Keeping listed buildings warm in an energy crisis

Listed buildings and low carbon: How do the green options measure up?

Climate change and the rise of energy costs have focused attention ever more sharply on low-energy homes. Advances in technology mean there are more low-carbon options for heating homes, but what options are viable for listed buildings? Richard Harris, Partner and Heritage Specialist at Carter Jonas, answers some key questions.

Air source and ground source heat pumps are talked about as a greener alternative to heating but are either suitable for listed buildings?

Both air source and ground source heat pumps run on electricity, so if renewable generation is not part of the electrical supply mix heat pumps are the least green option. However, as utility prices continue to rise, heat pumps are likely to become the most economical as well as the lowest carbon form of heating available in comparison to gas or oil-fired boilers.

Ground source heat pumps tend to be more efficient, but you’ll need to ensure there is a sufficient power supply by contacting your local supplier. This could be a challenge in rural locations, and it can be expensive to upgrade, so heat pumps are not viable on some projects we’ve worked on.

If you have sufficient electricity supply, air source heat pumps have lower capital costs, but you can’t retrofit it to a fossil fuel heating system because you need bigger radiators and pipes. This can be an issue with listed buildings installing new pipework and the appearance of very large radiators particularly where you have historic interiors.

There is also an outside unit, similar to an air-conditioning unit, which requires listed building consent and planning permission if the installation is not considered a ‘permitted development’. These can be screened with a bit of thought and consideration so not to impact the look of the building but the fans do generate some noise.

Ground source heat pumps also require listed building and planning and are more expensive to install. Horizontal pipes are easier to install but take up much more space. Vertical pipes using boreholes is an option if space is an issue but require pilling rigs which adds to the cost.  You will also need internal space for the heat pump unit which is typically the size of a large fridge.

I’ve seen schemes where bore holes have been installed in the garden of a small Victorian cottage, so you don’t necessarily need acres of land.

However, for both systems to work effectively, buildings need to be well insulated and have a good level of air tightness. This can be a problem with listed buildings and older properties as heat pumps might not provide sufficient warmth for a draughty building where retro fitting of insulation can be challenging particularly if the building is listed. 

How easy is it to insulate listed buildings?

The more historic fabric you've got in a property, the more difficult it is. It’s a popular misconception that, particularly with Grade II buildings, the listing only applies to the outside when it applies to the whole building, inside and out.

Walls are the biggest challenge. If insulating from the inside, condensation and mould forming out of view behind your new insulation can be a problem, and, as you are essentially creating an insulated box, inside floor space is lost. Historic details such as timber framing, panelling, picture and dado rails, window reveals and door frames can also be problematic.

Is there a case for putting in double glazing in a listed building?

Where previous modern interventions can be identified, we are starting to see the case being made for double glazing with Conservation Officers allowing double glazing in certain circumstances. 

For instance, if windows are a mix of historic on the front elevation but have been replaced in the past on the rear elevation, then you can argue for replacing modern windows with double glazing. 

It’s not a carte blanche to install off-the-shelf uPVC windows from Howdens or Travis Perkins; they must be designed to look like part of the historic fabric. So be prepared to pay for purpose-made windows. You also need to identify the age of a window and establish whether it has historic significance. This is not as straight forward as it seems and requires specialist advice.

Are woodchip boilers an option in historical buildings?

We're just installing a big biomass boiler in a listed property in Sussex, but it isn’t suitable in many places because of the space required and the visual impact of the flue. There are smaller boilers out there which require much less space, but you still need a garage or attached outbuilding to install everything.

The boiler needs to be topped up regularly, so you need space to store the pellets. 

Some locations are in a smoke-free zone or have restrictions on wood-burning appliances, which means wood chip boilers aren’t suitable which is becoming more of an issue particularly with wood burning stoves. 

And like oil and gas heating, biofuel prices can change depending on the supply chain – the Ukraine war has pushed up prices of wood chips by about 40% but is expected to come down in price as other sources of pellet fuel come online. 

Surely getting planning permission to add solar panels to a listed building is impossible?

Difficult, yes, but not impossible. If you can demonstrate to conservation officers and Historic England that you can locate solar panels on a roof where they won't be visible from a lot of vantage points, then it can be considered.

I'm aware of a few Grade I and Grade II listed churches with solar panels hidden behind parapets so they can only be seen from above. Kings College in Cambridge have recently installed PV panels on the Grade I listed Chapel roof.

You could look at putting solar panels at ground level if you have the space and can screen them so it doesn’t impact the setting of the building, but screening can affect their performance.

Are there any relatively easy wins for creating energy efficiency and reducing carbon?

Updating the heating system is one way to achieve greater energy efficiency installing modern boilers and heat pumps.

We're putting new heating systems into a listed building with zoned control. It has separate circuits for the ground, first and second floors, so the heating can be switched on and off in different parts of the house depending on what is in use during the day or night. 

And if you've got a traditional cold roof with flat ceilings and a roof void, then insulation is fairly straightforward as long as you aren’t blocking any ventilation routes otherwise condensation problems can develop.

Introducing secondary glazing, draught proofing windows and doors, and replacing open fires with wood burning stoves to reduce heat loss will improve energy efficiency but this needs careful consideration as heritage buildings are designed to breath and reducing cross ventilation can lead to issues with condensation although this can be offset by mechanical ventilation to some extent.

Upgrading lighting to energy efficient bulbs can be a cost-effective way of improving energy efficiency as well.

For further information on historical or listed buildings, please get in touch with:
Richard Harris
Partner
01865 404427
Richard.Harris@carterjonas.co.uk