Insulated drywall over existing drywall

LIS

Hi guys,
I have a converted attic room which is already drylined and plastered....there is no dampness but the room is cold.i discovered that there is no insulation over the ceiling(only foil backed board).
I know it is important to have airflow over the top so I'm wondering if it is a good idea to fit some insulated board over the existing drywall....the side walls are heavily insulated so I assume it's the ceiling that's making the room cold.....thanks in advance for any advice

TheLastMohican

If you can reduce the ceiling height by 6" you could fit 2" x 6" timbers to the existing ceiling joists, fit 6" thick insulation, reslab and skim. Or you may be able to get an R13 rating on a 2" x 4" rejoist.

LIS

TheLastMohican wrote: »

If you can reduce the ceiling height by 6" you could fit 2" x 6" timbers to the existing ceiling joists, fit 6" thick insulation, reslab and skim. Or you may be able to get an R13 rating on a 2" x 4" rejoist.

Would I have to re batt?.....could I not just go straight onto the existing board....the original boards are on battens & joists already.....thanks for your help

DublinDilbert

LIS wrote: »

Would I have to re batt?.....could I not just go straight onto the existing board....the original boards are on battens & joists already.....thanks for your help

Yes you could put 50mm insulated slab directly on top of the existing insulation.

Bit that seems like a lot of trouble. If it's a fairly standard attic conversion I would just get 50mm rigid insulation and push it between the rafters and also the dwarf walls. No need to re plaster then.

owen85

give ballytherm/ xtratherm/ isover a call. they should offer you some sound advice. id be careful what advice you'd get here, rotten roof joists and a collapsed roof wouldn't be so much fun.

i'd call isover

LIS

owen85 wrote: »

give ballytherm/ xtratherm/ isover a call. they should offer you some sound advice. id be careful what advice you'd get here, rotten roof joists and a collapsed roof wouldn't be so much fun.

i'd call isover

Thanks for your reply,rotten roof isn't a problem as the original ceiling was fitted to the rafters leaving at least 6 inches of a gap,my question was that instead of insulating the gap could I just stick another layer from the inside which would still maintain the existing gap.would it be a waste of time?

owen85

Hi Lis, I understood your thought from the beginning but I would still call one of the above. my reason for saying this is that if you insulate the attic, the room side will be warm, the cavity between the roof will stay cold if you do it the way you have said. if there are air leaks between the insulation etc condensation could occur in the cavity causing damp, mould and/or rot.

i am not in expert in this and and this is why i suggest you call isover etc...its the price of a phone call and you wont waste time wondering which is the best idea suggested to you by one of us here. isover offered me some sound advice in the past and didnt push to sell their products, and sure if they suggest you use some of their products, tape etc, well you can chose if you want to buy it, either way you still will have some sound advice.

MicktheMan

LIS wrote: »

the side walls are heavily insulated so I assume it's the ceiling that's making the room cold...

I wouldn't assume this (especially in a converted attic).
Top tip: Investigate / research airtightness

Calahonda52

owen85 wrote: »

.... id be careful what advice you'd get here.....

Indeed, never a truer word, especially when you are plugging them not once but twice.:D

Op: the issue here is that the foil backed pb is vapour impermeable.

Adding on insulation on the warm side of such a layer is a no-no because the temp profile across the insulated being will bring the dewpoint inside the foil back, so the condensation will aciculate in the pb causing mould.

the proper practice is to try stop the moisture getting passed the warm side and cater for its quick movement through the buildup with ever decreasing vapour permeability.
The ACDs here http://www.environ.ie/en/TGD/ may helps as may this
https://www.nsai.ie/S-R-54-2014-Code-of-Practice.aspx

Describe the roof makeup from the roof tiles in.
Is it a dormer attic conversion?
do u have a solar gain issue in the summer?

LIS

Calahonda52 wrote: »

Indeed, never a truer word, especially when you are plugging them not once but twice.:D

Op: the issue here is that the foil backed pb is vapour impermeable.

Adding on insulation on the warm side of such a layer is a no-no because the temp profile across the insulated being will bring the dewpoint inside the foil back, so the condensation will aciculate in the pb causing mould.

the proper practice is to try stop the moisture getting passed the warm side and cater for its quick movement through the buildup with ever decreasing vapour permeability.
The ACDs here http://www.environ.ie/en/TGD/ may helps as may this
https://www.nsai.ie/S-R-54-2014-Code-of-Practice.aspx

Describe the roof makeup from the roof tiles in.
Is it a dormer attic conversion?
do u have a solar gain issue in the summer?

The roof is a double pitched tile roof built in the mid 60s with the black almost like cardboard felt,the one that crumbles if you crush it 😂
In the summer it's very warm which means the roof window is open a lot......might be based on your advice better to see if a pro could do something with the existing setup,thanks for your help

LIS

Thanks for all your advise,might just get a pro in to take a look ˜‚.....might be easier......anyone recommend someone in the co Clare area?

Sorry about all the double and even triple post,just discovered every time I click back it reposts

Calahonda52

OP: was the attic like the attached pre-conversion?

to address the solar gain u need to consider decrement delay as a performance factor of any insulation so standard eps or PIR or PUR just wont do it.
You may indeed need a pro, but one who knows what they are talking about as opposed to any old, or young pro.

LIS

Calahonda52 wrote: »

OP: was the attic like the attached pre-conversion?

to address the solar gain u need to consider decrement delay as a performance factor of any insulation so standard eps or PIR or PUR just wont do it.
You may indeed need a pro, but one who knows what they are talking about as opposed to any old, or young pro.

Don't really know,the conversion was done before I bought the house.from what I can see it is like that with drywall screwed to it.....there is like rockwool around the side walls held in with plastic but nothing on top only foil back board

Calahonda52

okay,
lets try again:
do you have the 3 surfaces marked 1, 2, 3 as shown in the attached:
i.e. do u have a knee wall (3) sloped bit (2) and flat bit (1)

LIS

Calahonda52 wrote: »

okay,
lets try again:
do you have the 3 surfaces marked 1, 2, 3 as shown in the attached:
i.e. do u have a knee wall (3) sloped bit (2) and flat bit (1)

Yes,exactly that....going by your scratch id say number 3(knee wall) insulated with rockwool with industrial plastic holding in against wall.number 4 has insulation on floor of crawl space.....no insulation on 1 or 2,only foil backed wall board.

Calahonda52

Is the insulation in No 4 on the floor or crawl space or between the joists?
Whats the eave construction, not shown in my sketch?
Is it ventilated?
The industrial plastic, if well fitted, will become an issue once u warm, and airtight the room as it is vapour impermeable and on the cold side of the construction,
if its poorly fitted then the kneel insulation is less effective.

I would research the issue of decrement delay for insulation on the sloped and flat ceiling, take off the existing pb and use p[art of the rafter space as per regs for insulation and then add more across the rafters and finish with whatever the supplier recommends: may not be pb skimmed.

What height is the ceiling from floor?
does the room comply with the habitable room regs?
Is it 2nd or 3rd floor, iff 3rd does it meet fire regs?