Hello-
First post for me. Have an addition that has walls rotting from the inside; weird moisture issues. To resolve, I’m planning on putting 1″ ridgid foam over the plywood sheeting, then using furring strips over that to create a rainscreen drainage plane. What I’ve never understood about this is: where do you put the housewrap? Over the foam? If so, staples won’t hold it, so how to fasten? If I use the foam that has a foil face and tape the seams, do I even need to use housewrap? I surely would appreciate some wisdom on this. I’m in the Portland, OR area and I’ve never even seen this done; my local lumberyards don’t know what “rainscreen” means.
Thanks A LOT! Ian Thompson
Replies
Welcome Ian.
I don't have a definitive answer for you but a few thoughts/questions:
You said: >> Have an addition that has walls rotting from the inside; weird moisture issues. << Is there some kind of moisture source in the house like maybe a often used bath/shower with no exhaust fan that vents to the outside? How about an often used for cooking kitchen with no exhaust fan to the exterior. If there are fans, are they used? Maybe a damp crawl space that is permeating moisture up through the house? Maybe a combination of that coupled with a plastic vapor barrier in the ceiling is driving moisture into the walls? If not any of those, where do you think the moisture is coming from? Are there any exterior leaks? Sounds like the wall assemblies aren't breathing (drying) properly. If you add foam do you think that might add to the lack of drying? What is the perm rating of the foam you intend to use? In the current wall assembly are there any vapor barriers such as polyethylene or vinyl wall paper? What does the current wall assembly consist of?
Edited 8/5/2009 9:56 pm ET by Matt
Matt-
Thanks for taking the time. No obvious sources of inside moisture. Its a sunroom, on a slab. Construction, 15 years ago, 2x4 w/ craft-faced fiberglass ins, 1/2" plywood, tar paper, cedar lap siding.... so by my book it should have breathed a little better. Roof is fine. but yes, the water seemed to be just behind the tar paper. The framing was toast but the sheetrock was fine... we found it because the cedar siding was starting to rot from the back. We've had weeks of hot dry weather and the wood was soaking wet when we pulled it apart. The idea with the foam was to move the condensation point outside the wooden wall. I've seen it done (always east coast, it seems) by the fine homebuilding guys but the housewrap was not addressed, to my memory. No idea about perms.
Maybe they didn't put poly down before placing the concrete slab... What is the floor covering? If there is any place where the bare concrete floor is showing tape a 2'x2' piece of poly plastic down to it tepmorarily so you can see of if moisture is coming up from below. Is there concensation forming on the inside fo the windows?
BTW - if you are going to put cedar claps back on cedar has natural chemicals called tannins (SP?) in it that can deteriorate housewrap.
House wrap goes over the sheathing board.
It is not a vp.
It is there to keep water and wind out of the structure.It is vapor permeiable to allow interior moisture out. Placeing foam board over it slows that ability down. To keep from defeating the vapor transmission property of the house wrap you need to use "stucco wrap" (wrinkled housewrap) under foam board according to Dow. You can also use foam board that is grooved on the back.
Tape the foam board seams and install the furring strips over it.
sounds to me like there is no VB under slab.
so hot sun is drawing ground moisture up into the living space
then it conmdenses in the wallsthis foam on outside , if I am right on the above, will make the problem worse. Put the foam on the inside face of the studs and tape it.
Put the house wrap on the outside face, then furring< siding
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
To answer your question, you don't need a house wrap with foam. You just tape the joints and no rain will get thru.
But as others have said, you probably have other problems. You get out of life what you put into it......minus taxes.
Marv
>>You just tape the joints and no rain will get thru.
You are going to trust tape for the life of the house?
I've seen it fail durring installation.
I'll use house wrap or building felt paper.
Is the foam on the inside just to stop moisture transmission? Would it act differently than poly?
What about stucco-wrap on sheeting, then foam, then strips? No?
Thanks for your time!
Ian
Why ask about poly? Are you putting her on the inside face of the studs?That would be a definite no-no with foam on the outsdie face. And you are still talking about puting foam on the outside. If moisture is ccoming from inside, you are letting it getinto the wall asembly before stopping it from getting out by putting th efoam on the exterior - thus the rotToo much missing info here. Have you got any pictures of existing conditions?
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Hi Ian,
Have an addition that has walls rotting from the inside; weird moisture issues. To resolve, I'm planning on putting 1" ridgid foam over the plywood sheeting, then using furring strips over that to create a rainscreen drainage plane.
??? If walls are rotting from the inside....the foam outside will trap more moisture in the walls. So, you're going to need to get a handle on the interior issues before you compound it. Maybe shower vent fans not vented to the outside. A heater humidifier gone berserk. Kitchen range hood not venting to the outside, a spring in your crawl space etc.
Anyhow, once that's squared away, the foil backed foam with foil tape seal will eliminate the need for housewrap. I like ripping 3/4" treated plywood 2 1/2" wide for the furring, back it with 30 lb felt and screw it through the foam to the studs with 3" coated deck screws.
my local lumberyards don't know what "rainscreen" means
Of all places....isn't OR known for year round monsoons? Maybe they use a different name for it....uhhhh...drainage plane maybe?
Questions?
Pedro the Mule - You'll like foam as much as I like fur
Back just the strips with felt? What's that for?
My local lumberyard people don't get out much. They finally put peel and stick flashing membrane on the shelf about a year ago.
My understanding about the foam is that it puts the framing inside the warm part of the wall, and the condensation point is now outside the foam, where there's a drainage plane to serve it.
Its a slab floor w/ tile. I'll try the trick of taping plastic to the floor to check for moisture coming up.
Thanks a lot for your time... I appreciate it.
Ian
Hi Ian,
Back just the strips with felt? What's that for?
Keeps the "treated" plywood furring off the foil foam so you don't end up with a long term chemical reaction. Salt, copper, aluminum, rain water.....nice whole house battery <grin>.
I rip my plywood on an old tablesaw and then roll out an 8' piece of tar paper. Slip the plywood strip under the edge of the paper, slap a couple of roofing staples to it and run a razor knife right down the edge. It does take a little time but won't take too much as you'll get a rythm going and you'll be done quickly.
My understanding about the foam is that it puts the framing inside the warm part of the wall, and the condensation point is now outside the foam, where there's a drainage plane to serve it.
You got it!
Its a slab floor w/ tile. I'll try the trick of taping plastic to the floor to check for moisture coming up.
If it is, depending upon the type of tile that it is....you may be able to seal the whole floor with a grout sealer but I'd check with the tile maker first. If the person that poured the slab didn't put a vapor barrier under the slab, then shoot....um....never mind hahah but it is always better to stop moisture "before" it enters so a top seal may not be as effective but it may be your only option short of tearing all the tile and concrete out.
Pedro the Mule - Tile sealer is what I use when I run out of Dapper Dan's fur gel
Is it possible you moisture issues are coming from condensation on your sunroom windows running down and getting inside the wall somewhere. When I've seen rotted studs it was usually because of leeks around the windows or sills rotted out from moisture standing on them.