Crawlspace, insulation, vapor barrier and fire rating: how?
I was on the phone with the building dept. on Friday discussing preliminary ideas about converting my vented crawlspace to conditioned space, and it all seems doable by me, but I’m confused about the fire rating issue. I’d like to try to understand this better before I speak to the permit people again, so I don’t wear out my welcome before I even get to the stage of submitting my proposal. Here’s my confusion:
Basically, I put vapor barrier on the ground, rigid foam on the walls. I need to cover the rigid foam with a thermal barrier. I understand the reason is the toxic gases from the foam if it burns. Drywall fits the bill, but it’s not the best choice in my situation because it would be difficult to get down there and difficult to install. I see that there are a couple of people manufacturing rigid foam with a foil barrier, which may satisfy the fire requirement, and any other suggestions would be helpful. The inspector I spoke to said there was a flexible material that would work, but couldn’t remmember what it was called. Also, in my searching around the internet, I’ve found quite a few places selling heavy crawlspace vapor barrier material and in the information sections they are showing it run all the way up to the mudsill. Same goes for all the crawlspace “encapsulation” companies. No mention on these sites of insulation behind the poly. This makes me wonder if the poly itself is considered a thermal barrier? That doesn’t seem likely, but it also seems unlikely that people would go to the trouble of converting their crawlspaces to conditioned and not insulate the walls. Clearly it’s me that is confused here. It would really help if someone could help clear my confusion.
Thanks in advance.
Replies
Here's some info to chew on:
http://www.buildingscience.com/documents/reports/rr-0401-conditioned-crawl-space-construction-performance-and-codes/view?searchterm=CRAWL%20SPACES
Once you get the crawlspace sealed, you can treat it like a mini basement. That means you can frame up a mini wall inside your foam and drywall it.
Thanks, but...
I understand the benefits. My confusion is about the drywall. I'm looking for an alternative because getting the drywall down there in the crawlspace would be difficult. It would be a lot simpler if I could just install a single light-weight, waterproof panel which would serve as air seal, vapor barrier and insulation all in one. Indeed, the articles by the author you reference show exposed rigid foam panels placed on interior foundation walls in conditioned crawlspaces. According to my local building dept., this would be a fire code violation.
So, I was asking about fire-rated rigid foam. I've asked around town, at various suppliers, but nobody knows what I'm talking about. Moreover, I've looked at a lot of crawlspace encapsulation websites, and they show the heavy duty vapor barrier running right up to the band joist, which, as far as I can tell, would be a code violation if there is regular expanded polystyrene panels behind the vapor barrier, unless the vapor barrier itself is considered to be an ignition barrier.
So, I'm asking sort of a two part question: 1. What's the deal with fire-rated expanded polystyrene panels? Why doesn't anyone around here (2 hours north of Seattle) know about them? and 2. Are hundreds of basement encapsulation companies around the country installing systems that clearly violate codes?
Replying to my own post because I think I may have a little bit more understanding now. I thought this was a fairly simple question, but I am beginning to think that it's an issue that teeters on the definition of "living" space, vs "conditioned" space. In any case, I found a material, available locally, called Reflectix. It's a bubble-wrap, reflective insulation that comes in 48" widths. It claims to be a "class 1/ A" fire rated material, which is, therefore, equiv. to gypsum, as far as I can tell. My thought was that I could put up foam board and cover it with this material. Am I on the right track?
Don't assume anything without checking with your BI.
I'm sure there are hundreds of materials you could use to cover the foam panels, but none are as inexpensive AND easy to work with AND effective as plain old 1/2" drywall. Only OSB occasionally gets cheaper than drywall at $6 a sheet.
I'm not understanding your reluctance to deal with 4x8 sheets of drywall, when you are already dealing with 4x8 sheets of rigid foam panels.
If you are concerned about dealing with the weight or size of an individual panel, you can cut the panels down to exactly the size you need before bringing them into your crawlspace. Heck, since you know the size of your crawlspace walls, you could premake the entire perimeter then assemble it inside the space.
Fire Rated Insulation
Search for "Thermax" rigid foam board insulation made by Dow. I used it in my crawlspace to make it part of the insulated house envelope. It has the fire rating you need and can be left uncovered. For the rim joists, I cut plain old white, open cell styrofoam from 4 X 8 sheets and sealed it to the joists with "Great Stuff" at the edges then covered the entire piece with a batt of fiberglass insulation to get the fire protection.
Just using fiberglass batts alone can let condestation occur on the rim joists depending on how much air movement you have in the crawlspace. Also, don't forget to allow for air circulation with the rest of the house - cut in a duct for hot and cold air and allow for free airmovement back to the furnace either through an open door or cold air return.
Joe
I have some concerns regarding the use of Thermax, or any foam product, in an unprotected application.
Such products typically require the foam to be protected by a fire-resistance barrier with at least a 15-minute rating. The aluminum film will not give this protection; read the DOW resources carefully, and you will note a few interesting details.
