Polyiso/rigid foam on inside
jeniferkey
| Posted in Energy, Heating & Insulation on
We’ve got a new 2nd floor room that’s 20X20. Stick-bilt and we’re in Texas. 2X4 walls with fiberglass insulation in the walls and ceiling. Parts of two walls are against other interior walls. The exterior is plywood sheathing with hardipanels.
I thought it might be a good idea to put those silver polyiso panels up on the interior and tape the seams for insulation and against air transfer. I’d put the silver against the studs. We thought 3/4″ from HD. Any thoughts? A waste of money, put up plywood instead? I just pictured the room being like a little igloo cooler, and holding in A/C and heat better.
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The right place for this is on the exterior of the studs in a cooling climate like yours. Could lead to trapping moisture from condensation in the stud cavities in your area, depending on how the exterior is detailed and how much differential there is in in/out tempos and humidity
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So, if the exterior is finished (hired builders, we never discussed polyiso on the outside), would you just leave the inside with the fiberglass between the studs and put up the sheetrock or wood panelling? Is there no way to do an air barrier that isn't also a vapor barrier? What about plywood (that I've read about on here)?
We foamed a different addition for insulation, and after a leak, had to deal with pulling out soaking wet foam that worked like a sponge. It held the water tight against the plywood, which seemed to cause more rot than fiberglass would have. I know we shouldn't build with plans for leaking, but that left a bad feeling with foam, so we've put in fiberglass again.
Also, the fiberglass was put in with the paper side facing the room. I read on the building info site, that for Texas, no paper even. Does that seem like a huge deal? The paper does seem to let some water through (found a ceiling leak).
Thanks.
Jennifer
Well I would not worry too much about it if you were in the panhandle,and would definitely so no don't do it if you were in Houston.Foam is th e best option, but it sounds like you used open celled icythene instead of the closed cell polyurethene. Now you know why the poly is the better choice. One option still is to flash the sheathing with polyurethene then stuff the rest with FG batts.Or if you already have the foil faced polyiso, cut it tpo fit between the studs and then put the fg over it sans paper face
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Thanks everyone for their suggestions. No foam on the inside then.
They won't allow any vapor barrier on the insulation here in Austin.
He did mention that he had fiberglass insulation in the walls. Shouldn't that be enough to moderate the differential?"There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves."Will Rogers
so many photos trying to load, I got lost here, but I wanted to reply - I'm not sure what you are saying...
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No big deal. I thought since there was fiberglass insulation in the walls there wouldn't be that much of a differential between the inside and the outside. So the 3/4" polyiso would be ok."There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves."Will Rogers
It's the fact that it acts as a VB that places it on the wrong side of the wall for a cooling climate.
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ok"There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves."Will Rogers
Jenifer,
Changing the subject...it looks to me like there may be a large load on the central beam that is bearing above the double doors.
The header above the doors looks to be only double 2x6....hmmmm
Edited 10/26/2009 8:45 pm by homedesign
What's considered a large load? That's not the supporting end of the roof. No floor above, just a roof that we can walk on. Not defending it, because I didn't design it, just wondering.
The darn door leaks like crazy anyway, and we've had to pull it out a couple of times already (to no success). Water comes under the threshold and there was no flashing put behind it, so it comes into the room on occassion. If there was a need for larger headers, we could consider changing them if we need to take out the doors again.
http://www.draftymanor.com/house/ is the entire project. This is pretty much the last room. Still to go is A/C-heat, plumbing a bathroom and then finishing out the room. There are two leaks. First the door, and second where the 3rd floor door lets water in to leak in the second floor room.
I realize the builder should be fixing these things, but I don't know what to do when he says that he doesn't know what to do.
Anyway, so, you think the header should be bigger if the non supporting wall looks like ours does?
Jennifer
I've read that fiberglass insulation is not good at blocking radiated heat, especially in an attic. DFW area definitely gets plenty hot.Any DFW area builders use something besides fiberglass in attics?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
"That's not the supporting end of the roof"Since those are not trusses, it is supporting at least a portion of roof load, plus the ceiling dead load transferred via that center ceiling beam. See my note above.I'm about to look at your link, so maybe will see more of the detail;s that tell
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Nice catch. I can't see all the framing details and don't have the dimensions other than from counting studs to measure space, but there could be a ceiling dead load of about a tom on the end of that beam that lands over the door, plus if they loaded any of the roof onto it, so two tons would not surprise me. in a point load situation like that, the 2x6 header is entirely inadequate. It won't have a catastrophic failure, but it will sag over time and create problems with that door operating properly.
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I think i see the gist of things. There is a slight possibility that the overhanging parapet wall above that door was designed as a box beam to carry loads. I have no way of telling from what I see so far.
The cantilevered framing for that balcony outside the door is a common place for leaks and rot over time. I NEVER do a deck like that without at least 4" drop below the door because it is almost impossible to flash it well to keep water out from under the threshold. This is a design flaw in my opinion, and you will continue to deal with leaks until the cows come home, or you elect to raise a curb under the door and reframe there.
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Yep, after the builder built it, they realized the balcony was done wrong. It seemed a good idea at the time to keep the balcony strong. They did take the door out and put a 1X or 2X under the door to raise it. I think the water is running down the door and getting in that way. With the door raised, and the flashing solid over the curb to the threshold, we're all getting frustrated. But, with you saying a 4" drop, I guess it could still be getting high enough to get under.I doubt it's a box beam. If I have a chance, and the insulation doesn't cover too much, I'll take a picture of that wall above the door. Thanks for looking.Jennifer
photos that would help would be framing of the wall above the door, and how the roof frames to ridge and whether there are framing members transferring ridge roof load to that center beam, and dimensions.
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Here are the only ones I find from the actual build. We took tons of pics, but it's funny what you wish you'd taken pictures of. On the tower, I wish I had shots of all the electrical runs. This one I wish I had been more precise about pics of where the air ducts are. Also, I guess, more pictures before the siding or insulation was put up...
That is smewhat enlightening of the overall, and I do believe that some roof load transfers to the header over the door. next time you pull it, I would ad anothe rplate under it and flash it right, and reframe the header to be as tall as possible. a doubled 2x10 would be the minimum I would want there. better would be to use a pair of LVLs
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Sounds like that won't be too hard. I checked, and with this wet fall, it's definitely still damp inside by the door. Any recommendations of door flashing? I've seen plastic pans that the whole door thing seems to sit in that I'm considering. It's too bad my builder is out of ideas.
Thanks.
Jennifer (not Rapunzel, but I do have the long blonde hair)
I like the tower.... anyone named Rapunzel live there? :-)
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
BTW, it may be someone else who chimes in next to help you. This place is a mastermind. Who knows what we'll think of next;)
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