CONSTRUCTION: System-built detached bungalow with concrete walls
KEY FEATURES: external insulation, roof insulation, airtight building with MHRV, condensing boiler, solar thermal and triple glazing.
NUMBER OF BEDROOMS: 3
NUMBER OF OCCUPANTS: 2
The owners bought this cold, draughty, unmodernised bungalow and wanted to transform it to a comfortable dwelling with excellent energy efficiency standards. They approached us for a complete retrofit advice service.
Energy Performance Certificate
A before and after EPC showed that the improvements improved the energy rating from 40 (E ) to 63 (D).
The table below shows the effect of each improvement incrementally:
|Improvement||Rating after improvement|
|Cylinder insulation and thermostat||52|
|Low energy lighting||54|
|Solar water heating||66|
NB The ventilation system, although it brings many benefits, has the effect of reducing the overall energy rating, hence the difference in the figures shown.
Actual Energy Savings
|Gas consumption p.a.||14,300 kWh||6,250 kWh|
|Electricity consumption p.a.||2800 kWh||2,000 kWh|
|Carbon emissions p.a.||6.4 tonnes||2.9 tonnes|
The roof was insulated at rafter level with under felt spray-foam to 125mm depth achieving u-value of 0.19W/m²K.
The walls were insulated externally with 100mm Kingspan (phenolic boards) achieving a wall u-value of 0.21W/m²K with system specific thin acrylic render. As well as reducing heat loss, this greatly enhanced the appearance of the bungalow, and the render finish incorporates the colour, so doesn’t need repainting.
Heating and hot water
The outdated gas boiler was replaced with a Viessmann system boiler linked to a weather compensation feed which allows the boiler to run at lower temperatures when the weather is milder. Hot water is supplied by 4m2 solar thermal panels fitted by Llani Solar with stainless steel pre-insulated flexible pipes coupled to a 200 litre highly insulated pressurised hot water tank. As renewable energy, this qualifies for the Renewable Heat Incentive payments.
The existing metal-framed single glazing was replaced with wooden triple glazed windows and achieving u-value of 1.0W/m²K.
Airtightness and ventilation
Airtightness was achieved and draughts eliminated by fitting an Intello air-tight membrane where ceilings and walls joined. It was also fitted around the new windows and doors frames to prevent leakage at these important points. Special seals were also added around pipes and cables breaching ceiling and walls. The pressure test resulted in 2.05 m³/(h.m²)@50Pa.
Mechanical ventilation is important in a building with this level of airtightedness. Thus a Mechanical Ventilation and Heat Recovery unit (MVHR) was fitted, ventilating the house constantly with fresh air pushed into the house, and warmed by the outgoing air. 92% of the heat from the outgoing air is recovered in this way.
Fitting included a low flush toilet with 4.5/2L dual flush, eco shower head with 9L/minute and aerated taps. Outside, there is rain-water storage (about 1400L) for garden use.
The tarmac drive has been replaced with a plastic grid system filled with gravel and soil/lawn allowing rain water to disperse easily and mitigating the adverse effects of heavy rain.
MVHR and roof insulation
“We moved into the bungalow in December 2009 just as the hard winter set in and couldn’t heat the property to a decent degree After the retrofit project we have a comfy home with a constant temperature of 19-20°C, no draughts and very low bills at £47/month for gas and electric.”