Sorry for what I’m sure is a question with an obvious answer, but the building material supplier I’m deaing with is confused about what I want.
For my tub surround, I will have Schluter Kerdi waterproofing membrane around the tub surround, so to avoid a double vapor barrier I want something that’s permeable and *not* FG as insulation. Ok, says I after reading buildingscience.com on basement insulation, what I want is extruded polystyrene (XPS), because it is vapor permeable. My supplier maps XPS to Dow blueboard (Scoreboard), yup, that’s what the Tauton book identifies as foam board. But now the guy is telling me (based on reading the Dow web pages) that it is not vapor permeable, hell, they build boat docks out of it! He says it’s got a vapor barrier on either side.
For the rest of my bathroom, I want polyurethane foam. Job too small for an installer of spray foam, so I want to go with foam board. But what kind of board? Supplier says Scoreboard or something else (white), claims that both are closed cell.
Bottom line: if I walk into a store and want to ask for X quantity of XPS and Y quantity of polyurethane foam board insulation, what should I be asking for?
And if I can ask another question: how does one fasten these into stud bays? Use insulation hangers? Caulk around the edges? When do you tape?
Replies
Foam board is any sort of sheet building material made with some sort of plastic foam. A very imprecise term.
Ok to be more specific:
- What are brand names for XPS board? Is this what Dow Scoreboard is? Is it vapor permeable, as Taunton and buildingscience claim but Dow's web site seems to deny?
- What are brand names for (extruded?) polyurethane foam board? Is this polycicarbonate or whatever the heck you call it? I know this is usually used for house exteriors, is there anything wrong with doing a few stud bays with it in lieu of SPF? How do you do it?
I've looked at the Taunton book, which is sort of focused on cells and FG for insulation, and buildingscience, which advocates XPS for basement insulation. Is there anywhere else one can look?
- What are brand names for XPS board? Is this what Dow Scoreboard is? Is it vapor permeable, as Taunton and buildingscience claim but Dow's web site seems to deny?
The ½" Dow blue board sold by the home centers here has an added plastic surface that looks like it would be a great vapor barrier, not just XPS. The 2" XPS I've used, both Dow and Amoco were nothing but XPS.
Got an old chart here that lists XPS as "good" effectiveness as a vapor barrier. EPS comes in at "poor". Foamed in place urethane got the sole "excellent".
Amoco lists their XPS perm rating of .6-1.8, depending on product. Hope that means more to you than it does to me.PAHS Designer/Builder- Bury it!
VaTom:
Ebuild only lists one item (in various sizes) for unfaced XPS foam board insulation:
http://www.ebuild.com/guide/products/productDetail.asp?catCode=106&prodID=267516&pageNum=1&recNum=19&sortCode=5&F_151=6
Do you have any other information on the unfaced XPS you get from Dow and Amoco? Blue board is from Dow, I've got 2" faced XPS blue board.
Do you have any other information on the unfaced XPS you get from Dow and Amoco? Blue board is from Dow, I've got 2" faced XPS blue board.
Not being a GC, I don't buy very often, but purchases are by the truckload for our underground houses. I was referring to an Amoco publication I added to my files some time ago.
Are you stuck with only buying from a home center? Not much info usually available there. I can always get more information from the company who sells me the product. It's entirely possible that Dow no longer offers an unfaced product, or more likely, that your retailer only stocks that item. For small volume you don't have many options other than what's on the shelf. Buy a truckload and you get what you want. My primary concern was compaction and there are varying products for varying earth loads.
Happy to share more from the Amoco brochure but no idea what might be available to you, other than that you're going to have to go to the mfgs. and ask for product literature and then find out who they're selling your preferred product to.
Good luck.PAHS Designer/Builder- Bury it!
Thanks, I am using a distributor for builders in the NY/NJ area, not HD. They can deliver through a second-story window, so I'm sticking with them despite numerous mistakes. In any case I went to the Dow styrofoam web page:
http://www.dow.com/styrofoam/na/res-us/index.htm
It looks like some blue board is faced, but perhaps not all. In particular Scoreboard and Wallmate do not mention it at the Dow web page. I have Scoreboard and do not notice any plastic facing on it. So perhaps I am being led astray by my supplier and by ebuild, who both believe all blue board has plastic facing. I would call Dow to confirm, but there is no contact info.
For polyurethane foam, I think it's clear I should use polyisocyanurate foam board, which even Agent Orange carries.
I'm planning 3" of XPS behind tub surround, 3" of polyiso elsewhere in bathroom.
The Pink sheets are the same as the Dow XPS, just a different brand, Owens Corning.
And as you can see from Dow's web page XPS comes in many, many different characteristics.
I notice that you are confusing permability with allowing water to pass through.
Perm is a messurement of the ability for a material to allow for the pass of water VAPOR or gas. That is a completely different property that prohibits the movement of liquid water.
Thanks, I am using a distributor for builders in the NY/NJ area, not HD.
Glad to hear that. Now, to belabor the obvious, salespeople sell. If you want more, or more accurate, info you want to ask for printed matter. Your salesperson presumably is in a better situation than you are to get it. Lean a little (gently) and see what they come up with.
Clearly anybody who says that all of any class of product... well, needs some more educating. And likely they aren't all that interested as their job is to sell what's available.
