November frost checklist: lagging pipes before the first hard freeze

Frozen and burst pipes are one of the most common winter call-outs, and most can be prevented by lagging pipes in lofts, garages, outbuildings and other unheated spaces before the first hard frost. Use closed-cell insulation matched to the pipe size, UV-resistant insulation outdoors, seal every joint and valve, and follow BS 5422 for frost protection thickness on commercial jobs.

The clocks have gone back, nights are drawing in and the first hard frosts of the season are never far away in November. Every winter, water companies remind customers that frozen and burst pipes are among the most common and costly cold-weather call-outs, and that the fix is usually simple: insulate pipes in unheated spaces before the cold arrives. Severn Trent's standing winter advice is a good example, pointing out that a freeze followed by a thaw is when bursts tend to show up.

This is our seasonal checklist for installers, plumbers and facilities teams getting customers ready for winter.

Where pipes freeze first

• Lofts, especially above loft insulation, where pipes and tanks sit in the coldest air in the house.
• Garages, outbuildings and utility rooms with no heating.
• External walls and outside taps, including the short run of pipe through the wall.
• Underfloor voids with air bricks, and any pipework in unheated plant rooms.
• Condensate pipes on boilers and heat pumps that run outside.

Choosing the right lagging

The right product depends on where the pipe is and what it carries:

• Indoor, unheated spaces: closed-cell nitrile rubber such as Armaflex or K-Flex gives good thermal performance and resists moisture. Self-seal pipe insulation speeds up installation on long runs.
• Outdoors: standard black foam is not designed for sunlight and will break down over time. Use UV-resistant external pipe insulation or protect the lagging with a suitable cladding or coating.
• Heat pump pipework: outdoor runs to and from the unit need insulation that is both UV-resistant and thick enough for the job. See our heat pump pipe insulation range.

Make sure the bore matches the pipe size. A loose fit lets cold air circulate under the insulation. Our pipe insulation by size pages make it easy to find the right bore, from 15mm and 22mm domestic pipe up to large commercial sizes.

Wall thickness and BS 5422

For frost protection, thicker is generally better: insulation slows heat loss but does not stop a pipe freezing forever in prolonged cold with no flow. BS 5422 sets out the method for specifying insulation thickness for frost protection and other duties, based on pipe size, conditions and how long the protection needs to last. On commercial jobs, work from the specification or the BS 5422 tables rather than guessing. For domestic work, choose a generous wall thickness for lofts and outbuildings.

Finishing the job properly

• Seal every joint. Gaps at bends, tees and valves are where freezing starts. Use the correct adhesive and tape from our tapes and accessories range.
• Don't forget valves and fittings. Stop taps and valves in cold spaces need covering too.
• Protect outside taps. Insulate them, or isolate and drain them for the winter.
• Remind customers where the stop tap is and check that it turns.

Our frost prevention collection brings together the products most often needed for winter jobs.

Plan ahead

Demand for lagging rises sharply as soon as a cold snap is forecast. Stocking up in early November means you are not chasing products when every merchant is busy.

Need help choosing the right insulation or wall thickness? Call us on 0161 775 1190, Monday to Friday, 9am–4pm.