, drywall.
I’m unsure of what insulation should be used. CC Spray, rigid foam board, rigid Rockwool sheeting, other options?
I would also prefer to use structural masonry wall for the thermal mass and durability. I was thinking dry stack surface bonded block or maybe poured cement.
I would greatly appreciate feedback.
Thanks,
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Replies
Shane,
Joe Lstiburek often talks about the "perfect wall" or the "100-year wall" -- basically a CMU wall (you could substitute poured concrete, I suppose), with exterior rigid foam, an air space, and brick veneer. That's good, of course -- but not cheap.
Brick veneer over wood framing is more problematic. Plenty of brick veneer walls have had to be demolished after only 6 or 8 years, and the OSB behind the wall, it turns out, is mush. Just oatmeal.
There are lots of ways to screw up a brick veneer wall. If you want it to last for 100 years, it must be impeccable. That means you'll need stainless-steel flashing and stainless-steel brick ties (NOT galvanized steel brick ties). Your flashing details must be perfect; you can't have mortar droppings in the air space; and you need good weep holes (above grade), properly flashed. You also need good flashing details and weep holes above projecting roofs like bay-window roofs.
You also need a durable WRB and durable sheathing behind the brick veneer.
In short: these walls are somewhat risky, because there are so many ways to screw them up.
Shane,
Have you ever looked at insulated rammed earth construction?
Not sure how practical it would be for you, or if a home could be built with enough insulation for zone 6...
But it's hard to imagine a more durable building system.
We're facing the same decision on a shed and a workshop we want to build in our backyard. We could go for cheap and disposable but we'd much prefer to build something with at least a 50 year life expectancy and perhaps 100+ years.
One possibility we're looking at is Cross Laminated Timber. I understand a UK body has certified this as 60 years. I've visited recently built large timber buildings in Europe that have 200 year design lifetimes.
I think that a good, durable shell could be built using autoclaved aerated concrete (AAC) for the structural part, mineral wool or cementitious foam as insulation and another AAC layer with the appropriate synthetic stucco on the outside.
AAC has been in use for nearly 100 years and will never rot, warp, burn, serve as food for termites or substrate for mold; with correctly implemented steel reinforcement, it will stand up to earthquakes. Located on the inside, it will provide thermal mass, serve as an air barrier and replace water damage prone sheet rock (plaster is applied right onto the AAC); it also does not off-gas. AAC provides around R-1 per inch which, while not much, is considerably better than concrete or CMUs. Much of the increased conductive heat loss (relative to insulation) will likely be offset by lower convective heat loss as an AAC wall assembly is likely less air permeable than a stud (or CMU) assembly, and will stand up to time better than foams and caulks used to attempt to air-tighten a stud assembly.
Mineral wool (about R-4 per inch) will similarly not burn, rot, mold or off-gas; it is supposedly quite resistant to insects. It must, however, be kept dry. Cementitious foam (about R-3.9 per inch) also has these properties but would have to be filled into the cavity by a specialist.
Synthetic stucco specially formulated for AAC on the oustide should keep the wall dry, but allow moisture to escape.
In summary: build the wall using inorganic materials. Note that the Pantheon has been standing in Rome for nearly 1,900 years; I am unaware of any wood structure that has lasted that long.
The downside is that both materials are on the expensive side and might be hard to come by: Roxul is the only mineral wool product of which I am aware (it is used more frequently in Canada than here, I think), and there are very few AAC suppliers in North America.
One cautionary note: While I have some experience with AAC, I have never built a wall of the type described above.
Overall I think I am going to avoid the added expense of a CMU structure for a residential building. I really would like to have a lifetime cladding but the cost is likely too prohibitive. Since the cost is higher and masonry isn’t really green unless it has a very long life cycle I think i’m going to avoid masonry for residential.
Martin,
I really appreciate the feedback. I live in the thumb of michigan and we really don’t have the selection of builders available that a more population dense area would have. Since the devil is in the details I think I may be better off with a more fault tolerant and inspectable affordable wall system.
