Old houses leak heat in a dozen small ways, and much of that is the price of character: uneven walls, single-glazed sashes, floorboards that shift with the seasons. The mistake most people make is attacking the problem with materials designed for modern, sealed buildings. Spray foam and foil-faced boards can trap moisture inside a solid wall, which leads to damp, rot and blown plaster—the opposite of cosy.
There is a better route. Work with the way the building already manages moisture, plug the draughts before you spend a penny on insulation, and choose materials that can dry out. Done well, you gain real warmth and keep every bit of the charm that made you buy the place.
Most homes built before the 1920s have solid walls—no cavity, just brick, stone or cob, often rendered or plastered. These walls absorb moisture from the air and from driving rain, then release it again when conditions dry out. Lime mortar, lime plaster and breathable paints allow that cycle to happen.
Cement render, gypsum plaster and vinyl emulsion interrupt it. Moisture gets in and cannot escape, so it sits in the brickwork, softens the mortar, freezes in winter and pushes plaster off the wall. In timber-framed buildings, it can reach the frame itself. The practical rule: never make an old wall less breathable than it already is. Anything you add should be more vapour-open than the layer beneath it.
Insulation over a damp wall simply hides the problem. Before anything else, clear gutters, check downpipes for leaks, make sure ground levels sit below the damp course, and repair failed pointing with a lime mortar matched to the original. If there is rising damp or a persistent leak, deal with it first—and if the cause is unclear, a surveyor who specialises in period buildings is worth the fee.
Internal wall insulation is the usual option where you cannot change the outside of the house. Whichever material you choose, it needs to sit against a dry, sound wall, and it will slightly reduce the size of the room. Expect to lose a few centimetres on each wall.
What to avoid: spray foam in any form, foil-backed rigid boards taped tight against the inside face of a solid wall, and cement-based renders. They are all effective insulators, and all of them can turn a manageable old wall into an expensive repair. In a listed building or conservation area, most of this work needs consent, so check with your local authority's conservation officer before ordering materials.
A draughty house can feel colder than a well-sealed one with the same thermometer reading, because moving air strips warmth from your skin. Draught-proofing is inexpensive, reversible and often more noticeable than wall insulation. On a windy day, hold the back of your hand near likely gaps—or use a lit incense stick and watch the smoke.
Replacing original sashes usually costs more than it saves and rarely improves the look of a period facade. Secondary glazing is the quieter option: slim panes fitted inside the reveal, often removable in summer, which cut draughts and noise while leaving the outside untouched. Choose a frame colour close to the joinery so it disappears.
Textiles do more than people expect. Floor-length curtains with a good interlining, hung from a pelmet or a ceiling-fixed track that overlaps the window edges, stop cold air pooling at the glass. Add shutters or a simple roller blind in the reveal for evenings. Keep radiators out from behind curtains so heat reaches the room, and layer wool throws and rugs—warmth in an old house is partly a feeling, and texture carries it.
Some of the best gains are completely invisible. In the loft, top up insulation to a generous depth, but keep the eaves ventilation path clear so the roof can breathe—a simple plastic tray or baffle does the job. Lay boards over the joists if you need storage, and never compress insulation to fit.
For suspended ground floors, lift the boards, fill the gaps between joists with a breathable batt, and reinstate the boards. Leave the sub-floor void ventilated through its air bricks; blocking them invites rot. Insulating between joists from below is another route if you have access and headroom. Finally, if you are re-plastering, consider insulating behind panelling or in a service void rather than on the face of the wall—it keeps the room's proportions intact.
Tackle it in this sequence and you will notice the difference at each stage:
Work one room at a time, and live with it for a winter before repeating the approach elsewhere. If your home is listed, or you are unsure how a wall is constructed, take advice from a conservation-accredited professional before you start. Old houses reward patience. Treat the fabric kindly, and it will keep you warm for another century.
Photo: Kindel Media / Pexels
