Hi,

I am in the process of recovering an extension flat roof, about 4m
square. Waterproof covering is to be EPDM membrane, but I have fitted
100mm Kingspan TR27 over the existing felt as (I thought) the roof was
completely uninsulated.

When fitting the insulation, I noticed that it was relatively easy to
dent the surface with a point load, even by just kneeling on them. As
there is work to be done next spring on a dormer in the adjoining
pitched roof, I was wondering if it was sensible to sheath the
insulation boards with a thin layer of ply on top, screwed through the
insulation to the deck, to provide them with a bit of protection?

I realise that the additional fixings for this would increase the
overall U value a bit, but as I discovered there was already a 20mm
layer of PUR board underneath the felt when I began fixing the new
insulation, that gives me a total of 120mm PUR insulation overall which
isn't too bad.

Questions that I would like opinions on, please:

Is this worthwhile/a good idea?

Would 4mm exterior ply be sufficient?

Any problems people can see?

Thanks for your help

Mark