Good luck to you, but get your prices up!!
And it doesn't equate to £15 an hour either, simple math would seem to indicate it does I know, but you have to look at the larger picture...
Anyway, going into that is too long a post!
Try to aim for about a £1.00 per window and you won't go too far wrong, but also set yourself a minimum price.
At £5.00 you are really down in the cheap seats, £8.00 minimum is reasonable.
got to dash, work is beckoning!
But you will also find that these small accounts will not take you 20 minutes a clean either, if they are small houses you will find they'll take you more like 10 minutes once you get up to speed, though that takes time and a lot of effort to get that quick, but also...don't expect to do more than an average of 3 per hour!
time spent chatting to customers, travel between accounts and so on accounts for a fair amount of time over the course of a day.
Ian