How to Lag Pipes for Winter — Stop Frozen Pipes
A single burst pipe from a hard UK frost costs an average £4,700 in insurance claims. Lagging pipes correctly costs £40 and takes an afternoon.
Step-by-step method
1. Buy the right thickness
Loft & outbuildings: 19mm wall Climaflex or Armaflex. Boiler flue condensate: 25mm. Cheap 9mm foam is not enough for UK freezes.
2. Prioritise the risky pipes
Cold feed to tank in loft, condensate pipe from combi to outside drain, external tap runs, and pipes on outside walls.
3. Cut mitre joints
On bends and Ts, cut the foam at 45° so joints butt cleanly with no gap. Tape with duct tape or Climaflex tape.
4. Lag tanks and stopcock
Foam jacket the loft cold-water tank, lag the rising main up to and including the stopcock.
Frequently asked questions
Will lagging alone stop pipes freezing?+
For temperatures down to -8°C, yes. Below that, add trace-heating cable to exposed runs like condensate pipes.
How thick should pipe lagging be in the loft?+
Minimum 19mm wall for 15/22mm pipe. 25mm is better if your loft has no roof insulation above.