Guide to Conversion of Traditional Buildings

3.13 Heating

Mandatory Standard

Standard 3.13

Every building must be designed and constructed in such a way that it can be heated and maintain heat at temperature levels that will not be a threat to the health of the occupants.

Limitation:

This standard applies only to a dwelling.

3.13.1 Application of standard to conversions

In the case of conversions, as specified in regulation 4, the building as converted shall meet the requirement of this standard (regulation 12, schedule 6).

3.13.2 Commentary

Meeting the requirements of this essential standard should not present any real risks to the character of a traditional building when converting it to dwellings. It is accepted that practically all such conversions will involve the installation of some form of ‘central heating’ system, which will more than meet the required minimum standard.

Buildings of traditional masonry construction will often have internal walls, chimneys, vaults and solid floors that have a high thermal capacity. This thermal capacity may be considered when designing the heating system, as their ability to store heat can reduce temperature fluctuations within rooms. Where the external walls are of mass masonry construction and lined internally with lath and plaster, it is sometimes thought that they will act as a thermal store to the benefit of space heating. However, the presence of a ventilated void behind the plaster has the effect of reducing the thermal capacity of the masonry. As such, it will have a more limited capacity to store heat and will respond more quickly to changes in temperature.

3.13.3 Issues to be considered

Typical risks in the conversion of historic/traditional buildings

1. Heating regimes not matched to building fabric and room arrangements

Spaces (e.g. recesses and cupboards) not adequately heated leading to mould growth, condensation and potential fabric deterioration.

2. Heating of previously unheated or poorly heated spaces

The sudden heating of previously unheated or poorly heated historic spaces can cause a rapid change in the moisture condition of porous materials leading to serious shrinkage and cracking.

Heat emitters that increase localised and excessive drying of historic fabric can cause damage over time, particularly for timber panelling. Increased levels of precipitation and external humidity due to the changing climate can lead to longer periods of saturation of building fabric. Heat emitters can increase surface evaporation leading to localised decay of historic stone and plaster which may lead to the loss of historic decorative schemes.

3. Specification of low carbon heating require larger sizes of pipe work and radiators

Routing of pipework and siting new radiators may need to be sensitively designed where the interior of the building is of cultural significance. Where larger heat emitters are required, this might have a visual impact. Designing new heating systems for 55°C flow temps, to accommodate future heat pump installs, is not a requirement but it is good practice to prepare for future decarbonisation of heating.

3.13.4 Recommendations to meet the standard

The minimum heating requirements set out in this standard relate only to dwellings and are very basic. These requirements will therefore be exceeded significantly in almost every dwelling created by the conversion of a historic or traditional building. Guidance on ways of heating such buildings efficiently is given in the notes to Standard 6.3. However, it is important that the type of heating system is specified to reflect the inherent thermal properties of the building so that the most energy efficient approach is adopted. The heating should also consider heat losses from ventilation (Standard 3.14) and the need to ensure that surface temperatures will normally exceed dew point temperatures for the typical moisture vapour conditions of the building and its occupation.

The whole building approach should be taken to achieve the balance required between heating of spaces, surface temperatures and ventilation to prevent mould growth. This is likely to be more problematic in recesses and cupboards on external walls (refer to notes in Section 3.15). Unless particular care is taken in the design of space heating, it is possible that spaces within or adjacent to rooms, such as storage cupboards, may remain at temperatures below the critical temperature at which mould growth can occur.

Caution should be taken by using default U-values for heat loss calculations in the design and specification of heating systems. Reference to measured U-values for specific types of construction will ensure greater accuracy for buildings of traditional construction. Information to support these calculations can be found in HES technical Paper 10 (2011) U-values and traditional buildings and The SPAB Report 1 (2012): U-value Report.