I just had an expensive new bathroom installed, but the underfloor heating stops 10-15cm short of the toilet, one of the most important areas to have heating IMHO. I'd like to have it heated up to the toilet, or very close, and slightly down the sides of the toilet. Right now on a cold day the difference between the main part of the floor and there the front of your foot is when you're standing there is 6-8 degrees, a huge difference. The room is eight square meters, more or less.
The bathroom company (who are generally excellent) have said it's very very difficult to take up tiles, add more heating loops, then put it back down. They said the heating is a factory sealed unit, and while it might possible it's difficult, and it voids any warranty.
I've come up with an alternate plan. We take up a few tiles (3-5) around the toilet, put a metal sheet over the heating mat and over the unheated areas, then put new tiles down. That transfers the heat sideways, then lets it go up through the tiles. This would result in the same amount of heat being spread over a larger area, so it won't be as warm, but it will be a lot better than dead cold.
Does this sound like a good solution? Can anyone see any downsides I can't spot? Should I insist on them adding more heating element instead of this workaround?