Most people planning an extension think about the kitchen, the glazing and the finish. The part that decides whether it all stays put is underground, and it is usually the first thing on site.
1. Knowing the ground
Before a foundation is designed, someone needs to know what it is sitting on. On many plots that means trial holes to see the soil and how deep the firm ground is. Much of Cheshire sits on clay. Clay shrinks when it dries and swells when it gets wet, and trees and large shrubs nearby make that movement worse because their roots draw water out of the ground. That affects how deep the foundations need to go.
Your designer or structural engineer will specify the foundation. Our job is to dig it to that specification and to tell you early if the ground turns out different from what was expected.
2. The foundation itself
Common types for domestic extensions include:
- Strip foundations: a concrete strip in the bottom of a trench, with blockwork built up to ground level.
- Trench fill: the trench filled with concrete almost to the surface. It is quicker to build up from and is common where the trench is deep.
- Raft foundations: a reinforced slab across the whole footprint, used on some poorer ground.
- Piled foundations: used where firm ground is a long way down, often with a ground beam on top.
3. Building Control inspections
Under the Building Regulations, Building Control (from the council or an approved inspector) inspects the foundation excavations before concrete goes in. Leave time for it in the programme. Pouring before the inspection can mean digging it back out.
4. Drains under and around the extension
Extensions often run over or close to existing drains. If a public sewer is involved, the water company has to agree before you build over or near it. In Nantwich and most of Cheshire that is United Utilities. Private drains may need diverting, protecting or replacing, and new rainwater from the roof has to go somewhere. That might be a soakaway, where the ground allows it.
5. Ground floor and external works
Once the foundations are in, the groundwork continues with the floor build-up, any new drainage runs, and the external works around the extension: paths, patios and making good.
What to have ready before you ask for a price
- Drawings, even early ones
- The structural engineer's foundation design, if you have it
- Anything you know about the drains, such as a drainage survey or the location of manholes
- Access: how a digger and muck-away will get to the back of the house
Send us what you have and we will tell you what we need to price it properly.