Dow is might selective in what UL evaluations they have, and are quite vague in their assertion that it meets building codes. Chances are, the inspector will still want the material protected. Please note that the 'legacy report' clearly states that the product is not suitable for use in fire-resistive assemblies.
So ... exactly what does the city want? Once you know that, all you need do is find an 'approved assembly' and build it. One free source of such assemblies is USG's "Gypsum handbook," available at their site.
There are many things that can be used in place of drywall to give the protective finish. Indeed, with the moisture issues of basement and crawl spaces, you're probably best advised to avoid drywall where you can. Products like DuRock, tile backer board, HardiBoard, and others are available. OK, so the smaller pieces mean more taping. They also mean it's easier to handle.
As suggested in the link, your solution to moisture issues lies in ventilation, rather than sealing the space. That's what happens when you 'condition' the space; you greatly increase the amount of dry air flowing through it, and remove the moist air.
I would "design" with a space between the walls and the foundation. This would allow any moisture - either leakage or condensation - to drain to the floor.
I would use a levelling compound, such as gypcrete, to make the floor dead flat, with a slight slope to a drain.
I would have my walls spaced slightly up off the floor. Any place that might collect water - like the channels for steel studs - I would arrange to drain.
Whatever is near the floor would be very water tolerant. Plastic trim and cement board in place of drywall, for example.
Thanks, everyone, for the additional comments. I have done more research since my original post, and I am reconsidering the idea. As it turns out, sealing crawls may be a great idea in a hot, humid climate, since "ventilating" a crawl in the summer in such a climate only serves to increase moisture levels. However, where I am, in the PNW, the evidence from the only study I know of shows that radon levels soared, and moisture wasn't really any better. Most of the "information" in favor of crawlspace sealing/conditioning that I have been able to find on the internet is written by people with an interest in selling me something. I no longer think sealing my crawlspace is worth the trouble/expense. I plan to improve the vapor barrier on the dirt and better air seal/insulate the underside of the floor. That said, if I were building a new house, I would probably not use a crawlspace, but, then again, there are several things about my 20 year old house that are outdated in terms of energy efficiency.
For the record, I now share the concerns about thermax, and about the product I mentioned earlier (a similarly foil covered product). I think that they are able to call it a class 1/A fire rated item in terms of ignition, but ignition isn't the whole story. I'm obviously no expert here, but another factor is how long it provides thermal protection. Drywall creates a barrier for a good amount of time, in addition to not being easy to ignite, so it really is a better material in a living space, since it gives people time to get out. Since crawl spaces aren't "living spaces," this is a grey area, sort of like attics.
BuildingScience looked at this - sealing up the floor, or ceiling of the crawl space.
They applied a foam board to the underside of the floor joists, with batt insulation in the bays. You could just put OSB over that.
If you are in a heating climate, like say middle Canada, where the outside air is cold and has very little moisture, the primary source of moisture in a home is the walking meatbags that occupy a home, with their breathing and showering and cooking.
Coastal reagions, Rain forests, and the American South get their moisture from the outside - so that is where the vapor barrier is. You keep the cold wet air out, or the hot humid air out.
Ok, well, I guess it's back to the drawing board for me. The whole reason I was considering insulating the foundation walls (and sealing the crawlspace), instead of just doing exactly what you are describing is that I investigated doing what you are describing and came to the conclusion that it would lead to mold problems in the floor. I guess I completely mis-read everything. Currently, I have faced batts between the floor joists. They are installed with the vapor barrier toward the inside (i.e., agains the subfloor), so, apparently, that is incorrect?
http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space
Looking at the pictures, #4 has the answer: It doesn't matter, either way they will rot out.
On the other hand, the article DOES say that in the PNW, vented crawl spaces do perform better. All building details are local, so take what I'm saying with a grain of salt.
Using the Thermax foil faced stuff, combined with batt insulation, with sealed edges and seams will keep the moisture out of the floor. Build enclosures to keep pipes and HVAC inside that insulated space. If a covering is required beyond the foil face and foil taped seams, you can use OSB or exterior grade drywall. You're treating the floor like a 5th wall.
If you've got alot of penetrations, then that's not going to work. Sealing /insulating at the crawlspace walls makes more sense then.
I've got more pondering to do with this. In terms of utilities, it makes more sense for me to insulate the perimeter walls (all my HVAC and plumbing is in crawl). If I end up going this way, I think I will probably use drywall, despite all my efforts to avoid it. My objection to drywall was mainly that the access to the crawl is across the living room, down a narrow stair, and then I have exactly enough space to pivoting the sheet around to fit in front of the access hole. Then I feed the sheet into the hole, crawl through, drag the sheet to where I want it. Lightweight, rigid foam is no problem. Heavy drywall is more of a problem. I realize I can cut it, but I thought there might be something easier. I was also concerned about humidity, but, I suppose, if I'm doing all this other stuff to reduce humidity in the crawl, I should be less concerned than I am.
