Slip membrane?

6 Jun 2007
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United Kingdom
Hello everyone. I'd appreciate a bit of advice please.

I'm building an extension (it's been 2 years now!) and I'm about ready to fit the steel hip support for the sun room which is mostly glass with a blockwork pillar at the corner.
The support consists of 2 steel angles (125 x 75) about 4.2M long bolted together. There will be 'cranked' sections welded on the top and bottom to provide horizontal seating. The top is bolted/welded to a seating angle that has been resin anchored into the existing house wall. The bottom will rest on the blockwork corner pillar on a pad stone topped off with a steel plate to help spread the load.

My spec says that the bottom of the support is bolted to the padstone/steel plate through eleongated holes to allow for movement due to expansion and requires a slip membrane to be inserted.

What would you professionals use as a slip membrane? I've searched the net but have only found reference to large scale commercial builds. The landing area of my support is only about 150mm x 1500mm.

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Thanks very much Woody. I'll put in 2 layers of 'slippy' polythene type DPC.

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Personally I wouldn't bother. You aren't going to get much thermal movement over that length; and, if the designer is trying to allow for any dead and live load deflection, just don't bolt the beams down onto the padstone until the roof/wall are constructed and their loads applied to the support; that way only live load deflection and hence movement at the pier bearing, will occur.

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