Sandwich flat roof
 

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

Sandwich flat roof
 

Mark Hindley wrote:

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?

snip

Would 4mm exterior ply be sufficient?

IIRC Kingspan sell a product comprising sheets of their insulation
bonded to sheets of 4mm ply, just for this purpose, so i would have
thought it should be fine

David

Sandwich flat roof
 

In article , Mark Hindley mark@hindle
y.spamnospam.uklinux.net writes
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?

Overall it sounds like a nice solution although I might have gone for
something tougher for the waterproofing but I'm not exactly sure what.

On the 4mm question, I suppose it depends how flat the flat roof really is, I
assume there is a small fall to shed water. If you use 4mm then you risk
pulling dimples into the surface at the fixing points, when you tighten the
screws, and water may end up pooling there. If you use 12mm then I think
you would avoid that.
--
fred
Plusnet - I hope you like vanilla

Sandwich flat roof
 

fred wrote:
In article , Mark Hindley mark@hindle
y.spamnospam.uklinux.net writes
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?

Overall it sounds like a nice solution although I might have gone for
something tougher for the waterproofing but I'm not exactly sure what.

On the 4mm question, I suppose it depends how flat the flat roof really is, I
assume there is a small fall to shed water. If you use 4mm then you risk
pulling dimples into the surface at the fixing points, when you tighten the
screws, and water may end up pooling there. If you use 12mm then I think
you would avoid that.


could you use 4mm and glue it? never tried it


NT

Sandwich flat roof
 

In article .com
, writes
fred wrote:
In article , Mark Hindley mark@hindle
y.spamnospam.uklinux.net writes
Would 4mm exterior ply be sufficient?

Overall it sounds like a nice solution although I might have gone for
something tougher for the waterproofing but I'm not exactly sure what.

On the 4mm question, I suppose it depends how flat the flat roof really is, I
assume there is a small fall to shed water. If you use 4mm then you risk
pulling dimples into the surface at the fixing points, when you tighten the
screws, and water may end up pooling there. If you use 12mm then I think
you would avoid that.


could you use 4mm and glue it? never tried it

I thought 12mm would be more resilient over all, particularly with the
prospect of ongoing works, steps bearing etc, just too much capacity for
doh! factor with the thin stuff.
--
fred
Plusnet - I hope you like vanilla