Case Study: Underhill House

Construction of a house designed to meet the German Passivhaus standard and be carbon neutral, with its design to be truly outstanding and groundbreaking. Project is to be featured on UK Channel 4’s Grand Designs programme.

The structure of the underground house is entirely concrete, much of which is left exposed internally to exploit the benefits of its thermal mass.

A successful waterproofing solution for the base, walls and below ground roof was key to the project and Seymour-Smith Architects approached Fosroc for a total waterproofing system.

Fosroc's team of technical experts proposed a complete solution using the fully integrated range of Proofex waterproofing membranes and ancillaries.

Proofex Engage waterproofing membrane was selected because it mechanically bonds to the underside of the concrete floor slab when the concrete is poured, allowing the entire slab to be exposed within the building for the benefit of its thermal mass.

Precast panel construction was used for the walls, again to maximise the benefits of thermal mass, with Fosroc's high strength, non-shrink Conbextra HF grout being used on all the joints around the panels.

Accommodation for movement within the panel joints was provided through use of Expoband H45 , a flexible expansion joint overbanding strap prior to installation of Fosroc Proofex 3000 wall membrane and Proofex Sheetdrain 8 protective drainage sheet.

Fosroc Polyurea WPE, a spray-applied waterproof coating system was specified for the structure’s roof deck, which was then buried under topsoil and landscaped. The complexity of the roof design meant that the unique properties of the spray applied product provided the only effective solution for ensuring complete watertightness.

Underhill house has become the first Certified Passivhaus project in England.

Fosroc’s comprehensive waterproofing product range meant that full compatibility between the various components was assured, providing highly durable protection for the full building envelope.

Use of Fosroc’s in-house waterproofing CAD detailing allowed for accurate and effective installation.