Repairing/Replacing my Pitched Ceiling Information, help and advice on many architecture, self build and design problems and issues

[DIY_Luke]

Hi there!

My House
I recently moved house and am making so many improvements and giving the place a bit of love.
I now live in a three-story townhouse in Canterbury and plan to convert one of the rooms on the top floor into a small office.

Ceiling Damage
The ceiling has some patches of staining and old mould on the right-hand side due to water damage. I'm not sure what caused it, whether it was damp or a leak, but there certainly seems to be no sign that the problem remains (there's no dampness in the room, and after a couple of periods of relatively heavy rain, no sign of any leaks).

The Ceiling Construction
The ceiling is attached to the rafters on the underside of the pitched roof.
I've pulled away a piece of the ceiling, and from what I can see it was insulated with polystyrene.
On top of the polystyrene, and under the plasterboard, is a layer of silver sheeting, presumably the moisture barrier and added insulation.

The Photo
You'll see some patches where there has been damp, which it seems the previous owners painted over. So far it seems as though there's no longer a damp issue, but any further advice for assurance is welcome!
The big patch of missing mortar on the wall - This is where the mortar crumbled due to the previous water damage. I removed all of the damaged mortar until I reached a line where the mortar was stable and intact.
The big chunk of plasterboard that is missing is what I pulled out to see what was underneath! Also, you obviously can't tell this from the photos, but there seems to be a small draft. Worth noting! Not sure if this was deliberate to enable the roof to breathe, or maybe this is what originally caused the issue. Not my area of expertise either!


What i'm Thinking of Doing
As it's a small room, i'm thinking the easiest thing to do will be to just replace the ceiling. I'm even considering replacing the insulation with something more efficient than the polystyrene with something more efficient, pending advice.
I'd love to do this myself, and hopefully, with a bit of support, advice and guidance, I can do just that! I've never done a job like this before, but i'm aware it's important to get the layering and materials right so as to avoid future moisture problems.

I was thinking of using something like Rockwall, layered with a silver moisture barrier (similar to what is on there already, but needs replacing), and then plasterboard on top.

What are your thoughts and recommendations? Will this be efficient? and What else do I need to consider?

Thanks in advance for your time and support!

Luke

[stoneyboy]

Hi diy_luke,
Because of the location of the damp area it is more likely to be condensation, especially if it’s a north facing roof.
If you are going to replace the ceiling check that the roof is ventilated - if not install some. Fit PIR insulation between the rafters leaving a ventilation gap above it, fit further PIR below and over the rafters and then your plasterboard.
Avoid Rockwool and expanded polystyrene products because of their much higher thermal conductivity.
Regards S

[DIY_Luke]

Hi S,

Thanks for your reply, and for your advice!

I did a bit of investigating yesterday and took a photo from the loft. There is also a small gap at the back of the polystyrene, but that's no good if there aren't any vents providing ventilation! (Which i'm assuming there isn't given the condensation, but yet to investigate and confirm).

It's interesting though that when I first opened the ceiling, there was a bit of a draft running along the bottom, where that red metal join is in the photo I uploaded in my first message. This isn't efficient enough to air out the insulation, especially if it's only running along the bottom.

How much of a gap should be behind the polystyrene?

Also, i'm considering sourcing some second-hand Kingspan and using that instead of the polystyrene, but should I bother?

[DIY_Luke]

Okay, so some additional information that might be useful:

I had a look and it seems there is some ventilation along the soffit. However...

It's probably worth noting that I live in a semi-detached townhouse, and the wall and ceiling in my photos is the valley where mine and my neighbours' roofs join. I don't imagine the vents on the soffits would be sufficient enough to supply air to the valley, would they?

Looking at the roof from the ground I can't see any obvious sign of a louvre or vent pipe either.

[stoneyboy]

Hi diy_luke,
Thanks for the reply and further information.
If you have continuous soffit vents then the easiest way to provide high level vents is by fitting vent tiles into the loft area.
The gap you have between the under-slaters felt and the insulation should be OK.
I doubt it's worth swapping Kingspan for the expanded polystyrene, you could leave the EP in place and overboard with your Kingspan.
Regards, S

[DIY_Luke]

Hi S,

I understand, thank you for your guidance! As I continue my research I am feeling as though the lack of proper circulation is the issue.

I have no idea how easy the vents are to install, but i'm thinking of having an inspection done and then getting them fitted (if the need to be fitted through the roof i'm not sure I want to mess about getting up ladders and doing all that). At least then that side of the project is taken care of, leaving me to tidy things up, add the moisture barrier and then add the new plasterboard.
Thanks for the reply and further information.

I think overboard with the Kingspan is a great idea actually. If I do this, would it even be necessary to bother with a moisture barrier do you think?

Thanks,
Luke

[stoneyboy]

Hi diy_luke,
The kingspan should have an integral vapour barrier so seal the joins so this becomes a continuous barrier.
Regards S

[DIY_Luke]

Perfect, thanks for the guidance!

Warm regards,
Luke