We just bought a Victorian cottage that's listed and want to improve the insulation, but my builder says we need to be careful about what's allowed. Seems like internal insulation might be the way to go, but I'm not entirely sure what that means or if it actually works.
Talk to your local conservation officer before doing anything - they're the ones who actually decide what's allowed, not your builder's assumptions. Internal insulation means adding insulation to the inside of external walls, which works reasonably well and usually gets approved since it doesn't change the building's appearance, but it does eat into your room space and can sometimes trap moisture if done poorly. External insulation is often off-limits for listed buildings because it changes how the facade looks, though a few councils are more flexible about it. Your best bet is getting written confirmation from planning before you commit to any method, since listed building rules vary wildly depending on where you are and how strict your local authority is.
Internal insulation is generally your safest bet for listed buildings since it doesn't alter the external appearance that planning authorities care about. You add insulation to the inside of walls, ceilings, or under floors, which means no changes to the facade, windows, or original features. It does work reasonably well, though it slightly reduces internal space and needs careful installation to avoid condensation issues - your builder should know about vapor barriers and breathable materials. Before you proceed with any method, it's worth contacting your local conservation officer or planning department directly, as listed building consent requirements vary significantly depending on your building's age, grade, and location, and they can often advise on what's acceptable.
Internal insulation is your best bet for listed buildings because it doesn't alter the external appearance, which is what planning departments care most about - you're basically adding a layer of insulation and a new inner wall or membrane inside your rooms rather than changing how the cottage looks from outside. The tradeoff is you'll lose a bit of floor space and need to be careful about moisture, especially in older properties like yours, since the walls need to breathe properly or you can end up with damp issues. Your builder's right to be cautious; I'd honestly recommend getting the local conservation officer to sign off before you start anything, since they can be quirky about what materials and methods they'll accept. Solid wall insulation does work reasonably well, though it won't perform quite like it would on a modern house, so manage your expectations on energy savings.
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