Bathroom ceiling - replace or skim

hatt55

I have a small bathroom upstairs in my terraced house. It forms the back of the 'L' shape of the terrace so the roof is half pitched and half flat (although externally the whole thing is pitched so there must be a bit of a cavity above the internally flat bit - not sure what the terminology is!).

The bathroom does not have great ventilation so there has been steam damage in the vicinity of the shower. Its a textured ceiling (tested negative for asbestos) and a little stretch along the pitched and flat roof has been filled in by the previous owner.

I'd like to install a vent and perhaps change the light fittings. Due to a minor leak - which is due to be repaired by re-rendering the chimney - there is also some minor staining in one corner. I think it would be sensible to inspect the roof timbers here before sorting stuff out. My questions are then:

1) Is it possible to inspect the roof timbers from outside whilst the re-rendering is happening? Otherwise I assume you would need to remove part of the ceiling internally. Perhaps this depends on the exact type of roof and I may not have a good answer!

2) I'd like a smooth finish on the ceiling. Given that a vent and new light fittings would involve cutting bits in the ceiling anyway, and I may need to have another bit of the ceiling cut open to inspect the timbers (subject to the above), would it be worth just taking down the ceiling a replacing the plasterboard? I have a feeling that the textured ceiling might be too 'nobbly' to skim, but I don't know if taking down a ceiling is significantly more expensive than overboarding. Less messy I suppose!

I think that the ceiling might be insulated as the bathroom doesn't get incredibly cold in the winter. I have a pitched roof without insulation in another part of the house and compared to that the bathroom is balmy. However, it would also be good to actually confirm the nature of the insulation, so perhaps something else to lean towards taking the whole ceiling down. 

FreeBear

One advantage of taking the ceiling down is you can make sure insulation goes right up to the edges of the walls - Been doing that here, and it reduces the cold spots around the perimeter of the room(s). However, it is a very messy job if you have a lath & plaster ceiling.

ThisIsWeird

hatt55 said:

The bathroom does not have great ventilation so there has been steam damage in the vicinity of the shower. Its a textured ceiling (tested negative for asbestos) and a little stretch along the pitched and flat roof has been filled in by the previous owner.
I'd like to install a vent and perhaps change the light fittings.
I'd like a smooth finish on the ceiling. Given that a vent and new light fittings would involve cutting bits in the ceiling anyway, and I may need to have another bit of the ceiling cut open to inspect the timbers (subject to the above), would it be worth just taking down the ceiling a replacing the plasterboard?
I think that the ceiling might be insulated as the bathroom doesn't get incredibly cold in the winter. I have a pitched roof without insulation in another part of the house and compared to that the bathroom is balmy. However, it would also be good to actually confirm the nature of the insulation, so perhaps something else to lean towards taking the whole ceiling down.

For a number of reasons, I think you'd be best taking the ceiling down. And I doubt that the cost will be much more than a plasterer doing an awkward patch-and-skim job.

It'll be easier and far more enjoyable for a plasterer to redo the whole caboodle than to start patching and tackling different surfaces.

It will give you access to properly insulate the ceiling, because chances are the sloping part, at least, won't be. INSULATE! The simplest way is to use insulated plasterboard, which is fitted straight on as easily as normal p'board. However, it'll lower your ceiling by the amount of the insulation layer, and you should be looking at 2" as a min. A better way, then, would be to fit - say - a 2" layer of rigid insulation board in between the joists/rafters, and then overboard with 1" insulated p'board. More work in neatly cutting the Celotex-type stuff to fit neatly and tightly between the timbers, tho'. Could you do this part?

It'll give you good access to fit the extra ventilation - I presume you mean an extractor? You need an extractor, not just for steam, but smells. If a roofer is in attendance anyway, then the easiest route might be through a roof/slate/tile vent.

It'll make wiring the new light fitting(s) and the extractor easier.

You should give this job some thought - what needs to be done at the same time as the ceiling; roof leak, insulation, ventilation, wiring.

It'll also be worth finding out the very best type of paint finish to give the skim so it's as resistant to moisture as possible.

FreeBear

ThisIsWeird said:

hatt55 said:

The bathroom does not have great ventilation so there has been steam damage in the vicinity of the shower. Its a textured ceiling (tested negative for asbestos) and a little stretch along the pitched and flat roof has been filled in by the previous owner.
I'd like to install a vent and perhaps change the light fittings.
I'd like a smooth finish on the ceiling. Given that a vent and new light fittings would involve cutting bits in the ceiling anyway, and I may need to have another bit of the ceiling cut open to inspect the timbers (subject to the above), would it be worth just taking down the ceiling a replacing the plasterboard?
I think that the ceiling might be insulated as the bathroom doesn't get incredibly cold in the winter. I have a pitched roof without insulation in another part of the house and compared to that the bathroom is balmy. However, it would also be good to actually confirm the nature of the insulation, so perhaps something else to lean towards taking the whole ceiling down.

