I did a similar job in Burlington last year. An older house, no
plywood... just T&G board sheathing, cellulose insulated 2x4 (full 4").
Many people suggest that the 'Deep Energy Retrofit' jobs add significant
foam insulation -- up to an R40 wall. Pretty tough to go this high but
might be a possibility if budget allows... Any time siding is replaced, foam
insulation should be installed -- not just the 1/4" stuff the vinyl siding
people install. Here are some of my observations:
-At the band joist, we installed 2x pressure treated ripped to the
width of the foam insulation to be installed. I ordered a case of 4" star
drive screws (google star drive screws...) When bought by the case, the
cost comes down. Other builders suggest the long screws used by commercial
roofers -- Harvey has them..
--I covered the board sheathing with Tyvek, then Tyvek tape. If
plywood sheathing you may not need the tyvek, but you might tape all the
joints for an air barrier.
--We added 2" (R 10) of extruded polystyrene, Dow "Wall Mate" with
rabbetted edges to accept strapping . I found a lumber yard in Williston
that could get me bundles of full 1" strapping (cheap). The Hardi siding
rep told me that if the nailers were a full 1" Hardi considers it framing
material. Standard 3/4" strapping might not meet their fastening
--We tacked up the styrofoam with 3" green cap nails then secured
with strapping using 4" star drive screws. The screws were placed into the
sheathing boards so we didn't need to find studs in the wall. If plywood
sheathing, I would place square-edge 2" foam then 1" strapping into the
studs (16" centers, etc..), then add additional 3/4" foam between the
strapping to get a better R-value. The full 1" strapping with 3/4" foam
then allows for a 1/4" rain screen / vent space for the back side of the
-- windows on this project had been replaced earlier so we built jamb /
sill extensions from Azek-type pvc trim (the windows were white vinyl
replacements..) Trim, corner board, etc details were all worked out.
Fastening through the layers of foam required some longer screws. Nailers
attached through thinner foam at the corner boards / window casings, etc
can allow standard trim to be nailed and not screwed into place.
Retrofitting insulation to existing buildings is going to be our
industry's challenge. When finishes are changed out is the perfect time to
stretch the budget and go for the big energy upgrade.. I would love to get
any feedback as to how your job comes together. Good Luck, Dennis Bates,
Vermont Sun Structures.
----- Original Message -----
From: "Tim Yandow" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, March 10, 2010 8:29 PM
Subject: Re: Suggestions on Insulation retrofits
> Hello all,
> On the subject of green building, I am soon beginning renovation work on a
> 1960's home in Burlington. We are adding an addition to the south and west
> sides of the house. The new envelope will be 2x6 with damp spray
> cellulose. The existing house is 2x4 with fiberglass and the owners would
> like to bottom up the house more, so we are thinking about adding a layer
> of insulation to the outside of the house since all the old vinyl siding
> is coming down and the windows all replaced (most of them have broken
> seals). I am trying to figure out the best way to insulate from the
> outside and make provisions for new corner boards and hardi-plank siding.
> With polyisocyanurate, for instance, there is the problem of not being
> able to add house wrap and needing to use longer fasteners for siding and
> to secure window flanges. Or can strapping be used over that? Then there
> is the issue of extension jams either inside or outside...I would love to
> know if anyone has worked out a good solid system to do this. What I have
> read and seen so far does not satisfy me. Thanks.
> Tim Yandow
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