Insulating between joists

[RonnyRaygun]

I moved into my house just over a year ago and the loft currently has just 4" of glass fibre insulation between the ceiling joists. Over the top of the joists sit chip board loft boards.

I am trying to insulate the house as much as possible as my other half really feels the cold! I've already stuck 100mm kingspan between the joists at ground floor level. Unfortunately the walls are solid and therefore very difficult to insulate.

I want to use something that will give a U-value equivalent to that of the current reg of 270mm of glass fibre, while retaining the loft boards to keep usable storage space in the attic (I work as a structural engineer and while I am very aware that attic joists are not designed to carry high storage loads, I have done a calculation and surprisingly I could stand a 10 stone person on every square metre of the attic without over stressing the joists - an absolute maximum and not recommended!).

Anyway, I have seen layered foil products that supposedly give an equivalent U-value, but have only seen it used between rafters. The same goes for Kingspan and the like. However, it seems illogical to me to allow heat to rise into the attic space if it can be halted at ceiling level.

I have also read that one must be careful when insulating near electrical cables due to overheating issues. As my lighting circuit runs between the joists in places what can be done to overcome this?

Thanks for any advice.

 

[PaulJR]

The foil multi layer stuff is intended to underdraw the roof pitch, not really any use to you.

Why not lay kingspan over the joists - 100mm would get you very close to the U value, (you can do the calc's as easily as I can) and use the chipbord laid over that to provide a walkway. The PUR is plenty strong enough for storage.