Cost house front elevation

Cost house: front elevation

Internal Wall Insulation (IWI)

Celotex GA4000 100mm Insulation Board (75KB) was used to insulate the internal walls. The board was fixed to the internal side of the walls using 50mm x 50mm battens which were overlaid with plasterboard. This created a void for services to be run through and enabled fixing to be installed without fixing or damaging the insulation board. Joints between the sections of insulation board were taped to create a continuous vapour barrier. The insulation enabled a u-value of 1.5 W/m²K to be achieved.

Thermal Bridges

To all return walls 12mm Celotex TB4000 insulation board (75KB) has been fixed to the walls with adhesive. The insulation is installed here to help reduce thermal bridging, where heat can escape through junctions and between elements of the building.


Joints in the external envelope of the building were sealed with Siga airtightness tape by Natural Building Technologies (NBT). NBT’s tapes are free from toxins, solvents, plasticisers and formaldehyde. It is said that they have a very high adhesive strength and that they will maintain their peak performance for over 60 years. The tape is flexible and therefore designed to accommodate building movement. The purpose of the tape is to increase windtightness by preventing cold outside air from cooling the buildings’ insulation and reducing its effectiveness, and to reduce uncontrolled heat loss from the building. An airtightness test carried out after the refurbishment showed the airtightness to be 5.48 m³/hr/m² @ 50 p a. A new building constructed to the requirements set out in Part L of the Building Regulations is required to have an airtightness of 10 m³/hm² (@ 50 Pa).

Replacement Windows

The existing windows to the property were replaced. The new windows are timber double glazed sash window units with low e coated glazing; draught stripping and brush seals to improve airtighness. They were supplied by Mumford and Wood. The windows have been manufactured to match the existing window fenestration with responsibly sourced FENSA approved timber; they have a high thermal performance with a U value of 1.5 W/m²K.

Insulation to the Windows

The window frames were lined with insulation so as to reduce the thermal bridging at the junction between the window frame and the window opening. 5mm Spacetherm Aerogel Blanket insulation was wrapped around the windows as they were installed; this was then overlapped by the internal wall insulation board used to line the reveals, so that the insulation is continuous. The Aerogel Blanket is a high performance flexible insulation that still maintains its performance under compression.


The existing concrete hard-landscaping was broken out and replaced with SUDSCAPE, a Sustainable Urban Drainage System. This porous paving solution prevents surface water run-off being sent into the drainage system by allowing the water to filter down into the ground. This helps to reduce the risk of flooding by relieving the drainage systems. The system comprises a 150mm base layer of compacted aggregate, which is topped with a layer of shredded rubber made from recycled car tyres. This is then topped by a surface layer of resin-bound pea stone.