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lhort 09-12-2012 07:50 PM

Dow Weathermate or Tyvek house wrap?
I was wondering which product was better, Dow Weathermate or Tyvek house wrap? I live in NY and have a uninsulated 1950 block/stucco house with high humidity levels inside, predominately during the winter with condensation on windows and mildew in a few spots on outside walls if furniture is up against the wall . We are planning to have the house vinyl sided. They will be putting foam insulation on over the existing stucco then wrapping the house in Weathermate housewrap. Tyvek has a much higher Permeance rating than the Weathermate. Because of the moisture in the house would it be better to go with a wrap that has a higher rating?

nealtw 09-12-2012 08:49 PM

Moisture from within the house should not get to the wrap as the foam will be a vapour bearier. Moisture in the house should be addressed with fans and the like if it is still a problem after the insulation is installed.

lhort 09-13-2012 04:13 PM

It is my understanding that foam insulation is not impermeable nor is it a a vapor barrier. A vapor barrier would go on the inside walls and it's plastic or another impermeable material.

nealtw 09-13-2012 06:12 PM

Nothing is impermeable 100% and yes some foams are vapour beariers, they all have rating. You can read what the experts say about the insulation on the outside of the building.

lhort 09-13-2012 06:40 PM

Thank you. If it wasn't for the block walls and window condensation this would not even be an issue, either one would be fine!

GBR 09-19-2012 03:53 PM

I'd use Tyvek. You are mostly heating, not cooling, so the moisture drive will be from interior to exterior. The Dow is >5 perms, very tight, with Tyvek at 56, if I remember correctly. Pages 24, 25;

No vapor barrier inside: footnote #10;

No mesh tape/mastic (doesn't permit movement) on the f.b. seams;

Use the window flash tape and leave an "expansion/shrinkage" fold in the middle between sheets. Or a good (compatible) caulking with backer rod; Never mind, I just realized; install the Tyvek first, then the foam. Use Tyvek "stucco" wrap, with the air space to help as the secondary drainage plane;
That material will give you a little space for extra drainage rather than wood furring (as vinyl requires full-backing). Anything to help keep the water from the stucco (moisture storing cladding). Have you checked any areas of block with a moisture meter for water source? What thickness foam board?

P.S. Is the stucco so bad that it leaks? Otherwise, just add f.b. to the inside and furr out the windows/doors/elect. boxes; Fig. 3;

lhort 09-19-2012 07:09 PM

Nealtw - Hi, Thank you for the link.I read it and I believe it said...... that you can add insulation foam to the masonry wall with no problem and you can either put the house wrap to the face or behind the insulation foam. Is this correct? I think they recommended putting it on the face of the foam???

lhort 09-19-2012 07:54 PM

GBR - Thank you for the info.
No, I have not checked any areas of block with a moisture meter for water source? Our stucco is in pretty good shape.
So, if I understand you right...... install Tyvek stucco wrap on the stucco, then the foam board, then the siding. Is this correct.
OK, by putting the "stucco tyvek" on the stucco it should prevent moisture from accumulating on the stucco. Because the stucco is not perfectly smooth, wouldn't that allow for water drainage anyway, even without the stucco tyvek? Can you just use plain Tyvek? Is the foam OK with out Tyvek on the face of it? Thanks. Sorry if I am being dense. lol Lori

GBR 09-20-2012 08:37 PM

Either wrap will work, in front of-or behind the foam board, because of the stucco. If a normal wall, H.W. behind the foam helps protect it from construction damage of the cladding (siding) installation, secondary; it helps keep it from billowing due to pressure differences in/out-side the cavity. pp. 5;

Some stucco has a broom finish that could direct any moisture to drain at a window/door, but with the foam over the stucco, highly unlikely --unless a major flying projectile (piece of another house) in a high wind area. Then you would other things more important to worry/be concerned about. Use regular Tyvek outside the f.b. My previous post was presuming the stucco leaked in the first place, hence the precautions.
My question as to how thick the foam, depends on the Zone you live in, NY has 3 Zones, find the closest city below the map in the State listings;

Then you know the minimum thickness foam board for your weather, based on that Zone;

More on foam and joints opening-up, click on pics at the bottom;
How are you integrating the window head flashing?

P.S. You are not being dense, I didn't know it till I learned it also! LOL

lhort 09-21-2012 04:00 AM

GRB- The contractors were going to put furring strips on the stucco then put 3/4 foam vertically then another 3/4 foam going horozontally then the house wrap and finally the siding. Would it be a good idea to put it in between the 2 foams or do you still think on the outside, final layer. I know we could use more insulation but then again we don't want to build out 6". Our house is not really drafty either. The main problem is the high humidity/condensation inside. That is the problem that we are trying to solve,the insulation is a good idea too of course. Thanks for all the info, my google did not pull up these articles. Are you a contractor?? Lori

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