insulating a concrete roof

[dyslexicwinker]

just started a wetroom and it is in an existing outhouse.

We have inserted joist hangers into the wall and then made the new ceiling. Can anyone see any probs with attaching celotex then plasterboard straight onto the joists?

I think we should have glued the insulation direct to existing so that i dont have to cut it for the lights etc but its done now! any solutions? or do you think that is ok? There is plenty of ventilation above the new joists



basically what i have is this with a bigger void and joist would be directly above insulation.

ta

ps i think the existing roof has fibreboard attached on the underneath? this has been left in place

 

[PrenticeBoyofDerry]

Looks fine, what vent gap have you.
So downlights, beware of the fire hazards, get fire rated ones, or fire hoods.
They get hot, and should be 150mm clearance between them and insulation.
Plus it's a wet room so need to be suitably IP rated too and notification is needed to install them as it is considered a special location.

 

[dyslexicwinker]

thanks for reply.

there is about 10 inches from existing to bottom of joist. ie bottom of new celotex insulation. have put 4 air bricks into area and there is also a extractor going in for wet area. plan was to have 4-6" hole in insulation then fit to plaster board but i thought that might comprimise the reason why i put the insulation up in the first place! If you tell me no then great!! the insulation is attached directly onto bottom of joists and plasterboard will go directly onto that. Am thinking of running led so they are "cold" but they seem bloody expensive!!!!

 

[dyslexicwinker]

im not very good explaining hopefully this helps??!?!?

 

[Blagard]

Am thinking of running led so they are "cold" but they seem bloody expensive!!!!

You will find the IP rated downlighters expensive to. PrenticeBoyofDerry mentioned the need for IP rated fittings. I am emphasing that point - It is absolutely essential that electrical fittings in such an environment are of the correct type. For further awareness see the link below
http://www.protectingpeople.co.uk/fire_tech/ip_explained.htm

 

[Deluks]

Do you only have 25mm celotex? have you not insulated between the joists as well?

Just to clarify. IP rated means suitable for use in 'wet' areas, bathrooms, outside etc. The higher the rating the more protection you get against moisture.

I don't think fire hoods or fire rated downlights are necessary in this situation, as you have a concrete roof and no rooms above. If they caught fire it will be unlikely to spread. However the need for airspace around any hot running lights or transformers is essential.

 

[Blagard]

..............Snipped

I don't think fire rated downlights are necessary in this situation

I have never heard of any fire ratings applying to light fittings. Is this something new?

Edit: Ah got it - Applies regarding integrity of fire rated ceilings. I must admit that one I was ignorant about.

 

[dyslexicwinker]

I have ip65 rated fire downlighters for each zone. The area is broken into 4 smaller area and for the sake of a few quid I just thought it would better to be safe than sorry. Only 25 mm celotex. Have had to bring ceiling height down from 2.4 to 2.1m so couldn't afford much more. There are 6 inch squares cut out the celotex where downlighters will go. Haven't filled in between it's not really practical for us. Have sealed the insulation at joints with duct tape. I'm hoping everything is ok with what we've done I'm sure it will be.

 

[noseall]

Any application whereby the insulation sits below the roof structure is deemed a 'cold roof' and will require adequate cross ventillation throughout the void layer or air gap.

Most scenarios shown by insulation manufacturers illustrate the 'warm roof' method whereby the insulation sits above the roof deck.

This is preferred for its simplicity and reliability regarding the problems associated with the dreaded condensation.

 

[dyslexicwinker]

Hi been trying to read up on that. It isnt possible for us to make a warm roof. Well it is but seems pointless and will be far too expensive for what we are doing. I know its not ideal but we have inserted 4 air bricks into the space and have a extractor in the wetroom area although as far from the shower as we can get it. Hopefully this will suffice but the space doesnt allow much flexibility. We didnt get condensation in the area before but i suppose with ch and ufh heating going in this could change??

ps we have cut 6" holes out the insulation but realise that this means the insulation has a hole in it but i cant see any other way of doing it! Thoughts?

ta

 

[noseall]

We didnt get condensation in the area before but i suppose with ch and ufh heating going in this could change??

Many people will have said the same thing before last winter!

Sometimes it is only when external temp's are very low that condensation issues become a problem. This forum was inundated with queries regards mould, water staining etc, all due to the extremely cold temperatures experienced last winter.

You have been warned!

 

[dyslexicwinker]

???? not sure what you're implying. Im tryign to solve a problem and want help. The room was there last winter but with no amenities. There was no condensation present. im wondering whether the fact i am installing ch and ufh and putting a "cold roof" in ( it was previously a cold roof also) then the risk of condensation increases or decreases?

 

[noseall]

???? not sure what you're implying. Im tryign to solve a problem and want help. The room was there last winter but with no amenities. There was no condensation present. im wondering whether the fact i am installing ch and ufh and putting a "cold roof" in ( it was previously a cold roof also) then the risk of condensation increases or decreases?

....and now you are turning into a wet room....?

Of course the risk of condensation increases.

 

[dyslexicwinker]

why? and how is any different from my loft? bathroom upstairs. No extractor plasterboard, ceiling joists and insulation with a large uninsulated roof? Just fail to see where the problems are arising? is it the fact that the roof is flat and if so why is this a problem?

ps i have foil either side of the insulation and using duct tape to seal joints etc. Will be using moisture plasterboard i assume this has a foil back aswell. anything else i could do. What would i seal the plasterboard joints with?

ta

 

[noseall]

A roof has a large air gap between it and the moist air, though this is no guarantee against condensation occurring on the underside of conventional roofing felt.

What you are proposing is filling a room full of moist air with an exposed concrete roof a a ceiling.

Think about it.....