Epc

[meregirl]

We have recently installed solar panels. In order to get the grant we have to put more insulation in our loft. The loft is boarded out, joists removed and a window installed by the previous owner, and one day we intend to turn it into another room. Will we be able to insulate the roof with boards, to get the grant, or do we have to do the existing floor, which has 4 inches fibreglass under the floor boards.

[HansUrbancka]

I think you need to put the questions to your Local Authority, if that is where you will be applying for a grant.

Hans.

[The Builder]

I'm afraid I don't know how the grants work, but It certainly is possible to insulate the roof slopes.

If you intend to use it as a room one day, then that would definitely be the way to go.

[buildersmate]

The is a different question to the one you asked last Saturday, as your roof space has now apparently sprouted a former window, which you didn't mention before.
Sure, as TB says, you can insulate the sloping surfaces so as to make the enclosed roof space part of the "thermal element" of your house. You would have to do that to meet Building Regulations to be able to use the space as a habitable room.
The problem is getting enough insulation into the sloping void. You will almost certainly need half of the thickness of whatever fibreglass you were told to put over the boarding floor, but using rigid insulation board like Celotex. The reason for this is because the insulating properties of this board are 2x the performance of fibreglass. You may just have enough depth on the sloping depth of the timber trusses to do that.
However this solution will not be adequate if you converted the space into a room because the insulation already under the floor becomes useless as part of an external insulating shell around the warm house, if you have made the loft a part of that warm shell.
In that case you have to use a combination of rigid foam and multifoil insulation. This foil is very expensive but worth it for those doing loft conversions.
This is not a DIY job and you need paid for advice from someone who can survey onsite.
You certainty won't qualify for grants for this, it is a home improvement project.

[The Builder]

@ BM and Meregirl ..................

This is the one I use a lot .......... TLX Silver. Under rafter installation...

http://www.just-insulation.com/002-brands/tlx-silver-mult-foil-bba-certified.html

[buildersmate]

Boss - you may now be ahead of the game in knowing the latest on use of multifoils on their own to meet the necessary standard. There was a whole lot of controversy about six years ago because different types of test gave very different results. For a time, some Building Control departments would accept multifoil on its own, others only when combined with rigid foam abutting.
Is it your belief it is sorted out at a national level. The Secretary of State got involved.

[The Builder]

No universal sorting out yet BM, as far as I know. It's down to the discretion of the Building Inspector.

I happen to live and work "on the cusp" of two District Councils. In my village, Mid Devon District allow multifoil on its own, although I usually add loftroll for added insulation.

Half a mile down the road, East Devon don't allow it on its own. It has to be with either a special loftroll with a very high "R" value (very expensive too), or a huge thickness of ordinary roll, or Celotex.
The insulation values are extremely good though :o)

So there you are. They still haven't agreed on the results of the heat/flame tests completely, but they're getting there.