Petroleum-free vapor barrier?
Hello,
I am in the process of building an off-grid home where we plan to pour 3″ adobe floors over a plywood subfloor (with radiant heating in the adobe). In order to do so, we need to lay down a vapor barrier to de-couple the adobe from any floor movement, and to protect the plywood from the moisture that will be in the adobe when it is poured. However, at this point I’m rather appalled by the amount of petroleum based products we have had to use in order to get good air sealing on the exterior envelope (not to mention the mountains of plastic packaging all our materials have come in). So, I’m wondering if there are vapor barrier products out there that are not plastic based. Alternatively, are there any manufacturers that utilize better production practices that are less harmful on the environment than the industry standards?
Any assistance would be greatly appreciated!
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Replies
mwk,
With a bit of planning you should be able to completely eliminate poly from your build. You don't say what foundation type you using, but probably the hardest place is as a moisture barrier under the basement or crawlspace slab. Gypcrete and concrete are routinely poured on plywood subfloors without poly vapour barriers. I'm not sure one is necessary under adobe, but would bet other materials would work as both a slip-sheet, and provide enough protection during drying. Unfortunately the one the comes to mind is building-felt, which is asphalt impregnated. Another alternative would be a vapour-barrier paint and rosin-paper.
Aha! You are in luck, assuming you’re in North America. Most polyethylene in this region is NOT produced from petroleum. Most polyethylene in this region is produced using natural gas as a feedstock. This has become especially true with the recent natural gas production boom.
Now let’s assume you want a polyethylene product that isn’t sourced from either oil or natural gas. There is what is known as “biopolyethylene”, which is polyethylene produced using ethanol (usually from corn or sugarcane) as a feedstock. You’d probably have to hunt around to source this material as I’m unaware of any products specifically mentioning that they are made this way.
Most plastics are interesting in that they do NOT have to made using petroleum. Petroleum is just an efficient carbon chain rich soup to use as a feedstock. There are other ways to do it, but oftentimes the tradeoff is you don’t use oil, but you use a more energy intensive manufacturing process to arrive at the same final material. Plastics are just polymer chains, basically looong strings of carbon atoms with different element groups sticking off the sides. Petroleum is basically made up of various carbon chains too, so there isn’t much processing needed (relatively) to use it as a starting point to manufacture plastics. You can start with anything that has the right atomic makeup if you want to invest the time and energy to do it.
Regarding your specific application, I really think polyethylene sheet is probably the best option. Most natural materials will break down when in areas that are constantly damp. I’d look into either biopolyethylene, or just use regular polyethylene knowing it was probably made primarily from natural gas in North America. The final product is identical in terms of atomic makeup either way, so both have identical properties.
Bill
Hi Bill ,
Thanks for the info on non-petroleum plastics! Do you know anything about the life cycle impact of the biopolyethylene? Does it biodegrade when in a land fill? Or is it easily recycled? One of the reasons I'm trying to get away from plastic in my building is because we're looking at the building materials in terms of full life cycle impact, including what happens if they whole place gets torn down at some point in the future.
Looking forward to hearing from you,
Maya
Biopolyethylene and regular polyethylene are identical in terms of the physical properties of the product.
What makes a material the way it is, and that includes physical properties, including how it will break down over time, is the arrangement of the atoms that make it up. The place those atoms were in before they were rearranged to make the final product doesn’t matter. What this means is if the atoms started out in petroleum, or natural gas, or corn growing in a cornfield, once they’ve been rearranged into polyethylene they all behave the same.
This ultimately means that both polyethylene made from petroleum or natural gas, and biopolyethylene made From corn or sugar cane, will all break down the same way in a landfill and can all be recycled the same way too. The final product are all identical in terms of their chemical makeup — the type of, and arrangement of, the atoms that make them up.
