Installing Foil Loft Insulation

[adorableade]

Hi All,

I am looking at installing foil insulation on my rafters. The loft is well insulated between the joists but I now have my boiler, unvented cylinder and digital shower processor up in the loft. It does get very cold up there in winter and I am concerned.

My query is do I need to leave gaps top and bottom for ventilation? Won't this negate the effect of the foil? Or can I seal the foil completely leaving air free to vent between the rafters from eaves to apex between the foil and the roof? Cheers

 

[tony1851]

Don't waste your time as the roof will still be cold in winter because of the ceiling insulation you already have.
Aside from that, foil insulation has to have sealed air gaps both sides to be fully effective

 

[adorableade]

Cheers Tony, I thought that maybe the bit of heat the boiler gives off may make a diffrence if the rafters are insulated.

What do you mean by sealed air gap?

Thanks for your help.

 

[tony1851]

To work effectively, the air each side of the foil needs to be still. On the ceiling side of the foil, this is not a problem as you usually fix battens to the underside, and then plasterboard.
On the rafter side of the foil, it can be a problem as you need to keep air flow above the foil to clear any condensation that may occur. This reduces the efficacy of the foil.

 

[adorableade]

What about creating an insulated enclosure (with an air vent for the boiler) around the boiler and tank? Would that be of any help in a cold loft? It would be easily removable for access.