Any PassivHaus homes built using green roughcut lumber?
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| Posted in PassivHaus on
Is it possible to build to Passive House standard using just milled green rough cut lumber. What are the possible problems with air tightness and shrinkage?
Thanks.
Chris
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Chris,
Do I get to use any other materials? Nails, maybe?
How about housewrap? Will you give me housewrap?
Tape? Gaskets? Maybe a little foam?
Work with me here, Chris.
Chris,
Assuming you have no objections to using the usual catalog of building materials from Home Depot -- many of which are handy to lower a home's air leakage rate -- there's no reason you can't use green lumber.
All the usual caveats apply: work slowly, in hopes that the framing lumber will dry as you work. If you are including large beams or joists, use a design that accounts for shrinkage.
Martin,
Yes, all appropriate materials to help in the job of sealing the envelope would be considered. I'm new to these practices of super tight building. Actually quite ignorant at this point. My question were where I was wondering if sealing might be compromised by the shrinking of say green studding. Where the lumber would shrink away from the gasket or caulk.
I shouldn't have used the word "just" in my initial posting.
Nice to read that it is doable.
Are there any Passive House builds that you know of that have used green lumber?
Chris, if you do this, be ready to replace at least 10% of the studs after your done framing. I have experience with this, and regardless of what Riversong or Martin will tell you, the green lumber will move, warp, and bow especially under vertical loads. Also beware, most local code jurisdictions require graded lumber to a structural spec on construction projects. There is no doubt that it is doable, just want you to know that green lumber moves A LOT! I personally use kiln dried lumber, less chance of movement, less chance of mold.
Matthew,
It depends on the species. What species of lumber did you use? Something squirrely?
if using tape and panel (e.g. OSB) as air barrier, supposedly the EU tapes (e.g. siga) can move with movements due to settling and such without losing integrity. so it may be possible, but 0.6ACH50 isn't the easiest to achieve, and building in uncertainty with green lumber probably won't make it any easier.
Matthew, it is my understanding that in New York State there is an unmarked structural lumber law regulated by the New York Department of Environmental Conservation. It supposedly says that as long as a mill signs a form stating that their lumber is #2 or better it is okay to use. Although I have read that green lumber is prohibited. I'm trying to find a copy of the rule.
Anyone know what the rules are in Vermont? Robert Riversong's homes are put up green.
Concerning my planned home built to Passive House standards, I do believe in the need to support local sawyers and mills over the big box lumber suppliers, or even over local lumber yards selling lumber from somewhere else other than my region. However, if it is going to make what I see as a somewhat difficult project of building to Passive House standard more difficult, then it looks like I'll do a pass on using the locally sawn lumber.
Thanks for the heads up.
Chris
Chris,
If your goal is a deeper shade of green, and you've been looking at Riversong as a model, then are you sure it makes sense to forgo the first argument (about locally sourced green lumber) in favor of Passive House as a target? Riversong has argued repeatedly that PH sets benchmarks that push designers to make not-so-green choices.
I tend to agree with him. One basic problem with trying to meet the PH standard is that you don't need an extreme building to meet PH energy limits. You could meet them in a yurt. Then there's the resource consumption required to build a house to PH standards, with all the material that goes into an extreme thermal enclosure. Green building is supposed to be about consuming less.
Q. "Anyone know what the rules are in Vermont?"
A. In most towns in Vermont, there is no residential building code whatsoever, except for an energy code that is entirely voluntary. There is no system of code inspection or code enforcement in Vermont.
"Then there's the resource consumption required to build a house to PH standards"
outside of extreme climates, it's really not that more intense than other superinsulated strategies, if designed properly. if you use the right glazing. you don't need uber thick walls. you can achieve PH without foam insulation.
@ Martin and whom it may concern. I have used green Doug Fir to frame with. Oregon provides a massive amount of this lumber to many parts of the U.S. and the world for structural and aesthetic wood uses. Doug Fir is considered to be one of the best species for stability, especially tensile strength. The problem with green lumber is that it store memories of being a tree, and after milling it will go back to that shape, and most trees are not perfectly straight. Remember as well, the higher the grade, the fewer knots and imperfections likely to be present. Also keep in mind that most milled lumber now comes from second -succession trees at best, and this offers less stability than old growth. The tighter the spring wood, the more stable as well.
On the PassivHaus specs.... I've always wondered who can afford 14" of EPS under a slab of any size, and then, can you ever pay for it? I don't know PH "rules" all the way around, but I have seen the use of 14" under a slab and question it in all but the most extreme environments (none of which are in the Lower 48, IMO.) Not to bash PH; it is a great movement, but perhaps a bit overzealous in a few spots.
John, yesterday I attended an excellent talk given by Jesse Thompson about the Passive House concept.
The heart of it is, if you are thinking about putting in a $25,000 heating system into a conventionally built house, put $19,500 of that into the shell, $5000 into an HRV, and $500 into a super simple heating system. In order for a $500 heating system (such as electric baseboards) to heat the house on the coldest night of the winter, you need thermal mass working for you. That's what the slab does if it's totally isolated from the ground.
