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Neil
I would consider the void below a timber suspended floor to be accessible – it is easy for people to lift floor boards to lay cable in the void for example (I’ve done it myself!). Therefore put a venting layer below the membrane and make sure the concrete over the membrane is sufficiently thick to protect it.
The sand blinding and well compacted hardcore will not be suitable as a venting layer as they will not be permeable enough. You need as an absolute minimum 20mm single size material for a small house with perforated pipes or geocomposite strips in it .
The pipes should have with sufficient perforations in them to give the required gas/air flow and the composite should have sufficient permeability to give the required air flow.
If you do not put a venting layer below you should make sure the verification and testing of the membrane meet the highest level in the latest CIRIA guidance as you will be placing a lot of reliance on it.
Steve Wilson,
UK Registered Ground Engineering Adviser
Technical Director
on behalf of EPG
Tel 07971 277869
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From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Neil Stirling
Sent: 25 August 2014 18:22
To: [log in to unmask]
Subject: Gas Membrane for Suspended Timber Floor
Hi All
Has anyone come across a gas protection system for a suspended timber floor where the ventilation layer (i.e. solum (sub-floor) vented by air bricks) is above the gas membrane? How confident would you be in the effectiveness of such a solution whereby the membrane is providing the primary protection and the ventilation secondary (as opposed to the standard solution where ventilation is the primary defence mechanism)? The above would seem to represent a standard detail for protection from Radon in buildings with a suspended timber floor.
The membrane lies below a concrete screed forming the base of the sub-floor and is laid over a sand blinding layer which in turn overlies a layer of well compacted hardcore. Therefore, would it not be possible to vent the layers below the membrane and indeed would this not represent a better solution?
Any comments gratefully received.
Many Thanks
Neil
Neil Stirling
Scientific Officer (Contaminated Land)
Environmental Health
Environment Services
Aberdeen City Council
Business Hub 15
3rd Floor (South) Marischal College
Broad Street, Aberdeen AB10 1AB
Tel: 01224 523211
Fax: 01224 523887
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