It sounds like you want to make a structure with a minimum overall environmental impact. This is a complex question, because there are many ways to look at the problem. Is “minimum environmental impact” minimum energy use over the life of the structure? Maximizing the useful life of the structure? Using materials with the lowest embodied energy? Using materials sourced from only natural materials? Which is your preference? I don’t like thinking in terms of “natural materials”, because ultimately everything came from nature, it’s just a matter of how much processing went into things. Even petroleum is a natural resource, just a gooey sticky one. Embodied energy is better than thinking in terms of embodied carbon too, but both of those two is just my way of looking at that part of the problem.
I would recommend trying to keep things in balance to try for minimum overall impact. Don’t try to make your structure last 500 years, that would require a lot of fancy materials. Don’t rule out any product just because of how it’s raw materials were sourced. Try to minimize energy usage of your structure, but be reasonable — too much insulation gets into diminishing returns, and that means you would have achieved more by allocating your own resources differently.
If this was my place, I’d put a lot more insulation than code requires, but not crazy (no R100 attics, for example). I’d use plastic materials in places they make sense, like under slabs. If materials in those locations biodegrade too quickly, you have to rebuild part of your structure — that’s a LOT of energy use that could have been avoided by using a different material.
Wood is a good basic building material. Trees used for lumber are usually farmed these days, so they’re a crop just like corn or wheat — basically a renewable resource. No one is clear cutting old growth forest to produce 2x4s. Rigid foam is great for insulation, even though it’s usually made with plastic materials. The tradeoff is that foam will save you a LOT of energy over he life of the structure.
I’m an engineer by profession, so everything I do involves trade offs. When you’re doing your design work, think about which trade offs are most important to you. Sometimes the best overall solution isn’t what you’d first expect. If you focus on only one particular property of any given material, you may miss that that material could actually help you in some other way more important than the particular negative property you focused on.
There is a lot of info on this site, and lots of people with different ways of looking at complex problems. We can all learn from and help each other. Building things is fun, and everyone has their own priorities on different projects.
Bill
" Building things is fun"
Tell that to my thumb. It had fun with Mister table-saw yesterday.
Hope you’re ok Malcolm.
A carpenter on a recent project I was on came in with some newly damaged fingers a while back. The saw stop system was the talk of the job site that day. I myself have a shiny new compact paslode framing nailer. I am always wondering if it will nail me some day...
Bill
Thanks Bill, it's nothing that won't heal.
I wish I had sprung for a Saw Stop years ago. Don't worry about the Paslode. I've put three through my fingers over the years. They come right out.
Try not to drive Paslode nails into your fingers lengthwise. I have a ball of scar tissue on the grip side of my right (primary) index finger that has reminded me of that on an hourly basis for the last ten years. And having seen the aftermath of tablesaw accidents, if I could afford it I would definitely go with a Sawstop.
Michael,
Two of the three were in the early 90s using one of those old Sencos which had a smooth safety tip that let the nose slide too easily. I'd still rather drive an air-nail through my thumb than hit it square with a 25 oz dimple-head Estwing.
Hi Bill,
Thanks for the advice. Just to clarify, I am a licensed architect specializing in sustainable design and construction, and am well aware of all the trade offs that go into designing and building a structure. The question I am trying to get answered here boils down to:
Are there any materials out there other than plastic and asphalt that can function as a vapor barrier?
My own research and investigations have not turned up anything promising, which is why I reached out to this forum.
Hopefully someone out there has dug further into this and can come up with a product with a lower environmental impact than those used in standard construction. I've already got an entire crawl space covered in plastic, and several truck loads of plastic trash taken to the dump due to the excessive packaging all our building materials come in. So, I'm hoping to avoid adding more plastic to my build or the land fill.
Looking forward to hearing more thoughts on the subject.
About the only other thing I can think of that would work would be a thin metal sheet, stainless steel or copper. My guess is that metal processing is probably more resource intensive than the manufacture of polyethylene sheet though, so I’m not sure you would accomplish your goal of reduced environment impact by switching to metal here.
