Running cold water pipe outside

I'm running some plumbing to the attached garage of my house for a washing machine, and have a choice of two routes - I can run the pipe inside the house but it's a less than ideal route and can't be hidden without quite a bit of work, but it's not the end of the world. I could also run the cold water supply on the outside of the house, which is a much shorter, simpler run.

Now, I've already read about running cold water pipes outside, I know it's been asked before, and the general answer is no because of freezing in the winter, which makes sense, however it's really not an issue if I have the odd spell of a few days in winter when I can't use the washing machine, the advantage of the extra space in the kitchen would be worth the trade off in spades, so I don't really care so much if the pipe does freeze.

The question is how susceptible are 15mm plastic pipes (and the associated push fittings) to bursting or cracking if the pipes freeze? I would expect an eventual leak with copper, but with plastic is there enough give to allow the expansion without cracking or bursting?

My current plan if I ran outside would be;

- Isolator inside prior to the run (which would be under the kitchen sink) so that if something did burst, I can at least isolate the supply without having to turn everything off, and then can repair when it suits me (although hopefully this doesn't need to be used).

- Run the pipework in 15mm and add pipe insulation to help at least reduce the chance of freezing slightly.

At some point when I redo the kitchen I'll do an inside run, so don't mind taking a bit of a risk (i.e. should be fine, but if we have an unusually cold winter then there could be problems) and because the outside run is so accessible, in the event of a repair it would be fairly straight forward.

Probably a terrible idea, but any thoughts would be useful!