Vaulted ceiling & Insulation

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redbiro

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I'm at the design stage for our two storey self build and I'm considering having a vaulted ceiling in the master bedroom (maybe partially exposed beams?) and standard attic for the rest of the first floor. I'm concerned about insulation and was wondering if anyone could offer any advice especially as regards potential pit falls
 
assuming 150 rafters...
id install 100mm polyiso or phenolic foam cut to suit between rafters with any gaps filled with canned spray foam insulation,....
this affords you the retention of 50mm venitilation gap.

again, if you have the budget, i would continue and slab the roof with insulation backed plasterboard (40mm).....
 
You won't be able to fit the amount of insulation you need into the rafters to meet U-Value requirements, with a 50mm gap if you want exposed beams.
 
There is a specific detailing for this which needs to be strictly adhered to or you will be looking at a lot of trouble with condensation and/or heat loss. Get your architect to supply the detail or pass your plan on to the technical people of one of the reputable insulation firms and they will get you sorted out.

The actual construction and insulating needs to be carefully done and it is essential that you have someone there to keep an eye on things.
 
Get a BRE U-Value calculation done by an insulation company.
 
in the construction ive described above, the exposed beams would be located below the roof construction, and be purely decorative......

in my experience, prefabricated structural enginnered decorative beams are awkward to detail into eaves when your switching from a tradition build.. (like whats described above)....
 
Regardless of what you do, you will need to satisfy U-Value requirements.
 
There are 2 options that I know of:

1. Insulate between the rafters. In this case the depth of the rafters will determine the thickness of the insulation. The performance of the roof will be determined by the depth and type of insulation used. I would recommend 200mm rafters with e.g. rockwool. You won't have the rafters exposed, but could if you wished put on additional rafters below the ceiling for cosmetic purposes (I wouldn't be a fan of this).

2. Insulate above the rafters, in this case you would have to build a deck above the rafters (e.g. could be plasterboard then OSB, or could be exposed T&G timber depending on how rustic you want it to look). In this case the thickness of insulation is not limited by the thickness of the rafters. The insulation should then be foil back rigid insultation. I think this is the better solution if you want exposed beams, the one downside of this is you end up with a very thick roof build up overall which may affect your ridge height, eaves detailing etc.

As outlined by Nutty Nut above you will have to be careful with your vapour barrier to avoid condensation. Also with both options it is hard (but not impossible) to put in downlighters, so maybe you should take that into consideration.

J2K
 
hi redbiro

we have just done this in our sitting room of our new build. We put in 9x2 ins rafters and got breathable felt put on the roof. We then put 10ins of rockwool insulation into the space between the rafters and attached insulated plasterboard to the roof. we have exposed beams under the plasterboard

regards nb
 
newbuild,

youve described how it shouldnt be done.....
your 10 inches of rockwool prevent any ventilation of the roof space, condensation and water vapour cannot be removed, which will eventually lead to rot.....
 
hi sydthebeat

your right mate wrong measurements on my behalf (blonde moment). We put in 150 mm (6ins) of insulation not 250mm (10ins) and then put an airtight membrane with 40mm of insulated plasterboard on
sitting room feels prety warm already which is good.
 
my only fear with that newbuild is whether 150mm of whatever insulation you have incorporated meets the building regs.....
 
yea that was one of our orignal fears but the engineer reckons with the insulated plasterboard we are ok.
its a very hard one to call as most rafters are only 5 x 2 or 7 x 2 so that leaves very liitle for insulation unless you fork out and get rigid boards and then cut them to size, unless there is some other way that i might not have though of.
 
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