How this calculator works
Foam lagging is sold in pieces of 1 or 2 metres, split along one side, in sizes to match the pipe (15 mm and 22 mm for most houses). The number of pieces for each size is the length of pipe, plus an allowance for cutting at corners and fittings, divided by the length of a piece, rounded up. Each join between two pieces, and each corner, is taped.
Worked example: 12 m of 15 mm pipe and 6 m of 22 mm pipe, with 10% extra, takes 14 pieces of 1 m for the 15 mm pipe and 7 for the 22 mm (21 in all), with 28 joints and corners to tape. With no extra it would be 18 pieces. In 2 m pieces it is 7 and 4. A loft with 8 m of 15 mm pipe takes 9 pieces, and a large house with 30 m of 15 mm and 15 m of 22 mm takes 50 pieces.
Lagging for common lengths of 15 mm pipe (1 m pieces, 10% extra)
The number of 1 m pieces.
| Pipe | Pieces of lagging |
|---|---|
| 3 m | 4 |
| 6 m | 7 |
| 10 m | 11 |
| 15 m | 17 |
| 20 m | 22 |
| 30 m | 33 |
Tips before you buy
- Start with the pipes in the loft, the garage, the cellar and outside walls, since those are the coldest.
- Push the foam on with the slit at the bottom or the back, and tape the joints so that cold air cannot get in.
- Lag the cold water pipes in cold places as well as the hot: it is the cold pipes that burst.
- Know where your stop tap is, so that you can turn the water off if a pipe does burst.
- Keep the heating on at a low level when you are away in winter, since lagging only slows the cold.
Tools & materials for this project
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Frequently asked questions
How much pipe lagging do I need?
The length of pipe, plus about 10% for cutting, divided by the length of a piece: 14 pieces of 1 m for 12 m of 15 mm pipe.
Does pipe lagging stop pipes freezing?
It slows the loss of heat, so a pipe takes longer to freeze, but it cannot stop it in a long hard frost. Keep the heating on low, and know where your stop tap is.
What size lagging do I need?
The size of the pipe: 15 mm lagging for 15 mm pipe, and 22 mm for 22 mm. Most house pipes are one or the other.
Which pipes should I lag first?
Those in cold places: the loft, the garage, the cellar and under the floor, and any pipe on an outside wall.
How do I fit pipe lagging?
Open the slit and push it over the pipe, with the slit underneath, and tape or tie the joints. Cut corners at an angle so they meet without a gap.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.