Hi all
Sorry or butting in on your thread but I'm now at the stage when it is time for me to decide what to do regarding the roof insulation.
For background purposes, I am having a 6m x 6m single story extension. The joists will be 9"x3" The firings will be 140mm down to 1mm which is a drop of approximately 1:45. This can be reduced if necessary (maybe 80mm down to 1mm)
The joists are going from left to right on my extension but the firings are going in the other direction. Unfortunately I cannot budge from this.
I live in NW London.
If there are any other questions you'd like to ask me to be able to come up with a more precise answer, please do ask.
So, before reading this thread I was all ready to go out and but some XR4120 insulation and sandwich it between some 18,22 or 25mm plywood. I thought that the foil underside of the insulation would act as a Vapour Control Layer.
Then I thought I'd get some TD4126 and not have any plywood on top and lay the EDPM directly onto the ply of the TD4126.
After reading this thread I thought I'd go with the option of using TD4126........that was until I looked up the price of the Insofast!!!!!
If I'm right in thinking, they are about £1 per screw. That is VERY expensive (for a screw). I will need about 14 sheets of TD4126 so this will increase the cost of the roof by about £170 (after I've damaged a few!!!)
What I'm really not sure about is the benefit of using TD4126 when I've got to put 12mm ply on top whatever. Would I not be better using XR4120 instead and then maybe (to be extra safe) put 22mm ply on instead?
I'm also not very understaning of the 'top cap' part of the roof.
I'm sorry for appearing stupid but I'm totally new to all of this so please don't bite my head off!!
Sorry or butting in on your thread but I'm now at the stage when it is time for me to decide what to do regarding the roof insulation.
For background purposes, I am having a 6m x 6m single story extension. The joists will be 9"x3" The firings will be 140mm down to 1mm which is a drop of approximately 1:45. This can be reduced if necessary (maybe 80mm down to 1mm)
The joists are going from left to right on my extension but the firings are going in the other direction. Unfortunately I cannot budge from this.
I live in NW London.
If there are any other questions you'd like to ask me to be able to come up with a more precise answer, please do ask.
So, before reading this thread I was all ready to go out and but some XR4120 insulation and sandwich it between some 18,22 or 25mm plywood. I thought that the foil underside of the insulation would act as a Vapour Control Layer.
Then I thought I'd get some TD4126 and not have any plywood on top and lay the EDPM directly onto the ply of the TD4126.
After reading this thread I thought I'd go with the option of using TD4126........that was until I looked up the price of the Insofast!!!!!
If I'm right in thinking, they are about £1 per screw. That is VERY expensive (for a screw). I will need about 14 sheets of TD4126 so this will increase the cost of the roof by about £170 (after I've damaged a few!!!)
What I'm really not sure about is the benefit of using TD4126 when I've got to put 12mm ply on top whatever. Would I not be better using XR4120 instead and then maybe (to be extra safe) put 22mm ply on instead?
I'm also not very understaning of the 'top cap' part of the roof.
I'm sorry for appearing stupid but I'm totally new to all of this so please don't bite my head off!!