Bill
Hi Bill
thank you so much for explaining this
I'm an architectural consultant for building enclosure technical design.
Ive recently started doing some research in non plastic or asphalt air vapor barriers and was recommended to look into wax-paper. I've also been looking into mycelium, which would be easy to install in cavity walls in particular.
do you happen to know what kind of wax has similar properties to that of a self-adhering air vapor barrier product? im not a chemical engineer and would appreciate any feedback.
There are sealing waxes used commercially, usually to fix adjustments in place in electronic equipment. I have never seen wax used as an air or vapor barrier, but I could see wax being used as a spray-on sealant to use on sheathing. You’d want a wax that wouldn’t get eaten by critters, and you’d need something that would last.
I’d suggest calling some chemical companies to ask about this. Dow chemical might be a good first call since they make building products and might have more familiarity with things like you’re asking about.
If you could get a spray applied wax coating you might have an interesting product idea.
Bill
Thank you Bill
Et al-
researching earlier today and found this for a brief history of air and vapor barrier products:
https://nrc-publications.canada.ca/eng/view/accepted/?id=db9bccc2-eff6-4249-8a3f-0d2224dc30db
Also I found this: http://www.airbarrier.org/wp-content/uploads/2019/09/ABAA-Technical-Note-2-Air-Barrier-Materials.pdf
Beeswax paper
Linseed oil wax breathes and is water resistant, its not marketed for the use you're describing but it does what you're seeking to achieve. https://www.earthandflax.com/product-page/viking-pigmented-linseed-oil-wax-oak
mwk,
After the initial cure of the adobe, and given there will be radiant heat in the floor, why do you need anything to protect the subfloor from moisture?
Bentonite clay. Just be sure to compress it in the process of installation to ensure top effectiveness.
Our friends here appear to discount the effect of fractional distillation in the petrol-derivatives supply chain and excruciatingly high kiln temperatures required to product frankencement aka "Portland" cement in the overall "embodied energy" tally, e.g. Of course, I'm discounting the mining efforts of clay mining... though clay mining can be executed in a pinch by anybody with a shovel near a source. Fractional distillation and 1300C kilns? Not so much.
My partner and I are looking to do something similar. Were going to use linseed oil paint which is vapor permeable and resists water on ply or ramboard. Its a bit of an experiment but so are all these petroleum plastic sheets everyone is using.
Linoleum. (Typically, ingredients are flax, pine rosin, wood flour, cork dust, calcium carbonate, and jute.)
Yes. Real old-school linoleum. I reckon pine tar can play a role, mixed with linseed oil - certainly on real wood surfaces. Options are available. Thanks for posting!
You’d need a really big sheet of linoleum, and the tradeoff would be more installation labor I would think, at least compared with polyethylene sheet.
I can’t see bentonite working as a vapor barrier. I work with that material a lot, and moisture can migrate through it, similar to how concrete isn’t a vapor barrier. It has somewhat goofy properties too when it gets wet (it expands). It’s good for underground grouting, but I’ve never seen it used for much else as a construction material.
Bill
Could be that pine tar / linseed oil is best option of the lot. I use it on clapboard; of course, shipbuilders have used pine tar for centuries.
Keep in mind that many substances that are waterproof are not vapor barriers. Latex paint is not a vapor barrier. Drylok is not a vapor barrier. I wouldn't assume that linseed oil or pine tar is a vapor barrier.
Also, just because something is naturally-occurring doesn't mean it's safe. Creosote occurs naturally in wood, for example; you don't want it anywhere near your home.
Yet creosote is living in millions of homes. And we thrive. I want creosote, I have creosote, and I produce more creosote in and on my homestead every day. A contrarian’s contrarian? Hmm
As with most things, it’s how creosote is managed - not its mere presence - that matters.
Polyethylene is a very stable material. It doesn’t leach out into things, it doesn’t offgas, almost nothing reacts with it, and it’s not toxic. Polyethylene is a much safer product to use in a home than anything treated with creosote.
