Need No VOCs – How to accomplish?
A_Moonstone
| Posted in Green Building Techniques on
I have an extreme chemical sensitivity (yes, basically I’m allergic to life! lol), but I want to build myself a tiny home on wheels. I wonder if this can be accomplished.
I think that wool insulation would suit my needs best, but I’m not sure about the exterior because I’m very sensitive to off-gassing materials like Tyvek, etc.
I was thinking perhaps cedar shingles, but would I still need some sort of vapour barrier? Then I was thinking plaster and lathe, but I live in a cold climate with strong winds and temps down to -50°C…
What to do?! Any ideas?
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Replies
By “wool insulation”, I mean sheep's wool, and by “no VOC”, I really do mean ZERO VOCs.
A. Moonstone,
You don't need a vapor barrier. However, it's good to pay attention to airtightness. Plaster and lathe are fairly airtight.
Thank you! ☺️
Part of the challenge here is being sure we understand what types of materials you are sensitive to.
For example, many natural materials do emit VOCs--pine sap has VOCs in it, cedar even more, and if the wool has residual lanolin on it, that contains VOCs. Or if the wool is stripped of the lanolin, who knows what your sensitivity to the chemicals used to strip it might be. But perhaps you have been around freshly cut pine, and perhaps even sheep, and you know that those natural VOCs are not as problematic as petrochemical VOCs.
If we made a list of materials you are OK with, we'd then be able to figure out how to build with them. Here's a guess at a start at that list:
Metal
Pine
Wool
Glass
Wood glue
concrete
Can the metal have factory-painted baked-on finishes? Or should it be bare metal, such as stainless, aluminum, and copper? Are there any plastics or rubber materials that are OK?
As far as trying to do conventional building with a limited set of materials, you are right that the water-resistive barrier (WRB) on the outside is tricky. If we back off from modern housewraps to more traditional materials, we would be using asphalt felt, which has got to be worse from a VOC standpoint. The other modern option is plastic foam based approaches, but I assume that is off the table. Aluminum sheets make fantastic water barriers, but their zero vapor permeability would be a problem in your climate. So you might be stuck going back to building with no WRB. That's probably OK if you use relatively moisture tolerant sheathing such as pine, rather than OSB, which you'll probably want to do anyway to avoid the glue in OSB, and you include a good rainscreen gap and meticulous flashing (soldered copper perhaps?). The siding could be cedar shingles, or aluminum siding that has ventilation built in.
One thing I don't like about that plan is that it wouldn't be air sealed on the outside, but you could probably do all your air sealing on the inside, and particularly with tongue-and-groove boards for the sheathing you wouldn't have too much wind-washing of the insulation. If you are willing to use carpenter's glue, you could glue the boards together.
Can you tell us which climate zone you live in? There's a map on the front page of the Q&A section.
If you're thinking of building a new house, then of course you're right in starting off by not putting any offending materials into the house. I suspect that your ventilation system will end up being something that takes a fair amount of thought at the design stage, in part because you may be more sensitive, and partly because you're planning on living in a small space. Plus, venting a well-sealed dwelling while it's really cold outside may present some challenges if you're trying to keep it both comfortable and efficient.
Moonstone,
Moving your air-brrier to the interior will help keep materials that you are sensitive to outside the conditioned space of your new house.
Hi folks!
I find that natural VOCs are not as problematic.
Metal, pine, wool, glass, and natural latex rubber with no additives seem to be fine, but I have to avoid things like wood glue and concrete.
It would have to be bare metal. I can't deal with any kind of paint job that is newer than ten years old (off-gassing), unless it is natural mineral paint/milk paint/beer paint.
I like the idea of pine sheathing! Wonderful! So cedar shingles could go over top of that as the siding?
I'm in Climate Zone C (plant hardiness zone 2b).
I did not even consider ventilation, Andrew. Thank you for mentioning that!
There was an article on GBA that talked about a woman with MCS and how they determined what she was sensitive to by exposing her to a very small amount in a glass jar. She would take the lid off and know immediately if it was acceptable.
