How to Improve Insulation in Older British Homes

Why period homes need a different approach

Older British homes were built to breathe. A Victorian terrace with solid brick walls, lime mortar and suspended timber floors manages moisture by letting it move through the fabric and evaporate away. Wrap that same building in cement render, spray foam or foil-backed plasterboard and you trap water inside the wall, where it eventually finds the timber lintels, joist ends and skirting boards.

So the goal is not to make an old house airtight and hermetically sealed. It is to slow down air movement, keep the structure dry, and use materials that allow vapour to pass through. Before you spend a penny on insulation, deal with the obvious: leaking gutters, overflowing downpipes, cracked render, blocked air bricks and soil piled above the damp-proof course. A damp wall is a cold wall, and no amount of insulation will fix that.

Start with draught proofing, not insulation

Draught proofing is the cheapest, least invasive and most immediately noticeable improvement you can make to a period property. In a typical Victorian house, uncontrolled air leakage through gaps and openings can account for a significant slice of heat loss — often more than the walls themselves.

• Chimneys: an open flue is a permanent hole in your thermal envelope. A chimney balloon or a sheep's wool draught excluder makes a real difference, but remove it before lighting a fire.
• Sash windows: brush or spring bronze seals fitted into the staff beads and meeting rails stop rattling and cut draughts without sealing the window shut.
• Floorboards: gaps between boards in a suspended timber floor will chill a room fast. Fill with a flexible filler, or lift the boards and lay breathable membrane beneath.
• Skirting, keyholes and letterboxes: the small stuff adds up. Silicone sealant along skirtings, a brush seal on the letterbox and a cover on the keyhole take half an hour.

One caution: never seal up a room that relies on an open flue, gas appliance or solid-fuel stove for ventilation. If in doubt, fit a humidity-triggered extractor fan or trickle vent first.

Windows: secondary glazing without losing character

Original sash windows are almost always worth repairing rather than replacing. A well-maintained timber sash with new cords, draught seals and a discreet secondary glazing panel can comfortably outperform a cheap modern replacement, and it keeps the proportions that make a period house feel right.

Secondary glazing is the sweet spot for listed buildings and conservation areas, where replacement windows are often refused consent. A slim aluminium or timber frame is fitted inside the reveal, leaving a 100mm air gap that acts as an extra insulating layer. Specify low-emissivity glass and you will reduce heat loss, condensation and traffic noise in one go. Fix the frame into the reveal, never into the historic joinery, and make sure the panels are easily removable for cleaning and ventilation.

Don't overlook what hangs at the window. Heavy lined curtains, thermal blinds and original Georgian shutters all slow heat loss overnight, and unlike glazing they cost almost nothing if they are already there.

Lofts, floors and the breathability question

Loft insulation is the easiest big win, but old roofs need airflow. Keep the eaves clear so air can move above the insulation, use rafter trays or baffles to protect the ventilation path, and avoid blocking the gap at the wall plate.

For the insulation itself, breathable materials suit older structures well. Sheep's wool, wood fibre and hemp batts are vapour-open, handle moisture without losing performance, and are pleasant to work with. Aim for a healthy depth — around 270mm in a loft — laid in two crossed layers to reduce cold bridging.

Suspended timber floors are often overlooked. Insulate between the joists with breathable batts held in place by netting, but keep the sub-floor air bricks clear. Blocking that ventilation traps damp under the floor and rots the joists from below — a very expensive mistake for the sake of a warmer living room.

Solid walls: the tricky one

Roughly a third of British homes have solid walls, and they are the hardest to improve. Internal insulation using wood fibre boards, calcium silicate boards or an insulated lime plaster is usually the more sympathetic option. It is also disruptive: you lose 50–100mm of room width, radiators and sockets must be moved, and every joist end and partition becomes a potential cold bridge that needs careful detailing.

External insulation keeps the floor area and warms the wall mass, but it changes the appearance of the building and often needs planning permission or Listed Building Consent. It also needs a genuinely dry wall and skilled detailing at reveals, sills and the eaves.

Be realistic about payback. On a solid wall, insulation is often about comfort, condensation control and doing the right thing for the fabric, not about a quick financial return. Talk to your local conservation officer and building control early — they are usually far more helpful than people expect, provided you ask before you start.

Planning, phasing and where to spend first

Work in a sensible order and do one thing properly rather than five things badly:

• Fix water: gutters, drainage, ground levels, leaking roofs.
• Improve ventilation so the house can manage moisture.
• Draught proof chimneys, windows, doors and floors.
• Insulate the loft and any accessible suspended floor.
• Repair and secondary glaze windows.
• Consider wall insulation last, and only with breathable materials.

Alterations to thermal elements can trigger Building Regulations, though there are exemptions where full compliance would unacceptably alter a historic building. Check first, keep records of what you install, and photograph anything hidden behind plasterboard. A phased, breathable, well-detailed approach will keep a period home warm, dry and standing for another century.