Loft assistance

[AndersonC]

I've a rather complicated job on at the moment of sorting out the loft.

I've searched through many posts here and there appears to be different schools of thought on things. I'll keep my questions as simple as possible.

First of all the back pointing from the roof is falling off resulting in the lost being a right mess. I intend to prevent this falling into the loft by fixing plasterboard to the rafters. Does normal plasterboard suffice for this job or are there benefits in using foil backed/thermal type boards? Is 9.5mm OK or would 12.5mm be better?

Secondly I would like to improve the insulation from it's current bedraggled state. I have not decided whether it is worth binning the current insulation - it is truly ruined and full of dust from the back-pointing. I pondered the use of kingspan etc to insulate at rafter level but decided against as I'm not bothered about the loft itself being warm. The intention is to get about 150mm of insulation on the loft floor with no insulation between rafters. Do I need to start considering vapour barriers? Is it worth the effort and mess removing the old insulation to clean the place up? Or just go over it?

I also intend to board part of the floor to store suitcases and Xmas decs. In order to meet my desired depth of insulation I need to raise the height of some of the ceiling joists from 3" to 6". If I do this then which way do I lay the new timbers? There appear to be two schools of thought here:-
1. Lay them on top as the existing joists are supported at their ends and thus support the weight of the new ones
2. Lay them perpendicular which can improve the overall 'strength' of the ceiling joist set up, however they would not be supported at their ends.

The last thing I have to tackle is the wiring - currently there is 1.5mm T&E for the lights tacked on the old ceiling joists with insufficient 'play' to enable it to be lifted over the new insulation, it would therefore be insulated over. For 100W bulbs in the lights is this an issue?

Sorry for the long questions but I am in some confusion over what I've read on this forum so far.

Thanks

 

[JohnD]

1.5mm T&E is rated at 20Amps single phase clipped direct. If buried in insulation you halve it to 10A max. This is still below the 6A fuse/MCB that (should) be on the lighting circuit.

If you have rewirable fuses it comes down again to 7.25Amps which is still OK.

However if the loft gets hot you have to down-rate it again. However if it is touching the ceiling, with the insulation over the top of it, it won't be so hot.

Does anyone know what the heat rating should be for Method 15?

edited to add: If you have an Immersion Heater or Electric Shower cable up there, it will be running nearer its max rating already, so you will need to calculate and probably move or replace it.

 

[AndersonC]

John

Thanks for the wiring tips, the light circuit is indeed on a 6A RCD.

I don't have any other wiring in the loft other than lighting and have no plans to have an electric shower.

What I am considering now, is putting 170mm insulation between the ceiling joists and moving the wiring so it sits on top of the joists where possible to prevent it being covered by insulation. Obviously in the area which is boarded this is not an option however I guess something like 80% of the lighting wiring in the loft would not be covered over by insulation.