Could a similar process help you?
Interesting that you need to avoid concrete...I thought that would be completely inert, but then I googled it and learned that it can have a wide variety of chemicals added for various purposes. A study commissioned by the concrete industry reported VOC emissions rates on par with materials like vinyl, although it concluded that the emissions were non-toxic and not a concern. But obviously that "not a concern" doesn't apply to you, and one should probably take it with a grain of salt in general.
Anyway, a tiny house on a trailer base is a good way to build without needing concrete!
Yes, pine board sheathing, with cedar over it as siding could work. For maximum structural benefit the sheathing should be diagonal. Diagonal is a little more work, that wouldn't amount to much extra labor on a tiny house, and the bracing it provides is important if is going to be moved around. I would cut the boards in "shiplap" fashion to make it a little more wind and water resistant. It's probably not necessary, but I'd consider whether there's something goey you could use to seal the joints--maybe beeswax? The traditional boatbuilding approach is to use a fibrous material stuffed in and sealed with pine tar. Pine tar might be OK for your sensitivities, but that might be pushing your luck for little benefit. I'm not sure whether having some wool yarn in the crack would improve or degrade air tightness without any sealant. All in all probably not worth bothering with trying to seal it but beeswax or yarn dipped in molten beeswax might help.
Without housewrap, furring strips to allow airspace between the sheathing and shingles are a good idea. For shingles, some people just run the furring strips horizontally. But doing both horizontal and vertical as shown here:
http://studio-tm.com/constructionblog/wp-content/uploads/2011/03/cedar+shingles-siding-strapping.jpg
is a good idea for maximizing the potential for draining and drying of any water that gets in there, and I think that's a good idea if you don't have housewrap.
You could consider a metal foil layer as an air/vapor barrier on the interior, between the studs and the wallboard (is drywall OK for you? Maybe the interior will be plaster?). Metal foil is better barrier to block VOCs than pretty much anything else, so that would be extra insurance in case something somewhere in the outer layers of the walls isn't as safe for you as expected. In your climate, an interior vapor barrier is an OK thing to do, even though it's not strictly necessary and it's problematic in other climates.
I do wonder about a plaster interior cracking when you drive over bumps. You might need to re-do the cracks after moving it--how much do you envision moving it?
You'll probably want an unpainted metal roof. Options could include copper or unpainted galvanized steel. Perhaps Martin can comment on how to make that robust without the use of asphalt or plastic underlayment layers.
I'm sure some people will think that going to these lengths is unnecessary. It may be true that a good interior air/vapor barrier would allow you to use pretty much anything outside of that barrier. But I think it's a good exercise to think through what's possible sticking to your list of safe materials, and if it can be done well sticking to that list, why not play it safe?
Aaron, yes, I'd be able to tell, but I'd also suffer consequences. I kind of just have rule of thumb that if it contains any ingredients created in a lab, it's probably not for me. ;) Thank you for the suggestion though!
Wow, Charlie! That was so incredibly helpful! Thank you so much!
You are correct: "not a concern" generally does not apply to me. I'm a special snowflake. hahaha
Okay, so we've got diagonal pine sheathing cut shiplap-style, and cedar shingles attached to furring. I like it! Great photo.
The beeswax sounds good; I can get lots of that locally and fairly inexpensively. I can also harvest pine sap quite easily and it would be free. Or do you think lime mortar would work for sealing?
I'll look into metal foil for sure. I can't use drywall at all, but I wouldn't mind keeping lime putty around and sealing cracks when I moved, though hopefully I'll rarely have occasion to move. It's more like an "insurance" measure since the land is owned by a friend, and friends are occasionally known to move, die, or change their minds. Or maybe I could just do a tongue and groove pine interior...
Copper sounds like a gorgeous roof! I like that idea. Oooh, or maybe I could do solar shingles? But then I still need something under it. Nope.
Okay, I think we're really into something with all this. Yay!