Inverted Warm Flat Roof advice

[sc00byd00]

I am building a Garden room it is 6.5m x 4m block with cavity and I am now getting towards putting the roof onto it.

Have been researching different options of flat roof anf like the idea of the Inverted Warm Deck.

I am thinking of using a 1200g Polythene DPM that I used under the Floor Slab. Is there any reason why this would not be suitable?

Assuming that I can use it would it be ok if laid loose on my timber deck with insulation on top then a filtration layer then some concrete slabs on top.

Any idea how much I would need to Beef up the joists to cope with the extra weight?

Cheers.

 

[HomeInspector]

I am building a Garden room it is 6.5m x 4m block with cavity and I am now getting towards putting the roof onto it.

Have been researching different options of flat roof anf like the idea of the Inverted Warm Deck.

I am thinking of using a 1200g Polythene DPM that I used under the Floor Slab. Is there any reason why this would not be suitable?

Assuming that I can use it would it be ok if laid loose on my timber deck with insulation on top then a filtration layer then some concrete slabs on top.

Any idea how much I would need to Beef up the joists to cope with the extra weight?

Cheers.

I suggest you employ the services of an architect. Roof structures are complex in the extreme and if you get it wrong ... !