I agree that in anything resembling conventional construction, insulating under the slab is the last place to spend insulating dollars. In a Passive House you need all the help you can get.
Chris, sorry about the hijack. I've framed with green hemlock and there is no way I would trust it for a Passive House. Other woods don't move as much as hemlock as they dry, but in any case if you want good air sealing I would use nothing any wetter than lumber air dried to 20% or less.
John, you can get 14" of EPS from Home Depot for $5.00 / SF, and cheaper from other sources ($1.00 / SF from foam salvage sources!). That doesn't seem like much of a deal breaker for most custom home projects when you think of how many people easily spend over $100 / SF for countertops.
Michael,
Martin has written a lot here about the cost trading concepts of low energy design, and there are many situations where that cost reduction threshold occurs before the Passivhaus level (many houses don't start with a $25k heating system!), but it's still the critical concept to keep in mind. We should be constantly trying to shift the focus of our design away from expensive and short lived machinery and towards well insulated and durable building shells.
Jesse,
I couldn't agree with you more. It makes me tear out my hair in frustration when I see a house with a $30,000 ground-source heat pump and cheap double-glazed windows.
For crying out loud, you don't need a GSHP! Take all that money and buy some decent windows already!
Jesse and Martin,
I agree with you both. I just need help figuring out how to convince our clients that it's worth it. As someone wise once said, insulation is not sexy. If people want expensive countertops and Buderis heating systems, and can afford $10K a year in heating bills, how do you force them to spend their money differently?
14" EPS would cost me a little over $6/sf, maybe closer to $7. With a ranch house, that gets the initial price way up there. A $25K heating system and $100/sf counter tops are a bit extreme, though I am sure you can go even higher if you work at it. A Viessmann Vitodens 200W boiler, which is a pretty nice condensing propane unit, is about $4K, plus PEX, etc. Way under $25K. Remember, too, that most people don't have 3600 sf of counter top. Putting 14" under the slab is admirable, of course, but that is not where the big heat loss is; it's at the edge and through the walls. The delta T below the slab in nothing compared to the outside temp (cold climates), though it is constant. I understand wanting to heat w/ a candle or a mini Dachshund, but 14" is still a lot of insulation to pay for with, as far as I can tell, a slow pay-back rate. Arguable either way, so each person has to run their own numbers and make a call. j
John, you're not really making a fair comparison. You're in Alaska, right? Code already mandates you have R-10 under your slab, so you've already paid for 2 1/2" of that foam, so it's the incremental increase we're talking about, not the total cost.
As well, that Viessman doesn't come free, it requires distribution, pumps, manifolds, radiators or baseboard, and someone has to install it. We've never managed to install a nice German mod-con for $4k in any of our houses, most people quote at least $10,000 - $12,000 to install a system like that.
Whether or not it makes economic sense to put that much insulation under your slab will depend on what your energy model says, do you have one going yet?
Jesse: No, no system is free, but $25K seemed a tad on the long side. The $4K I mentioned is just the boiler, yes, "plus PEX, etc", as I mentioned. Energy model: Yes, I have looked at various sub-slab insulation levels, and I wish I knew exactly how to calc heat loss in that area. It seems there is no real consensus on it. Do you treat a slab like a wall with a smaller Delta T (which ignores edge loss, specifically) like I chose to do, or do you use Siegenthaler's equation, which is based on particular and different parameters? Or something else? My method gave me 15% more heat loss through the slab than Siegenthaler's equation, btw. Using my numbers, I'm spending $413 to heat the slab with 6" under it. To go to 14", which I originally considered, following the PH lead, would cost me an additional $13,700. Even if I saved the whole $413, 14" is not a great way to go, I feel. So, unless I screwed up my numbers somewhere, it is hard for me to see 14" of foam under a slab, because you just don't have a huge heat loss down there.... apparently. If someone has numbers on what these fancy pants software packages calc for a slab heat loss/sf/hr, let me know all the details, because I just don't see a slab as a huge loser. BTW: I will have ~R50 outside the foundation wall and slab edge. Keep in touch. john
John Klingel,
John Straube agrees with you. He ran some numbers on the different options; in case you didn't see the article, it's here: Can Foam Insulation Be Too Thick?
Note: in a sealed-tight home, if you're going to heat with a candle OR a mini-dachshund, you're going to need careful ventilation. Just saying.
Thanks for the grin.
Martin: Yes, I read that article a while ago, and it helped convince me that I was not too far off bubble; or at least not alone. I used a ground delta T of 40 in my calcs, based on scant ground temp data I have been able to find. That may be a bit conservative, but being conservative may "neutralize" the fact that the ground will never gain you anything, like air does in summer. I am planning on installing thermocouples under my slab in hopes of adding to the available data. Thanks.
Joew: Yes, noxious gasses come out of, or off of, both.
Elsewhere on this site it is noted that the passivhaus spec does not require 14 inch underslab, it is an artifact of a flawed process. There is no point south of the permafrost of having that much foam. None. The Delta T to the ground is never going to be over 35F, probably 20F, as long as the perimeter is properly insulated.
One could argue that massively insulating the perimeter and leaving an unheated slab uninsulated contributes to thermal mass. Dunno if I would go for it