insulating a flat roof ceiling ??

[paulyoung666]

put the insulation between the joists or at 90 degress to it , i have space and to do either , just wondering what would be the best way , i was thinking at 90 degrees to the joists but am i right :yikes:

 

[Alan.P]

Nah Paul, go with the joist, easier that way, make some form of wedge, wood / plastic ..other to keep it up, bobs ya uncle.

 

[paulyoung666]

would it be considered wrong to go the other way though ?

 

[mikethetile]

No it wouldnt , sometimes its easier to keep them up as gravity doesnt take over

its not done like that because its time consuming cutting each bit to length

 

[Alan.P]

No it wouldnt , sometimes its easier to keep them up as gravity doesnt take over

its not done like that because its time consuming cutting each bit to length

Exactly, not wrong just time, it might be easier for you that way if your working on your own, then wedge them in, otherwise, some sort of retainer might be needed.

 

[Ajax123]

I just got some advice on this from building control. They said if it is unvented then go in between the joists but leave an air gap then place a vapour barrier on the warm side before plasterboarding (or what ever)

If it is a vented roof then there are actually regs covering the size of air gap and the depth of insulation and you would probably have to go with a rigid board insulation rather than a mineral wool. You still go with the joists. For added insulation I was told to place a further 25mm of polyurethane (cellotex) board on the underside of the joists. Tape the joints and this acts as the vapour barrier. The plasterboard as normal.

I of course am ignoring all of this advice and doing my own thing.........

 

[paulyoung666]

the reason i was thinking of going across the joists is that the rolls of insulation are in a bag to avoid all the nastiness associated with fibreglass and they are 5 metre rolls , the room is 5 metres long ...............

 

[Alan.P]

the reason i was thinking of going across the joists is that the rolls of insulation are in a bag to avoid all the nastiness associated with fibreglass and they are 5 metre rolls , the room is 5 metres long ...............

Lost me there Paul, are you saying ypu want to follow inbetween the joists ie follow the full 5 m with the 5m roll or cut into strips of 300mm +/- ?

 

[paulyoung666]

Lost me there Paul, are you saying ypu want to follow inbetween the joists ie follow the full 5 m with the 5m roll or cut into strips of 300mm +/- ?

it is joisted narrow , i want to use the 5 metre roll across the joists along the length of the room if that makes sense :lol:

 

[mikethetile]

the insulation needs to go between the joists otherwise you cant fix your boards to the underside of the joists