Existing house energy upgrade reveals shockingly leaky structure

The semi-detached house was built in the 1980s and as was acceptable at the time, it is built with single leaf hollow block exterior wall with plasterboard drylining (non insulating) to the inside face, raised timber floor and flat roof kitchen and garage annex. When analysed with DEAP the original house as built, would have achieved an indicative E2 rating. Since construction, the windows have been upgraded to double-glazed PVC by the previous owner. Shortly after he moved in, Brian converted the attic and garage to additional habitable rooms, upgrading the insulation of these areas in the process. This has resulted in an improvement in the DEAP score from an E2 up to a notional D1 rating.

The DEAP software is designed to provide a standardised measurement system for all new buildings. It is not intended to provide accurate energy use calculations. It is very useful as a design tool to analyse options for reducing energy demand. Brian used the software to determine how best to upgrade his home. The energy reductions from insulating or installing a more efficient boiler can be quantified. Reductions in primary energy demand measured in kilowatt hours per metre squared can be related to cost. This can allow the home owner see how much they will save on energy bills due to whatever level of investment they choose to put into the upgrade. The DEAP software is not designed to accurately calculate energy use for a particular design. Assumptions are made on occupation and hot water use is related to floor area. It is also assumed that the building is heated to 21 degrees in bedrooms and 18 degrees in living rooms for 8 months of the year. Many older buildings would need to use almost double their current spend to achieve those levels of comfort. Brian confirmed that the house was not heated to such levels.  At a D1 rating the software indicated heating bills of approx €1,500 but actual bills for the house exceeded €2,000. Save Energy Consultants performed an air tightness test to check if the source of the extra spend on energy could be determined. Air tightness for a dwelling should be less than 10m3/hr/m2 at 50 pascals for a new build. We expected perhaps 20 but got a result of 35. This is approximately 1.7 air changes per hour at storm pressure. This equates to having to heat the air circulating in a building three times more than is necessary when it’s windy outside. However the fact that the building wouldn’t pressurise at up to 20 pascals indicated that air leakage is a problem in calm conditions.

The main areas of leakage were primarily around pipe penetrations, which was responsible for approx 50 %, the raised timber floor was responsible for 20% and gaps between insulation in the attic and seals in the PVC windows accounted for the rest. When the air test result was inputted into the DEAP software, the rating dropped an entire band, from E to F. The energy rating more closely resembled the heating and hot water bills. This indicates that air leakage factors in DEAP are applicable only to new houses. The next stage for Brian’s upgrade project is to airtighten his house. This can be done quite cheaply with a silicon gun and expandable foam; for €40 he can save €300 annually. Brian is currently using DEAP to help him move up to a B1 rating, which will involve external insulation, with a new eaves ventilation detail, new highly insulated floors, efficient gas boiler and room thermostats and additional airtight insulation and lining of the attic study.

Studies of existing houses in a north Dublin village indicate that most of the building stock built between 1990 and 1970 performs at a level of G down to [a notional] J, consuming on average 600kWh/m2 for space and water heating. To put that into perspective, the new Part L will limit new houses to circa 90kWh/m2. The average fuel bill is roughly €2200 but we are told by occupants that this heating spend does not provide for a comfortable house by today’s higher expectations. To do so would cost approx €3,500 (21 degree living areas, 18 degree bedrooms). The heating spend does not provide sufficient hot water – in most cases electric emersions and showers are used to supplement water heating.  We have shown in our studies that intervention of approximately €8,000 will result in carbon savings of on average 40% and more importantly for the occupant heating bill savings of the same order. Our studies correspond with the performance gains that Energy Action have achieved in Dublin’s inner city by upgrading existing buildings. Their 35-40% savings are achieved  with 300mm plus of attic insulation, 91% efficient boilers, thermostats, a 50mm insulated cylinder and draftproofing, all for €7,000- €8,000.

By including air leakage testing and thermal imaging investigation into our calculations, we show existing buildings performing approximately 20% worse than expected. Physical testing will be required to get an accurate assessment of the energy performance of new and upgraded buildings. The methodology for rating existing buildings should include this factor. Air leakage cannot be assumed for a building based on its year of construction.

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