[Greenbuilding] Insulating brick unframed envelopes

[Alan Abrams]

thorny question, with vast variables--foremost, the composition and
porosity of the bricks and of the mortar. plus, an understanding of
freeze-thaw cycles and rainfall.

here's the risk--consider a typical late 19th/early 20th century row
house---load brg masonry with a big radiator under the front windows--the
assumption is that heat loss through the wall prevents or retards freezing.
If freezing occurs in saturated mortar, its expansion pops the face of the
brick off (exposing the brick's more porous innards, etc)

It may be less of a factor in walls with pre-portland based mortar--the
vintage lime based mortar had a somewhat plastic nature--then again, some
of that housing stock had very thin mortar joints, which could diminish
this resilience.

I don't know how to work around this risk, but one approach would be to
analyze the entire wall area for heat loss. given that vintage row houses
often have a very high ratio of glass to opaque wall area, it may likely
produce greater net reduction of heat loss to go with higher performance
fenestration. (I can hear the collective gasp of the preservationistas)

WRT to the bonus question--I would not minimize the porosity of party
walls--which typically appear as though they were laid up with the clinkers
and broken bricks, probably using inferior or dried out and re-wetted
mortar--and executed by the hod carrier, instead of the master mason who
was doing the showy stuff in front. So there is an issue with vapor
migration that would come into play in summer, if the neighbor's home were
not conditioned.

plus, the two feet or so of party wall that intersect the roof and end
walls function as thermal bridges--so insulating those regions could be
beneficial--with somewhat less risk as described above. as the tops of
party walls terminate in parapets, they are already subject to
wetting/freezing/thawing...

AA


Alan Abrams

*certified professional building designer, AIBDcertified passive house
consultant, PHIUS*
*certified passive house builder, PHIUS*
cell     202-437-8583
alan at abramsdesignbuild.com
HELICON WORKS *Achitecture and Education*
<http://www.heliconworks.com/index2.html>

On Mon, Mar 16, 2015 at 12:56 AM, Jason Holstine <jason at amicusgreen.com>
wrote:

>
> We are trying to tackle a holy grail—insulating old brick-front homes
> without covering or redoing the exterior brick.
> Buildings are vintage 1890-1950. Typically brick with plaster interior and
> that’s about it. These are often rowhouses with rear extensions (not
> bricked), so it’s typical that we’re only talking about doing 1 or 2 sides
> of the building.
>
> It’s in the DC/MD region in the heart of mixed-humidness, but it’s
> noteworthy our winters are getting harsher. This is a concern I have.
>
> We’d like to avoid framing out the walls to minimize the loss of floor
> space. So, we’re thinking about air sealing then insulating on the interior
> with 2” foam board or mineral wool 2” board (R8). In either case, the plan
> is to attach sleepers and drywall right on top. We figure this isn’t ideal
> but is certainly an improvement.
>
> A main concern is that insulating the brick walls may lead to brick
> damage, but how much of this is germane only to cold climates?
>
> How nuts is this plan?
> If we go foam board, how imperative is closed-cell or open-cell?
> If not using closed-cell foam board, should we apply a vapor-smart weather
> barrier on the inside of the brick first?
>
> Bonus question: Any risk of also insulating bricked party walls that show
> leakage?
>
> Thanks,
>
>
> Jason Holstine
>
>
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