Civil Engineering Reference
In-Depth Information
Chapter 10
WINDOWS AND DOORS
Structural box frames
We need to consider the design of window
and door frames and openings for several
reasons. We must make sure that they are
structurally sound and able to take the loads
above them if necessary. We also need to
ensure that they are airtight and don't let in
draughts, that they are the right size and in
the right place to maximise solar gain without
overheating, and that they allow enough
daylight into our homes and offices.
A simple way of dealing with openings is to
make a structural box frame into which the
actual window frame or door frame is fixed.
The design of these box frames must take
into account the fact that the straw walls
will settle under the weight of the floors
and roof above. It is impossible to know
exactly how much settlement will occur, as
it depends on the density of the bales and
the amount of loading applied to them -
although it's possible to be pretty accurate
if using construction grade bales all from
the same source. 75mm (3”) is usually
sufficient, and the frames are therefore built
to be 75mm less than the height of a whole
number of bales.
Loadbearing methods
All window and door openings in loadbearing
houses must have some way of supporting
the weight of the bales, floors and roof above
them, as well as be able to withstand the
pressure of the bales wedged in beside and
below them. Owing to the flexibility of straw,
the use of concrete or steel lintels is inapprop-
riate and their weight in fact would create
problems - as they sit on only a small bearing
surface they would compress the straw too
much in a small area. Weight (load) needs
to be spread over as wide a surface area as
possible.
Except in unusual circumstances, structural
frames should be multiples of bale dimen-
sions, so external dimensions of the frame
could be anything from half a bale to
three bales in width and any number of
bale heights minus 75mm (3”) to allow for
compression or settlement.
Frames are pinned into the bales with hazel,
through the base during construction,
and through the side once settlement has
finished. Door frames would not have the
