Civil Engineering Reference
In-Depth Information
When designing foundations, the first thing to
decide is whether the ground itself can provide
us with a natural foundation. If it can, there's
absolutely no need to dig it away and create
an artificial one.
foundation has to be able to hold up 60kN
of weight - much less than a conventional
brick-and-mortar building (see table over-
leaf). The foundations of a typical strawbale
house are 450mm (18”) wide, which has
the advantage of spreading the weight
of the building over a wider-than-usual
surface area.
The majority of building sites in the UK and
Ireland are on good bearing soil, and this
type of soil will easily take the weight of a
strawbale house (and most other houses in
fact, including stone ones). The types of soil
where we need to think a bit more carefully
about foundations are:
For stability, find out what your subsoil is
There are several ways you can find out what
your subsoil is and if it's good bearing soil.
•
Look at houses in the area (as long as
they're pre-1900 and made without cement)
and see what their foundations are made
of. If they're quite shallow, you've almost
certainly got good bearing soil. Not only
that, but you can use the same foundation
designs for your own house.
• silty soils
•
heavy clay soils
•
made-up ground (i.e. you're not sure
what it's made of because it isn't undis-
turbed subsoil)
•
Ask older people in the area, who might
remember houses being built in their
youth, what foundations were like then.
• wet soils
•
Consult your building inspector, who
should have a good local knowledge of
older houses and subsoil in the area.
•
moving sand soils.
All other types of subsoil should be good
bearing soil.
•
Dig two or three pits about 800mm (31”)
deep in the place where your foundations
will be, have a look at the profile of the
soil, and take photographs of it to show
your building inspector. Does it seem
solid? Does any of it fall away? What's
it made of - is it gravelly soil, stony or
clayey?
For flexibility, use appropriate materials
There was a major change in foundation
design that occurred around the 1920s and
1930s when cement started being used in
mainstream construction, and this was a
shift from flexible foundations to rigid ones.
It might seem strange to think that founda-
tions and whole houses made of stone or
brick could be flexible, but because of what
An average two-storey strawbale house
has a bearing weight of about 60kN/m
2
.
This means that every square metre of
