Mark Bowman of Marmox explains why addressing cold bridging has become more important than ever for specifiers in the housebuilding sector.
Even with plans to utilise land in the so called “Grey Belt,” the new Government will undoubtedly find it very tough to achieve its ambitions to build 1.5 million new homes during the next five years: with a shortage of skilled labour as well as many types of materials, compounded by ever greater emphasis on cutting energy losses in the quest to hit net zero. The construction industry, then, must embrace technologies which offer answers to multiple challenges: simplifying the build process while ensuring the continuity of insulation across the outer envelope.
Undoubtedly, wall and window performance have improved dramatically over recent decades, but getting the junction details right has remained stubbornly difficult since the BRE first identified the issue in its 1969 document ‘Avoiding Risks,’ with the wall-floor interface being the first focus as most projects get out of the ground. Fail to deal adequately with the problem of thermal bridging, and the penalty is not just an unquantified increase in the annual cost of heating a home, but also almost inevitable highly visible effects along the interior walls – and potentially life-threatening medical risks for building occupants.
“Avoiding Risks” – like other publications cataloguing common short-comings with traditional construction techniques – contains numerous illustrations of the manner in which thermal bridging can cause condensation to form on plasterwork and other internal finishes, in turn leading to black mould disfiguring the surfaces and as the introduction of the Social Housing Regulation Bill in 2023 underlined, the effect is not just visual, as mould growth releases dangerous microscopic spores into the living environment, presenting a particular danger to those living with asthma and other respiratory conditions.
Named in memory of the tragic death of a young boy whose family lived in seriously substandard accommodation, Awaab’s Law stands as a chilling reminder not only to social housing landlords, but all property managers and the wider building industry: that poor construction practice can have the most serious consequences.
Certainly it is possible to wrap the entire structure in an ‘outsulation’ cocoon, but it is cumbersome and logistically difficult to achieve, while if a more traditional approach is sought, the load-carrying capacity of the materials forming the junction become a limiting factor, even when using a timber or light-gauge steel frame.
Popular on the continent, foamed glass insulation can offer a solution in some situations, but the hard truth is that the product solutions available only offer a compressive strength of less than 3 MPa – or 3.0 N/mm2 – which does not even match that of lower strength aircrete blocks, while the top performer in the Thermalite range achieves 10 N/mm2. Foam is probably fine then for laying a raft foundation under your £1,800 per square metre dream Passivhaus, but if the industry is actually going to confront the housing crisis, a more practical and cost-effective answer is required.
Consequently, the construction of a truly individual new home in West Sussex made full use of a composite solution which is increasingly being specified to address thermal bridging on projects ranging from schools to multi-storey social housing developments. The six-bedroom, five-bathroom dwelling near the village of Lurgashall was built by Grangewood Southern for a private client, with Fusion Brickwork being the specialist subcontractor responsible for laying 140 mm wide Thermoblocks, both around the ground floor perimeter and where the slab spans a substantial basement.
The project’s unusual wall construction features an inner and outer leaf of concrete blockwork, faced with random natural stonework. Some 250 of the 600 mm long by 100 mm deep composite units were installed using sealant to secure the overlapping end joints, while their XPS encased mini concrete columns create the fully insulated support zone at the base of the blockwork.
Mark Bowman is technical manager for Marmox