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we discover a major difficulty...

Posted Jan 27 2013 5:09pm
We have worked since November lining the walls and ceiling with glass fibre Majpel sheeting and sealing all junctions with various Majpel tapes.

Today was an asupicious one: we had lined the final bedroom and bathroom walls with polystyrene sheeting and then wrapped Majpel around to complete this part of our airtightness work. More sealing will be needed to create airtight seals around all windows and doors, but the huge job looked complete.


Roger was working at the top of ladder, close to the ceiling when he discovered a draught: the yellow tape used to seal the sheeting was letting a draught in. And when I examined another area of ceiling I found that the Magpel  sheeting had worn away along both sides of the line of the ceiling tape.

To give you an idea of how calamitous this is, we can only have a total accumulated air leak the size of a UK 5p piece in the entire internal surface area of the building...

Majpel sheeting with yellow sealing tape and battens secured to rafters
What seems to have happened is that the fabric has been put under extreme stress due to the windows not having been installed. Gusts of wind enter the building and you can watch the airtight membrane being sucked back and forth between the rafters as air pressure rises and falls in the building. This is causing the membrane to wear and weakening the sealed joints. A further worry is that we have punctured the membrane at every point where we have screwed battens into the rafters that will support plasterboard. Ordinarily, the heat of the screw being driven in will cause the Majpel to melt and seal the puncture around the screw. With the fabric being under stress, we are concerned that each of these punctures will have been stretched away from the screws, creating hundreds of air leaks.

Our window install is still unfinished, and we have no idea how much our problem will grow until this is done...

We now realise that we have not programmed the work properly. We should have had windows installed and roof water tight before considering the ceiling airtight membrane.

Not what we wanted......

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