It will give you access to properly insulate the ceiling, because chances are the sloping part, at least, won't be. INSULATE! The simplest way is to use insulated plasterboard, which is fitted straight on as easily as normal p'board. However, it'll lower your ceiling by the amount of the insulation layer, and you should be looking at 2" as a min. A better way, then, would be to fit - say - a 2" layer of rigid insulation board in between the joists/rafters, and then overboard with 1" insulated p'board. More work in neatly cutting the Celotex-type stuff to fit neatly and tightly between the timbers, tho'.

Ceilings would need 150mm (6" in old money) of Celotex/Kingspan or 300mm of fibreglass/rockwool to hit current recommended u-values. This may not be possible, so one should aim for the best possible.

ThisIsWeird

FreeBear said:

ThisIsWeird said:

It will give you access to properly insulate the ceiling, because chances are the sloping part, at least, won't be. INSULATE! The simplest way is to use insulated plasterboard, which is fitted straight on as easily as normal p'board. However, it'll lower your ceiling by the amount of the insulation layer, and you should be looking at 2" as a min. A better way, then, would be to fit - say - a 2" layer of rigid insulation board in between the joists/rafters, and then overboard with 1" insulated p'board. More work in neatly cutting the Celotex-type stuff to fit neatly and tightly between the timbers, tho'.

Ceilings would need 150mm (6" in old money) of Celotex/Kingspan or 300mm of fibreglass/rockwool to hit current recommended u-values. This may not be possible, so one should aim for the best possible.

6" ma botty.

Yes, if you can stuff 6" in between yer rafters, then good for you. The chances are pretty remote, tho'. So, that means adding part of this insulation layer to your reduced ceiling height. Again, if you can do this, then great - and do so.

I'm talking practicalities. If you can get 4" in there, one way or t'other, then nice result already. You will not detect any additional saving going 6" in your annual energy bills, or comfort.

When building from scratch, then - yes - stuff the place FULL of insulation; design it in from the beginning. When retro-ing, you may need to compromise.

hatt55

Thanks both. Some really useful information here and certainly points me in the direction of just replacing the ceiling. I don't think the existing once is lath and plaster so it may be a tidier job. I'm really beginning to understand how doing one thing means that you should probably think about doing 5 other things at the same time. Good for avoiding disruption but a little bit harder on the budget!

And yes, I did mean an extractor fan. Would this go directly above the shower?

Finally, are there any considerations in terms of ensuring there is good airflow to the timbers etc. when installing insulation? I've been doing a lot of reading about making sure the house can 'breath'. The roof was re-tiled about 10 years ago so it has a fairly new membrane. Would I need to ensure that there is a gap between any insulation material and the joists?

FreeBear

hatt55 said: The roof was re-tiled about 10 years ago so it has a fairly new membrane. Would I need to ensure that there is a gap between any insulation material and the joists?

You need to leave a gap between any insulation and the roofing felt/membrane - 50mm is usually enough to allow for airflow.

ThisIsWeird

hatt55 said:

And yes, I did mean an extractor fan. Would this go directly above the shower?
Finally, are there any considerations in terms of ensuring there is good airflow to the timbers etc. when installing insulation? I've been doing a lot of reading about making sure the house can 'breath'. The roof was re-tiled about 10 years ago so it has a fairly new membrane. Would I need to ensure that there is a gap between any insulation material and the joists?

Yes, adequate air flow is required as you say. Once the old ceiling is down, you'll see what depth the sloping roof rafters are, and the ceiling joists (trying to be technically correct as 'rafters' make up the roof construction, whereas 'joists' make up floors and ceilings.)
If the ceiling joists have a loft void above them, them you can completely fill the space between them with insulation - there will be plenty of ventilation in that space above. So by all means stuff around 4" of Celotex tightly in there, flush with the bottom edges of the timbers. Fill any gaps with spray foam. Or, can you get above this part after the new ceiling is in place? If so, then normal 'loft' insulation will be cheaper and easier to add afterwards.
The sloping section is the bit where you need to take care, as the space between the sloping ceiling and the roof will be limited to the actual thickness of the rafters. So, allow a good 50mm between the insulation and the under tiles for a good draught to sweep up to the apex and keep that dry. Fit whatever Celotex thickness you then can, and consider over boarding it all with insulted plasterboard for the ceiling. 
Do you have a dwarf wall in your bathroom under that sloping part? Can you get to behind this via an eaves space, for instance?

Yes, I'd fit the extractor vent above the shower - remove the damaging steam at source. 

FreeBear

ThisIsWeird said: Yes, I'd fit the extractor vent above the shower - remove the damaging steam at source. 

But do make sure you can get to it easily from the loft space should it ever need servicing. And use rigid ducting rather than that flexible concertina stuff. Airflow is better, and it is easier to support without sags developing. So no pools of water developing where mould & bacteria can breed.