Site Progress - Faringdon Extension

Holmes Architects are working on a rear extension project for a family in Faringdon, Oxfordshire. The existing home featured a conservatory that was poorly insulated which created both uncomfortable extremes of cold during the winters, and excessive heat from the sun during the summer that had the power to melt the children's crayons.

Holmes Architects received the approval for a Lawful Development Certificate from Vale of White Horse District Council, and works to the extension began on site in August. The Lawful Development Certificate is an optional step that we recommend when undertaking extension projects under Permitted Development rights to ensure that the works you are undertaking are compliant with The Town and Country Planning (General Permitted Development) (England) Order 2015. Permitted development rights can be removed on properties through planning conditions, or Article 4 directions, and the rights are restricted in some areas such as Conservation Areas, and Areas of Outstanding Natural Beauty etc.

The blue band around the base of the inner leaf of blockwork is Marmox Thermoblock which is a 65mm course of loadbearing thermal bridging blocks. The Marmox Thermoblock is aligned with the insulation in the floor and the walls to ensure that the insulation is continuous. We specify these blocks on all of our private residential projects as they reduce the amount of heat that escapes through the wall junction by removing the gap in the insulation. The insulation is 115mm Celotex Thermaclass 21 which fits within a 125mm wall cavity with a 10mm residual gap for drainage.

We are delighted with the reconstituted stone which looks to be a perfect match to the existing building, and the builder has done a good job matching the course heights. The stone is Oolite by Bekstone which is from the local quarry in Burford, Oxfordshire. The stone has a tumbled finish which makes it less regular and rounds off any sharp corners, giving it an aesthetic that is well suited for small scale domestic projects. The brick is Hadley Red Smooth by Michelmersh.

Many rear home extensions feature the challenge that they want to create as much space as possible, both in their interior height and their internal floor area. A pitched roof with a vaulted ceiling (where the internal ceiling follows the pitch of the roof) is a good method to get the additional height, but often the challenge is to make this roof fit underneath the existing first-floor windows. The Faringdon extension is no exception and it required a very low roof pitch of 15-degrees to both maximise the space within the extension and to avoid interfering with the existing first-floor windows. Low roof pitches limit the building materials that are appropriate for the extension and the technical design of the project is important to get right to ensure that the roof tiles and the roof membrane are both suited for use in this low-pitch scenario.

Holmes Architects have designed the extension with the Klober Permo Extreme 200 roof membrane that is designed to allow roof tiles to work below their normal recommended roof pitches. It features a fleece layer that reduces the chance of condensation forming, and the joints have a self-adhesive seal that improves air tightness. The roof also has a 50mm clear ventilation void between the membrane and the insulation below.

The roof tiles are Wienerberger Sandtoft 20/20 in 'Flanders', which are an interlocking tile that are suited to the low 15-degree roof pitch if they are used with a 100mm headlap. The leadwork, guttering and downpipes are the next steps to complete the roof, and the downpipe from the main house will also be relocated so that it does not drain onto the roof of the extension.

We look forward to the internal works starting shortly.

Contractor - Olivewood Renovations

Brick - Michelmersh Hadley Red Smooth

Stone - Bekstone Oolite Tumbled

Roof Membrane - Klober Permo Extreme 200

Thermal Bridging Blocks - 65mm Marmox Thermoblock

Wall Insulation - 115mm Celotex Thermaclass 21

U-values (lower is better):

Walls - 0.16W/m²K

Roof - 0.15W/m²K

Floor - 0.15W/m²K

Windows and Doors - 1.4W/m²K