How to Improve a Listed House’s Energy Efficiency – a Period Home Expert’s Guide

How do listed buildings deal with moisture & why is this important?

It’s important to understand how older buildings deal with moisture. Unlike modern houses, they were constructed from permeable materials, with no moisture barriers. As a result, they naturally absorb excess water from rain, the ground and vapour generated inside.

The permeability of the fabric means that all this moisture can evaporate when conditions are favourable, creating an equilibrium that results in a dry, healthy building. To maintain this optimal performance, any materials introduced during a renovation project must be permeable to water, both as liquid and vapour. Rather confusingly, this process is generally referred to as breathability.

How can you ensure that your listed home is dry?

Traditional, listed buildings tend to have thick walls with high thermal mass. They therefore have the potential to be surprisingly thermally efficient, so long as they’re able to dry out – wet walls are very good heat conductors. For this reason, the use of permeable materials is critical to the sustainability of a renovation project, as well as the health of the building’s structural fabric and its occupants.

The next essential element to ensuring a dry building, is the rainwater goods (gutters and downpipes). It is safe to assume that an old house has defective rainwater goods – in 20 years of consulting, I’ve never seen a house where they’re working properly! Other factors that can cause damp walls include poor details that concentrate rainwater runoff, raised ground levels and leaks from plumbing.

What past mistakes are you likely to encounter when undertaking a listed house renovation?

The importance of breathability was not well understood for much of the 20th century, and a worryingly high proportion of the construction industry still don’t really get it. As a result, inappropriate, impermeable materials were used very widely in traditional buildings.

This can have serious consequences for the building fabric (preventing water from evaporating) and therefore a negative impact on thermal performance. Most sustainable renovations will start with the removal of inappropriate materials such as cement render and pointing, plaster, plastic masonry paints and concrete floors.

How can you improve a listed house’s airtightness?

Once a building is dry, the most effective measures you can take to boost thermal performance are to improve airtightness. Old, listed buildings tend to be leaky, mostly as a result of wear and tear. Draughts have a negative impact on internal temperatures but a much greater influence on comfort levels for occupants – humans are very sensitive to air movement; if you feel cold, you will feel the need to heat the house to a higher temperature. Those few extra degrees on the thermostat can defeat your eco efforts.

This wall has been finished with a lime plaster base coat – a more eco-friendly and appropriate choice than gypsum for heritage homes

Air leakage tends to occur around ill-fitting doors and windows and where there are gaps in the building fabric, particularly at junctions. Finding them is fairly simple: you can sense most draughts with the back of your hand. The key thing is to carry out a thorough examination of the whole house and deal with every issue you find – to the level of detail of keyholes and letter flaps. Chimneys are a particular issue, leaking large amounts of hot air. Any unused chimneys should be sealed, but a small amount of ventilation must be maintained to minimise dampness.

Some background ventilation is essential for a healthy living environment, and it is almost impossible to be so effective with your draughtproofing efforts that this is eliminated. Generally, even if you do all you possibly can, the result will still be slightly more leaky than optimal. You should not need trickle vents in new windows (and listed buildings are exempt from the regs that demand these).

What’s the best way to insulate a listed building?

Roofs and floors are the main priorities here and, as with everything else, the use of breathable materials is essential. A standard cold roof structure is easy to heatproof with rolls of insulation, just be sure to maintain a space for ventilation at the eaves. Warm roofs (which are occupied) are more complicated and require expert specification.

Suspended timber floors suffer heat loss and draughts – both can be fixed by carefully lifting the boards, draping an airtightness membrane to create pockets in between the joists, and filling those spaces with insulation.

It is sometimes possible to insulate over solid concrete floors, if there is plenty of headroom and the floor is not causing any damp problems in the base of the walls. More often, though, the floor must be removed and a new version installed with permeable insulation below, which is a major undertaking. There are very effective buildups available from specialist suppliers that use foamed glass insulation and have system approval from building control.

What is embodied energy & how can this be reduced when renovating a listed house?

A very large proportion of the energy use and emissions involved in construction and renovation lies in the materials supply chain. Extraction, processing, manufacturing, packaging, transport and waste will each have a major impact on the sustainability of your project. Many modern materials are highly energy intensive, resource hungry, polluting and transported vast distances.

On the flip side, the materials used to build a traditional house were typically sourced very locally, minimally processed, naturally derived and easily reused. The closer your supply chain can get to that, the more sustainable your renovation will be and the more compatible the materials will be with the original.

What is operational energy & why is it important to a house’s sustainability credentials?

The final element in the sustainability equation is the energy efficiency of all the equipment you install to live in it. This is often the headline consideration, but unless the building’s thermal properties are up to standard, the benefits are greatly reduced despite significant expense.

Once your house is inherently dry and warm, an eco-friendly, sustainable heat source such as a heat pump will be effective. Other considerations should be energy efficient lighting and appliances, low flow plumbing and sanitary fittings, and rainwater/greywater harvesting.