Best Building Practices
It is very important to us that we provide our customers with sound advice on the most appropriate construction method to reflect site conditions, based on our extensive local knowledge, past experience, and what a building inspector may consider ‘best practice’ although companies are under no obligation to do so where a conservatory is deemed to be exempt from building regulations particularly as this may increase costs and effect the competitiveness of their quote significantly.
On projects where building control does apply it is often our practice to exceed the minimum requirements because it is the right thing to do.
Standard Construction Method
- Excavate trench up to 2m deep (min 1m)
- Bridge pipes & fill with concrete
- Lay oversite brickwork to DPC
- Lay hardcore min. 100mm
- Lay blinding screed of sand
- Lay damp proof membrane over up to 100mm insulation
- Lay min. 100mm concrete to take 50mm cement floor screed
- Cavity wall construction with up to 100mm of insulation
Where the ground drops away more than 450mm from the DPC the floor is normally suspended with a void below.
Traditionally this was achieved using timber joists & floorboards, which although the lower cost option does not meet modern standards of energy efficiency and current construction standards
We therefore would always advocate the block & beam method to form the floor when site conditions require it.
The presence of large tree specimens, conifer hedging, and even very large shrubs should alert you to a potential risk particularly in clay soil conditions. In the right environment excessive ground water can be removed undermining the clays stability as it dries out & cracks coupled with the effect of shallow root systems on traditional trench foundations. A reinforced concrete raft foundation although an additional cost will ensure the integrity of the building even if the ground fails in one isolated area.
On clay sites the roots of trees (or even large shrubs) can rip off by osmosis water molecules that are chemically adsorbed to the surface of the molecules of the clay causing large volume changes (shrinkage or heave) of the clay which can cause movement of foundations bearing onto the clay.
If your property has piled foundations it indicates that the site is high risk with poor ground conditions. Consideration has to be given to either match the existing foundations at a higher cost or accept the potential risk relying on conventional foundation methods where this choice is permitted under building regulation exemption rules.