March 2006

THE PROBLEM

Millwood Homes (Devon) Limited, a developer from Newton Abbot, Devon contacted RIW to seek advice on how best to protect a proposed development in Brixham against water ingress and Radon emissions. The Sharkham Village development was to be constructed on a sloping site and consisted of a number of new town houses that stepped up a slope thus creating a series of single-sided basements. As the development steps up the hill a suspended beam & block floor was selected rather than a ground bearing slab.

Millwood Homes were keen to develop a tanking detail that would conform to the Building Regulations and provide adequate protection against the potential for ingress of water and radon emissions. Whilst liaising with Millwood Homes, RIW understood that the proposed detail not only needed to prevent the ingress of water, water vapour and Radon but that it also needed to be as simple as possible to install on site due to the consequences should the waterproofing prove inadequate. If possible, the proposed detail should avoid sequencing problems to avoid unnecessary delays to the construction programme.

THE SOLUTION

Mark Anstee of the RIW Technical Department proposed the use of RIW Cavity Drain as shown on detail SD / Typical / 007 which can be linked in to the DPM with RIW Sheetseal 9000 DPC. This detail ensures continuity between each element of the waterproofing design and encourages cross ventilation through the cavity to ensure the Radon emissions disperse freely. The use of RIW Cavity Drain vertically also eliminates any direct water pressure allowing water that passes through the vertical structure to drain freely in to the void under the block & beam floor. Also if wall ties are required to tie back the internal masonry wall they can be screwed into the brick plugs used to fix the Cavity Drain system thus avoiding the necessity to puncture the membrane and break the waterproofing/Radon integrity.

Nigel White of Millwood Homes said “We wanted a solution that was straight forward to build and would not delay progress on site, but we didn’t want to have separate waterproofing and Radon barriers. We initially considered an external tanking system but this could not easily be linked to the Radon barrier. We were therefore very pleased when we contacted RIW and they suggested the Cavity Drain system. This resolved all the problems and allowed progress to continue unhindered on site as all the tanking could be installed after the in-situ concrete foundations and retaining walls had been constructed.”

PROJECT DETAILS