[Greenbuilding] Exterior insulation retrofit
elitalking at rockbridge.net
Thu Apr 28 07:42:27 PDT 2011
Yes, I have just completed a project very similar. My house was built in
1995 with conventional fiberglass batt and electric plugs in wall.
Therefore I left those walls as they were. I mounted 3" isocyanurate boards
over the existing plywood siding attempting perfect seals with acoustic
caulk at seams. I use spray foam cans to fill and seal gaps that occur.
Recognizing the difficulty of perfection, I installed building wrap over the
foam boards that is fastened at the top and bottom as a redundant attempt at
continuous air barrier. I installed 4"x 3/4" osb vertical furring strips
using long screws through foam and into original framing. I also dabbed
acoustic caulk on back of furring strip where screws came out in an attempt
to seal the hole in building wrap I was creating with long screw. The
furring strip created the drain plain that John Straub was talking about.
Over this I installed textured plywood and 1x3 battens to create a board and
batten look. Other sidings could be used. It is stained, therefore, have
that continuing maintenance issue. My concern about cedar shingles is that
they are highly flammable. I had to install jamb extensions on all the
windows and doors and reinstall the trim. I was able to reuse some most of
the original trim wood. This only describes the walls. I also installed 3"
isocyanurate under existing ceiling and installed new finish ceiling below.
Also, I am installing 3" iso boards below floor in crawl space with building
wrap again and osb sheathing for rodent protection.
We actually removed our heatpump; therefore no longer have the option to
cool in our mixed humid Virginia climate. However, the 3 inch continuous
tight foam should keep surface temp on hot side above dew point, even if we
install cooling. When the house envelope is completed, we can consider a
high efficiency mini split air source heat pump and a grid tied photovoltaic
as a path the net zero.
It was a lot of work. However, I am practicing what I preach. Good luck
with your project. You are on the right path.
----- Original Message -----
From: <bill.allen at verizon.net>
To: "Green Building" <greenbuilding at lists.bioenergylists.org>
Sent: Thursday, April 28, 2011 8:45 AM
Subject: [Greenbuilding] Exterior insulation retrofit
> Hi all,
> I am researching a project for my single family home. Classic 1926 stick
> construction. Zero insulation in the walls...time yet again for an
> external paint job. Would really appreciate comments on the following
> We never want to paint again...are thinking of natural cedar shingle
> siding, maybe with preservative but otherwise left natural. Don't like
> the embodied energy in the various cement siding
> While the siding is down, fill the wall cavities with cellulous from the
> Replace original double hung windows with new construction insulated, R-5
> if we can afford it, windows mounted "innie" on the plane of the original
> dimensional 1x lumber t+g sheathing.
> Add external insulation....rigid styrofoam. Since there is no interior
> vapor barrier (plaster on wood lathe), I am worried about the dew point
> ending up in the center of the wall...therefore, per the building science
> article, add 4" of styrofoam to the outside to keep the dew point external
> of the sheathing.
> Will require careful details at windows and other penetrations.
> Big job...has anyone done this? Any comments on any part of the above
> would be most welcomed.
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