I like to say “just because it’s all natural and organic doesn’t mean it’s safe. Remember that bubonic plague was also all natural and organic, and it caused the Black Death that killed nearly half of the population of Europe.”
There are synthetic materials that are better than natural ones if you want to be healthy, and this would be one of those cases.
Bill
I guess I'll die any day now due to my use of natural and organic materials in my house lol. Along with billions of others.
(I treat nothing with creosote, to be sure - someone else claimed creosote is contained in harvested and dried wood lol.)
Gregg,
That’s an unhelpful comment as that wasn't what Bill was suggesting.
I can’t keep track, Malcolm. Both DCcontrarian and Bill are suggesting wood and wood derived products are either dangerous or inferior to petroleum products in homebuilding applications, without exception! I find these assertions laughable at best and dangerous at worst. To quote Bill: “There are synthetic materials that are better than natural ones if you want to be healthy, and this would be one of those cases.” I’m as healthy as they come, and I built my house with almost no petrol inputs. Ask my Airbnb guests their impression of my home. The hundreds of reviews are unanimous on health and well being.
Gregg,
They are saying something quite different, which is that the distinction between "natural" and synthetic materials doesn't always equate to healthy and unhealthy. I don't think that's an assertion many people would dispute.
Well-being is so nebulous a term in this discussion that it really has no useful meaning.
Reply to post #27:
I did not say or imply that "natural" products were "dangerous or inferior" to "synthetic" products in [implication is all] applications, "without exception". What I meant was that synthetic materials CAN BE superior in SOME applications. It's not an all-or-nothing deal here, but just because something is "natural" does not mean it is somehow inherently "healthier". A great example would be asbestos: it's all natural! It's rock! It's fireproof! It, well, also can cause cancer. Bummer. Mineral wool does pretty much all the same stuff, but without that dissapointing carcinogenic property.
In the case of polyethylene, which is NOT usually produced from petroleum (see my earlier posts from several years ago), it's often the best product for the job. It's relatively low impact to make, it's easy to work with, it's very safe and long-term stable, and it's an excellent vapor barrier. It's great as a vapor barrier. I wouldn't use it as a primary air barrier though, I'd much prefer to be using drywall or plywood for that. You need to pick the best material for the application in each case, and just going for "natural" doesn't mean you've found the best or healthiest material -- it's more complicated than that.
There are also different goals. We see in these forums people who want longevity, people who want lowest energy consumption over the life of the home, people who want the lowest embodied carbon, etc. Different goals. Different materials are better for different goals. I always try to advise people towards what I think is the best product for their stated application and their stated goals first, and if I think there is a better way to go that might not meet their goals, I will usually describe that second, along with my reasoning why I think it's better.
To try to imply that "natural" is always best is also a problem, and that's where a lot of the "greenwashing" stuff occurs. That stuff is deceitful, and I try to put a stop to it where and when I can. Spreading false information helps no one in those cases. In some ways, "natural" can even mean different things: petroleum, as one example, IS a naturally occuring material, even though many people (including me) would consider products derived from it to be "synthetic" products.
Bill
[Reply to #29]
Bill --
It's not worth responding any further. When someone deliberately mis-represents your position they're clearly not interested in an exchange of ideas.
Hi, Bill. Thanks for clarifying.
The driver of decisions is the goal of the project or client, indeed.
I reckon for this thread we've both answered the question posed. So-called natural materials as well as "other" materials offer pros and cons in specific applications.
As for asbestos... my house had asbestos siding when I purchased it. All good, to be sure. Asbestos doesn't cause cancer as it sits outboard my house protecting it! Lots of folks in my city sport asbestos siding. Works wonderfully well for the application.
Onward!
DCcontrarian: "Creosote occurs naturally in wood, for example; you don't want it anywhere near your home."
You're welcome to flesh out this confusing passage.
[Replying to #32]
"You're welcome to flesh out this confusing passage."
