How Much Pipe Lagging Do I Need?

What Pipe Sizes to Measure

• 15mm (microbore): Radiator feeds, small branch pipes
• 22mm: Main heating flow and return, hot water distribution
• 28mm: Mains cold water feed in older properties
• 35mm or 42mm: Larger commercial or multi-storey distribution

Where to Lag Pipes

• Loft space: All pipes — greatest risk of freezing
• Unheated garage or outhouse: All accessible pipes
• External walls: Pipes running in or against external walls
• Under suspended ground floors: Especially in exposed subfloor voids
• Cold water storage tank: Tank jacket plus all connected pipes

Insulation Thickness

• Frost protection only: 13–19mm wall thickness foam
• Energy saving (heated pipes): 19–25mm wall thickness
• Building Regs compliant: 25mm minimum for new installations (equal to pipe diameter for pipes up to 40mm)

Material Types

• Foam pipe insulation: Cheapest, pre-slit for easy fitting. ~£1–2 per metre
• Mineral wool wrapping: For bends and awkward shapes
• Rubber (Armaflex): Professional grade, UV-resistant for external use

Tips

Ensure lagging is continuous with no gaps — frost will find the weakest point. Use tape or cable ties to secure joints. Pay particular attention to bends, tees, and valves which are often left exposed. Lagging hot water pipes saves energy and reduces heating bills by keeping water hotter for longer.