Frost Protection for Domestic Pipes

When dealing with frost protection on pipes inside a domestic building your aim with insulating them is to delay the onset of freezing for as long as possible; it is not possible to guarantee a pipe filled with static water will not freeze by insulation alone. The better the insulation, and / or the thicker the insulation used, the longer you will give yourself. Under normal circumstances you aim to give yourself about 8-10 hours protection against sub zero temperatures. With pipes inside a home this is usually long enough to be sure the pipes will not freeze as it is only when the water is not moving that you are at most risk.

If pipes are not protected then ice formation inside the pipes will lead to an increase in pressure. As the water tries to flow this pressure will increase, and eventually will lead to a frost burst. A burst pipe can cause a lot of problems, not least of which is a lot of damage to your property which in turn incurs a great deal of cost which will be far in excess of the cost of some basic frost protection measures.

Water regulations state that all water pipes (excluding warning or overflow pipes), taps and fittings should be protected against frost wherever it is practical to do so. Where this protection takes the form of pipe insulation, the below table gives a guide to what thickness of insulation ought to be used. 

You will often see Water Bylaw 49 used as a reference point - in 2025 this is no longer in effect and we would instead look to BS5422: 2023 for the most up to date calculations.

This standard gives us tables of the required thickness of insulation to accommodate both 8 hours and 12 hours protection against freezing for copper and steel pipes, given below. In the standard there are tables for starting points of 7C and 2C; the figures used here assume the lower starting point as a "Worst Case Scenario"

The only type of common material to come under the 0.025 W/m.K column would be phenolic foam pipe insulation, for example Kingspan Kooltherm. This type of material cannot be used outdoors without additional protection but the insulation itself is the most efficient insulation available; if used indoors you do not need to do anything else to it. This means you can insulate your pipes with far thinner material, ideal if you are tight on space. If you were to use the material outside then you must protect it with a suitable jacketing material such as ProClad 150, Foster's Vaporfas or PIB Rubber

Nitrile rubber or polyethylene foam pipes insulation such as Isopipe TC Solar, Climaflex, Tubolit or K-Flex would be classed as 0.035W/m.K materials. This means using these types of product 15mm pipes need to be lagged with 25mm insulation, 22mm & 28mm pipes need at least 19mm insulation and 35mm & 42mm need 9mm insulation to protect against overnight freezing. Of these materials only Isopipe TC Solar can be used outdoors long term without additional protection, although Climaflex or Tubolit should last around 5 years if they do not get much sunlight.

Finally, EPDM materials such as HT/Armaflex would come under the 0.040 W/m.K column. The material can be used outdoors long term without additional protection but the trade off is that the insulation value is not as high and thus you need to use thicker insulation to achieve the same results. It is also worth noting that this product is the only one listed in this blog that is not pre split.

 Places that would be particularly at risk of frost bursts are pipes installed near windows, air bricks, external doors, insulated roof spaces (where they are above the loft insulation and deprived of heat from the house), unheated cellars, unheated garages or outhouses; essentially anywhere where draughts are likely to cause heat to be taken away from the pipes.

In indoor areas where damp is a risk it is best to use a closed cell product that will not absorb water, such as Climaflex, Tubolit or K-Flex. Wet insulation is worse than having no insulation at all, as water fills all the air gaps and insulation works on the premise of trapping air which is really where your insulation value comes from.

Also, as you increase the surface area by putting insulation on it will cool more quickly so freezing becomes more likely when then product is wet.

Protecting your pipes from freezing is not difficult and does not have to be expensive. A little forward planning, a bit of pipe insulation and a suitable sealing tape (note NEVER cable ties) goes a long way to preventing the inconvenience that frozen pipes can cause.