EPS tape
NormanWB
| Posted in Energy Efficiency and Durability on
My insulator is using 2″ EPS behind my 2×4 knee wall. I want to air seal it and plan to tape the seams before putting a radiant barrier over the EPS. The foil tape I have for the radiant barrier does not stick well to the EPS even when rolled, so what do you recommend? I would like to avoid black tape to cut down on heat absorption.
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EPS is generally considered air permeable, so taping the seams won't really help you much. Radiant barriers are air tight, so taping the seams in the radiant barrier might get you there, and foil tape on a foil radiant barrier would be appropriate.
You haven't told us what climate zone you are in. Unless you are in a very warm climate, you need to be careful that you are not installing a wrong-side vapor barrier with your radiant barrier.
Also, air sealing just the back of the kneewall won't help you much unless the air barrier is continuous with the rest of your air barriers. You should be able to specifically identify which layers of construction are your air barriers, and they should all join each other. If you are just trying to prevent wind-washing of the fiberglass in the wall cavity, you could put your air barrier inside of the EPS. Tyvek or another synthetic building paper would work. You could also use Thermoply over everything, which is a foil-faced wood fiber product that is rugged enough to protect the insulation, airtight, and has a radiant barrier on the surface. It is also a vapor barrier.
Sorry, CZ 3A.
I am usually pretty good about that, but it was early and I had not had my first cup.
The wall is designed to dry to the inside of the EPS as well as to the outside via the ventilated knee wall.
See here for using EPS as an air barrier. Some EPS comes with a radiant barrier already attached.
https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/22198/rigid-eps-insulation-effective-air-barrier
I have used Venture red tape on XPS, eps and eps with foil on one side. A window sill had some exposed xps (inside, basement) and I taped/sealed the interior framing to the xps to the window buck. The tape took a beating through the window for a couple years, it actually turned clear in some parts but never let up, cracked or split.
Peter Engle wrote that "EPS is generally considered air permeable."
This is untrue. For more information on the issue, see this Q&A thread: "Is rigid EPS insulation an effective air barrier?"
That thread also has an answer to Norman's question: Albert Rooks recommends using Siga Wigluv tape for EPS seams.
A JON R aludes to, instead of using unfaced EPS + radiant barrier, have the insulator use foil faced EPS. It's not a big upcharge, and could even be cheaper. (Type I foil faced EPS is sometimes cheaper than Type-II unfaced EPS). Foil faced polyisocyanurate is another possibility. Foil faced goods are easier to cut cleanly than unfaced EPS, and easier to tape than unfaced goods too.
I'm interested to hear what you used. I called 3M and was told their 8087 tape is the one to use. I've tried many others that just didn't stick.
I agree with calling the manufacturer of the product that will be used. If it is 3M, then there you go. The manufacturers often (?) know best what works on their products. Of course, it may be a tape that they also produce/sell/profit from. Once you have the tape name, then you hope you can find that product somewhere in stores or online...