[Greenbuilding] Exterior insulation retrofit

Alan Abrams alan at abramsdesignbuild.com
Fri Apr 29 09:31:33 CDT 2011


>
>>
>> On Fri, Apr 29, 2011 at 7:34 AM, jfstraube <jfstraube at gmail.com> wrote:
>>
>>> I am not near by: Waterloo and Boston.
>>> If you look at at the article by Betsy Petit in the retrofit of a 1916
>>> Sears Roebuck house, you will see one approach we have used numerous times.
>>> strip to board, drill holes and densepack with cellulose, IR scan to
>>> confirm all cavities full, Tyvek Drainwrap taped and seal (as air barrier
>>> and secondary drainage plane), special care at mudsill and roof with tapes
>>> and foam, then two staggered layers of foam insulation, outer layer taped
>>> (as primary drainage plane), 1x3 screwed to nominal 1" sheathing boards,
>>> cladding.  I think TimberLok are too big and I know that we dont need them:
>>> we use them because they are locally available in the 6-10" lengths we need.
>>>  For other project we order roofing screws from commercial roofing supply
>>> stores.
>>>
>>> You would be "safe" with just 1.5" of polyiso over 2x4 with cellulose,
>>> but I would recommend more, two, 1.5" layers would mean you are done for the
>>> next 100 years.
>>>
>>> The larsen truss on the exterior requires more care and effort to get
>>> good performance, because foam plastics are air impermeable,
>>> non-hygroscopic, and vapor semi-impermeable: using cellulose as exterior
>>> insulation is a completely different animal and requires better care and
>>> control of air flow control, reverse water vapor drive (particularuly with
>>> shingle cladding) etc.  Is, has, and can be done, but lots more things that
>>> have and do go wrong.
>>>
>>>
John-
What's your assessment of the impact of thermal bridging, comparing the
larsen system and the 2 layers of polyiso?
AA
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/attachments/20110429/2b404679/attachment.html>


More information about the Greenbuilding mailing list