constructireland.ie - Does old mean cold?

Does old mean cold?

Page 2 of 7

10 North Great George’s Street,
the case study house

Energy upgrading issues
Historic buildings can be upgraded but generally not to the same standard as contemporary buildings due to the inherent cultural and historic interest of the fabric of the buildings, which should be retained.

Careful consideration of any interventions to the building fabric is necessary in relation to moisture movement and increased condensation risk. Research in this area has become more sophisticated in recent times and specialist advice and modelling software is available. Recently developed materials may also offer solutions to some of the problems.

Developments in industry measurement techniques such as air-tightness testing, thermal imaging and in-situ U-value measurements have a definite role in assessing the thermal performance of historic buildings and planned upgrades. A recent example of the application of thermal imaging analysis in a conservation context was part of the Changeworks upgrading works to 1820s Lauriston Place Georgian tenements, Edinburgh (2). Different upgrading measures to the windows of the apartments were introduced. As the windows all feature on the same elevation, the relative heat loss could be observed by thermal imaging when all the apartments were heated to the same temperature and the effectiveness of the upgrades ascertained.

An interesting example of the use of air pressure testing on historic properties is illustrated in works to the English National Trust Berg Cottage, a 17th century timber framed thatch cottage (3). The obvious route of upgrading the windows was avoided until the air pressure test was undertaken which indicated a very high air leakage rate – 24 m3/hr/m2 at 50 Pa. It was discovered that it was the fabric of the building and not the windows that was the principal source of air infiltration. Unnecessary work to historic windows was avoided once the test had provided a better understanding of the building’s characteristics.

From CIBSE guidelines, it is recommended that historic buildings receive 0.8 – 1 air change per hour (double that of a modern building) under normal air pressures in order to reduce condensation risk and potential mould growth to uninsulated walls and within the building fabric generally. This is a general rule of thumb and would vary depending on the construction and the amount of evaporation occurring within the fabric. However, this level of ventilation would typically be exceeded, so draught proofing can be one of the least intrusive ways of improving comfort and reducing heat loss. Plastered solid walls typical of most Irish buildings are an inherently air-tight form of construction. Typical areas that require attention include sash windows and the junctions of shutter casings to walls, unused open fireplace and roof spaces, especially around attic hatches. It is therefore possible to measure the air infiltration rate and adjust the air-tightness of the building accordingly depending on the ventilation strategy to achieve a balance between thermal comfort and an acceptable ventilation rate.

Upgrading of services and controls where the works are non-invasive is an area where energy savings can be easily made and should be examined at the outset. Renewable energy sources and microgeneration have their part to play. Consideration could be given by government to grant aid owners of historic buildings to install biomass systems or other renewables to offset the potential high energy demand.

Case study
A case study commercial building energy rating of a typical Georgian building in Dublin’s North Great Georges St was undertaken to establish the energy rating of the historic building and thus compare it to contemporary building stock. Practical interventions were then examined and their effect on the rated energy demand and C02 emissions of the building quantified with the energy rating software. The building is a typical example of an eighteenth century Georgian townhouse building and it is expected that some of the findings will be applicable to other similar buildings. The building is listed on the Dublin City Council record of protected structures.