The cold room in your house: find the cause before buying a heater
Almost every house has one room that never gets comfortable. The instinct is to add heat, and it rarely works, because heating a room that loses warmth faster than the rest just costs more to stay cold. The fix depends entirely on why it is cold, and there are only a handful of common reasons. Working through them in order saves money and usually reveals something simple.
Work out which cold you have
The symptoms tell you a lot before anyone touches anything.
Symptom and likely cause. What you notice | Likely cause | Direction of the fix. Cold feet, warm head — Uninsulated suspended floor — Insulate between joists, seal gaps; Cold draught near windows — Air leakage at frames and reveals — Draughtproofing and reveal detailing; One outside wall always cold — Solid or single skin wall — Internal insulation, correctly detailed; Cold bay window area — Uninsulated bay roof and floor — Insulate the bay itself; Room over a garage or passage — Exposed floor underneath — Insulate the ceiling below; Damp patch and cold together — Moisture, not just heat loss — Diagnose the water source first
Damp and cold travel together
A damp wall conducts heat away faster than a dry one, so damp rooms feel colder at the same air temperature. That is why insulating over a damp wall makes things worse rather than better: the moisture stays, and now it is trapped.
If there is any staining, salting or musty smell, the water source is the first job. Only once the wall is dry does insulation make sense.
Cold conservatories are a special case
A conservatory is cold because it is mostly glass, and no amount of heating fixes an uninsulated glazed roof economically. Insulating the roof, improving glazing and dealing with draughts changes the room's behaviour rather than fighting it.
Conservatory insulations are a service we carry out regularly, and it is usually the difference between a room used two months a year and one used most of the year.
Draughts before insulation
Air leakage is cheap to fix and often the biggest single contributor. Gaps around floorboards and skirtings, unsealed loft hatches, old letterplates, disused chimneys and poorly fitting doors all move a surprising amount of air.
Do this first. It costs little, and it makes the effect of any later insulation much more noticeable.
When internal insulation is the answer
For solid walls, internal insulation works well when it is detailed properly: continuous, correctly specified, taken around reveals, with the junctions considered so you do not create a new cold spot at the edges.
Done badly it causes condensation at the edges of the insulated area. That is a detailing failure rather than an argument against the approach, and it is why the reveals and junctions get as much attention as the main wall.
Frequently asked questions
Why is one room in my house always colder?
Usually more exposed external surface, an uninsulated floor or wall, air leakage, or damp in the fabric. Identify which before spending on heating, because each has a different fix.
Will insulating a wall stop it feeling cold?
Yes if the wall is dry and the insulation is detailed continuously around reveals and junctions. Insulating over a damp wall traps moisture and makes the problem worse.
Is a cold conservatory worth insulating?
Usually. Insulating the roof and improving the glazing typically transforms how much of the year the room is usable, and costs far less than replacing the structure.
Should I fix draughts or add insulation first?
Draughts first. Sealing air leakage is inexpensive, makes an immediate difference and improves the effect of any insulation added later.
Can a cold floor be insulated without lifting it?
It depends on the construction and whether there is access from below. A suspended floor with an accessible void can sometimes be insulated from underneath, otherwise boards are lifted.
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