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Groundwork & Foundations

How to fill the 6 inch gap between a new build extension and the neighbours extension

I am looking at building a 5 m X 3m extension. However the foundations will be 1 meter deep X 600 meters wide with a trench fill depth of 670 cm.

The neighbours has a flat roof and my propsed extension will be pitched.

BCO advise I need to build centrally on the foundations but this would leave a 6 inch gap and inaccessable for maintenance, etc.

How could I block off this gap espectially where the flat roof will meet my extension wall.

I assume I can use single brick to brick off the vertical and in fill the gap with extra insulation but how can I bridge the gaps between the roof and my extension wall.

The altenative advised by BCO is to obtain structural calculations to build 3 cm from the edge of the foundations making it easier to bridge and fill the smaller gap.

I do not want to tie into the neigbours wall as their extension in falling forward so they advised.

Does any body have and advise how I can over come this issue

4 Answers from MyBuilder Groundworkers

Best Answer

on face build the brick work past and key the corner in as usual 6 inch back to fill the gap mentioned and insert a movement joint up this join. then at the top insert tightly cut kingspan trapping dpm between wall and kingspan. then above the kingspan create a small frame secured to your extension board this with marine plywood. then make a lead tray which falls to one end and fashion an end to this into a suitable fall pipe in case of water run off.


Answered 19th Apr 2012


Obversely reducing the extension size would help eliminate the problem, could you switch the roof pitch direction around so the maintenance areas such as guttering and fascia boards are facings the front of the extension rather than down the sides against the neighbours wall, if this is not possible You could also ensure that your proposed pitched roof guttering is as close as possible or even overhanging to the neighbours wall to take the rain water preventing it from penetrating the side elevation brickwork of your extension and the neighbours existing wall.

You could also have these areas of the extension constructed so no maintenance is required, e.g guttering attached to the brickwork via brackets that are built into the brickwork no fascia of sofit board is then required, a sketch of the proposed extension and the existing buildings would help to maybe advise further, thanks.


Answered 19th Apr 2012

Hi, i thought this wood of been work out for you in the plans and spec, perhaps a thicker wall large cavity or even a samll valley something on those lines, might be wrong but a idea, look forward to knowing what you do thanks col.


Answered 19th Apr 2012

Have you had a chat with your neighbour, I am sure he doesn't want the problem either, it might cause him damp, you may be able to work it out together he may want to modify his roof as well


Answered 18th May 2015

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