In any case, I think I will put this project on hold while I focus on other, more pressing energy loss areas in the house.
Fire barriers over XPS insulation
I can only speak to what our local codes dictate (Portland, ME). I've been using intumescent paint for years, for the nerds out there Building Science highly regards this practice. While pricey, about $100/gal, it is a 15 minute ignition barrier, as long as it is applied at the recommended thickness (about 20 mils). Typically, I roll 1 heavy coat on the 4x8 sheets upon delivery, install sheets, foam perimeters, trim excess spray foam, and apply very heavy 2nd coat. It's a pretty thick, pancake batter consistency, and mineral based with extremely low VOC content. Muralo is the only manufacturer I have access to.
I have done quite a few unscientific on-site tests using off-cuts of foam with 1-3 coats. I've tried matches, cedar shims, and a propane plumbers torch. The paint "puffs-up" then releases from the surface of the foam while the foam gets a concave depression behind the paint. No smoke or noxious odors noted (not that I'm trying to smell, XPS is disgusting stuff). But real world scenarios usually play out like this: if fire makes it to your crawlspace, it's usually because your burning house has collasped into it.
Most homes here are posted with skirting walls. I dig a permeter trench inside the plane of the framing, 6-12" deep. Install XPS into joist bays flushing out to the sill beams and skirting wall framing, making sure to spray foam the perimeter of the bays. Then install 2" XPS from trench to subfloor. Space each sheet with 1/8-1/4" gap to allow for 1-part polyurethane closed cell spray foam (Handi-Foam 10# tanks with hose kit). Trim excess foam, apply final coat of intumescent paint, allow to dry, and backfill trench. Then roll out 15-20 mil vapor barrier (VB) over ground, taking care to grade and remove sharp stones/objects, all seams are over-lapped and taped with 4" polyethylene VB tape. The perimeter is lapped up onto the XPS, by about 12", pinned with 1x3s, fastened thru the XPS to skirting wall framing with 4" screws. Then the VB is folded down over the 1x3s and stapled. All interior concrete footings should be wrapped with VB and "collar" taped or, better yet, boxed with XPS to keep cold concrete from condensing water vapor onto the VB. Raise/jack the posts off the footing and slip the VB between to act as a capillary break and fold down over footing XPS onto ground VB and tape.
If there is a slab, insulate to it and coat slab with epoxy (EpoSeal thru mcmastercarr.com). It takes a bit of effort to clean and prep the slab but there are no worries as far as VB punctures.
There are always tons of variables with every basement and crawlspace. Wiring is usually the biggest headache. It has to be detached from sill beams and joists, foam installed, then reattached to solid framing screwed through foam. It goes on and on. Fuel tanks/drain/supply lines too close to walls and sump pits to name a few.
Drywall, paperfaced or not, is a huge pain. Hard to manipulate into the work area and finicky to install to rigid foam, especially into joist bays. I have done it in basements and used PurStick foam adhesive applied with an applicator gun. Not too bad, you just have to make sure the panel is braced as the foam cures, takes about an hour.
While I'm on my horse... Thermax is polyisocyanurate which should never be installed where moisture can enter its open cell structure. One could take the time to tape/seal the panel edges but that sounds crazy, especially since the foam has to go behind the floor VB. Or in the case of a slab, the bottom edge abutting the slab would have to be sealed from water vapor. Probably best left to above grade walls and roofs.
I would love to hear feedback from someone who has used rigid mineral wool insulation. R-4 per inch vs R-5 for XPS and none of the blowing agents or bromated fire retardents.
(I wonder why there isn't a readily-available foam product with a flame-retardant coating of some sort, for these situations?)
There is: DOW "TherMax"
As already mentioned, DOW Thermax is the only rigid foam insulation board fully tested and listed to be installed without a thermal barrier.
http://www.icc-es.org/reports/pdf_files/NES/NER681.pdf
It is installed and approved by code officials without an additional thermal barrier all the time.
It meets all smoke developed and flame spread requirements. It is listed as a Class I interior wall finish...the same classification as wall paper or wood paneling.
It's only drawback is that it is not listed as a vapor retarder, and one must install a vapor retarder when using this product wherever a vapor retarder is required.
Dow Thermax is also much cheaper than using drywall or even intumescent paint, which, as already mentioned, can cost more than $100 per gallon with a coverage area of less than 100sf per gallon in most instances.
we have used Roxul insulation for crawlspace insulation covered with 6 mil poly (local BI approved)
On concrete walls below grade we install 6mil poly against the concrete walls only up to gradelevel to avoid condensation.
I cannot understand the fuss about this fireretardent. If the house burns down the woodstudding is long gone before you would have to worry about the foam insulation off gases
I think maybe the bigger problem is flashover in the crawl. Turns a little fire into a big one real quick.
Did you use cofortbatt or comfortboard 80? And 6 ply under AND over? I'm trying to condition my crawlspace in my new build and very interested in Rockwool products. But of course looking at budget I'm between Thermax and Rockwool. Thanks!