Insulating Problem - Workshop roof with crossmember

[meb97me]

could someone be so very kind as to give me some pointers with regards to insulating my timber workshop roof.

The roof will be covered with felt shingles and i'd like to use rockwool to insulate due to the size and cost.

The problem i'm trying to get to grips with is that the roof truss has a crossmember going across it so it makes boarding all the way up to the ridge very difficult i'm therefore not entely sure what to do as it introduces a large oid between it and the ridge.

I've drawn a little diagram of my musings so far

but hopefully someone with a better idea can point me in the right direction.

Also the other thing i've not included ion my diagram are the cross battens that would run parallel to the rafters holding the rockwool in place but also providing an air gap between theinsulation and the vapour barrier/plylining.

The other issue as is see it is that as the battens run the length of the building the ventilation in the soffits would have to be on the front and back of the roof rather than on the sides as other wise the air wouldn't be able to circulate, is that correct? this may cause a proble as there aren't really any soffits on the front or back of the building

thanks in advance for all your help

 

[Regencyroofingipswich]

You could ditch the rockwool and go with a multi- foil insulation such as actis which is nailed on top of the rafters or i believe it can also be nailed onto the back of the rafters in some applications.

http://www.insulation-actis.com/home.php?p=3&l=3

 

[meb97me]

due to the size of the roof (large 10m x 3m) and that its only going to be used occasionally(evenings & weekends) i don't want to spend an absolute fortune on the expensive foam insulation.

because i'm using felt shingles i have to have them attached directly to the roof boards rather than across battens otherwise they will sag. I guess my question is whether i can fit rockwool between the rafters directly under the roof boards and felt shngles, cross batten the underside of the rafters to hold the rockwool in place and provide an air circulation gap on the inside across the rafters and then ply board over the battens with a polyethene vapour barrier between the ply and the battens. The airgap between the insulation and the vapour barrier/plyboard can be ventilated to the outside via the gaps in the eaves.

the main differnece being that the air gap in on the building side rather than the sky side of the insulation

will that work?

thanks for any help

 

[big-all]

leave the space open the roof void is so handy for storing stuff
http://s21.photobucket.com/albums/b270/bigall2005/?action=view&current=workshop007.jpg