Is pipe insulation required by Building Regulations?

Yes. UK Building Regulations (Part L) require that all hot water and central heating pipes in unheated spaces (loft, garage, under suspended floors) must be insulated to BS 5422 standards. This applies to new installations and replacements. Pipes exposed to freezing conditions must also be insulated to prevent frost damage.

What thickness pipe insulation do I need?

For standard domestic heating pipes (15mm and 22mm), the minimum insulation thickness is 19mm for foam and rubber, or 25mm for mineral wool. Larger pipes (35mm+) need thicker insulation. Our calculator shows the minimum thickness required per BS 5422 for your pipe size and insulation material.

What is the best pipe insulation material?

For most domestic applications, foam tube insulation (polyethylene) is the best value — cheap, easy to fit (pre-slit), and effective. For higher performance or commercial work, rubber (Armaflex) offers better thermal performance and moisture resistance. Mineral wool pipe sections are used where fire resistance is needed.

How do I insulate pipe elbows and bends?

For foam tube insulation, mitre-cut two pieces at 45° angles and tape together around the bend. For a neater finish, pre-formed elbow pieces are available for common pipe sizes. Use self-amalgamating tape or PVC tape to seal all joints and prevent heat loss at connections.

Should I insulate cold water pipes as well?

Yes, insulate cold water pipes in unheated spaces (lofts, garages, external walls) to prevent freezing in winter. Frozen pipes can burst and cause severe water damage. Building Regulations require cold water pipes in vulnerable locations to be insulated. In heated living spaces, cold pipe insulation is optional but can reduce condensation.

Pipe Insulation Calculator — How Much Pipe Lagging Do I Need?

Calculate pipe insulation quantities to meet Building Regulations and BS 5422. Includes elbows and tape.

Pipe Size

External diameter of pipe

Total Pipe Length

Total length of pipe runs to insulate

Insulation Material

Include wastage allowance

Adds 15% for cuts, joins and fitting

Wastage Percentage

15% recommended for pipe runs with bends

Include elbows/bends

Add extra for pipe bends

Number of Elbows/Bends

Count 90° bends in your pipe runs

Include tape

PVC or self-amalgamating tape for joints

Price Per Piece (optional)

Price per 1m piece

How We Calculate This

This calculator works out pipe insulation quantities based on your total pipe run length, pipe diameter, and chosen insulation material. It includes the minimum thickness required by BS 5422 (the British Standard for pipe insulation).

The formula

Pieces = (Total pipe length × Wastage factor ÷ Piece length) + Elbow extras

Minimum thicknesses (BS 5422)

15-28mm pipe (foam): 19mm wall thickness
15-28mm pipe (mineral wool): 25mm wall thickness
35-54mm pipe (foam): 25mm wall thickness
35-54mm pipe (mineral wool): 30-40mm wall thickness

Standard piece lengths

Foam tubes: 1m lengths
Mineral wool sections: 1m lengths
Rubber (Armaflex): 2m lengths
Phenolic foam: 1m lengths

Frequently Asked Questions

Related Calculators

U-Value Calculator

Calculate the U-value of wall, floor and roof constructions.

Insulation Thickness Calculator

Determine the insulation thickness needed to meet UK Building Regulations.

Heat Loss Calculator

Calculate room-by-room heat loss for heating system sizing.

Cavity Wall Insulation Calculator

Estimate cavity wall insulation quantities and potential savings.

Loft Insulation Calculator

Calculate loft insulation rolls needed for your loft area.

Last updated: February 2026

All calculations are estimates. Verify with your supplier.