How to insulate external water pipes

Good insulation can prevent your pipes from bursting and causing water damage. Learn how to look after your pipework, what pipe lagging involves and why it’s important.

Eve Powell
Eve Powell
Updated 24 January 2022  | 4 mins read

Why do external pipes need to be insulated?

Throughout the seasons your external pipes are exposed to the elements, as well as any extremes in temperature, while they carry water into your home.

But when temperatures drop, the water in your outside pipes is at risk of freezing. And pipes in unheated areas of your home like lofts, garages, and basements are also at risk.

This can make water pipes crack or burst causing costly damage, plus the inconvenience of having to turn off the water and central heating until the problem’s fixed.

Insulating your pipes is known as lagging and it works by sealing in heat and keeping the cold away from pipes, helping prevent them from freezing during cold snaps.

Key points

  • Cold temperatures can make pipes crack or burst, causing water damage and leaving you without water and heating
  • Insulating your pipes can protect them during cold snaps
  • Lagging your pipework is simple to do using materials found in most DIY stores
  • Be aware that if you don’t take appropriate measures to avoid your pipes freezing, you may not be covered by home insurance

What does lagging mean?

Lagging simply means wrapping your pipe in insulation to keep the cold from getting into the pipe and stop any heat inside from escaping.

The insulation usually comes in the form of foam-based tubing that you can cut to size and wrap around your pipes.

It’s simple enough to do yourself and everything you need should be available at your local DIY shop.

What are the benefits of lagging your pipes?

  • Adding a layer of insulation around your pipes can help prevent them from freezing
  • When cold pipes come into contact with warm air it can cause condensation - pipe insulation prevents this and the corrosion the moisture can cause
  • An insulated pipe covering can keep people safe from touching pipes that are extremely hot or cold
  • Lagging can help prevent heat loss from pipes to the outside air
  • If you’ve shown good home maintenance by lagging your pipework, but still experience a burst pipe, this can help with a successful home insurance claim

Which pipes should be lagged?

Any exposed pipework outside is likely to be at risk from freezing when the air temperature drops, so these should be top of the list.

You should also insulate any pipe in your home that’s not well insulated in unheated spaces, like lofts and basements.

Indoors, you should try to insulate all hot water and central heating pipes to help prevent them from losing heat.

What types of insulation can you use?

Lagging materials are available from most DIY stores. For external pipes, this typically comes in the form of tube-shaped insulation. The most common types include:

Polyethylene foam

This is the most popular type of pipe lagging and is easy to find online and in DIY stores. It usually has a slit cut along its length to help you easily fit it over a pipe.

Rubber pipe insulation

Just like the foam, rubber pipe insulation often comes with a pre-cut slit. It can be used to prevent condensation and can handle higher temperatures, so works well for hot water pipes. It’s also a good option in humid environments as it’s not prone to mould growth.

Self-seal pipe insulation

This comes in both foam and rubber types of pipe insulation. One side of the tube’s slit is lined with self-adhesive tape, so you can easily stick both sides together for a perfect seal.

Pipe wrap insulation tape

This is a weather-resistant insulated foil tape designed to wrap around pipes. It’s useful for insulating complex piping and can be used to fit around joints and bends easily.

Before you begin

There are a few things to consider before you get started. Not least is the thickness of the insulation you’ll need.

The general rule is that smaller pipes will need a thicker layer of insulation than larger pipes - because smaller amounts of water will freeze more quickly.

For best results, choose the thickest depth that will fit into the space around the pipes.

You’ll also need to note the diameter of your pipes. Insulation tubes come with holes of different widths cut into their centre, known as the bore size, so choose one that will fit.

Then measure the length of insulation that you’ll need and allow a bit more for fitting around bends.

What you’ll need to insulate your pipes

Before you can start the insulation fitting, you’ll need to have a few essentials lined up so you can be ready to go. This includes:

Pipe lagging - It’s available from DIY shops. Take your measurements with you and don’t be afraid to ask for advice if you’re not sure what to get

Insulation tape - This is different to pipe wrap insulation tape, instead it refers to the duct tape or insulating tape that you’ll need when joining pipe insulation together

Tape measure - Essential for measuring out the right lengths of lagging that you’ll need to cut to fit your pipes

Sharp knife or small saw - You’ll need to cut your insulation to size as well as cutting angles into it to fit around any bends in pipes

Insulated tap covers - These are a good idea if you’ve got outside taps, and they can usually be found at DIY stores

How to fit pipe insulation

  1. Measure the first length of pipe you’re going to lag and cut the piece of insulation to the right size

  2. If there’s a 90° bend in the pipe, you’ll either need to cut two lagging pieces at a 45° angle to join them, or cut out notches on one side of a single piece to help it curve around

  3. Open the slit in the insulation tubing and slide it over the pipe. To seal the two sides together you’ll either need to use self-adhesive tape or add an adhesive

  4. If you need to join two lengths of insulation together, use duct tape or insulation tape to seal the join

  5. Seal each end of your lagging with tape to make sure it’s secure and that no heat will escape

Burst pipes and home insurance

Water damage is usually covered as standard with buildings insurance policies and is often referred to as an escape of water.

To reduce the damage if a pipe bursts, you’ll need to turn your water off at the stopcock and turn off the central heating - then open all taps in the house to drain the system.

The next step is to contact your insurance company and explain what’s happened, most will have a 24-hour helpline.

Your insurer may want a loss adjuster to assess the level of damage. They’ll give you details on what needs to be done, who’ll be doing it and timings for when this will happen.

Will my burst pipe claim be accepted?

It’s likely you’ll have a better chance of a successful claim if your home and its pipework are well-maintained, and you already had preventative measures in place.

But there are situations where you may not be covered for a leak or burst pipe.

For example, if you’ve had a slow leak that you’ve never fixed or you went away in winter and didn’t leave any heating on (or kept it at less than a specified temperature), this could cause the pipes to burst and invalidate your insurance policy.

So try reading your policy wording to help understand the terms and conditions. You can even contact your insurer to confirm what is expected of you.