Vaulted ceiling problem!

[martin88]

Hi,

made the mistake of not under boarding my rafters with foil insulation or adding a polythene VCL.

I have 150mm foiled back insulation in between rafters only and 15mm wallboard screwed to the rafters, now the weather has turned I’m getting isolated condensation spotting (which is really annoying!)

due to the room (being a kitchen) is full fitted out my only options to sort I think are

1. overboard with a 37.5mm insulated plasterboard and re skim.

or

2. Try and find a Vcl type proven paint.

i Don’t really want to remove the existing plasterboard due to the size of the room and the mess in a finished kitchen

anyone got any other ideas to help me please

thanks

 

[Notch7]

Do you have underfloor heating as your primary heat source?
I ask as radiators generally create sufficient conducted heat that the ceiling is warm.




Do you use your cooker hood whenever using the hob?
Do you get condensation on windows?


Your problem is thermal bridging, VCL is irrelevant in regards to visible condensation.

the solution is insulation, insulated plasterboard would work, as would PIR insulation and then plasterboard: which can be better as the joints can be staggered.

 

[martin88]

Thanks for the reply.
If I’m being honest, we do use the extractor but it is not vented outside only a carbon. Filter ( job I never got round too!) the kitchen is floor area 32m2 with 3nr 660 x 1180 roof lights which two are on constant vent.

The room is heated via two double radiators

The ceiling doesn’t Have condensation on the face, I think the warm moist air is passing through the plasterboard and condensating on the felt then building up and running down the foil insulation (within rafter) and coming through a joint (not foil taped either)

Appreciate I’ve probably done everything in this build up wrong, this is why I need to address as it’s so frustrating.

Thanks

 

[robinbanks]

Overboard with as thick an insulation as you can find fixings for

And sort out something to deal with the fact that this room potentially generates more moisture than anywhere else in the house bar the bathroom; heat recovering extractor fan for example

 

[martin88]

I was just going to overboard it with an insulated backed plasterboard over the top of the existing skimmed ceiling.

I wonder if I need to polythene the ceiling (VCL) before putting the insulated plasterboard up.

 

[noseall]

I was just going to overboard it with an insulated backed plasterboard over the top of the existing skimmed ceiling.

I wonder if I need to polythene the ceiling (VCL) before putting the insulated plasterboard up.

ALWAYS fit insulation across as well as between. Then robustly foil tape all joints and fill those bigger gaps* with foam first. I can't emphasise enough the importance of a robust VCL in vaulted, vented roofs - especially those in kitchens and bathrooms.

*Note the foam around the edges in the first image.

Vaulty2

• noseall
• 15 May 2022

Vaulty1

• noseall
• 15 May 2022

Foil2

• noseall
• 2 Apr 2019

Foil3

• noseall
• 2 Apr 2019

 

[robinbanks]

I'm not sure I'd bother if the insulated board is well fitted and sealed together, but it's little harm or cost, so it may help you sleep at night!

I found that 2 parts spray foams work much better than expanding foams for joining PIR sheets - https://www.abbuildingproducts.co.uk/expanding-foam-insulation.html

 

[noseall]

Also note (in both jobs above) provision was made for (heavy) light fittings with timber nogg's brought through the insulation layer - and taped of course. Nowt worse than an irate electrician hunting for a fixing point!

 

[martin88]

Wish I knew what I do now… mine was no where near as good as yours unfortunately.

I just don’t want to spend all this money and miss anything and have the same problem!

 

[^woody^]

Or overboard with a foil backed plasterboard if height is tight.

But do you have a vented air void above the insulation. Is the venting adequate or can it be improved?

 

[noseall]

Wish I knew what I do now…

I have become more and more obsessed over the years in my battles with condensation and the like. I learned the hard way too. My formative years were spent fitting 100mm glass wool insulation into flat roofs.

 

[robinbanks]

Erk.. All that work and no extract for moisture!

 

[martin88]

Yeah This going to be an expensive mistake, but would rather just fork out now and not have to worry every winter!!

Woody, I have 10mm over fascia vent and a 25mm gap between insulation and roof membrane, there is a draught, but clearly due to my poor understanding there is too much vapour getting in, also my cold bridge on the timber as no insulation under the rafter.

 

[martin88]

Robinsbank…. I can’t see this being the main problem… appreciate will defo be contributing too my problem

 

[noseall]

If I’m being honest, we do use the extractor but it is not vented outside only a carbon.

Schoolboy error for a kitchen. How on earth did you get that passed Building control? Or has it not been signed off? Or inspected?