Advice on insulation under new flat rubber roof please :) pics added

sean oc · 22 Jul 2020

Hello,

Currently getting my conservatory windows lifted and a proper roof added on (well i say proper) Flat rubber roof. Its being tied into my utility room roof and all replaced with one big roof.

I am after advice as the room has quite a lot of glass so i could want to insulate the roof and roof as best possible.

I am tempted to redo plasterboard the walls with insulated plasterboard were i can.

The utility room already has wool type insulation in it already as you can see in one of the pics

I am after advice on how insulating the roof before i plaster board the ceiling, what's my best bet? they joists are 90mm deep? can i fill the void totally insulation slab at 90mm or am i best with something smaller and leaving an air gap and then just plaster board ceiling.

Any advice will be appreciated

Thanks

Mw Roofline · 24 Jul 2020

With insulation, plaster, OSB, rubber and a few inches of snow that roof is gonna sag like my 80 year old neighbours melons when she’s out doing the weeding. I know you’ve done good spacings but 6x2 would’ve been better. Perhaps someone else can comment as I’m not overly up to spec with these things as never done one. Perhaps I’m being cautious. Assume you reinforcing the windows.

JohnD · 24 Jul 2020

Load-bearing window frame.

frutbunn · 24 Jul 2020

I think I would be more concerned about the grossly undersized roof joists, they are going to be banana shaped!!!. I'm guessing you haven't applied for B Regs for a change of use either.

sean oc · 25 Jul 2020

Mw Roofline said:
With insulation, plaster, OSB, rubber and a few inches of snow that roof is gonna sag like my 80 year old neighbours melons when she’s out doing the weeding. I know you’ve done good spacings but 6x2 would’ve been better. Perhaps someone else can comment as I’m not overly up to spec with these things as never done one. Perhaps I’m being cautious. Assume you reinforcing the windows.

i duno, i left it to a long well established roofing company so thought they would know what they are doing

Do you think they will sag quickly? is there anything i can do now? rubber is all one. they have one more day to trim it up and they will be gone. not sure how they are going to build up from the window. Had a few companies look and alot of them said i i could of left windows one course of block down and just framed of the top and it would cause no issues. These guys built the brick pier to take some of load

sean oc · 25 Jul 2020

frutbunn said:
I think I would be more concerned about the grossly undersized roof joists, they are going to be banana shaped!!!. I'm guessing you haven't applied for B Regs for a change of use either.

no just leaving external door going into the room just extra space but not a proper room. i got in a well known roofing company so just trusted their judgement on what would work out.

Will it sag quickly? they added a brick to take the weight on the front they said? would i be better taking the window out and pilllars added on each side to take the weight? I had about 5 people look at the job and they all said the same it would be fine, one person even said just leave the window and timber frame of the top saying it will be able to support it no issues

sean oc · 25 Jul 2020

Could i add some bigger joists myself after or well get another roofing company to take a look and see if something can done maybe to strength in? Worried it will sag now as i did all this work to make it hassle free for as long as possible

I could see the joist timber is smaller than the one in the existing roof which is same span but i thought maybe its improved over the years or a stronger timber, is c24 marked.

Thanks

sxturbo · 25 Jul 2020

Double the joists bolt together if your worried about sagging

Also 50mm insulation required (from memory when I had my old roof done) but you also need to have an air gap.

If 6x2 was used it would have been easier

sean oc · 25 Jul 2020

sxturbo said:
Double the joists bolt together if your worried about sagging

Thanks for the reply, i may just do this once they have gone, hang ones side by side and then drill and stick some bolts through. reckon that will be the best soultion? rather than hanging some larger ones in-between

Just worried after paying out so much for it to be done(hoping for hassle free install and long ish life), got a roofing company hoping they know what they are doing!

frutbunn · 25 Jul 2020

What is their exact size, spacing and clear span and I will give a more detailed reply.
The work require B Regs, the existing building is an exempt building however, by virtue of the work being carried out it is a material change of use and now requires an app.
Regardless of B regs any reputable Co would have realised the joists are pretty useless.

frutbunn · 25 Jul 2020

sxturbo said:
Double the joists bolt together if your worried about sagging

Also 50mm insulation required (from memory when I had my old roof done) but you also need to have an air gap.

If 6x2 was used it would have been easier

Doubling up would be of limited benefit, they need to be deeper.
50mm!!! When was that 1983?

sean oc · 25 Jul 2020

frutbunn said:
What is their exact size, spacing and clear span and I will give a more detailed reply.
The work require B Regs, the existing building is an exempt building however, by virtue of the work being carried out it is a material change of use and now requires an app.
Regardless of B regs any reputable Co would have realised the joists are pretty useless.

Thanks so much

Span is 2.8m ish

Timber is 95mm x 45mm C24 and spaced approx 430mm apart

Yeah I got a company in which had good reviews etc, he brought some contractors he has working for him

sean oc · 25 Jul 2020

frutbunn said:
Doubling up would be of limited benefit, they need to be deeper.
50mm!!! When was that 1983?

So would I best with adding extra joist In between my current ones at large size? i know they cant be fixed to the board now the rubber is on but it will support the roof?

frutbunn · 25 Jul 2020

sean oc said:
So would I best with adding extra joist In between my current ones at large size? i know they cant be fixed to the board now the rubber is on but it will support the roof?

Even taking the lowest loading in Euro code 5 (TRADA) the max span is 1.75! Fixing a 145 x 47 alongside will be OK.

noseall · 25 Jul 2020

sean oc said:
Timber is 95mm x 45mm C24 and spaced approx 430mm apart

Yeah I got a company in which had good reviews etc, he brought some contractors he has working for him

Too lean by at least two increments - i.e. should have been 6" instead of 4".

I hope that slender pier on the right, is not going to be doing all the work of holding up the roof and resisting racking and restraint, surely?

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Advice on insulation under new flat rubber roof please :) pics added

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