[greenbuild] Re: celotex
- From: "Jon Harrod" <insul8er@xxxxxxxxx>
- To: <greenbuild@xxxxxxxxxxxxx>
- Date: Mon, 2 Jun 2003 15:02:49 -0400
Hi Genevieve,
A couple thoughts on your inquiry--
The first is that, as far as I know, polyisocyanurate ("Celotex") and
extruded polystyrene ("Styrofoam" or "blueboard") are still being
manufactured with HFCs, which damage the ozone layer and contribute to
global warming. Which is not to say that these products should never be
used, but just that they should be used judiciously, where they can provide
benefits that outweigh their negative impacts. There are a couple questions
I would ask in making this assessment.
--How much insulation do you have in the wall cavities?
--What type?
--How much potential is there to increase the cavity insulation with less
damaging products (i.e. cellulose)?
--How leaky is your house? Would air leakage around the foam and into the
wall cavities reduce the effectiveness of the foam insulation?
With answers to these questions, an energy auditor can work with you to look
at the energy costs and benefits of adding the foam versus other options.
The second issue relates to potential moisture problems. Celotex is
completely impermeable to air and moisture (i.e. it is a great air/vapor
barrier). In cold climates, you want the air/vapor barrier on the interior
side of the wall cavity. By placing an impermeable barrier to the outside,
you create the potential for condensation, which would lead to mold on the
osb. Whether this condensation actually occurs depends on a number of
factors including the permeability and leakiness of the interior wall
covering, the type of insulation, the thickness of the foam board, and the
moisture level in the house.
On balance, my recommendation would be to steer away from exterior foam
unless it is part of a comprehensive plan to improve the building envelope
in a way that prevents future problems.
Good luck,
Jon Harrod
Performance Systems Contracting
-----Original Message-----
From: greenbuild-bounce@xxxxxxxxxxxxx
[mailto:greenbuild-bounce@xxxxxxxxxxxxx]On Behalf Of Genevieve DeClerck
Sent: Monday, June 02, 2003 1:53 PM
To: greenbuild@xxxxxxxxxxxxx
Subject: [greenbuild] celotex
In my readings of ways to improve energy efficiency on a house I came across
a few mentions of using
polyisocyanurate foam core panels (e.g. Celotex) on the exterior of house
under the siding... the
argument being that having a thermal barrier like this reduces thermal
bridging through the studs.
I'm considering using this material on my old house which will be fully
re-sided this summer. The
proposed idea is to sheath the house as normal with OSB, then cover that
with Tyvek, then fasten
celotex panels to the studs, then finally apply pine clapboards to the studs
(if we can find them!).
Does anyone have any experience with this? Any info, opinions, advice would
be greatly appreciated.
Thanks,
Genevieve
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