Lucas,
To be honest I have heard of rammed earth and assumed that all rammed earth construction was dirt rammed into used tires. Your post prompted me to look deeper into rammed earth. I like the concept and I did look into SIRE wall. I may consider rammed earth on a rubble trench for outbuildings like a barn or shed where insulation is not required. I’m really looking to super insulate and get over an R-40 whole wall R-Value. Adding 6 to 8 inches of rigid foam is a bit of a put off for me.
David,
I have looked into timber framed houses before and I don’t feel the few advantages of timber framed houses outweigh stick built. I feel a timber framed house is in the same ballpark as stick framed for building longevity. When I think of a building that will last 200+ years it really needs to be masonry of some sorts.
Florian,
I really like the concept wall you suggested. It fits my requirements of durability and would have an extremely long life. The proposed wall would likely be expensive and I can’t convince my wife to have rooms with interior conduit runs. I would need to add a service cavity and drywall. I really like the idea but as my wife constantly tells me I over do things. The doghouse I build for our great danes has far better whole wall R-value and air sealing than my first house. I feel a double masonry wall with insulation such as rock wool would be a durable long lasting wall. I like the idea of cementitious foam but it hasn’t been around long enough for me to consider it a durable building material. I have concerns with small movements over time turning it to dust. This is just my gut feeling but time will tell.
Thanks
Martin, I have noticed before that you have a Brick Veneer Phobia....
The vast majority of homes built in N.Texas in the last 50 years include brick veneer.
I have NEVER EVER seen or heard of the type of Failures you write about....
and even you write That inward solar vapor drive "failures" are rare
Can you Cite any Failures
other than the "Zaring Homes"
John,
Sure. First of all, there is the home described by Mark Parlee in Comment #3 on this page:
https://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-wall-rot
Then there are all the disasters described by Harrison McCampbell in this article:
http://www.jlconline.com/Images/Troubleshooting%20Brick%20Veneer_tcm96-1532283.pdf
Another JLC article -- one by Jerry Carrier -- details best practices that he advocates based on years of investigating failures. Many brick veneer homes lack the flashing details spelled out in Carrier's article:
http://www.jlconline.com/Images/Keeping%20Water%20Out%20of%20Brick%20Veneer_tcm96-1158016.pdf
Then there are the stories of brick veneer failure due to rusting galvanized steel brick ties. I don't have the links handy, but I could track them down. Once the brick ties rust, a strong wind can suck the brick veneer off the leeward side of a wood-framed home.
John,
Here's a photo of a brick veneer failure in Texas (I don't know any details of the mechanism):
http://www.flickr.com/photos/90557979@N00/306995822/
Another Flickr photo (again, I have no details):
http://www.flickr.com/photos/disastersafety/2859559449/
Collapse of a brick veneer wall on an older building in Georgia:
http://www2.wjbf.com/news/2011/feb/28/falling-wall-raises-questions-building-safety-ar-1519097/
Just throwing this suggestion out there-- in terms of a cladding material, what about a nice steel or aluminum product? There are plenty of products that use coreten steel, and so long as your not on the beach, it'll probably weather nicely. All of the above thoughts about ventilation would apply, of course.
And If I can impose an interpretation on the building systems--
perhaps a low-maintenance system should not necessarily include maintenance for aesthetic purposes, but merely maintenance required for functional purposes to keep the house from actually withering. If the future owners don't want to maintain it, then perhaps the veneer of paint will peel but the underlying cladding will remain safe and resilient against the elements.
The coreten steel suggestion (probably prohibitively expensive) is a nice compromise between these-- the weathering/rust is precisely why the you see it on all those metal and glass jewel boxes in Napa Valley
Another food for thought which I'm sure you've given some thought to-- is the house designed in some ways to adapt to the future of function and purpose? E.g. will it have a nice robot butler charging station for when those become reality ;)
I can't imagine what technology we'll have in 100 years. Most of the projects I work on demo the old houses-- not because they're dilapidated, but because it's simply more expensive to modify them in order to support the new functions and lifestyles that their owners require/desire. And that's not for a lack of green ethos either.
