Whether you want to replace a single broken roof tile or build an extension, the correct specification of materials is vital to any work on listed and conservation area buildings. But you’re not on your own: there are set procedures to follow and experts who can guide you through them and help you assess everything you can – and can’t – do.
Can I extend a listed building?
It is possible to extend a listed building, but you need to apply for a special form of permission called Listed Building Consent. Permitted Development rights do not apply to listed buildings and buildings in conservation areas, so you will also need to apply for Householder Planning Consent.
“Because there are no Permitted Development rights, standard loft conversions with box dormers are completely out of the question,” Kevin Clarke says. Any extension must enhance the existing building and not detract from the heritage value and historic elements associated with the house.
Kevin explains that any extension should be subservient to the original house. “This usually, but not exclusively, means it should be small and to the rear of the property,” he says. “The local planning authority and Historic England [or your local equivalent] will also expect materials and fenestration [windows] to match the existing house.”
If a proposed extension affects any trees on your property, be aware that trees in conservation areas are likely to be subject to Tree Preservation Orders. If you want to carry out work on trees that are not yet the subject of a Tree Preservation Order, you must give the local authority something called Notification of Proposed Works to Trees in Conservation Areas.
Does an extension have to be in the same style as the original building?
A modern extension may be considered acceptable, but there are strict caveats, Kevin says. “The design must be of an exceptionally high standard. You will need to prove to the authorities that it’s an improvement on a more traditional alternative.”
Conservation officers can vary in their opinion about how best to extend listed buildings, as Denis Hayes explains: “Some look for something in keeping with what’s already there. Others believe a modern extension that contrasts with the original building and doesn’t seek to replicate it is more sympathetic. It’s subjective and you should seek advice about what might be most successful in your local area.”
What about repairing or replacing windows?
“Original windows tend to be single glazed with a distorted or unperfected look,” Lior Brosh says. “Therefore, the council will assess the impact of any replacement or repair. It’s very likely they’ll ask for the replacement to be like for like.” This means the colour, material and profiles should be identical to the original windows.
“You need to be careful,” Denis says. “You can get modern replicas that mimic single-glazed sashes, but the frames are almost always too chunky and are often refused by conservation officers.
“In that instance,” he continues, “it’s always seen as better to repair than replace. You may be able to upgrade the existing glazing to improve the performance, but keep the same frame. Whatever you choose will need to be approved by your local conservation officer.”
Are there other glazing options?
“The most common method to enhance acoustics and thermal buffering [insulation] in a listed building is to add secondary glazing behind the original windows,” Kevin says. This solution increases performance without changing the exterior appearance.
“But there are many high-quality heritage-style double-glazed options that are considered acceptable,” he says. “Quite often, Heritage England [or your local equivalent] and heritage officers in local planning authorities acknowledge that the existing fabric of the building is no longer fit for purpose. In this case, they will often approve an upgraded window or fenestration grouping on the assumption the aesthetics are on a like-for-like basis.”
Why is damp a particular issue in listed buildings?
“Many period properties suffer from damp simply because of their age and the constant movement of the building,” Lior says. “Newer listed buildings might have a damp-proof membrane or damp course that over time has broken in one or more places.”
Once there’s a break, he says, the brick becomes a sponge and absorbs water. “If there’s no proper ventilation, bacteria can start growing into mould and rot, which can also affect human health,” he says. It’s very common and treatable, but must be tackled as soon as possible.
A lot of Britain’s historic housing stock, however, was built before modern plastics and damp courses were introduced into the construction industry and, as a result, can suffer from moisture penetrating through and rising up from the foundations.
“All old buildings were built to be breathable, with plenty of passive ventilation,” Denis explains. “They are what’s known as ‘hygroscopic’ in nature, meaning that any moisture is absorbed by the walls and released slowly over time.”
Therefore, be wary of introducing modern materials, such as insulation and vapour barriers, into older buildings, he says. “They can prevent air flow and ventilation, altering the performance of the building and causing major damage, including damp and decay.”
Kevin adds, “Many listed buildings have basements or cellars that have not been tanked or water-proofed internally, which subsequently causes damp. Trying to resolve damp issues like this on listed buildings can be costly and time-consuming.”
The correct specification of materials is vital, Denis says. “Engage with an architect as early as possible to discuss what is the most appropriate approach when upgrading a listed building element.”
What do I need to bear in mind if I want to repair or replace roofs, chimneys, guttering or drainpipes?
“If the roof is made from a particular natural slate or the guttering from cast steel, you’d need to source the exact same product,” Denis says. “This can be expensive, both in material costs and the specialist labour required.”
It’s important that no material changes are made to the exterior of a listed building that alter it from its original state, he says.
“In a conservation area, a chimney needs to remain untouched, because it forms part of the streetscape,” Denis continues. “Chimneys are also often integral to the whole structure of the building. Many older properties have shallow foundations and the whole thing settles into the ground over time. As a result, removing the chimney could impact the structural integrity of a historic building. It’s always best to consult a structural engineer prior to carrying out any works involving a chimney.”
How do I insulate a listed building for energy efficiency?
“It’s often incredibly difficult to do this,” Kevin says. “While windows can be upgraded on a like-for-like basis, walls, floors and roofs are trickier.
“Older listed buildings are unlikely to have a cavity to allow insulation to be pumped into the walls,” he says. “External insulation is ruled out because it would alter the aesthetics of the building. Dry-lining the walls internally is likely to be impossible, as it would require skirting boards, architraves and cornicing to be removed to achieve full coverage of the wall.”
Alternatively, look at improving insulation elsewhere, Denis suggests. “You can, for instance, upgrade loft insulation to reduce heat loss without any impact on original features.”
What about draught-proofing?
“Draught-proofing is one of the most cost-effective and least intrusive ways of improving the comfort of occupants and reducing the energy used for heating,” Denis says, “and there’s little or no change to a building’s appearance. It also has the added benefit of reducing noise and keeping out dust.
“You can draught-proof the windows throughout,” he says. “Research has shown that this can reduce air leakage by at least 33%, significantly reducing the heating requirement needed for a room.”
Can I do anything about draughty floors?
“If you need to insulate a wood floor because of draughts, the local planning authority will require you to carefully number and set aside the floorboards,” Lior says. “You’ll need to install the insulation without any damage to the floor joists and then carefully put the boards back in their original location.”
“Obtain professional advice on this beforehand,” Kevin advises. “This will ensure the process won’t adversely affect the thermal balance and breathability of the house or create condensation issues.”
“Whatever you have in mind for your listed building,” Lior concludes, “make sure you have all the drawings and information describing the work you want to carry out, so the local planning authority can assess and guide you through what can and what can’t be done.”