Plasterboard above shower discolouring - help

The whole point of a warm roof is that it is completely sealed against moisture ingress and thus does not require ventilation.

Richard

No, not the roof. The room/space beneath it. Otherwise, where does the moisture from inside the building go?

My misunderstanding I thought you wanted to treat a warm roof like a cold roof which does require ventilation in the roof space. Yes, the room below does require ventilation especially one where considerable moisture is produced. What I would avoid is providing that ventilation through the roof as there is the risk of affecting the seal, ventilating through a wall or window would be advisable.

Richard

you are supposed to have an air gap between the insulation and the tiles/slates that is maintained to the eaves and has exit vents at the rood ridge

Out of the mandatory trickle ventilation

Before you start ripping expensive holes in the ceiling, do the easy stuff first and seriously consider condensation and lack of adequate ventilation!

Has anyone recently started using a hotter shower, thereby generating more steam with a resulting increase in condensation? Is the existing ventilation fan doing it's job properly, or has the fan speed got reduced recently? Has the ventilation pipe got blocked in some way? Some of these ventilation systems have a one-way shutter built into the ducting, to stop back-draughts, which may have got stuck in the closed or partially closed position (the shower room in my previous property had one such; you could hear it clattering when a gale blew). Simply accessed by removing the fan assembly (couple of mounting-screws) to expose the shutter that fitted in the ducting right behind the fan.

Yes, there is - only about 30mm though, slender rafters. Ventilated ridge tiles were fitted.

As above, I was meaning the living and storage space below the roof.

All good points and commented on below:

No change, and it's been a warm summer here in the East Midlands :)

The shutters are on the outside and they open when the fan pressure forces them open.

Additionally, the flat roof is a cold roof and there is adequate ventilation.

Now to find my Stanley knife!

I thought the OP said this shower room had a flat roof, but with all the services carried inside it (unusual).

So it *might* be a 'warm roof' (no external cross ventilation).

If it really is an old-fashioned cold roof, flat roof then the insulation should be immediately on top of the PB but this then means any water pipes up there need their own insulation because the cross ventilation (if the builder bothered) means that they are effectively sitting outside at outside air temperatures.

Where are the water pipes located inside this cold roof though?

Some confusion has crept into this thread. The OP did say he has a flat roof over his shower hence the discussion of warm roof and cold roof. RJH did not specify what type of roof he had installed so I assumed we were still talking about flat roofs. I get the impression he is talking about a pitched roof and I am assuming by calling it a warm roof his insulation has been installed between the rafters as would be the case of a pitched warm roof. Perhaps RJH could elaborate.

Richard

Yes, sorry, it drifted a bit - mine's a pitched tiled warm roof, with insulation between the rafters, and a gap between the insulation and the tiles.

I'd assume a flat warm roof is just a series of sandwiched materials, with no gaps.

A warm flat roof is a series of sandwiched material. Insulation is placed on a deck which sits on the rafters with a vapour barrier between both. The top deck is secured by screws through the insulation into the rafters. To prevent cold bridging by the screws deep sockets are inserted through the top deck and most of the insulation these allow the screw heads to be well below the surface and PU foam to back fill the screw head hole. Finally, the weather proof material is applied to the top deck.

There is also what is called a hybrid roof beloved of garden office builders since it allows maximum headroom inside whilst not exceeding the permitted development restriction of 2.5m height to the eaves. In this case a kinda warm roof is created by inserting insulation between rafters but a vapour barrier is essential under the insulation and care needs to be taken if downlighters are to be used to ensure the vapour barrier is not compromised.

On pitched warm roofs where there is a loft conversion, the trend is to fill the rafter spaces with insulation and then add a further layer of insulation below the rafters and a vapour barrier before finally finishing off with plasterboard. The rafters are thus completely encased by insulation except the side below the breathable membrane and the tiles.

Richard

Interesting, thanks.

Thanks - that's what I'm going to work towards. I'm assuming foil backed PIR, with foil at the edges and joins, is an effective vapour barrier.

I take the point upthread on trickle vents (there are 2 in the space), but I'd like (in a perfect world, probably) some sort of mechanical extraction/ventilation. It doesn't seem right to seal and insulate something, and then in effect make heat escaping holes in it. But implementing the ducting in the space I've got would be difficult.

Sympathises. I've buried a fan in a ceiling void defined by a joist and its failed for the SECOND time now.

Making an access panel vapour tight is more work than ripping the plasterboard down AGAIN and fixing it.

(according to Big Clive they all fail because of one electrolytic capacitor...)

Are there any options other than above the ceiling and below the roof decking?

Just to tidy this one up - thankfully I didn't get round to doing anything such as removing the section of plasterboard to investigate otherwise I would have merely opened up a pathway to a wasp nest!!

For anyone interested, I stuck a bradawl up expecting drips of water to come down, instead I had an insect leg attacking the device.