First Floor Void – DraughtBusters

In the void between the ground floor ceiling and the first floor floor boards many problems exist. Basically air or wind from outside can blow through small gaps and cracks to the sides and above floor joists, these result from the fact that the joists shrinks by up to 10mm in height and 4mm in width. The blockwork is not always fully filled with mortar, there is often none between the good end of a block and a joist, some missing from perp-end joints and gaps around service penetrations. It is easier to see this from the following set of pictures with descriptions.

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This shows a gap between the blocks in the floor void that should fill the space between the joists. note that the bricks of the outside skin should not be visible, cavity batts not installed properly at all!

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This is why most cavity walled homes in the UK are so cold and draughty, outdoor air gains access to the void between the ceiling and the first floor floor boards all the way round causing a massive wastage of energy and draughts in the heart of the house.

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Newly sealed in joist end, this is only the first stage of the air tightness improvement works.

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An open gap between the edge of the g/f ceiling and the blockwork, these can vary in size from a few millimeters to large enough to accommodate pipes, see last few pictures in this section — An open gap between the edge of the ground floor ceiling and the blockwork, these can vary in size from a few millimeters to large enough to accommodate pipes, see last few pictures in this section

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Stage two, seal gap between the ground wall lining board and the blockwork by foaming filling the edge of the ceiling. — Stage two, seal gap between the ground floor wall lining board and the blockwork by fully foaming filling the edge of the ceiling.

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Stage three, add a board to fully seal any gaps or cracks in or around the blocks, any sheet material will do.

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Stage four, seal round the sheet and then up behind the plasterboard above (not yet done in this picture).

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Here the void between the wall and the lining is wide enough to allow uninsulated pipes to fit in it.

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Retrofitted wiring with the back of the coving visible but note that the gap between the top of the wall lining and the blockwork has been fully foam sealed across the top.

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A whole set done, the next job is to foam from the top of the new boards to behind the bottom of the lining sheets, relay rge floor boarding, refix the skirting and return to normal. — A whole set done, the next job is to foam from the top of the new boards to behind the bottom of the lining sheets, relay the floor boarding, refix the skirting and return to normal.

1980’s house near Eastbourne, how much energy has this wedge cost? and how many saw it and ignored it during construction?

For the the very technically minded among us we will realise that air and wind can still enter the void between the plasterboard and the blockwork, sadly it can exit through socket outlets, go round corners and get behind internal wall linings, we have even seen it come out over internal door heads 🙁

And from Jeff of GBF fame sealing his joist ends with sheet insulation and a foam gun