[Strawbale] retrofit in N.C.

[David Neeley]

First, I'd suggest you do a careful survey of the house with an eye
toward sealing air leaks. It is relatively rare that a fiberglass bat
insulation job would not have many air leaks, which are often the
source of most interior discomfort.

Next, I'd look with care at the insulation and ventilation in the
attic. Generally, about 65% of heat gain in Summer and a sizable
percentage of heat loss in Winter is through the roof structure, while
this is also usually the fastest, cheapest, and easiest upgrade you
can make for energy efficiency.

Substantial overhangs are strongly recommended for strawbale, to
protect the walls from rains. Thus, when you add nearly two feet of
bales and render, I would find it rather incredible to think you'll
have adequate overhangs then.

Unless I have been misinformed, roofs "blowing off" are more due to
the Bernouli effect of winds passing over the roof coupled with less
than robust fastening between the roof and the wall structure. Thus, I
doubt whether your fears are justified on that account--yet the need
to have a good shelter for rendered walls from rains will still be
there.

To do a strawbale retrofit under these circumstances, I'd consider
putting the bales on edge. You'd still have a substantial increase in
insulation and would require fewer bales for the job.

Note that you'll need to consider relocating the windows to the bale
portion of retrofitted walls.

Before doing a bale wrap, I'd also examine the feasibility of putting
a sunspace on the Southern side of the house. This would be the more
ideal place to go for thermal mass--likely in the floor of such a
sunspace. You could use removable glass panels with screens for the
warmer weather, to get full use of the space as a semi-outdoor room
year round. You could also build it to serve as a greenhouse if you
wish.

That would mean putting bales essentially on the remaining walls. That
way, you may find you'd have more effective solar gain during winters
with good performance the rest of the year, too.

David

On 2/25/07, S. Janssen <andakjam at earthlink.net> wrote:
> Retrofitting strawbale
>
> I also have been lurking on this list for a while and was also wondering
> about strawbale retrofit.  Our house was designed to be passive solar
> (although they did go overboard on the West facing windows).  Unfortunately
> we don't have sufficient thermal mass because the slope of the land made a
> slab difficult.  So we are on a crawlspace.  It is somewhat passsive solar.
> We turn our heat off at 8:30 or 9AM on a sunny day and it stays warm until
> the evening when it gets cold fairly quickly.  We couldn't afford 2x6s for
> the framing so we have 2x4 with Fiberglass R-15 insulation, chipwood w/vapor
> barrier surrounding entire house, then hardiplank.  We don't have a lot of
> money and are trying to make our house as energy efficient as possible.  The
> other thing is that we have these great overhangs which in the era of global
> warming and worsening storms are more likely to lead to having our roof
> blown off.  My idea was to put a shell of straw bales around the whole house
> to increase insulation and also decrease the exposed overhang.  Is this a
> crazy idea?  Can anyone point us in a good direction for getting more ideas?
>
> Sarah Janssen
> Hillsborough, North Carolina