Insulating roof space - Help needed!

[Seasal]

Last weekend I took down the ceiling in the box room as a) it was in a really bad way, and b) it's the coldest room in the house so thought it would be a good idea to insulate it. (There previously wasn't any insulation in the roof space above the ceiling).

Now I've taken down the ceiling I'm scratching my head as to what to do next. I've got three problems which I need advice on -

1) The rafters are shallow - only 9cm deep. What's the best way to insulate between/under these? Best products?
2) One of the rafters is in a bad way - looks like it's rotted away. (We had the roof replaced 3 years ago, so I'm assuming it rotted like this before we had the new roof put on). It's dry to touch. What do I do to sort this rafter?
3) I've attached photos for this one (well, hopefully, if I've done correctly!)... I've discovered that one of the walls (external) is only bricked up to below the ceiling joists. Above that it's all held up with timber and plaster by the looks of it. Again, what's the best thing to do with this? I expected it to be all brick, right up to the top, so I was a bit surprised to find it wasn't.

Apologies if I should have put my 3 questions in 3 different threads (I'm new to this!!) Any help or advice you can give me these 3 issues would be greatly appreciated!

Thanks!

 

[Doggit]

Add another rafter alongside the rotted one, and bolt it in where you can. It should have been replaced when the roof was redone, but you can only do you're best now to rectify it.

Although the vertical wall isn't brick, if there are no other issue, then don't worry about it.

You can roll 170mm of loft insulation over the ceiling joists, and then put 75mm of celotex between the joists before you reboard the ceiling.

 

[Seasal]

Thanks Doggit! You've put my mind at rest about the vertical wall!

 

[foxhole]

I would recommend minimum 400mm of insulation.

 

[Doggit]

Why so much foxhole, current regs say 270 of rockwool, and I suspect 400 would start to compress, so not be so effective. I wonder what the optimum level is.

 

[foxhole]

I put in 270mm in my two storey conversion but building control insisted it be increased to 400 mm.

 

[foxhole]

My brother in law house was built with over 500mm of insulation . It has not compressed , makes working in the loft a nightmare.

 

[Doggit]

I would have referred the BCO to current regs, and asked him to justify his request, but they do seem to be a law unto themselves a times.

 

[foxhole]

I would have referred the BCO to current regs, and asked him to justify his request, but they do seem to be a law unto themselves a times.

Yes, but regs are minimum required, the whole property design should be taken into consideration when assessing insulation, if you have large areas of glass then more insulation is wise to compensate the excess loss of heat.

 

[Doggit]

Fair enough foxhole, I can see where you're coming from now. Thanks for the explanation.