By "it" I hope you realize that I meant creosote and not wood.
From the Wikipedia article on creosote:
"Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood, or fossil fuel. They are typically used as preservatives or antiseptics."
From the Wikipedia article on Tar:
"The heating (dry distilling) of pine wood causes tar and pitch to drip away from the wood and leave behind charcoal."
The tar is in the wood. The creosote is in the tar. Creosote is a "natural" product, you just have to heat the wood to get it out. It's not the result of any chemical synthesis.
Also from the creosote article, on the health impacts:
"According to the Agency for Toxic Substances and Disease Registry (ATSDR), eating food or drinking water contaminated with high levels of coal-tar creosote may cause a burning in the mouth and throat, and stomach pains. ATSDR also states that brief direct contact with large amounts of coal-tar creosote may result in a rash or severe irritation of the skin, chemical burns of the surfaces of the eyes, convulsions and mental confusion, kidney or liver problems, unconsciousness, and even death. Longer direct skin contact with low levels of creosote mixtures or their vapours can result in increased light sensitivity, damage to the cornea, and skin damage. Longer exposure to creosote vapours can cause irritation of the respiratory tract.
"The International Agency for Research on Cancer (IARC) has determined that coal-tar creosote is probably carcinogenic to humans, based on adequate animal evidence and limited human evidence."
I looked into the question of whether linseed oil is in fact a vapor barrier. I couldn't find a specific perm rating, but some linseed-oil-based paints are sold as a more vapor-open alternative to latex paint, which is itself pretty vapor-open.
Hi Bill! I've really appreciated reading through your answers, and learning more about this today. Thanks so much for sharing what you have! I am building a tiny home on wheels, and like those in this thread, am inclined to use 'natural materials' where I can. I appreciate your cueing in more deeply to all the trade offs there are to consider in what is most valuable.
I am in the step of choosing exterior insulation and am coming into some questions.
My build mentor has suggested halo exterra as a rigid exterior insulation, which is surfaced in such a way that you dont need to add house wrap.
I also found a 'plant panel' made by hempitecture, that is intriguing to me, and my gut is inclined to try it. Each come in a 2" depth. Would you suggest one over the other? Would it make sense at all to have the hemp on the inside layer, and put the halo on top of it, so that the hemp material is more what could reach my air space, if any ingredients from the halo would seep into my air space, but that the halo would be an extra exterior layer facing the outside? Or would that be more ext insulation than necessary, and I ought to choose one or the other - the halo or the hemp board with a house wrap?
I am looking to put the hemp wool most likely between the cavities of the studs. The hempwool has an r value of r20, at 5.5".
The hemp board exterior plant panel has an r value of 3.25 per inch, at 2" thick.
The halo board has an r value of r 5 per inch, and comes in tihicknesses of .563”, .625”, 1.0”, 1.5”, or 2.0”.
I am building this home to be good in varied climates, specifically Maine and Colorado. Their building codes ask for r20 between the studs and r5 on outside, or r13 on inside and r10 on outside. It looks like just the hemp wool and one layer of either should cover those specifications. I will have big windows on two sides, so I wonder if doubling up on the exterior would help be more of a 'winter jacket,' or be unnecessary.
This is my first big riddle in the materials choice process, and I'd love to take each step as it comes, and hopefully allow them to feel more clear and straightforward. I appreciate your way of talking through things, and really appreciate any feeback you have!
Here are the links to the three materials!
Thank you so much for anything you see there!
-Erin
Hempitecture plant panel x - https://www.hempitecture.com/plantpanelx/?srsltid=AfmBOoqrtcc0QUeYIgQaloG-7PWOUswTsw4kC2TNT7qubuamD-RsnAqh
Halo Exterra - https://buildwithhalo.com/halo-exterra/
Hemp Wool - https://www.hempitecture.com/hempwool/
I don't think building codes apply to tiny homes on wheels, as they are mobile. I may be wrong on that though. I think your primary concern with such a home would be trying to maximize your interior living space, since you're already working with a very small structure. Cleverness and efficiency are key here!
