[GSBN] Earth plaster and Cellulose

[kim thompson]

Hello all,

I have had a note in progress for GSBN'ers for weeks to ask a question related to Jacob's.
A building I am currently involved with was built in 1764. We recently moved the 2.5 storey home 
nearly 5 km through central Halifax to a lot where it will be rehabilitated and used for affordable housing for youth.

The Morris House has become an interesting demo of how we can make heritage buildings more energy efficient (and
keep them out of the land fill). It has a number of unusual (for Halifax) features including solid brick nogging which fills the cavities in the
first and half way up the second floor levels of the Georgian timber frame. There has been considerable discussion amoung committee members
involved with the Project about whether or not to fill in the currently uninsulated wall sections, and if so with what. Heritage folks want to employ 
minimal intervention strategies and add nothing - they are concerned that introducing insulation will bring with it moisture which will 
compromise the timber frame.

I have proposed a few options and would so appreciate thoughts from this group on the building science side of things for
our northern maritime climate. Thermal comfort (cold walls especially) will be important to the young people living there, as will be 
heating costs... construction materials and systems on this project will certainly be cited as recommendations for future heritage rehabs. 

So my question is  what might be the pros and cons of insulating the currently empty wall cavities above the nogging with one of the following:
(a) dense pack cellulose (b) light straw clay (c) hempcrete  (d) reuse of brick from the chimneys of the Morris. (e) blown in or batt wool  (f) aerogel.
Assuming any one of these would be installed with great care to avoid air leakage. 
Exterior cladding is painted cedar shake, interior is lime plaster/lathe, no vapourbarriers and removal of  the nogging is not an option.
Are there other choices apart from providing "extra sweaters"  for the tenants that would not compromise of the structure.

Am hoping that John S. in particular might chime in on this.

Thank you all!

Kim Thompson
www.themorrisproject.ca


On 2013-04-25, at 11:46 PM, Jacob Deva Racusin wrote:

> Hello,
> 
> My apologies for the cross-post, but I'm trying to do a very quick and broad survey.
> 
> I was just contacted by a former student I am advising, who is project managing a building currently in design phase, in the mid-Atlantic region in the eastern US.  The wall assembly was initially to be straw-clay, with plaster finish on both sides. Budget and logistics have directed an insulation switch to cellulose.  He is currently advocating for wood lath with lime-stabilized earthen base coat, with finish lime coat (our standard approach for finish exterior plaster).  The architect is balking, suggesting that the moisture storage and release dynamics for which we rely upon the plaster in straw-based designs will not play out the same way with cellulose, that the cellulose will be overwhelmed with moisture and push the dew point deep into the wall.  This is all second-hand reporting of the conversation - I know no more than what I just reported - but I am due to speak with the architect and client tomorrow on my student's behalf, and I'm curious as to whether or not any of you have direct experience with earth base plaster over wood lath outboard of a dense-packed cellulose-insulate wall, or any reason to believe the cellulose would not behave adequately in concert with adjoining plaster (as opposed to straw).
> 
> The architect is spec'ing (outward from the framing) plywood, housewrap, drainage gap, stucco lathe, plaster.  My impression is that this suggestion would certainly work, but is hardly the natural wall system initially intended.  It seems to be playing off of the concerns of sun-powered vapor drive pushing vapor deep into the wall cavity as a result of a reservoir cladding adjoining the insulation.  As long as there is no interior vapor barrier or Class II vapor retarder, I feel this dynamic is identical to that we've created with straw-insulated walls, and if anything the cellulose would stand up better to incidental vapor or liquid moisture intrusion.  Also note generous overhangs and 24" grade separation are spec'd in the design, as is multiple coats of limewash (and potentially a silicate top coat for durability), which will further reduce bulk water absorption and minimize incidental solar-powered vapor drive.  The wall is designed to dry to both sides of the assembly, in keeping with the variable moisture drive of that region.
> 
> Perhaps there is another concern here I'm not understanding - I'll find out more tomorrow - but in the meantime if anyone has any perspective on why this situation would work for straw, and not cell, or any direct experience in a comparable climate executing such a system, I'd be grateful for your input.
> 
> Thanks so much,
> Jacob
> 
> -- 
> Jacob Deva Racusin
> New Frameworks Natural Building, LLC
> P.O. Box 15, Montgomery, VT 05470
> (802) 782-7783 (c)
> (802) 326-2209 (h)
> www.newframeworks.com
> jacob at newframeworks.com
> 
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