How to insulate a water pipe in an uninsulated building?

I have a water service pipe in an uninsulated building, how do I keep it from freezing?

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If it gets really, really cold, you should look at trace heating, where heating cable is strapped to the pipe and low power heating keeps the line from freezing.


Can Christmas tree lights be used in place of this thing you call, "heating cable"? I mean the old kind with small, filament style, light bulbs, not LEDs.

I doubt it. Heating tape works because you have a large surface with good thermal contact to the pipe, so only half of the power is wasted. With a light string, the thermal contact is just about nil, so all of the heat is radiated away.

I agree.

Insulations don't generate heat. Thus, they don't prevent the water from freezing. Insulations only slow down the process the water loses its energy. If you permanently withdraw water then the relative cold water in the pipe will be incessantly replaced with relative warm water and the water won't freeze even without insulation. But if the water stands over night then the best insulation might not even help if the temperature in the room is low enough.

rickharris22 days ago

Usually proprietary foam pipe insulation is used.

But practically anything that will trap air c an be wrapped round the pipe.

Standard rock wool type loft insulation for example.


There is a NASTY geometry when insulating pipe... Initially the surface area around the pipe increases faster then the "R" insulation value which will make the heat loss worse then no insulation at all !!! Until depending on the "R" val you exceed a critical

diameter around the pipe and actually increase insulation from there on outward...

True, In the UK this is catered for because all domestic water pipe is 15 mm or 22 mm dia - There is a thicker version of the insulation for the bigger pipe.

Most attic areas in the Uk will get below 0 deg C in the winter because the floor of the attic is lagged (by law) unless your house is very old. In my case there is over 18 inches of lagging on the floor. (very warm house.)

What do the UK terms "catered" and "lagged" mean ?

Catered for = allowed for - our domestic pipe sizes are standardized. 15mm and 22 mm. The pipe insulation is sized as required. Bigger for the larger pipe.




provide with what is needed or required.

  1. "the school caters for children with learning difficulties"

    synonyms:serve, provide for, oblige, meet the needs/wants of, accommodate, entertain, receive;

Lagged = insulated.



past tense: lagged; past participle: lagged

  1. enclose or cover (a boiler, pipes, etc.) with material that provides heat insulation.

    "all pipes and tanks in the attic should be lagged"


late 19th century: from earlier lag ‘piece of insulating cover’."