I don't see anything wrong with the Halo Exterra panels, they are GPS (graphite loaded EPS, a well-known insulating material), with an exterior facing. The downside I could see with this material is that it may be pretty expensive. I haven't worked with it myself. My first thought though would be to use foil faced polyiso on the exterior, partly because I'm very familiar with that material, but also because you may be able to find reclaimed polyiso to save some money. The foil facer can also act as a WRB when taped at the seams. You will ABSOLUTELY want some type of exterior insulation here though, since it's much more effective than "between the studs" insulating materials of any type.
I would try to use reduced depth studs if possible, to increase interior space. I'd also use some type of structural sheathing (i.e. plywood) on the exterior, to give the walls good levels of shear resistance. When you're driving down the road, bouncing over potholes and slamming on the brakes when some #$%^! driver ahead of you does something dumb, you don't want your tiny house flexing too much and cracking details or breaking the structure. You need more strength than a fixed house does, because a regular home doesn't have to go bouncing down the road. Potholes are on my mind a lot as of late, since snow melt is making a mess of the dirt road I live on.
I would try polyiso on the exterior, reduced depth studs, and possibly cut EPS panels between the studs (i.e. 1.5" EPS if you us something like 2x3s on the flat). Note that I have never built a tiny house myself, so I can't speak from experience on the structural details that are preffered here, but I can offer ideas to think about regarding space and insulating materials.
The hemp board exterior panel is poor in terms of R per inch. GPS, EPS, and polyiso are all far superior here, so I'd use one of those to maximize the R value you get in the available space. Maine I understand can get pretty cold. I have family in Colorado, and I know many areas out there can get pretty cold too! You want R value. Since you're tight on space, I'd choose materials with a first priority specification being R per inch.
Hemp wool has an R value, using your numbers, of abobut what medium density fiberglass batts offer, so it's not the best out there R value wise, but you aren't really losing any R value using it, either. Mineral wool is a bit better, but not much (about 10% or a bit more). I would not have a problem using this material in studwalls if you use full depth walls, or if you don't want to use rigid insulating panels (EPS, polyiso, etc.) cut to fit tightly between the studs.
Bill
You're the best, Bill!! Thank you for this very thoughtful reply. Thanks for taking the time to listen, give it some thought, and share your instincts!! Taking in your considerations as I read, and integrating it into my research! I'll respond here as I keep making decisions in case it is insight giving to stay in touch along the way!
Thank you so much!!!
Erin
There are some others on here who have built mobile tiny homes before, so I recommend you start a new thread about your project and ask for insights. Things I've seen come up before have to do with the structure, bracing, the trailer and attaching the structure to it, and vapor control layers. There are probably other things I'm forgetting too :-) There are many knowledgeable people here who can help you.
Bill
Google search aluminum foil: https://superiorsaunas.com/products/aluminum-foil-vapor-barrier?currency=USD&variant=40177122771033&utm_source=google&utm_medium=cpc&utm_campaign=Google%20Shopping&stkn=17d3a8aa1009&gad_source=1&gclid=EAIaIQobChMIoYztktLwiwMVtklHAR0bnwWLEAQYAiABEgLg0PD_BwE
The cool thing with aluminum foil is that it can block radiation as well so it might block your wifi and cell signals. It's also good for hats for this reason.
That's probably pretty fragile and tricky to install.
It will block wireless signals, but if you have a window, cellphones will still work, just with reduced signal levels. Wifi would be fine IF the access point was located INSIDE, but you'd have very limited coverage if you went outside due to the foil blocking the signal from going through the walls. It actually takes a lot to completely block RF signals, since they can sneak in through all kinds of gaps.
Bill
There's glue that can be used to install it. It's available in a spray can. Probably petroleum based though, lol. There are likely environmentally friendly ones available as well though.