How to Insulate Outdoor Pipes

If you’ve got water pipes on the exterior of your home, for example if you use an outdoor tap, these will get very cold during the winter months. This can lead to the water inside them freezing, meaning they’re no longer usable, and heightening the risk of them bursting, which can be an expensive repair.

By insulating them, you’ll slow down the cooling process, greatly reducing the risk of freezing and damage. This sounds like a tedious task, but it’s actually suitable for DIYers of all levels. For guidance, keep reading to find out how to insulate an outside pipe.

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You should insulate outdoor water pipes as they can freeze in winter, leading to burst pipes and costly repairs. Insulation slows heat loss and greatly reduces the risk of freezing.
To insulate your external pipes, use foam pipe lagging in a waterproof variety that's of the correct size for your pipes. Then measure the pipes, cut the foam to fit straight sections, corners, and t-joints, and secure everything with weather-proof tape to prevent cold air from getting in. This process is best done in autumn before the cold weather sets in.

What is pipe insulation foam?

Pipe insulation does what it says on the tin - it insulates your pipes, preventing your pipes from being exposed to cold air while keeping warm air from getting out.

The easiest and most reliable insulation for pipes is foam lagging. Foam lagging often comes in the form of long, tube-like pieces (that look similar to pool noodles) with a slit down one side and a tube cut out of the middle to fit around your pipes.

You can get foam lagging in multiple sizes, so you’ll need to measure the width of the pipe you’re insulating to make sure you buy the right size foam.

You'll also find water pipe insulation that’s suitable for both internal and external pipes, so make sure to buy the external variations that are waterproof when dealing with a pipe outdoors.

When should I install exterior pipe insulation?

We recommend installing external pipe insulation in the autumn months as it’ll be in its best condition, ready for the cold in winter. If you choose to leave it until December, you could already be putting your pipes at risk of freezing.

How to insulate external pipes

Now you know why and when to insulate your pipes, it’s time to get started. Below is everything you need and a step-by-step guide on insulating pipes.

Pipe insulation to fit your pipes (a waterproof variety)
Weather-proofing tape
Handsaw
Retractable blade
Tape measure

Measure the width and length of your pipes and take note of the measurements, so you can cut your lagging accordingly.

Use the width measurement to choose the right-sized foam tubes. This will likely be 15mm, 22mm or 28mm. Then use your length measurement to determine how much you’ll need to order.

When insulating external pipes, make sure to opt for waterproof foam lagging that’ll stand up to adverse weather conditions.

Once you’ve measured your pipes and ordered the insulation, you may find that you need to make little adjustments to the lagging to ensure it fits your pipe.

For simple straight pipes, you can measure the length from top to bottom and cut the foam to this size using a saw. When you come across a right-angled bend, you’ll need to create a mitre joint. This involves cutting a 45-degree angle into two pieces of foam insulation, so they meet up perfectly at the corner.

Once you’re happy with the fit, you can begin the installation.

Focusing on the straight length of the pipe, slot the foam onto the pipe, making sure it’s snug. Then cut pieces of tape long enough to wrap around your foam (plus a little extra) and apply these all the way down your insulation. This will stop cold air from protruding through the slit in the foam lagging.

Often you’ll need to account for corners and t-joints, which will require a little more engineering.

Cut a few small pieces of weather-proof tape, each around 6 inches long, and use them to secure the two pieces of foam together like this:

Place one across the outside of the corner
Place one across the inside of the corner
Place one on either side, following the direction of the top pipe
Place one on either side, following the direction of the bottom pipe

Now the corner has been secured, you can tape up the straight parts of the pipe as detailed in step 4.

If your piping has a t-joint, there’ll be some extra cutting and taping involved. Take the foam for the intersecting piece of pipe (this is the piece that will form the lower section of the ‘T’) and use a retractable blade to cut off the corners at the end to create a ‘V’ shape.

Take the longer piece of foam that the former will intersect and cut a matching ‘V’ notch where it meets the other piece. They should slot together when held in a ‘T’ shape. Then place the foam onto the pipes, slotting them into position. Tape around every part of the joint, leaving no gaps for air to escape. Lastly, tape up the rest of the pipes as detailed in Step 4.

Note: If your pipes are secured to the wall with brackets, you’ll need to measure and cut small notches in the foam insulation to accommodate for these.

Once everything has been insulated, your external pipes should be ready to make it through the winter. All you really need is some inexpensive foam insulation and weather-proof tape, and your pipes will be well-insulated in the colder months.

If you’re working on pipes that lead to an outdoor tap, it may be worth investing in a tap frost cover. This gives you an extra layer of protection, preventing any cold air from seeping in through the tap itself.

Maintenance and lifespan of pipe insulation

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Usually, pipe lagging lasts between 1-3 years as it’s exposed to extreme weather, UV rays, moisture and temperature fluctuations. We recommend you regularly inspect it and replace it if it looks worn or damaged (i.e. splits or cracks).

FAQs

Outdoor pipe insulation like polyethylene foam lagging and weather-proof tape works well on both hot and cold-water pipes. However, you should make sure to read the insulation’s temperature rating before using it on hot pipes.

Pipe insulation foam tubing (also known as foam lagging) is the most affordable, straightforward, and effective way to insulate pipes.

If you’re seeing condensation, it’s usually an indicator that warm, humid air is seeping through the insulation, or there’s moisture trapped inside it. To resolve this, we recommend making sure the seals and joints are properly secure and snug and check for any damage in case replacing your insulation is required.