Replies

1. 
   Davo304 | May 24, 2002 07:11am | #1

   Who the heck framed your house? 

   Truth is, I don't think 1/2 insulation board is gonna do you much good.  Housewrap should act as a wind barrier. All those nooks and crannies won't be a big concern with the housewrap. As for the ridgid insulation, there are many different schools of thought.

   Housewrap blocks drafts, yet will still allow water vapor to pass through. This is a good thing. Water vapor buildup on the inside of your home can pass through to the exterior and then be wicked away.  Ridgid insulation is pretty much vapor proof. Water vapor passing toward the outside will become trapped between the housewrap and the ridgid insulation. Possible moldy conditions may occur and/or even some rot.

   Normally, 1/4 inch, fanfold insulation is used as a "backer board" for vinyl siding. This insulation is perferated with zillions of very tiny holes that will allow water vapor to escape. However, rainwater that may get behind the vinyl siding will not pass through the fanfold. The fanfold will act as a water shield when this occurs.

   As for insulation value, I don't think 1/2 inch adds that much.  This is just my opinion.

   Davo

1. 
   55512122 | May 25, 2002 06:09am | #3

   95% of the gaps are 1/16 or smaller. I am talking about the fact you cannot get a airtight joint between 2 pieces of 2x4 nailed together, or can you fill that void with anything. The 1/2" insulation board will ineffect create a thermos type insulation value. Drilling small holes throught the top plates will disperse any buildup mositure inside walls. JMHO

1. 
   danusan1 | May 25, 2002 08:23am | #4

   caulk small gaps  & aerosol foam larger ones.

1. 
   fdampier | May 25, 2002 03:43pm | #5

   You are looking at the prime reason I used sips in the construction of my house. Those "holes,gaps" do allow air infiltration into the heated areas of the house. Housewrap will slow down the transfer, however do have their own issues like Mold.

     the problem is worse with fiberglass insulation than with sprayed in foam. Neither is perfect although sprayed in foam does have the advantage of sealing most of those gaps.   The problem now becomes the studs which hold up the walls. Their "R" value is nothing (or very close to it) so every 16 inches you have 1 1/2 inches of no insulation.  (except where they are doubled up or worse).

     If you are going to insulate with foam on the outside you risk trapping moisture in the wall cavity.  That will lead to rot and mold issues you don't want any part of. Foam on the inside is much better, yet not without it's own issues.  Loss of interior space and what do you nail to for example. 

     The best compromise for stick built houses is the spray foam that comes in a can.  From personnel experiance do not do on a windy day wearing shorts and a tee shirt.  It will be about two weeks of scrub brush baths before the last of it is off...  (any in your hair, don't touch, let harden, cut out.....)

1. 
   55512122 | May 26, 2002 11:39am | #6

   I had seriously considered SIPs however I found it difficult to find any one experienced enough with them in this area, so I fell uncomfortable in using them, just to many unanswered details and the extra cost was also a factor.

   To me it doesnt make sense to use both housewrap and insulation board. Should be either or. But I do need to keep the rain out till my windows arrive. You know they make a ton of the 1/2 insulation board so someone is using it. Wondering here; how does moisture move through wood? Does it follow air currents or migrate from wet to dryer areas? I am sure research has been done on this issue just have to go out and find it, Roger

2. 
   55512122 | May 26, 2002 12:04pm | #7

   Bit of info I came across using insulation board;

   Potential Moisture Problems

   In cold weather, warm inside air containing water vapor can get past the wall finish and insulation and condense inside the colder wall cavity. In hot-humid climates the same thing can happen, just in the reverse direction, humid outdoor air in the summer can condense inside cool/air conditioned wall cavities. If enough of this happens, and the water cannot escape, wood rot, mold, and other moisture-related problems are likely to occur. For this reason, building codes often require installing a vapor diffusion retarder on the warmest side of the wall cavity.

   Foam board insulation is commonly placed between the exterior finish (i.e., siding, brick) and the studs of exterior walls. To prevent air infiltration, you should place rigid insulation boards tightly together and seal the seams with tape or caulk. However, this practice may worry some builders in cold climates since the foam board may act as a second vapor diffusion retarder. Studies have shown, however, that condensation rarely occurs in these areas unless something else is seriously wrong with the wall assembly (i.e., massive uncontrolled air leakage into the walls from the house.) If the assembly is constructed correctly, the inside surface of the foam board stays warm enough to keep water vapor in its gaseous state long enough for it to escape.

3. 
   Piffin | May 26, 2002 03:13pm | #8

   couple things wrong with what you quote above.

   "Foam board insulation is commonly placed between the exterior finish"

   It is also true that mold is now commonly being found in wall assemblies done that way in this past generation. Now I admit to being a cold weather builder.

   "If the assembly is constructed correctly, the inside surface of the foam board stays warm enough to keep water vapor in its gaseous state long enough for it to escape."

   Correctly, in this case, means perfectly. With the profusion of multiple tradesmen on a site, when was the last time you sawa perfection applied to a wall assembly?

   And how is that gaseous vapour to escape when the foam acts as a vapour bar?Excellence is its own reward!

4. 
   55512122 | May 27, 2002 05:07am | #9

   Piffin, please fill me in where insulation board is normally place if not on the exterior?

5. 
   Piffin | May 27, 2002 06:11am | #10

   On the inside of the studs, behind the sheetrock.

   Twenty years ago when it first got into regular usage, Thermax provided literature recommending this approach and pointing out how it was better than building with 2x6 @24" OC and r19 fibreglass.

   Still holds true, except there are more studies to back it up now.

   Excellence is its own reward!

2. 
   FrankB89 | May 24, 2002 03:52pm | #2

   If the framing voids you describe are small, just use the aerosol foam.  If they're larger, fill them (loosely) with fiberglass insulation.

    Some people would bitch even if they were hung with a new rope.