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Lime Tree Lodge, Norfolk

Lime Tree Lodge

Construction of a single, two-bed, mono-pitched bungalow built to Passivhaus standards in Swaffham, Norfolk. Construction on the bungalow took 28 weeks to compete with the inner aircrete shell going up in three weeks.

Aircrete products were selected for this project due to their high thermal performance properties which helps meet Passivhaus standards. Passivhaus is achieved by the application of high levels of insulation, avoidance of thermal bridging within the structure, and low levels of air leakage, all of which are qualities addressed with the use of aircrete blocks.

The contractors offered a design and build package utilising a local architect. This was the first Passivhaus project for the team with aircrete specified for the internal leaf. Having looked at other alternatives, to meet the stringent Passivhaus standards, the contractors opted for aircrete due to the delivery time, speed of construction, stability, thermal mass and the contractors experience with aircrete blocks. 

Faced with both brick and timber the bungalow has an external U-value of 0.096 W/m2K for the timber faced walls and 0.098W/m2K for the brick faced walls. Aircrete was a key contributor to achieving these results with a thermal conductivity of 0.15W/m2K 

Wall construction: 140mm and 100mm Aircrete Block Standard Grade 3.6N with a thermal conductivity of 0.15W/m2K used in an effort to reach Passivhaus standards. Brick faced walls with a U-value of 0.098W/m2K and timber faced walls with a 0.096 W/m2K 300mm cavity fully filled with EPS insulation.

Compared to a timber frame solution aircrete products allowed for a faster build process, enhanced stability and better thermal mass qualities allowing us to reach Passivhaus standards. This was the preferred building material for the contractors too due to previous experience and now desire to again build using aircrete.

The developments energy efficiency rating and environmental assessment was a primary concern.  By using aircrete blocks with a conductivity value of 0.15W/m2K they were able to achieve the Passivhaus standards they were aiming for. Aircrete has the advantage of having an inherent thermal efficiency which helps achieve low fabric U-values. Further benefit is gained with reduced heat loss from thermal bridges and hence reduced energy demand to provide heat in winter.