Porch guidance

10 Sep 2008
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United Kingdom
Currently planning a new porch, external dimensions 2.8m wide x 1m deep. Dwarf wall 600mm high.

For the footings: Ground is loam to clay, solid from about 300mm down, so plan to dig to 600mm deep, 450mm wide - and probably mass fill. Does this sound OK?

For the dwarf wall: I'm in two minds as to build single skin (brick) and line or a full cavity (brick outer, block inner) - internal space is a concern. The UPVC bits and the roof are from a porch I dismantled elsewhere. The walls for that were built double skin brick (but no cavity) - UPVC and corner posts rested on outer skin - would I be best doing the same here?

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I'd build a single skin wall - maybe 150mm block if you want to save space - and line with insulated plasterboard. If your ground conditions are firm a 300mm wide footing would be sufficient. Don't be tempted to go less than 600mm if it is clay. Depth adds nothing to loadbearing but less than 600mm deep clay can freeze or dry out, which will cause movement. 900mm deep is extra safe. 600mm deep is safe in most circumstances. Any less is dodgy.

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