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Cut-to-Falls Multiboard Spec Speeds Protection of Semi-Basement to Somerset Home

An architect led refurbishment project on a private residential property near Exmoor has included the specification of cut-to-falls Marmox Multiboard, chosen for the versatile product’s highly beneficial physical properties, together with the practical considerations to their inclusion.


The work on the home on the North Somerset coast, is being carried out by sector specialist builder and developer, NTG Property, while Peter Reid of P2 Design drew on his experience of using Marmox Multiboard, to address past problems, when faced by a semi-basement space whose concrete roof structure was leaking badly. The original waterproofing membrane having cracked and deteriorated, with damp penetrating the habitable room below.

Peter Reid commented: “As a practice we work right across the UK and have used Multiboard on a wide range of past projects, for applications such as lining existing walls or upgrading floor constructions prior to installing underfloor heating. It really is a very useful and adaptable product, ideal for refurbishment because of its thermal and waterproofing performance.

In this case there was a habitable semi-basement level where water had been getting in over a long period and causing damage and while it wasn’t designed under the Building Regulations but considered a repair of the existing, we went to Marmox to obtain calculations on the heat loss: to maximise the energy retention and avoid any risk of interstitial condensation forming within the new build-up. And there was also the added bonus that utilising the tapered boards allowed us to speed construction and do away with one of the wet trades. It has been a very successful application.”

With the 125mm concrete slab broken off the original beam-and-block roof structure and all the old phenolic foam insulation removed, the substrate was treated with a bitumen based, Alutrix, waterproof adhesive and the first of four layers of 20mm Multiboard bonded down. Subsequent layers, including the cut-to-falls sections, were laid with staggered 10mm joints: the uppermost being sealed using Marmox Jointing Tape. This was followed by the installation of stylish porcelain tiles with a waterproof grout detail to complete a classic, ‘inverted’ promenade deck or patio. All of the Marmox Multiboards and Marmox Tape were supplied through Boyden Tiles in Croydon.

Marmox Multiboards are manufactured from extruded polystyrene or XPS and offer a range of positive physical characteristics in addition to being fully waterproof. They are both light to handle and easy to cut, while still being able to sustain substantial loadings if required. They further offer good thermal insulation performance, helping to cut condensation risk.

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