Quick answer: Wrap foam pipe lagging around any pipes in unheated areas such as lofts, garages, and under kitchen sinks near external walls. Measure the pipe diameter first, standard UK copper pipes are typically 15mm or 22mm, then cut lagging to length and slide it over the pipe using its pre-slit edge. Seal joints and bends with waterproof tape, and don’t forget the boiler’s condensate pipe, which is one of the most commonly missed spots.
A burst pipe in winter is one of the more expensive and disruptive things that can go wrong in a home, and it’s almost entirely preventable with a few hours of straightforward insulation work before the cold weather sets in. Foam lagging is cheap, the tools required are minimal, and the job itself is genuinely simple once you know where to focus your effort.
Identifying the Most Vulnerable Pipes
Not every pipe in your home needs attention, but a few locations are consistently the most at risk and should be top of your list.
- Lofts and roof spaces: a top priority, since loft insulation keeps heat down in the living space below, which actually makes the air above colder for any exposed pipework.
- Garages, outbuildings, and sheds: unheated spaces where pipes are fully exposed to outdoor temperatures.
- Outside pipes: any exposed pipework running along an external wall or outdoor tap.
- Under the kitchen sink: especially where pipework runs close to an external wall or a cold draught from an air brick.
- The boiler’s condensate pipe: a plastic pipe, usually running outside, that drains a small amount of water from a condensing boiler. If this freezes and blocks, the boiler will simply stop working.
What You Will Need
- Foam pipe lagging, sized to match your pipe diameter
- A sharp knife or scissors
- Waterproof tape
- A mitre box, for neat 45-degree cuts at bends
- A tape measure
Step 1: Measure Your Pipes
Standard UK domestic copper pipes are typically 15mm or 22mm in diameter, and the lagging you buy needs to match the outside diameter of your specific pipe for a snug, effective fit. For pipes in more exposed areas, such as a loft or outdoors, a minimum wall thickness of 19mm is generally recommended for the best protection. For pipes in less exposed indoor locations, 13mm thickness is common and usually sufficient. Measure the total length of pipe you need to cover too, since lagging typically comes in one or two metre lengths.
Step 2: Cut the Lagging to Length
- Measure each section of pipe you’re covering.
- Use a sharp knife or scissors to cut the foam lagging to the correct length.
- For corners and bends, a mitre box helps you cut clean 45-degree angles so the insulation continues smoothly around the joint rather than leaving a gap.
Step 3: Fit the Lagging
- Standard foam lagging comes with a slit running down one side, allowing it to open up and slide directly over the pipe.
- Press the lagging closed along the slit once it’s in place, working along the full length of the pipe.
- At joints, valves, and bends, make sure there are no gaps, since these are exactly the weak points where freezing is most likely to start.
- Seal any joins between sections of lagging, and the seam along the slit, with waterproof tape for extra security.
Insulating Water Tanks in the Loft
If you have a cold water tank in the loft, wrap it in an insulating jacket, including underneath it, not just around the sides. A common mistake is to lay loft floor insulation directly beneath the tank, which actually makes things worse, since it blocks the small amount of rising heat from the rooms below that helps keep the tank from freezing. Leave the area immediately under the tank free of floor insulation for this reason.
Don’t Forget the Condensate Pipe
Many condensing boilers have an external plastic pipe that drains a small amount of condensate water, and this is a frequently overlooked freezing point. If it blocks with ice, the boiler detects the fault and shuts down, even though nothing else is actually wrong with the heating system. Wrap this pipe in foam pipe insulation specifically designed for the purpose, paying particular attention to any section that runs outside.
Additional Materials for Severe Conditions
Standard foam lagging suits most UK homes, but a few extra options exist for particularly exposed pipework or harsher winters.
- Fibreglass insulation offers higher thermal resistance and suits pipes in unheated areas like lofts for longer-term protection.
- Heat tape or electric heating cables wrap around pipes and provide active warmth, useful for pipes that are especially difficult to insulate conventionally or in regions with severe winters.
- Weatherproof covers for outdoor taps and valves add an extra layer of protection specifically at these common failure points.
Other Ways to Protect Your Pipes
- Keep your heating thermostat set to at least 12 to 15°C during cold spells, even when you’re out, to maintain a steady background temperature that protects pipework hidden behind walls and under floors.
- Most modern boilers include built-in frost protection, which automatically fires up the heating briefly if the system temperature drops too low, even with the heating switched off.
- Before the first frost each year, walk your property and check for any sections of exposed or uninsulated pipe you might have missed.
Inspecting and Maintaining Existing Lagging
Insulation degrades over time, so it’s worth checking annually, ideally before winter sets in. Look for compression, tears, or sections that have slipped away from the pipe, since compressed foam loses the trapped air pockets that give it its insulating effect in the first place. Check tape seals at joints too, replacing any that have loosened, and be aware that outdoor insulation exposed to UV light can become brittle and crack over time, needing earlier replacement than indoor sections.
What to Do If a Pipe Freezes
- Turn off your water supply at the stopcock immediately to limit any damage if the pipe has already started to leak.
- Open the nearest taps to relieve pressure in the system.
- Warm the affected section gradually using a hairdryer, a warm towel, or a gentle heater. Never use a naked flame.
- Once thawed, check carefully for leaks along the pipe. If in doubt, call a qualified plumber before turning the water supply back on fully.
Related Guides
Frequently Asked Questions
What size pipe lagging do I need for UK pipes?
Standard UK domestic copper pipes are 15mm or 22mm in diameter, so measure your pipe first and buy lagging sized to match. A wall thickness of 19mm suits exposed areas like lofts, while 13mm is common for less exposed indoor pipework.
Why does my boiler’s condensate pipe freeze?
The condensate pipe carries a small amount of water outside, and if it isn’t insulated, this water can freeze and block the pipe, causing the boiler to detect a fault and shut down until it thaws.
Should I insulate under my loft water tank?
No. Leave the area directly beneath the tank free of loft floor insulation, since a small amount of rising heat from below actually helps protect the tank from freezing.
What should I do if a pipe freezes before it bursts?
Turn off the water at the stopcock, open nearby taps to relieve pressure, and gently warm the frozen section with a hairdryer or warm towel, never a naked flame. Check for leaks once thawed.
Final Thoughts
Insulating pipes is one of the cheapest and most effective jobs you can do before winter, and it takes far less time than dealing with a burst pipe afterwards. Prioritise lofts, outbuildings, external walls, and the often-forgotten condensate pipe, and give your lagging a quick annual check so it’s still doing its job when the temperature really drops.