[GSBN] Earth plaster and Cellulose

Mon Apr 29 02:55:40 UTC 2013

Kim,

Wow, what a great project!  That's a really dramatic image of the Morris 
House next to the massive glass-faced skyscraper...good on ya!

I'm a bit hesitant to reply given the tremendous wealth of knowledge on 
this list, but it's a great question so I'll take a crack.  My 
understanding of 'nogging' is brick non-structural cavity infill, yes? 
And you are looking to insulate the empty cavity sections above the brick?

The concern about creating a moisture problem by introducing insulation 
is a valid one - there is plenty of precedence for this unfortunate 
dynamic.  The introduction of insulation reduces the drying potential of 
the assembly, and can create condensation problems which did not 
previously exist.  Insulation can be introduced safely, however, if 
moisture sources are considered and mitigation strategies are designed 
into the work.  First and foremost, keeping bulk liquid moisture out of 
the assembly is critical (wind-driven rain and window leaks are two 
notorious and insidious examples).  That's the most significant source 
of moisture damage, and even a small window leak that might have 
previously gone undetected can become a bigger problem when heat loss 
from inside the building is shut off and drying potential is reduced.  
The next step involves air-sealing, which you reference would be part of 
the protocol.  This is critical to reduce bulk-loading of moisture vapor 
into the wall through air leakage. When I do building performance work, 
I see plenty of examples of weatherization work done in the 80s, when 
insulation was added in attics without air sealing, and it is not 
uncommon to see evidence of moisture damage in particularly leaking 
locations.  I'm unclear as to how you would be accessing the interior of 
the cavity and addressing air leakage, but this would be an important 
move prior to/in concert with insulating (I note that none of the 
insulation materials you reference are air barriers themselves, 
requiring a separate air sealing approach).  In your climate, 
air-sealing from the interior - stopping the moisture drive at its 
source - is desirable, although a primary air barrier on the exterior 
can work well too if the detailing is tight and the air barrier is vapor 
permeable enough to allow drying to the exterior as need be.  You 
mention that there is no vapor barrier in the wall assembly; myself, I 
prefer such vapor-open strategies, but it is very important that these 
be deployed with rock-solid water control and air-tightness measures to 
be effective.  Diffusion through materials alone is very unlikely to 
cause a problem, but can push conditions in a wall or ceiling into a 
danger zone if there are other moisture issues also at play.

I like dense-pack cellulose because it has a relatively high R-value 
compared to other in-fill insulation, is fire-retardant without the use 
of HFRCs, performs a notable amount of air circulation retardation (not 
an air barrier, but does slow movement down a good bit), has a high 
hydroscopicity that allows concentrations of moisture to disperse 
throughout the material (avoiding higher concentrations in specific 
areas) and dry out if given the opportunity, is pretty 
ecologically-benign and not too industrially-intensive (depending on the 
specific product), and installs dry - a big plus compared to many of the 
wet-wall natural building materials I otherwise favor using.  I am 
unfamiliar with aerogel in practice, only in theory, so I won't comment, 
but my bigger concern around straw-clay and hempcrete would be the 
amount of built-in moisture you are introducing into the cavity. 
Provided you can ensure adequate drying within a reasonable amount of 
time they could work fine if you are alright using a relatively lower-R 
material, but since moisture is a chief concern of your committee that 
might be a harder sell.  We don't have much access to affordable wool 
insulation, but that could be an attractive option - again, providing 
thorough air sealing measures are taken, as it will be unlikely to stop 
air flow to any appreciable degree.  I like the idea of the reused brick 
- the lowest insulative value of any on your list, but I like the nod to 
finishing the original design, for whatever that's worth (perhaps not 
much, if your goal is to maximize comfort for the inhabitants).

I hope that helps.  There are some great case studies on both 
GreenBuildingAdvisor.com and BuildingScience.com that provide some good 
examples of similar situations, I can dig up some examples off-list if 
you have trouble finding them.  Best of luck, keep up the good work!

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

On 4/26/2013 12:50 AM, kim thompson wrote:
> 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 <http://morrishouse.ca> 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 <http://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 <http://www.newframeworks.com>
>> jacob at newframeworks.com
>>
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