If all else fails, track down the regional rep for the companies. I've done it (Amoco). It works wonders sometimes. He/she'll also know who bought the product you want so you don't have to call all over creation looking.
I couldn't find rolls of bentonite waterproofing anywhere in Virginia several yrs ago. Started at the Dakota factory and finally located a stash, under a heavy layer of dust, in the Richmond, Va warehouse of my local supplier. Local guy had no idea it was there. Obviously nobody was selling it. Got a great price to clean them out.
Not my business, but aren't you a little overly concerned here?
PAHS Designer/Builder- Bury it!
I'll give this a try; XPS means "Extruded PolyStyrene". Dow does make it, and the stuff I've seen recently has a thin plastic (tough but stretchy) film bonded to both sides. This film can be peeled off, but I would think that would be a lot of work. I believe it's that plastic film that makes the vapor barrier, but other things I've read seem to say that polystyrene (Dow's brand name for it was Styrofoam, maybe now it's called Scoreboard--some of it does have little grooves where you can snap the board to fit it in different sized stud bays) is impermeable to water vapor as it is. Maybe it just slows the transmission and the films help stop it. If you really want to keep it as a vapor barrier, you have to tape the joints with plastic tape. Probably should tape nail holes too.
We used "Foam Nails" to nail it--long, spiral shanked nails with big (quarter to fifty-cent-piece sized) slightly domed plastic heads. That way the foam doesn't just pull back off of the nails (and the plastic heads may keep the vapor barrier effect in tact). We also stapled Styrofoam with power (pnuematic) staplers.
Polyisocyanurate is sometimes called Tuff-R, R-Max, or Thermax and almost always is foil faced, both sides. Sometimes the foil is black.
Expanded polystyrene is like the stuff foam coffee cups are made from. As far as I know, it is permeable to water vapor (is not a vapor barrier). (It is white and you can see the beads that expanded and smushed together to make the boards. It is crumbly.)
I am not at all sure about extruded or expanded polyurethane except that the canned stuff (Great Stuff, for one) is basically polyurethane that expands when you spray it. I don't know how vapor permeable it is; the can might say.
Sorry, that's about all I can tell you.
FWIW..I am using 2'' EXTRUDED..polystyrene..by Owens -Corning..pink, with scores at 16'' and 24'' x the 8' length..there is no plastic film, I have seen it on thinner stuff and on Dow..
Yer right on the EXPANDED being little white globs..if ya ever noticed, coffe cups weep coffee..so in no way is it "impermeable" by vapor or liquids..
the dow blue that I have used has the film..it helps, if a sheet gets away in the wind and snaps, at least it can still be handled.
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Dow has trademarked Styrofoam. Scoreboard is one of the products they market made of Styrofoam, boards scored every 16" and 24" for obvious reasons. The stuff I have does not have plastic facing (unless it's so well bonded to the SF as to be indistinguishable....).
My impression is that you don't want extruded polystyrene, such as blue or pink board. Extruded polystyrene isn't all that permeable, as I understand it, that's why it's used in below grade installations. And if it's covered by a vapor barrier as apparently the Dow product is, obviously it would be less permeable.
If you want permeability, I believe you want expanded polystyrene, that is, the white foam bead stuff. It's not used for below grade work because it soaks up water which destroys the insulation value. It should be much more permeable.
You could also use vermiculite, which is quite permeable. Packing it in tightly would minimize settling.
As for the polyurethane foam, if the job is small enough, how about buying cans of Great Stuff? The installation does not need to be pretty, and it insulates so well if you are thin and lumpy in spots you'll still get good insulating value. In panel form the material is more strictly called polyisocyanurate. I've only seen it with foil facings, which form a vapor barrier, and somewhat of a radiant barrier. It's very prone to degradation by UV and hence must be covered. I don't think most building supply folks could pronounce polyisocyanurate, much less know what you mean. I'd call it "that crumbly tan stuff with the foil facing".
As for specific permeability ratings, you'd have to get them from the manufacturer's literature or representative.
To fasten it in, you don't care about getting a great moisture tight seal since you want permeability anyway, but you don't want gaps that air can just blow right through. I'd cut it to fit snugly, then foam in the gaps with Great Stuff.
Thanks for the clarification. Looking more closely at buildingscience.com:
- They rate foil-faced polyisocynanurate and XPS as "semi-permeable", but I now see the caveat "unfaced XPS". The Scoreboard has a plastic film facing. Great. I've cut a piece out of it so it can't go back. You really have to watch yourself with this stuff. So what's a store name for "unfaced XPS"?
- EPS is more permeable, but XPS is more tolerant of moisture, though in this case perhaps we are talking about significant water in a basement.
Does anyone know what the pink board at HD is?
I'll consider your idea of a lot of cans of foam. Perhaps the best strategy for the area outside the tub surround is Scoreboard covered with the canned foam. I'm not real wild about putting EPS behind the tub surround, but perhaps that's what I should do (air-sealed with tape and mastic, packing tape if I recall according to this forum).... Something doesn't feel right about insulating my tub area with coffee cups from McDonalds.... :-) I have heard rumors that the stuff (EPS) degrades to powder over time, any confirmation or refutation?
Edit: EPS has R-value of 3.5/inch. Ech. Let's make the tub surround the coldest part of the house? I don't think so. I am looking for unfaced XPS....
Edited 8/10/2004 10:43 pm ET by Taylor