As insulation levels in buildings improve, details such as thermal bridging and airtightness have a greater impact on the overall thermal performance of the building envelope. In new build this can mean the difference between meeting and failing building regulation requirements; having a finished construction that matches or misses the designed performance. In refurbishment it is becoming increasingly important to have accredited standards of installation in order to access work funded through initiatives such as the Green Deal. Attention to detail is crucial, and having the right training is often the key. Tony Millichap, technical manager at Kingspan, highlights some of the areas to be aware of and looks at some practical examples.

Thermal bridging

Areas such as window reveals can easily let the construction down if they are not treated so as to minimise thermal bridging. Linear thermal bridging is the term used to describe the heat loss at junctions between elements which cause the insulation layer to be interrupted or reduced. The heat loss is described as the psi value, and is taken into account when calculating the whole building carbon dioxide emissions, which will determine whether or not the construction is compliant.

For example, at a window or door opening in a wall using insulated plasterboard, the linear thermal bridge is the reveal. The linear thermal bridge can be reduced by insulating the reveal, and the key factor to take into account here is the thermal resistance, or R-value, of this insulation layer.


Another key aspect in reducing heat loss is airtightness, which also demands attention to detail and good workmanship. The Passivhaus standard provides an excellent working example of how effective a fabric first approach can be; combining very high levels of airtightness, insulation, MVHR and careful detailing to produce highly thermally efficient buildings.

Case study

Two different Victorian terraced houses recently became the first retrofit projects in the UKto achieve Passivhaus performance standards.

Princedale Roadand LenaGardensare both situated in a conservation area, so all insulation had to be installed internally. The exceptional results were achieved through careful detailing and an innovative approach from project designers Princedale Ecohouse, using a continuous layer of OSB to create an air-barrier at external and party walls, ceilings and basement floor, coupled with very high performing insulation. 

Detailing was a major consideration in order to prevent thermal bridging and to form the airtight seal. The thermal efficiency of a range of rigid thermoset insulation products from Kingspan Insulation also played a vital role in the success of the projects, providing the required thermal performance with the minimum thicknesses of insulation, keeping internal space at a maximum.

AtPrincedale Roadthermal bridging was a major issue because of the original timber joists slotting into the external wall. To minimise this, new floor joists were fitted and attached to a steel beam bearing on the party walls, providing a gap for a continuous layer of insulation and OSB to be fitted on the external wall, minimising heat and air loss.

AtLenaGardensthe window installation took advantage of the period sash boxes, originally used to conceal the counterweights for the sash windows. Filling these boxes with Kingspan Kooltherm K12 Framing Board insulation helped to minimise thermal bridging around the windows. The window frames were then taped to the OSB layer to ensure the airtight seal.

In both houses two layers of insulation were installed, one on either side of the OSB air-barrier, and doors and windows were connected to the OSB with a tape-jointed breathable membrane, in order to maintain airtightness. This attention to detail achieved an airtightness of 0.5-0.6m3/hr/m2 at 50Pa.

The benefits of detail

There are numerous benefits to be gained from paying attention to detail: it helps to raise standards and assure the quality of work; it helps to achieve better building performance and makes sure the design is met first time round, reducing the risk of remedial work. Better building performance means fewer carbon emissions and lower energy bills for the end user. All of this increases customer satisfaction and raises the likelihood of repeat business and word of mouth recommendations.

To install insulation and insulated plasterboard properly takes care and an understanding of the thermal performance of buildings. Kingspan Insulation will soon launch a training course for internal wall insulation which will help existing dry wall installers gain the necessary insulation detailing skills which will also help them access Green Deal and ECO work. If you are interested in the course, then please e-mail