Civil Engineering Reference
In-Depth Information
to allow the wire netting to pass through the gap. If you require the pitching beam to be
exposed, fix the wire netting to the back of the pitching beam. If the beam is to be
concealed with render, fix the wire netting to the face of the pitching beam and then feed
the netting through the gap between the droppers and the buck. If you insert a thin layer
of straw between the wire netting and the pitching beam it will eliminate any cracking of
the render at the junction of the pitching beam to the straw bales. Shape the wire to
emulate the final shape of render that you require and then staple the wire to the
droppers. The window stabilising bar can now be fitted on the outside of the droppers.
Position the timber against the droppers while resting it on the wire that is laid over the
buck. First nail the window stabilising rail to the droppers and then nail through the buck
up into the stabilising rail. Tightly pack the cavity between the droppers and the wire
netting with straw and then fix the loose end of the wire to the top boxing using heavy-
duty staples. I use a staple gun with heavy staples, however you could use fencing staples
if you are unable to access a staple gun.
Large window openings
Lintels supported on posts are needed for larger window openings with load bearing
construction.
Openings greater than 1.8 metres for load bearing buildings
In the past it has been suggested that the use of windows greater than about 1.8 metres in
load bearing straw bale buildings was unwise. There are two reasons for this. First there
was concern that the render at the junction between the bales and the windows would
crack as the bales continued to settle while the lintel over the window remained in a fixed
position. Second, if a lintel were to be fitted to support the roof and ceiling over the
windows at what height should it be fixed. It is impossible to accurately predict the
compression that will be achieved as all bales vary, as does the compression of them. One
of my owner-builders who built a house with load bearing walls has one window 3.0
metres wide and another 3.6 metres wide. The 3.6 metre window has a lintel spanning
about 3.9 metres as the bales are curved from the wall into the window which is set on the
outside of the building. The lintel and bale walls are carrying trusses that span about 8.2
metres with a 2-metre verandah also bearing weight onto the walls and lintel. The render
around this window has now been in place for almost two years with no sign of cracking.
With the introduction of polyester strapping the rate of compression has been
increased. This means that the bale walls carrying the roof load have been compressed
beyond the weight that the roof and ceiling will place on them. As long as the load of the
roof and ceiling is less than the pressure exerted through the compression process the
wall will not compress any further. This, added to the lateral securing of the bales to the
posts as previously mentioned in door bucks, means the junction of the bales to the
timber posts are stable and will not crack. The only remaining hurdle is the ability to fix
the lintel so that it lines up with the top bale boxing so that a constant ceiling and roof
line can be gained.
