[Strawbale] Radiative heat losses

[David Neeley]

In fact, there have been many studies showing the utility of radiant
barriers in the attic in a cooling climate. One such, for example, studied
houses in the Fort Worth, Texas, area. The study found that all other things
being equal, a radiant barrier reduces peak temperatures in the attic by
about forty degrees on the hottest afternoons. This makes a significant
reduction in cooling loads on these houses.

There is a great deal of information accumulating about cooling climate
measures to reduce energy consumption, especially through the Florida Solar
Energy Center. The problems in our climate are no less challenging than
those of heating climates, only often quite different.

Here in Texas, we have problems in cooling about seven months a year...five
months fairly continuously, two more months being more intermittent. As
always, careful siting and design are both necessary to reduce the impact of
climate and the need for excessive energy use.

While it is obviously possible to insulate more than strawbale, that can
become overkill in many cases. Since most studies agree that about 65% of
the heat gain or loss, on average, is through the roof structure, that is
the first place that attention should be paid. Next would be foundation and
wall penetrations. When you consider the environmentally favorable factors
of strawbale coupled with what seems to be an insulative value of perhaps
R40 or so (three string bale, careful detailing), that should be adequate in
nearly every climate.

At present, I am planning to use substantial amounts of blown-in cellulose
in the attic of the house I am designing for building here, coupled with a
radiant barrier and careful attention to ventilation issues. I do understand
that there is some interesting research on the utility of unventilated
attics, if properly done, but I do not yet have enough information to see if
my plans should be altered accordingly.

David



On Nov 28, 2007 7:08 AM, <dfugler at cmhc-schl.gc.ca> wrote:

> David,
>
> I do not see radiative heat losses as being a significant factor in terms
> of heating loads in well-insulated houses. So I ignore them. I have yet to
> see foil-covered products as being particularly useful, although there was
> some research showing foil radiant barriers as reducing cooling loads in
> Florida houses some years back. Those houses probably had poor attic
> insulation and the air conditioning system within the attic space, so the
> utility of radiant barriers there does not necessarily translate to their
> usefulness in typical houses in colder climates.