Insulating Roofs in Historic Buildings

Insulating roofs at ceiling level

For most roofs placing insulation above the ceiling of the top floor can be cheaply and easily achieved without significant modification. High levels of ventilation can usually be achieved which reduces the possibility of any condensation occurring within the cold roof space. 

Insulating roofs at rafter level

For buildings with rooms in the roof space, insulation can be added above, between or beneath the rafters or as some combination. However, the design of the building may restrict some of these options.

Adding insulation above the rafters can change the position of the roof covering in relation to abutments and eaves so this needs to be carefully considered. 

Insulating flat roofs

Many older buildings have areas of flat roof, typically over extensions or porches. Insulating these areas can in many cases be relatively difficult so care is needed to make sure the work is effective and does not cause problems.

If insulation work is being carried out to the main areas of roof it is important that flat roofed areas are not forgotten.

Insulating dormer windows

Older buildings often have dormer windows which come in a variety of shapes, sizes and materials. If the main roof is being insulated then it is advisable to consider insulating any dormer window which is a part of that roof.

Insulating thatched roofs

There are around forty thousand thatched buildings in England today, with some roofs dating back over six hundred years. Thatching is a key part of our vernacular architecture and closely tied to the country's agricultural heritage.

When properly maintained, thatch provides excellent weather protection and sound insulation. Locally grown thatch is also a sustainable material with minimal environmental impact throughout its life cycle.

Thatch offers significantly better insulation than other traditional roof coverings. With the right materials and detailing, a well-maintained thatched roof helps keep buildings warm in winter and cool in summer. The thermal performance of thatch depends on factors such as the type of thatch, how it is fixed, its thickness, condition and moisture content.

Adding insulation at rafter level is generally neither necessary nor appropriate. If the roof space beneath the thatch is not used as living space, insulation at ceiling level may be considered. However, unlike other roof types, traditional thatched roofs had very little ventilation. Gaps at eaves and abutments were typically sealed with straw dollies or clay infill. This draught-proofed construction also helped limit oxygen supply in the event of a fire, while moisture was buffered by the permeable materials used - mainly timber, plaster and thatch.

If insulation at ceiling level is considered, the material and detailing should be compatible with the highly permeable nature of the construction. Additionally, risks of condensation within the space should be minimised to prevent degradation of the thatch or decay of roof carpentry.

When planning energy efficiency interventions, we recommend that you undertake a whole-building assessment to understand how your building performs. Follow the energy efficiency hierarchy to guide your decisions.

For advice on fire safety, please refer to Historic England's guidance.

Open fires, chimneys and flues

Whether used or unused, fireplaces and chimneys can have an important role in improving the energy efficiency of a building. Open chimneys can be sources of useful ventilation but they can often let too much warm air out and cold air in.

More briefing on historic chimney design and use of open fires is given in our Open Fires, Chimneys and Flues web page.