I cannot find locally or for mail order eaves ventilators for rafters at
400mm centres (eg Manthorpe G435). Roofing merchants understandably
have only the vents which are fitted over the rafters before fitting the
slates/tiles. Any suggestions please as to where I can get them or how
I could DIY something equivalent to them?

Background is I foolishly believed the roofer who said there was no need
to fit eaves vents with a breathable underlay. Now, with 170mm
insulation over the joists, there is too little ventilation to keep the
rafters free from condensation (and a little surface mould) given there
is not a vapour barrier in the ceiling.


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R