In this new series, Chartered Surveyor Ian Rock FRICS – Author of the Haynes Home insulation Manual –  explains how to cut your energy bills by boosting your home’s thermal efficiency.



  Insulating Pipes and Water Tanks


 How much money are you losing every day through unlagged pipework and water tanks?



There are certain parts of the home where large amounts of heat leakage often take place without anyone noticing.

In a typical property there are lots of hidden nooks and crannies which make ideal spaces for running ugly pipework and ducting, concealed by a cloak of darkness. The trouble is, where pipework is exposed to cold it can be vulnerable to two major risks – heat loss and freezing.

Where for example you have long pipe runs channelling hot water through a cold, draughty attic, in effect you will be paying good money to heat up an uninhabited space.

The same advice applies to other neglected spaces such as cellars, cupboards on outer walls, and voids under timber ground floors. These can become extremely cold in winter so there will be a much greater chance of any tanks and pipes in the vicinity freezing

Loft spaces are one of the most important areas to check for unlagged pipework. But there’s a certain  irony with lofts because the better insulated they are the more danger there’s likely to be for any resident plumbing.

Lots of thick insulation above the ceilings should keep the rooms below nice and warm, but means that the warmth that would otherwise have escaped into the loft is now retained in the rooms, thereby making the loft colder.

Most lofts contain a fair amount of pipework, such as pipes serving cold water storage tanks. Sometimes boilers and hot water cylinders are also located in roof voids. But during a prolonged cold spell, the loft can become so cold that the water in the pipes supplying these devices can start to freeze, the resulting expansion causing them to rupture and split.

You would imagine that a burst pipe would be pretty obvious as copious amounts of water gush through the ceiling. But oddly enough, when a pipe freezes and bursts it’s not always immediately apparent that you’ve got an emergency on your hands – because the water can’t escape as long as ice stays frozen.

Only with the advent of warmer weather will it thaw suddenly turning into an indoor water feature. Odder still is the fact that these sorts of mini-disasters are entirely preventable. All it takes is a little time spent lagging the pipework. And yet so often this is a job that gets neglected.


Which lagging material?

There are 2 popular materials used for lagging pipes in residential properties:-

  • Hessian is the traditional fabric based material made from jute or sisal fibres. It comes in large rolls that can be wind around pipe runs. It’s a natural product but generally takes longer to apply than foam.


  • Foam insulation is the most widely used material, thanks to its relatively low cost. It comes in long tube-like lengths with a lengthways slit so it can be easily slid over pipes. However it is not very eco-friendly and it can be vulnerable to rodent attack.


Lagging pipework

Before buying foam lagging first check the diameter of the pipes to be insulated (normally 15mm or 22mm). Pipe insulation is usually sold in 1 or 2 metre lengths, so before ordering measure the rough total of all the pipe runs in your loft.

Depending on the pipe location thick foam insulation can be difficult to apply, for example where there are two or more pipes run close together or clipped to a wall. Even with relatively accessible pipe runs the lagging normally has to accommodate small obstacles such as pipe clips. In areas with very limited access, if all else fails a squirt or two of expanding foam can come to the rescue.


Other pipes

A quick look around your loft may reveal other pipes, such as plastic overflows or (very rarely) gas supply pipes.

Although these don’t need insulating, there’s no harm insulating it all just to be on the safe side so you don’t miss anything. Also modern plastic water supply pipes are more flexible than metal pipes and are much less likely to split or burst when water freezes. But they should still be lagged because even if they don’t burst, a pipe blocked with frozen water won’t be much use. And unlagged hot water pipes still waste energy whatever they’re made of.

However, when it comes to waste pipes, lagging isn’t necessary. This is because they’re considerably wider so a spot of expansion shouldn’t bother them, plus they spend most of their time empty, bar the odd trickle or gush, often of warm water being discharged. They’re also mostly of plastic which is less vulnerable.

The exception to this rule is condensate pipes serving modern condensing boilers. Where these are run externally they can suffer from freezing blockages in very cold weather causing boilers to cut out.


Lagging water tanks                                                             

A lot of homes have a couple of water tanks in the loft. The smaller one serves the central heating system, and the larger one is main cold water that supplies your hot and cold water at the taps (except for kitchen sinks which are normally supplied direct from the mains).  Most modern homes today are built without the need for tanks in lofts because they have mains supplied pressurised systems, such as combination boilers or unvented ‘Megaflow’ type hot water cylinder.

Airing cupboards are the traditional location for hot water cylinders. If your airing cupboard is empty the chances are at some point the original system was replaced with a mains-supplied combination boiler. If you’ve got a modern pressurised cylinder (usually large white or silver steel) it won’t need insulating.

However most homes have a conventional copper hot water cylinder which are ready-insulated, encased in a green or yellow foam covering. Older cylinders usually have a red insulation jacket embracing the copper casing. In both cases, fitting an extra insulation jacket or two on top is worthwhile, for example two 80mm jackets on top of each other.

Cold water storage tanks in lofts can suffer from similar problems to pipes. If uninsulated they can be prone to freezing in winter. If you’ve ever seen the film The Dambusters then you’ll have some idea what 230 litres of water cascading through your ceiling looks like.

But applying insulation should prevent your cold water supply getting too warm in hot weather, with the associated risk of bacteria-ridden water. Another worthwhile improvement is to fit a purpose-made, close-fitting plastic lid that should seal the top of the tank to keep out dust, dirt and vermin.

To keep stored water cool and clean the tanks need to be insulated properly. However where you’ve got a very old tank of galvanised steel, grey fibreglass or asbestos cement the best advice is to replace it. Most modern tanks are of black plastic for which you can buy purpose-made kits comprising an insulation jacket, a rubber seal, insect proof filters and a close-fitting lid . To ensure the new lid correctly fits the tank you need to first check the label on the tank, or else measure its length, height and width.

When it comes to applying loft insulation near tanks, conventional wisdom has it that you should leave the ceiling underneath it bare. The logic behind this is that warm air from the bedrooms below will waft up through the uninsulated ceiling, helping to maintain a certain amount of warmth to the tank, preventing it freezing.

Unfortunately this depends on the tank being encased with a robe-like covering draping down to the ceiling so that the warm air doesn’t go any further, where it could cause damp problems by condensing on cold surfaces. In practice, this is rarely if ever the case. So a better solution is to apply loft quilt as normal across the whole ceiling, and make sure the whole tank is wrapped in thick insulation, including its base and/or the deck.

Once your tank has been fully insulated with a firmly fitted lid, the water it contains should be safe from the double hazards of contamination and freezing.


NEXT MONTH:   Easy action – how to make your heating and lighting energy efficient


 Ian Rock’s home insulation tips are taken from the new Haynes Home Insulation Manual. For further information see