Post-works assessment
Owner’s feedback
The works were completed in December 2012. The owner reported the house was warmer and more comfortable during the colder-than-average spring of 2013 and ”fresher” during the warm summer of 2013. This is likely due to the fact that the thermal mass of the walls has been retained and is moderating internal temperatures. A psychological comfort effect relating to the knowledge that the house had been “wrapped” was also mentioned.
As the attic insulation and wall insulation were installed simultaneously to the entire house, the owner could not differentiate between relative benefits of either measure although the first floor bedrooms were noted to be substantially warmer.
Impact on BER rating/fuel bills
The BER of the building has been improved from a D2 to a C3 following the works. The BER would indicate that the heating energy load of the house has theoretically reduced by 30%.
Gas bills compared between spring 2012 and spring 2013 indicated an increase in average daily energy costs of 21% following the works and an increase in average daily Kwh consumption of 9%. The owner did not express regrets in relation to lack of payback/reduction in fuel bills – it was more important to her that the house was comfortable and that the façade and house had been refreshed.
The increases may be attributable to one or a number of factors:
- A longer heating season during the cold spring of 2013
- An increase in gas prices
- The fact that the house is now fully heated (with a new tenant in residence) whereas previously it had been partially heated
- There may have been a “comfort clawback” effect. “Comfort clawback” refers to the situation where homeowners’ fuel consumption remains similar following a retrofit with the retrofit measures contributing to higher temperatures/greater thermal comfort within the building.
Nevertheless, a similar 23% increase in daily energy costs and 10% increase in daily fuel consumption were also noted during the same period after the external wall insulation work, without any change in occupancy.
This case study house has a compact heat loss area to floor area ratio (1.63) and the lowest wall area to total heat loss area of all the case study houses (0.29). It’s not surprising therefore that the external wall insulation is not having a dramatic effect in real terms, particularly when the suspended timber floor remains uninsulated and not draughtproofed, resulting in ventilation heat losses. For more information, see section on Insulating a suspended timber floor [link to follow].
Impact of works on the architectural heritage
The original dry dash cement finish of the house is one of the defining characteristics of houses in Donnycarney which serves to unify the architectural ensemble of the area. Although details such as plaster bands over windows and cill depths were reproduced, the new acrylic render finish to the façade is very different from the original cement dash finish. The step-back to the next un-insulated house in the terrace is also very visible (although concealed somewhat by a rainwater downpipe) and as the original windows had been replaced with PVC in a previous phase of works, they were not moved out in tandem with the insulation work which results in uncharacteristically deep window reveals.
Nevertheless, the fact that three adjoining houses were insulated together gives a degree of uniformity and is preferable to individual houses receiving piecemeal uncoordinated overcladding. For more information, see section on External wall insulation [link to follow].
External wall insulation has become more common in suburban areas in recent years. It is an increasingly attractive option for homeowners as it does not disrupt the interior of the house and is currently supported by SEAI grants. Nevertheless, careful consideration in relation to visual impact is required in each case where there is a well-defined urban context and particularly where houses are terraced. In each case, the homeowner should check with the local authority if planning permission is required.