Planning the build
Why build an extension?
Initial design sketches
On-line Building Regs
Meeting planners
 Meeting building control
 Planning the foundations
 Planning the floor slab
 Marking out the footings
 Damp proof course issues
 Possible drainage problems?

 Construction of the walls
 Proposed roof structure
Windows diary
 Window challenges
 Initial window plans
 Making the casements
 Making the frame
 Designing leaded lights
 Making leaded lights
 Assembling the window
 The little window

 The door frame
Demolition diary
 The demolition starts!
 The demolition continues
 Still more demolition

Foundations diary
 Foundation issues
 Drain issues
 Digging the foundations
 Rethinking foundations!
 Pouring the foundations

Floor slab diary
 Rethinking the slab!
 Floor vent extensions
 Preparing the slab #1
 Preparing the slab #2
 Pouring the slab

Walls diary
 Preparing to build walls
 Build up to the DPC
 Build the walls #1
 Build the walls #2
 The gas men cometh
 Build the walls #3
 Finishing the walls
Roof diary
 Roof structure build
 Tiling the roof
 Finishing the roof
 Finishing the gables
 Roof insulation

 Floor screed
 Shower room
 Shower room floors
 Shower room walls
 Utility room
 Utility room walls
 Utility room floor
 Finishing the windows

Project finished!
 Final inspection
 The certificate
 Final thoughts

 Twelve months on!
 Material costs
Sister sites
 House re-roof project
 Home gas usage data

 Stop paint flaking
 DIY secondary glazing


Planning the strip foundation

The first major task to undertake will be digging the foundations for the extension. You will need to talk with your local planning control department to determine what the size and depth of the strip footing needs to be for your local soil conditions.

In my area, my subsoil is solid sand that will need to be shifted with a pickaxe - I know because I've done this before! The planning officer said that they needed to be 600mm wide and the bottom of the slab 450mm deep.

The basic construction of the extension foundations

In my case, the strip footing will be 600mm (24") wide and 200mm thick. The below ground part of the wall and up to the DPC will be built using standard engineering bricks on the inside and outside facing bricks reclaimed from the knocked-down external toilet wall.

The cavity will be in-filled to the ground level with a weak concrete mix. Above the DPC I will use heavy blocks as the outside face of the extension will be rendered to match the rest of the house.

The DPC on the inside wall should overlap the damp proof membrane placed underneath the floor slab as shown here. Once the DPC is in place, then an inspection is required by the planning control department.

Some minimum spacings as specified in building regulations

The main point to remember is that the level of the DPC - damp proof course - needs to be a minimum of 150mm above outside ground level to meet UK planning regulations. Ideally, it should be at the same level as the existing building, but this could prove to be a problem me. In my case the land is 25cms (10") higher at one end of the extension than the other, so the DPC will be 150mm at one end and would be around 40mm at the other. This will create a problem as the bottom of the door will be too high so it looks like I might have to take the DPC down by a brick level or two at the low end of the extension.

It may be simpler to just level the ground outside of the extension.

How the sewer passes through the foundations

The above drawing show how the main drainage pipe will pass through the strip foundations. The pipe will be covered by shingle then by several small slabs to take the weight of the wall.

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