Thickness of entire warm deck flat roof

[macadonald]

Hi guys,

Although I'm sure this can differ considerably depending on insulation etc, can anyone tell me what the approximate thickness of a warm deck flat roof will be including joists?

Reason I ask is because I'm trying to work out whether my upstairs toilet waste pipe will be high enough to divert on top of the flat roof to the side of the house. It currently comes straight down in the middle of the house, and for the rear extension, I'd like to free up this area. My other option would be to box it in on the inside. I assume I couldn't fit this through the joists in anyway?

Also, what is the min angle drop required for a waste pipe, drain etc?

Thanks

 

[tony1851]

The joist size depends on your span, but assuming you are going out, say, 3m or so, your joists would be about 150 deep; add to this the firring pieces for slope (say 75 max); 18 thickness of deck; min 125 thickness of insulation board, then finish on top. With plasterboard, you would be looking at a thickness of around 15" (perhaps a little less if you have a shallower fall with smaller firring pieces).

pipe falls usually min 1:40.

 

[macadonald]

Tony,

Thanks for that, very useful. Out of interest, you mentioned furring pieces for slope. As my flat roof will be enclosed by a parepet with the drainage point being in one corner, I knew I would need to build in the drainage slope towards this and thought I would do this using the joists themseleves, but furring pieces make much more sense. Do these strips come in pieces that taper down in thickness? or is it generally a case of simply downsizing the thickness as you span the roof?

 

[tony1851]

If you are draining the whole roof to one corner, you can try putting the firring pieces diagonally (45 deg.) across the roof joists. They increase in depth by a small amount each one (say 1/8"). The sheets are laid at 90deg to the firrings.

Untitled

• tony1851
• 30 Aug 2012
• 1