How to improve energy efficiency

Traditional buildings have been proven to perform better thermally than was previously thought, but there’s still plenty of room for improvement.

Some of the basic measures outlined in this guide can help building owners to improve energy efficiency and cut fuel consumption – reducing both energy costs and carbon emissions.

Applying a selection of these measures can significantly raise the thermal performance of older structures – both listed and unlisted. Occupants will benefit from improved thermal comfort and indoor air quality.

All measures used should be sympathetic to the character and construction of the building. In particular, ‘passive’ ventilation and moisture permeable materials, part of the design of traditional buildings, help to keep the fabric in good health.

Careful planning, selection of materials and delivery of measures will help to achieve both the full benefits and a durable, long-lasting refurbishment.

Listed building consent may be required in some cases, but this shouldn’t be seen as a barrier to appropriate improvement. Not all measures will suit all situations, and owners should assess the likely suitability of a measure for a specific site with the help of an experienced building professional.

Natural ventilation – enabled by windows, hearths and small vents – was a design feature of many traditional buildings. As air flows around building elements, water vapour is dispersed. Keeping the fabric free from excessive moisture in this way helps to avoid decay.

Materials were also chosen to allow the free movement of water vapour within the structure.

It’s vital not to alter these dynamics too much when taking steps to improve thermal performance. There’s no need to put up with uncomfortable draughts. But there should be enough air movement and exchange to keep both the building’s fabric and its occupants in good health.

Careful use of vapour permeable finishes can help you to manage humidity in the home. Reducing humidity will also reduce condensation on some surfaces, helping to improve indoor air quality.

Adding loft insulation is a good starting point for improving any building’s thermal performance. Around 25% of heat is lost through a typical roof.

You should fit at least 270mm of insulation for it to be fully effective. The loft access hatch should also be insulated and draught proofed. Roof space ventilation must be checked and increased if condensation is thought to be a risk. In some cases, it may be necessary to use a reduced thickness of insulation to lessen this risk.

Types of loft insulation include:

• natural materials such as hemp fibreboard or sheep’s wool
• recycled products made from newspaper
• products made from glass and modern materials

Natural materials are usually best to use in traditional buildings, as they’re better able to buffer moisture and prevent condensation.

Insulation can be fitted:

• at ceiling level, which creates a cold roof space
• between the rafters, for a warmer roof space

Standard loft insulation involves fitting the material on the horizontal upper side of the ceiling in a loft, rather than between the rafters.

Coombs should be well insulated whilst also allowing ventilation throughout the roof space. You should leave a 40mm gap between the top of the insulation and the underside of sarking boards.

Installing floor insulation can improve thermal performance and comfort. Cold floors absorb heat, and wooden floorboards can let cold air enter a room from below. A warm floor significantly improves thermal comfort for occupants.

Suspended timber floors

Timber floor insulation works best when fitted below the floorboards. You can install insulation on the underside of floorboards without disturbing the floor if there is enough crawl space to do so. This is rarely the case, however.

If boards must be lifted to fit wood fibre board between the floor joists, this should be done carefully to allow the floorboards to be reused. You may decide it’s not worth the risk.

Lifted with care, most floorboards can be re-laid, with some new boards added here and there to make good any damage. An experienced joiner may only need to remove every fifth or sixth board, limiting disruption and damage. You must weigh up the cost of such work against the benefit of the insulation.

Whether the insulating material is to be installed from above or below, it should allow a degree of moisture movement. Laying non-permeable insulating board on top of a timber floor will reduce water vapour movement, which may result in timber decay.

You must ensure that air movement is maintained in the space below the floor. This is normally done by fitting ventilation grilles in the walls.

Solid floors

Solid flagstone floors can be insulated, but you shouldn’t risk damage to an original floor by lifting flagstones just to lay insulation. You could think about adding insulation if the floor must be lifted for another reason. An insulated lime concrete floor laid beneath the flags will reduce heat loss.

Where new concrete flooring replaces original floor finishes that have been lost, adding a proprietary insulation can bring considerable benefits. Tests carried out by Historic Environment Scotland found that doing so improved the U-value – a measure of heat loss – of a modern concrete floor by six times.

Timber door frames perform well thermally, but door panels are often made of thinner wood. Fitting insulation to panels can reduce heat loss, and draught proofing the door edges, letterbox and keyholes will also help.

Insulation should be fitted only to the inside of door panels. This will ensure that the character of the door, as it appears to the outside world, isn’t affected.

You should use a layer of suitable thin insulating material. Such materials are less bulky than conventional products but perform much better, and so are more costly. But you will need only a small amount to sensitively upgrade the panels of a traditional door.

There’s little need to insulate internal doors, unless there are significant heat differences between rooms.

Fitting insulation

To fit insulation to door panels:

1. Choose insulation that allows vapour permeability and is thin enough not to greatly alter how the inside of the door looks.
2. Fit the material using an adhesive and so that it’s flush with the door framework.
3. Apply a thin layer of plywood on top.
4. Fix in place new beads or moulding in the original style.
5. Paint the door.

Single glazing has a fairly poor thermal performance, but a range of sensitive upgrade options can improve this without vastly altering the window fabric.

Draught stripping of sash and case windows can reduce air leakage by 80%, although it won’t improve the U-value of the glass panes. If draught proofing is fitted, you will need to think about alternative/additional ventilation.

Find out about fitting draught proofing to windows.

Closing internal shutters and heavy curtains can vastly reduce heat loss from sash and case windows. Using timber shutters is the most effective of the traditional methods of improving the thermal performance of windows.

Learn about repairing, improving or adding shutters.

Fitting secondary glazing can help to make sash and case windows more energy efficient. This can be by far the most effective option but it isn’t always appropriate.

Read more about adding secondary glazing.

The greatest reductions in heat loss may come from using a mixture of measures – for example, fitting secondary glazing and using shutters. Not all options are suitable in all cases, but there will always be a combination you can use to improve the thermal performance of sash and case windows.

Research has shown that replacing entire windows with double glazed units isn’t as cost effective as other energy efficiency measures. Your existing windows can be upgraded for less money to give you the same benefits while still retaining the original features and style that give character to your home.

Replacing the panes of glass in existing multi-paned sashes with double glazed panes is usually possible with the right type of slim profile double glazed panes.

External wall insulation

Installing external wall insulation is unlikely to suit many traditional buildings, as it would cover up high quality ashlar work or an attractive façade. But it may be appropriate – beneficial, even – for a harled or rendered building if the finish is failing.

Read more about external wall insulation.

Internal wall insulation

In Scotland, a dry masonry wall that is 60cm or so thick will generally provide a reasonable thermal barrier – though today’s thermal assessments tend to view them as thermally poor.

There are four possible options for installing internal insulation, depending on what survives of the original wall linings. Internal insulation that requires the removal of existing wall linings is only suitable if no historic materials remain.

Internal insulation can be either:

• blown behind existing wall linings
• applied on existing wall linings
• applied directly to masonry or plaster
• held in place by timber framing

Find out about insulating behind internal walls.

Read about applying insulation onto internal walls.

Discover how to hold insulation in place with framing.