Loft insulation

[MK22]

Hi all, I’m wanting to lay down some loft insulation over the boards in the loft. The boards don’t go right up to the edges, and I can see wires running under the boards from the edge. Obviously once they’re under the board I have no idea where they go (I didn’t lay the boards). I’m aware insulation should not be laid over wires, but is it safe to lay insulation over boards which is over wires?
Thanks.

 

[Wayners]

Insulation needs to be against the ceilings to insulate.
Also I've seen many crushed cable under loft boards

 

[Dereekoo]

Insulation needs to be against the ceilings to insulate.
Also I've seen many crushed cable under loft boards

Why is that, surely the air gap between the ceiling/boards/insulation act as a barrier to heat transfer in the same way that the air gap in cavity walls do. I would add that if at the perimeter of the boards the insulation isn't dipped down to run along the ceiling then this would be detrimental to the heat retaining properties of the air gap.

 

[Wayners]

If you put your hand under loft insulation in winter its warm.
Plaster ceiling is warm so no condensation forms as the dew point is high.
With your air gap that's not going to be warm, so you're ceiling will be cold and your going to get mould growing within week's.

 

[Taylortwocities]

If the wires in the loft are lighting then putting insulation over them should not be a problem. Where issues can arise is if cables are high-current (eg electric shower). Then it may be necessary to install thicker cable for that circuit.

 

[Dereekoo]

If you put your hand under loft insulation in winter its warm.
Plaster ceiling is warm so no condensation forms as the dew point is high.
With your air gap that's not going to be warm, so you're ceiling will be cold and your going to get mould growing within week's.

Heat migrating through the plasterboard warms the air gap, boards/insulation above the air gaps maintains the heat? Assume that if the OP existing cold ceilings do not have mould growing across them adding insulation above will not suddenly cause such an effect otherwise everyone insulating their loft beware. As an aside U value of ceiling with just plasterboard = 2.7 with 100 insulation/air gap/boards = 0.4

 

[Wayners]

@Dereekoo

The air gap would need to be air tight though? Any air gap will just blow cold air in lowering ceiling temperature.
They op is not creating a warm roof or cold roof.

I'm not sure what it's called as don't exist as a known way to insulate correctly.
What would this way of creating a insulated ceiling called?