Lagging is cheap, quick and one of the best ways to avoid a winter flood, but it only works if it goes on the right pipes. Pipes inside warm, heated rooms rarely freeze. The ones that split are in the cold, forgotten parts of a house. Here is a room-by-room guide to where to look. So which pipes need lagging? It depends on where they run.
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The loft
This is the number one freeze risk in London houses. Look for:
- The cold-water feed pipe running up to any storage tank
- The tank itself, which needs an insulated jacket and a close-fitting lid
- Overflow and vent pipes
- Any heating pipes that loop through the loft space
One common mistake: do not lay loft insulation underneath the cold-water tank. Leaving that patch clear lets a little warmth rise from the room below and helps stop the tank freezing.
Under suspended floors
Many Victorian and Edwardian terraces have timber floors with a ventilated void beneath. Pipes running through that void sit in moving cold air. If you have an access hatch, check for any bare copper or plastic pipe and lag it, paying particular attention to runs near air bricks.
Garages, utility rooms and outbuildings
Washing machine feeds, outside sinks and pipes in attached garages are frequent winter casualties because these rooms are rarely heated. Lag the pipework and consider fitting an isolation valve so you can drain the run in a cold snap.
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Along external walls
Pipes boxed in against an outside wall, especially on the north side of the house, can get far colder than the room temperature suggests. Kitchen extensions with pipes in the floor or along a cold wall are another common spot.
Which pipes need lagging outside the house
Outside taps, the pipe feeding them, and condensate pipes from heating systems all sit in the open air. Outside taps should be isolated and drained in autumn and fitted with an insulated cover.
Choosing the right lagging
Foam pipe lagging comes in sizes to match the pipe diameter (15mm and 22mm are the most common in homes) and in different wall thicknesses. Thicker is better in very exposed spots. Make sure joints are taped, bends are fully covered, and there are no gaps at valves and fittings, because frost finds the weakest point. Outdoors, use lagging designed for external use so it does not break down in the rain and sunlight.
Frequently asked questions
Do plastic pipes need lagging?
Yes. Plastic pipes are a little more forgiving than copper, but they can still freeze and split, and fittings can be forced apart.
Should hot water pipes be lagged too?
Lagging hot pipes in cold areas saves energy and keeps water hotter at the tap. It is not usually about freezing, but it is worth doing at the same time.
How long does lagging last?
Good foam lagging lasts many years indoors. Check it each autumn for gaps, crushing or damage from pests.
