My distribution box for the MVHR ( sometimes called spigot box or manifold) will sit beneath a flat roof , but above a ceiling.
The roof build up from top down is;
Alvitra Avalon over
270mm of insulation on
some super expensive vapour stuff - forgotten the name - the price was so traumatic
22mm OSB3
POSIs above the ceiling build up which is
Vapour control layer
25mm insulation
12 mm plasterboard
2mm plaster skim.
There's enough space for spigot boxes to sit comfortably under the POSIs. That means they are outside the heated envelope. (just)
The supplier says not to worry : but they would wouldn't they? Everyone has that problem, said the rep,
What do you think?