Apart from what Ben points out the difficulty in pricing the membrane is that you wouldn't build anything without a DPM in the first place so the installation of a gas membrane is an 'extra over' or 'abnormal' cost.
I recently worked up some costs for a basic taped unreinforced membrane as part of a potential claim and those came out at about £5/m2 on top of normal DPM construction. It didn't include for CQA, however for a taped membrane a pick test and visual assessment would normally be adequate at minimal cost.
Clearly a higher spec membrane with full CQA would be more costly and would be influenced by area, complexity of installation (corners, tophats etc) and who installs it (builder or accredited installer).
Mark Henderson MSc DIC BSc(Hons)
Principal Environmental Consultant
M L M ENVIRONMENTAL
Building 7200, Cambridge Research Park, Cambridge CB25 9TL
Tel: 01223 815600 Fax: 01223 815630
Web Site: www.mlm.uk.com
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