Loft Insulation And Boarding Up

[Steve ( West Mids )]

I've just completed two thirds of my loft adding 8 inches over the top of the existing insulation ( special offer in B&Q ).

I've got the centre section to do which is part boarded, part water tanks and a small part insulated four inches to the joist tops. So a few questions to those in the know:

1). is it true you should not insulate under the tanks?

2). I've currently got four inches under the boarded area ( approx 14 foot by 9 foot minus the hatch ). If I want to increase the insulation here I need to lift the board ( plain chipboard cut to suit not tongue and groove ), if I put new insulation down but compact it under the boards will it still give increased insulation? e.g say 12 inches compacted to 4.

3). current boarding is a bit iify in places ( it gives when you walk on it ) and one part got wet and gives a bit more :(

4). So do I put the existing stuff back down and put more on top or just put new stuff down

5). what is the best and easist stuff to put down baring in mind it will need cutting to fit and then fixing to where the joists happen to be. Standard gap distance is 24 inches, but I guess there will be some cross bracing around the hatch.

Any comments welcome.

[dave1]

Pointless compacting the insulation material as it will then give less insulation. If you want to increase the depth of it you will need to increase the height of your joists. As for boarding, VFM wise, flooring grade chip is probably best. I would take up any damp/damaged flooring anyway. Best to put new down rather than overboarding. Insulating under tanks stops any internal heat from helping to stop them freeze up but not sure what "official" policy is.

[standfreelee]

don't insulate under cold water tank as heat rises and stops it freezing.

replace old wet lagging as this is ****** and will be useless and as said above compacting it reduces it's effectiveness.

im a thermal insulation engineer (lagger) :)

[Steve ( West Mids )]

It's not the insulation that's wet, just part of the boarding got wet.

Thanks for the comments.

[Bazza]

check your electrical wiring !

by covering them with insulation you lower the current carrying capacity of them

keep them running parallel and clipped to the highest part of the joist and leave some air gap round them

[GlynnB]

I've always used the Wickes loft boarding which comes in a size to fit the hatch and with a bit of pva glue on the tongue and groove the joint doesn't need to be on the joist.

I've always wondered how much boarding increases the insulation but haven't managed to find out.

[Steve ( West Mids )]

Bazza - what I read was normal electic cables were OK but electric shower cables and the like with higher current need to be over the insulation. That's what I've gone with.

[Bazza]

Bazza - what I read was normal electic cables were OK but electric shower cables and the like with higher current need to be over the insulation. That's what I've gone with.

any and all cables are subject to heat overloads due to insulation

an example is if a cable is wrapped in insulation it has to be down rated in current carrying capacity by 0.5

so a normal 1.0 mm lighting cable that is rated 16 amps, when wrapped in insulation is only rated at 8 amps

which is not a great concern if its protected by a 6 amp fuse, but is when a 10 amp fuse is protecting it !

the bigger the cable and load the worse it gets

a shower circuit rated at 47 amps gets reduced to 23 amps