Venting upstairs bathroom into loft.

It sounds that you need a fan to meet building regs. But if you are fitting one then it must ventilate to outside and not into the loft.

They would be a standard fit to be building regs compliant these days. However "need" depends a bit on how the room is used. Baths only, and you might get away without. However high pressure shower etc, and you probably do need one.

What other ventilation is there in there?

If you think it would be worthwhile.

Absolutely not. Last thing you need is a rotten roof structure.

Outside - either through the wall, a window, or ducted up through the loft and out of the eves.

Or fit a humidistat controlled one. Then it only runs when its damp enough in there to need it.

A fan is a good idea but must be vented externally. You can get fans with humidistats that will only run for as long as needed rather than for a preset period.

Tim

Indeed. Venting steam into a loft with cold surfaces and timbers[1] is worse than leaving the steam in the bathroom.

I was just thinking that, I have no fan, but from experience of a neighbours one that does go to the loft, a alot of dust comes in that way and it all sticks to the paint and tiles after a while, and probably wet bodies as well!

Brian

Ours vents through trunking in the loft and out via the soffit. No non-return flap so occasionally we get a draught down from it and a little of our dust back.

If it's vented outdoors, and you don't live in Avonmouth, then it shouldn't be catching dust. Check that the flexi hose inside the loft isn't torn.

There should also be a non-return flap valve, because the wind will try to blow back down it at times. If this is mounted on the soffit at the exhaust fitting, and you're still getting dust, then that really does suggest a torn pipe in the loft.

I have yet to see a PIR that can decide if you are having a s*it or a piss:-)

And the OP did say he did not want the fan to come one when he was just having a piss.

A humidistat should be OK for either unless you have particularly messy habits.

MBQ

In that case, you probably should ventilate the room quite a lot.

Is it? The OP does not want the fan to extract the steam from his piss:-)

As long as the local birds cannot get in that way of course!

Brian

Luckily its not mine... My bathroom is quite old and still has just an air brick.

Brian

There is a grille at the exit through the soffit. Hopefully the local mice will not chew through the trunking!

Looking at this. Seem OK?

Grrr (poxy PS/2 to USB keyboard adaptor keeps lathing control key!)