Foundation Calculations
Any load from above must eventually rest on the ground. The Building Regulations – Approved Document A, requires justification that these loads are transferred safely to the ground. Before 1975 houses were built with shallow foundations, some less than 300mm deep. After the hot summer of 1975 houses were subsiding due to the ground drying out. We call this settlement or subsidence. When the rain eventually came, the clay soil expanded again and caused the clay to expand which caused heave. This was unacceptable and the Government invested in research to prevent these type of insurance claims.
When design foundation we have to consider, the topography of the ground, trees within the vicinity of the building and or course the ground bearing pressure. Research also found that water does not freeze below 750mm. When water turn to ice, the ice expands that can cause heave. So we design foundations to a minimum of 750mm deep. The width or the foundation will depend on the loadings that are transferred from the above structure.
Types of Foundations can be:
- Piled Foundation
- Pad & Beam Foundations
- Raft Foundations
- Strip Foundation
Timber Calculations
Like steel beams timber has a limit state before it will deflect. Normal design is to allow timber to deflect between 14-16mm. Beyond this ceiling cracking or floor boards bending may appear. More complex roof structures such as cantilever roofs will require structural calculations. When converting a loft space structural calculations are required to prove that timber/steel will not deflect on areas such as hip rafters, dormer cheeks, trimmers, floor joist spans, flitch beams etc.