Shropshire retrofit / extension

The project brief asked for dramatic increase of energy efficiency for this 1950’s semi-detached house, with a single storey extension to the living space facing the back garden. The budget was modest so it was clear that the AECB’s Level 2 Retrofit Standard would be a good target. https://aecb.net/aecb-carbonlite-retrofit-standards-level-1-and-2/

Our clients were a pair of novice self-builders, already armed with a good amount of research into the subject, allowing them to be informed about the decisions they had to make.

The solution arrived at aimed to maintain existing eaves / avoid alteration to roof; maintained detail of the front elevation with bay window and porch roof. We therefore proposed internal wall insulation to the front and external to side and rear (above the extension).

All solid floors had suspended floor removed and replaced with insulated solid floor with underfloor heating.

The extension has concrete block inner skin with external insulation (eps) and render system. The roof is a standing seam steel roof, with the ‘I’ beam rafters insulated with full-fill recycled newspaper / pumped cellulose insulation.

The loft of the existing house is insulated with pumped cellulose insulation (recycled newspaper).

Our clients proved to be very assiduous with their air-tightness detailing and produced excellent air test result at q50 = 0.76 m^3/(m^2.hr) (UK method) and n50 = 0.86 ACH (Passivhaus method).

The first Winter has brought some predicted energy figures for annual energy use. For space heat demand, PHPP predicted 46 KWh/(m2.a). Actual usage indicates it will be lower, with 39 KWh/(m2.a); with COP of 4 from the heat pump, this means that 1000 KWh p.a. of electricity is required.

An MVHR system was installed for ventilation. An air source heat pump provides heating.