Insulating water pipes is one of the most cost-effective home improvements you can make. It reduces heat loss from hot water pipes, prevents cold water pipes from freezing, stops condensation forming on cold pipework and helps comply with Building Regulations Part L. This guide explains how to do it correctly, from choosing the right insulation to sealing every joint.
Why Insulate Water Pipes?
- Reduce heat loss — uninsulated hot water pipes lose heat continuously, increasing energy bills and the time it takes for hot water to reach the tap
- Prevent freezing — pipes in loft spaces, external walls and unheated spaces can freeze and burst in cold weather
- Prevent condensation — cold water pipes in warm, humid spaces can sweat, causing corrosion and water damage
- Part L compliance — Building Regulations require hot water pipes to be insulated in certain locations
- Protect condensate pipes — boiler condensate pipes must be insulated to prevent freezing and boiler lockout
Step 1: Choose the Right Pipe Insulation
The right insulation depends on what type of pipe you are insulating and where it runs:
| Pipe Type | Location | Best Insulation |
|---|---|---|
| Hot water pipes | Heated space (airing cupboard, kitchen) | Armaflex or foam lagging, 13mm wall |
| Hot water pipes | Unheated space (loft, underfloor) | Armaflex 19mm wall |
| Cold water pipes | Loft or unheated space | Armaflex 13–19mm wall |
| Cold water pipes | Humid plant room or basement | Armaflex 19mm wall (closed-cell essential) |
| Condensate pipe (internal) | Unheated space | Armaflex 13–19mm wall |
| Condensate pipe (external) | Exposed outdoor run | Armaflex Tuffcoat 19mm wall |
For most domestic water pipe insulation, Armaflex elastomeric pipe insulation is the professional choice. It is flexible, closed-cell (so it won't absorb moisture), long-lasting and easy to fit. Read our Armaflex thickness guide for full wall thickness guidance.
Step 2: Measure Your Pipe Size
Pipe insulation is sized by the outside diameter (OD) of the pipe. The bore of the insulation must match the OD of the pipe exactly — too large and there will be an air gap; too small and it won't fit.
| Pipe Type | Pipe OD | Insulation Bore Required |
|---|---|---|
| 15mm copper | 15mm | 15mm |
| 22mm copper | 22mm | 22mm |
| 28mm copper | 28mm | 28mm |
| 22mm plastic (condensate) | 22mm | 22mm |
Read our pipe insulation sizing guide and copper pipe size vs insulation size guide for full details.
Step 3: Gather Your Materials
- Armaflex pipe insulation in the correct bore and wall thickness
- Armaflex 520 contact adhesive
- A sharp knife or scissors
- A tape measure
- A small brush for applying adhesive
If you are using Armaflex Self Seal, the longitudinal seam has a factory adhesive strip so you won't need adhesive for the seam — but you will still need it for butt joints between lengths.
Step 4: Fit the Insulation
Straight Runs
- Measure and cut the insulation to length with a sharp, square cut
- Apply Armaflex 520 adhesive to both faces of the longitudinal slit along the full length
- Allow to become touch-dry (2–5 minutes at room temperature)
- Open the slit and snap the insulation over the pipe
- Press the seam firmly closed along its full length
Bends and Corners
Armaflex is flexible enough to follow gentle bends on small-diameter pipe. For tighter bends, cut mitres at the corner and bond with adhesive. Read our Armaflex pipe bend guide for detailed instructions.
Valves and Fittings
Use Armaflex sheet insulation cut to shape to cover valves, tees and other fittings. Ensure the sheet butts tightly against the pipe insulation on either side with no gaps.
Step 5: Seal Every Joint
This is the most important step and the one most often skipped. Every unsealed joint is a gap in the insulation where heat escapes (on hot pipes) or condensation can form (on cold pipes).
- Longitudinal seams — must be bonded with adhesive along their full length
- Butt joints between lengths — apply adhesive to both faces and press firmly together
- Joints at fittings — ensure sheet insulation on fittings butts tightly against pipe insulation with no gaps
Read our Armaflex 520 adhesive guide for correct application technique, coverage rates and drying times.
Step 6: Special Considerations by Pipe Type
Hot Water Pipes (Part L Compliance)
Building Regulations Part L requires hot water pipes to be insulated where they run in unheated spaces. The minimum insulation thickness depends on the pipe size and location. Read our hot water pipe insulation guide for Part L compliance details.
Cold Water Pipes in Loft Spaces
Cold water pipes in loft spaces are vulnerable to freezing. Use Armaflex 13mm wall as a minimum, 19mm for exposed locations near the eaves. Ensure insulation is continuous from the tank connections to where the pipes enter the heated space below.
Condensate Pipes
External boiler condensate pipes must be insulated to prevent freezing and boiler lockout. Use Armaflex Tuffcoat for any exposed external run. Read our condensate pipe insulation guide for full details.
Cold Water Pipes in Humid Spaces
Cold water pipes in warm, humid spaces (plant rooms, basements) can sweat with condensation. Use closed-cell Armaflex — standard foam is not adequate for condensation control. Read our condensation on pipes guide for full details.
Common Mistakes to Avoid
| Mistake | Consequence | How to Avoid |
|---|---|---|
| Wrong bore size | Air gap between pipe and insulation | Measure pipe OD and match exactly |
| Unsealed longitudinal seam | Heat loss or condensation at seam | Apply adhesive to both faces before closing |
| Unsealed butt joints | Gap in insulation at every joint | Always seal butt joints with adhesive |
| Uninsulated fittings and valves | Cold spots, condensation, heat loss | Use Armaflex sheet to cover all fittings |
| Standard foam on cold pipes in humid spaces | Condensation, corrosion | Use closed-cell Armaflex |
| Standard Armaflex on external pipes | UV degradation within 2–5 years | Use Armaflex Tuffcoat for outdoor runs |
Frequently Asked Questions
Do I need to drain the pipes before fitting insulation?
No. Armaflex can be fitted on live pipework. The slit tube snaps over the pipe without disconnecting anything. Ensure the pipe surface is dry before applying adhesive.
How much pipe insulation do I need?
Measure the total length of pipe to be insulated and add 10% for waste and joints. Armaflex is typically supplied in 1 metre or 2 metre lengths.
Can I use the same insulation on hot and cold pipes?
Yes — Armaflex is suitable for both hot and cold water pipes. The wall thickness you choose may differ depending on the application. See our thickness guide for guidance.
What is the difference between Armaflex and standard foam pipe lagging?
Armaflex is closed-cell elastomeric rubber with a lower thermal conductivity and much better moisture resistance than standard polyethylene foam. For cold pipes, condensation control or any demanding application, Armaflex is the correct choice.
Shop Pipe Insulation
- Armaflex Pipe Insulation — All Sizes
- 15mm Pipe Insulation
- 22mm Pipe Insulation
- Armaflex Self Seal
- Armaflex 520 Adhesive
- Armaflex Sheet Insulation
Domestic heating resources: Shop pipe insulation, 28mm pipe insulation and BS 5422 Resource Centre.
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