High Performance Homes Benefit From Sustainable Construction

Natural Building Technologies’ (NBT’s) Thermoplan insulating wall system and the company’s high performance Pavaroof system have been used to construct two highly energy efficient and sustainable five bedroom homes for private developer, Kingerlee Homes, in Sutton Courtenay, near Abingdon in Oxfordshire.

In addition to minimising energy costs (estimated at around £600-£700 per year for space heating, lighting and hot water for the 320m2 properties), the houses were designed to create a healthy living environment, using sustainable and breathable construction materials.

Thermoplan comprises structural insulating blocks, used to build the homes’ walls, which are then rendered externally with NBT’s breathable render and finished internally with NBT breathable plaster. For these specific properties, which are constructed in a conservation area, some sections of the walls were finished externally in timber cladding, installed onto cross battens fixed directly to the Thermoplan blocks.

The blocks themselves feature a honeycomb cross-section, which delivers excellent levels of both thermal and acoustic insulation, while their microporous structure further benefits the insulation performance and delivers highly effective breathability. The Thermoplan system uses a true thin bed mortar, just 1mm thick, to secure rows of blocks, with interlocking dry vertical joints anchoring adjacent blocks along the row. The simplicity of the construction process enables Thermoplan block walls to be typically constructed three to four times faster than conventional blockwork structures, with no limitation on the height that can be built in a day and no drying out shrinkage.

For the Sutton Courtenay homes, 425mm deep blocks were used to deliver a U value for the walls of just 0.20 W/m2K.

The Pavaroof system features NBT’s interlocking Pavatherm Plus woodfibre boards installed in a continuous layer over the rafters, with cellulose insulation installed between the rafters. Externally the roof was finished with plain clay tiles. The Pavaroof system delivered a U value of 0.17 W/m2K.

While both Thermoplan and Pavaroof deliver high levels of airtightness, NBT’s Siga airtightness tapes were also used to ensure joints and connection junctions were completely sealed against air leakage. Airtightness tests undertaken on the homes after completion showed air leakage of just 1.7 and 1.9 m3/hr/m2@50Pa for the two properties.

As well as keeping the building warm in winter, Thermoplan and Pavaroof benefit from high thermal mass, which is essential in preventing summertime overheating.

NBT breathable paint was used throughout the homes to ensure the breathable properties of the building fabric are not compromised, as well as minimising the risk of toxins.

This breathability ensures that any moisture that gets into the building fabric is dealt with safely and efficiently, minimising the risk of interstitial condensation often associated with conventional buildings. In doing this, it safeguards the long-term integrity of the building’s structure, as well as ensuring a healthy living environment for the building’s occupants through the prevention of mould growth and other pathological organisms.

Complementing the high performance of the wall and roof structures, the homes feature triple glazed windows, a highly efficient gas boiler with MVHR, and energy efficient underfloor heating.

The two houses are also the subject of an ongoing monitoring study, being undertaken in conjunction with Oxford Brookes University, as part of NBT and Kingerlee Homes’ industry-leading commitment to the monitoring, learning and improvement of building design and construction.

Through the creation of a thermal shell, NBT’s woodfibre insulation systems deliver a thermally coherent structure, which, combined with their excellent thermal properties, provide outstanding thermal insulation.

NBT systems meet with the museum’s requirements for responsible sourcing, low toxicity and high-recycled content material. The woodfibre locks up more carbon than is used throughout its manufacture and delivery to site. It consists of 95% plus waste wood composition and is wholly recyclable. Furthermore, the hygroscopic properties of the woodfibre material makes it fully breathable, meaning that its use reduces the risk of interstitial condensation, resultant mould formation and the associated health risks to occupants and structural risks to the frame.