Roof insulation request for options

sas

Have 225mm rafters on garage.

Garage is 1.5 storey so the roof insulation line starts at wall plate,
- travels about 1/3 -> 1/2 up the length of the rafter
- turns to run along the flat of the ceiling
- turns back down the rafterline on the far side and runs to the wall plate.

I want to pump the rafters with cellulose.

This means I need some sort of rigid board outside the rafters to prevent the cellulose bulging the roof felt.

The roof is approx 100m2. I'm looking at approx 1k for 22mm softboard which is a little steep.
OSB wouldn't be alot cheaper and wouldn't be as breathable.

Garage may become a living space should we find ourselves in need of a granny falt etc down the line. No expectation of this but don't know what future holds and alot cheaper to do certain jobs now than
try and solve later. At the moment it's being pegged as a gym and I don't like the idea of my treadmill being cold along with it being covered in dust and lonely!

Any suggestions on cheaper alternatives?

Dabzarch

sas,

Have you considered looking at something like <SNIP>. I'm not fully up to speed with the product but i have heard good things about it.

It's thermal conductivity is very good 0.05Wm/K in comparison with OSB 0.13Wm/K.

In terms of breathability the spec document claims <SNIP> to be '...up to ten times more permeable than most other sheathing materials'.

worth a look...

Poor Uncle Tom

Please keep any specific product recommendations to PM, thank you.

Viking House

sas wrote: »

I need some sort of rigid board outside the rafters to prevent the cellulose bulging the roof felt.

Put latts between the slate latts to stop the membrane bulging! Are you cross battening?

sas

Viking House wrote: »

Put latts between the slate latts to stop the membrane bulging! Are you cross battening?

Not sure I follow.

Yes, both roofs will be counter battened and battened.

Viking House

First put on the membrane a bit loose and tape the joints, then put on the latts directly on top of the rafters, then put a loose lat in between each rafter on the membrane. Then put on the perpendicular cross battens. The loose latt will stop the membrane bulging.

Viking House

You could also use water pipes to do the same thing and use it as a low grade solar collector.