Construction Principles and Techniques
Construction Principles and Techniques tests your understanding of how small buildings are put together: foundations, walls, floors, roofs, openings and damp control. You need to name components, explain their order and identify where a detail would fail.
Core rules
- Strip foundations support load-bearing walls; pad foundations support isolated columns; raft foundations spread load over weak ground. Foundations must bear below the frost line and on undisturbed bearing strata.
- A cavity wall has an outer leaf, a cavity, insulation, wall ties and an inner leaf. Wall ties must slope down towards the outer leaf so water is shed outwards.
- A damp-proof course (DPC) stops rising damp in walls; a damp-proof membrane (DPM) stops ground moisture entering a floor. They must overlap or connect to form a continuous barrier.
- Openings need a lintel to carry the wall above, a cavity tray above the lintel, and a DPC under the sill. Roof pitch must suit the covering.
Worked example
At a window in a cavity wall, the sequence is inner leaf, lintel, cavity tray with stop ends, insulation, outer leaf, frame and sealant. The tray turns up at the inner leaf and discharges through weep holes in the outer leaf. The DPC under the sill laps the frame. If the tray stops short, water runs down the cavity and appears as a damp patch inside.
Traps
Bridging a DPC with mortar or plaster, omitting the cavity tray, reversing the wall-tie slope and leaving insulation gaps are frequent mark-losers.