Vcl positioning within sloping ceiling

[James94]

Hi all, I have been using an online u value calculator to make sure the build up of my sloped ceiling won’t cause any issues with dew point/interstitial condensation. 
 

I plan to put intello plus across the rafters so that I can minimise puncturing it.

Does this look ok?

 

Thanks James 

[A_L]

42 minutes ago, James94 said:

Does this look ok?

 

It does look OK but I would prefer the Intello on the warm side of the 50mm PIR layer, much bigger difference between actual and saturated vapour pressures. Are not 25 x 50mm battens inadequate without fixing to something else?

[Iceverge]

I'd go plasterboard, service cavity, intello, PIR.

 

At lease then if it gets punctured you can see the damage and fix it. Staples and screw holes don't make any difference really. 

 

Better still I'd swap out the PIR between the rafters to dritherm or metac batts or best of all pumped cellulose. 

 

 

 

[Gus Potter]

Hello all.

 

It's worth having a chat with the builders, hopefully some pro's on BH can chip in.

 

While there are lots of different insulation options you can explore some are much more labour intensive to install and this comes at a price. Also, for the small domestic market.. to keep your tendering options open then perhaps you don't want to put off your "local builder" by introducing a system / something that requires for example; more complex fixings / more care to install, that needs a specialist tool to screw something in.

 

Remember that some of the insulation systems are primarily designed for large projects for installation by folk that are doing it day in and day out.

 

It's often more economic for small DIY / projects to go for the simple stupid option.. yes you may pay more for the insulation (need more thickness maybe) but this is often easily offset by the labour savings and the fact that you will get more local / small builders saying to themselves.. yes this looks pretty straight forward.. I know / am confident how much profit I'll make off this as I'm familiar with the product so the risk is reduced to myself, thus I won't add on an extra "hassle factor" to my price.

 

By all means if you are total DIY then have a go, but if you are going to get a contractor in then it's worth a thought.

 

 

 

 

 

 

[James94]

Thanks for your replies,

 

I am carrying out all of the work myself. The 150mm is already in.

 

I have siga twinet tape to stick the vcl to the rafters, That’s why i going to position it in between both layers of PIR.
 

11 hours ago, A_L said:

 

It does look OK but I would prefer the Intello on the warm side of the 50mm PIR layer, much bigger difference between actual and saturated vapour pressures. Are not 25 x 50mm battens inadequate without fixing to something else?

I was going to use 25x38 roofing laths screwed through the pir into the rafters.