Post or door frame Expanded metal angle connecting post and straw bale Steel rods restrained in the foundation
bales are prestressed between foundation or grade beam and ring beam. The prestressing will create sufficient friction at the joints between bales and between bales and loadbearing structure, usually making additional connections unnecessary.
Wall corners In the case of loadbearing straw bale walls, the bales should interlock at the corners or be held in place by the posts for structural reasons; interlocking walls will reinforce each other against horizontal forces and will not buckle at the open ends. Figure 11.18 illustrates how doors and windows can provide bracing for the walls. At freestanding corners with interlocking bale layers it is advisable to connect the layers with sticks running vertically through two and half bales. Since it is difficult to thread the sticks through jumbo bales with their higher density, steel rods with U-shaped hooks can be used in this case.
11.17
11.18
Foundations, bases and connection to floor The type of foundation of a building will – above all – depend on the frost line and loadbearing capabilities of the ground. In the particular case of straw bale walls,
their relatively great thickness entails larger – and therefore more expensive – foundations. One solution to bypass this problem may be the provision of a beam supported by point foundations, as shown in 11.21. As the test building discussed in chapter 14, pp. 78–81, shows, this is also an economical solution. Another financially viable method may be the construction of strip foundations out of locally resourced natural stone or recycled bricks – provided the owners build them on their own account. Yet another cost-effective solution may be the construction of a floating floor slab on an insulation layer of crushed foam glass (11.19). The crushed glass layer consists of recycled glass in a size range of 0 to 90 mm. The layer is compacted with a vibrator, and in a highly compacted state it has a heat conductivity of 0.08 W/ (m · K) whereas in a loose state the value is 0.06 W/(m · K). In this build-up the closed cells of the foamed glass intercept capillary action. However, a waterproofing course against vapour and possibly radon should be included as well. It is important that thermal bridges in the foundation and base area are avoided. A rather unconventional but very economical do-it-yourself solution is the use of disposed car tyres filled with lean concrete: the tyres can be resourced free of charge from petrol stations or car
Wall build-up – Earth render, three layers – Straw bales between timber posts – Bituminous fibreboard – Ventilated weatherboarding
11.14 Stabilising of bales by adequate positioning of posts (horizontal section)
Wall build-up – Earth render, three layers – Straw bales between timber posts – Bituminous fibreboard – Lime render
11.15 Wall with boarding on both sides, plastered (left) and rear-ventilated (right)
Base – Lightweight vertically perforated bricks (Bessa blocks)
11.16 Stabilising of bales by adequate positioning of post with triangle borders
11.17 Bale connection according to New Mexico Code Floor build-up – Top flooring – Floating screed (concrete) – Sliding and separating course with vapour barrier – Crushed foam glass
11.18 Bracing of the wall with windows and doors 11.19 Base with crushed foam glass layer acting as insulation and water-proofing course 11.20 Base with lightweight vertically perforated bricks
57
11.19
Assembling the straw bale building
Floor build-up – Top flooring – Floating screed – Sliding and separating course with vapour barrier – Crushed foamed glass
11.20