[Greenbuilding] Insulation Problems

[JOHN SALMEN]

Bit confusing. Lot of different wall assemblies out there. 

The 2 inches of xps would be classed as semi-impermeable something around .5
perm.
The liquid coating on the sheathing is probably comparable and the ply would
be at about 1 perm. 

So drying to the exterior is fairly limited. Recommendations for colder
climates because of interior humidity would be to have more permeable
materials to the exterior but the real issues are moisture tolerance of
materials and moisture - sources of moisture and potential for drying.

The ply is good in that it can be subject to extreme moisture loading and
dry out if it has the opportunity. Framing less so.

Open cell foam in the interior cavity would have a high perm rating (about 8
for the 6"?). A 1" interior eps board would be about 5 perm. So the wall is
basically drying to the interior. 

Interior moisture is then the issue as well as all the worpersonlike details
that will prevent moisture from getting in over x number of years. Using a
spray foam is pretty affective for an air barrier and an interior board
allows you to potentially create an even better air barrier with decent perm
(than trying to seal studs or gaps in the spray foam) to limit moisture
laden air if detailed properly...

Next issue and probably the most important one would be interior
ventilation/dehumidification if the wall is to dry to the interior. I
remember it gets pretty muggy in queens. I modelled a similar wall with high
interior humidity levels and it didn't look good.

As for drainage plane and thermal values. The cladding I'm assuming mounts
to the horizontal z clips and there is probably some small gap between the
panels and the foam and between the foam and the gooped pywood and that
probably be sufficient as I can't see any materials being compromised other
than the metal clips (if they are clips and not a continuous z bar). If the
clips corrode the panels fall off.

I would include the 2" of foam in the thermal (what else is it doing?). Hard
to calculate the bridging from the clips and I don't think leeds is that
critical at this point. 

I think the 1" interior if done in eps would be very useful for bridging
thermal gaps adding significantly to the thermal value - and completing a
sealed interior as an air barrier if done well.

I have to say I am personally getting more fond of chopped straw and mud - a
little more physical activity and fewer spreadsheets and when it fails you
just have a bunch of mud and straw.

 


JOHN SALMEN ENVIRONMENTAL DESIGN
4465 UPHILL RD,. DUNCAN, B.C.  CANADA, V9L 6M7
PH 250 748 7672 FAX 250 748 7612 CELL 250 246 8541
terrain at shaw.ca


-----Original Message-----
From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of J
Messerschmidt
Sent: November 9, 2010 12:09 PM
To: Greenbuilding
Subject: [Greenbuilding] Insulation Problems

Hi Listers,
I have a 2 story house under construction, framed and sheathed, with no 
windows yet in Queens, NY.  It's a renovation only by DoB standards.  Some 
of the foundation is still there, otherwise it's new construction.  Don't 
tell anybody.  No thought had been given to green building or building 
science until now.  The outside has been insulated with 2" Dow styrofoam, 
but every 24" going up the wall is a horizontal z clip, attached to the 
sheathing, where the bronze panel cladding will be attached.  Is that a 
clear description?  So the profile from the inside out is 2x6 wood studs, 
3/4" plywood, some kind of rubber painted onto the plywood that could serve 
as a vapor/air barrier, and 2" styrofoam, cut every 2 feet going up the 
walls, with z clips in between, and then the bronze siding.

Can't take any of that off and start again, so I'm figuring the space 
between the styrofoam and the rubber, as well as the space between the 
styrofoam and the panels would have to serve as the drainage plane. Question

1: Can I count this r-10 styrofoam as part of the whole wall r-value?

Question 2: For the inside, we are thinking of spraying open cell foam in 
the wall cavities to prevent air flow and increase the r-value.  If we 
installed 1" rigid with no foil, behind the sheetrock, I think this would 
block conductive heat loss and would not add another vapor barrier.  Do you 
think this would work?


Thanks!



John




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