Worst temperature to burst frozen pipes?

[Pamela]

I vaguely recall ice expands to its maximum volume at -4 C.

Would less cold temperatures (such as -2 C) for a sustained period cause ice to expand enough to burst uninsulated 15 mm copper pipes in a loft?

[Jim Pennino]

A quick Google search of plumbing sites shows that the concensus is that pipes usually burst at -7 C after about 6 hours with copper being the most prone to burst and PEX the least prone.

[whodat]

I vaguely recall something from my youth that pipe bursting happens of temperature rise. Perhaps someone with some sensibility can provide accurate details.

[John Armstrong]

Yes, I'm sure max volume is at -4 C, so I suppose that is when pipes are most likely to burst.

But as ice is solid, it doesn't leave the pipe, so the problem only manifests itself when the temperature rises and the ice melts.

[charles]

The pipe bursts with ice formation, but intil the ice thaws you don't notice the leak.

[Martin Brown]

It is better to insulate them. The pipe will burst when the water freezes solid right through on the weakest point on the pipe. You may not notice this until the thaw comes and liquid water is free to flow again.

Foam insulation is very cheap, but anything over the pipes helps to protect them from frost damage - even a strip of carpet will help.

Usually the position that freezes has some sort of exterior draft of very cold air hitting it. I don't think there is a worst temperature - the colder it is outside the colder it will be in the loft.

The damage might be done when the ice is at its maximum expansion but you will have that state occur twice if the pipe gets even colder.

[Chris Hogg]

If you have a non-return valve in the line, such as for an outside tap, the non-return valve will initially prevent the expanding ice from allowing pressure back up the pipe, but will eventually fail and become completely knackered and refuse to allow water to pass in either direction even after the thaw.

[NY]

Thank you for the reminder. We have a water supply to the garage and to outside taps around the garden. Although most of the pipe is blue plastic, I'm sure some of it will be copper. I've just turned off all that pipework at a tap inside the house - and opened the taps so any remaining water was chance to expand out of the tap instead of expanding in the pipes.

[chop]

Depends on where it burst. If it pushes a joint apart, you can see the ice plug expelled from the now open end of the pipe when only the joint area has frozen and the rest of the pipe back to the supply isnt frozen.

[Brian Gaff]

I've not measured my piece of string lately. My gut feeling is it depends on the sort of connectors, how long the pipe is and how thick the walls are. Brian

[John Walliker]

I wonder whether vertical pipe runs will be less likely to freeze than horizontal, as there is the possibility of convection spreading heat around more easily. Has anyone noticed a difference?

John

[Tim Lamb]

Very bad idea to have an outdoor tap at the bottom of a pipe run!

[John Walliker]

Shouldn't that be the other way round? Ice does tend to float!

John

[Tim Lamb]

Exactly. With the pipe sealed at the top, further freezing pressurises the remaining water and bursts the pipe.

Garden standpipes were relatively safe from frost until non-return valves were fitted to taps.