Flat roof design 101 from basics for the Suffolkian idiot….

[G and J]

So, to restart my thinking I’ve gone back to basics.   
 

Here’s our flat roof. 

 

 

My first question is:  Is there enough room to get a cold roof sufficiently ventilated using those little upstand vents and the fact that the skylight mucks up cross flow?

 

[nod]

I did a similar one as a warm roof on our last build 

Less issues with condensation 

[G and J]

36 minutes ago, nod said:

I did a similar one as a warm roof on our last build 

Less issues with condensation 

If I promise to be your bestest friend can I have a look at yours…..?

[nod]

I used 9x2 joists boarded with ply Then a layer of multi foil Then fairings Toped with OSB 3

Plywood on the top of the blockwork 

and returned the fibreglass over to make a watertight seal 

First attempt at fibreglass 

150 kingspan between the joists 

Then boarded with 15 mil duplex and then skimmed it over with a couple of coats of multifinish 

[G and J]

Ta.  Is this an accurate cross section?

 

So presumably the foil was your air tight layer.

[Iceverge]

That ply between the foil and the PIR will be cold and attract condensation and won't be able to dry out again unless you have superbly low internal humidity.