The greenees out here just disassemble and donate the materials to a nonprofit for a tax deduction, thereby making the disassembly cheaper than demo (dump/recycle rates can be pretty high in the crowded West). Still, the mantra remains, "out with the old... in with the noveau riche."
A few thoughts:
1. Good hat and shoes i.e. roof and foundation are far more significant in building durability than what the walls are made of.
2. Lucas makes an excellent point about future adaptability being key to longevity - read Stewart Brand's 'How Buildings Learn'. Bear in mind masonry walls, whether load-bearing or veneer, are much more troublesome to adapt.
3. Plenty of wood-framed wood-sided homes in the US have lasted both functionally and structurally for two centuries or more.
4. Modern insulation and climate control systems have introduced new challenges to wood buildings but the excellent work of GBA et al. have shown how to meet these challenges with confidence.
Final thought: the double stud/R50 cellulose/fiber cement siding wall you first mention would be an excellent choice combined with a properly detailed roof with good overhangs and a well thought out foundation. Esoteric (to these shores) construction techniques are unnecessary, they almost always involve more trouble and expense and are usually best avoided unless you get a thrill from buying trouble.
BTW the Pantheon is still standing because of its concrete dome roof, not because of any special wall construction. Classical Roman buildings of similar construction but with lesser roofs are mostly crumbled ruins.
I am actually sort of surprised ICF was not mentioned (although poured concrete was). That is what we are building our house with currently under construction. Realizing the typical r value is far below the going standard on this forum, but some ICfs are offering thicker foams and ways to increase the EPS thickness. The form I am using gets me an r close to 30 worth of EPS (not accounting for any of the bs added mass concrete claims). While its under the r40 original target, it is strong, air tight, and very resiliant to moisture (far more than your wood walls would be). Running heat load calcs, the hit in r30 to r40, in my zone 6, was only about 1600 BTU. I am going with triple pane windows with a solar tempered design with high u's on the south. I think the overall design is just as important as the shell and structure. Simple roofs, none or reduced valleys and over hangs to help protect windows and cladding all can help play into prolonging the life of the roof and walls.
Shane, just in case you check this again: I also assume that the wall assembly I suggested would be expensive, however interior conduit runs would not be necessary. As long as they're not too deep, channels can be routed into the autoclaved aerated concrete (AC) and then patched with repair cement. This is pretty easy (regular woodworking tools will work on AAC if you don't love your tools very much) and as an added benefit all electrical lines and up being from anything combustible and any spot water could pool. See, for example section 3.7 in: http://www.hebel-usa.com/en/docs/Hebel_MC_v09.11.pdf If you can put sweat equity into the house, laying AAC is pretty easy.
James has a good point: a 200-year wall won’t stand for 200 years without a good roof. One way to ensure this (and to fireproof your roof) would be to use AAC roof panels, topped with insulation and a standing-seam metal roof.
Regarding AAC being esoteric to these shores: so were the Passivhaus standard, triple pane windows, etc. Conduction ranges, convection stoves, and mini-split heat pumps, already very popular in other parts of the world, are still considered “exotic” to some degree here, but are rapidly catching on because they are superior products. Maybe (after a longer than usual lag) autoclaved aerated concrete will also become popular – some builders, for example Sun Garden Houses (in North Carolina) already use the material.
A side note: this page http://www.baunetzwissen.de/standardartikel/Mauerwerk-Passivhaus-mit-Porenbeton_2382673.html (German, Google translate will give you the gist) gives three wall systems intended to meet the pretty stringent Passivhaus standard using AAC. The first system uses an AAC block size not available in North American, but the second and third option seem feasible; both are probably less expensive than the wall assembly I suggested initially.