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Full length furring strips?


Joe87

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Hi all, just a quick question. 

I have 6 meter length roof joists for a warm flat roof. Do I need furring strips that run the entire length of these 6 meter joists? Or can I use an easier to get 4 meter strip? Or, is there an easier way to do the whole thing? 

 

Also while I'm here, does anyone know the calcs to find the drop I need for the flat roof?

 

Cheers

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1 minute ago, Joe87 said:

Hi all, just a quick question. 

I have 6 meter length roof joists for a warm flat roof. Do I need furring strips that run the entire length of these 6 meter joists? Or can I use an easier to get 4 meter strip? Or, is there an easier way to do the whole thing? 

 

Also while I'm here, does anyone know the calcs to find the drop I need for the flat roof?

 

Cheers

Furring strips can be any length, what are you trying/wanting to do? and when you say calcs for flat roof, do you mean the fall required to allow water to drain? 

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2 hours ago, Joe87 said:

Also while I'm here, does anyone know the calcs to find the drop I need for the flat roof?

 

the regs say that it should be designed for a 1:40 fall to achieve a minimum 1:80 fall when constructed.

 

1:40 is 0.025, so for a 6m length you need a drop of 150mm (6 x 0.025) over the 6m length.

Edited by Moonshine
6 x 0.025 not 6 x 0.25
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2 hours ago, markc said:

Furring strips can be any length, what are you trying/wanting to do? and when you say calcs for flat roof, do you mean the fall required to allow water to drain? 

The furring strips are going to be used to create the fall on the flat roof. I just wasnt sure if they had to be the full 6 meters on top of the joists or not. Yes, the calcs is for the slope that I would need for run off. 

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  • 2 weeks later...
On 18/06/2021 at 09:49, Moonshine said:

 

the regs say that it should be designed for a 1:40 fall to achieve a minimum 1:80 fall when constructed.

 

1:40 is 0.025, so for a 6m length you need a drop of 150mm (6 x 0.025) over the 6m length.

 

 

This is a grey area after my own research. 1:40 is ideal however 1:60 or 1:80 is fine.  If solids in a sewer pipe can get away at 1:80 min then rain water can surely get away with 1:80 and no need to go as deep as 1:40. 

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33 minutes ago, cs21 said:

If solids in a sewer pipe can get away at 1:80 min then rain water can surely get away with 1:80 and no need to go as deep as 1:40. 

 

Sewer pipe is smooth plastic with no obstructions and laid to a consistent fall on a firm bed of shingle.

 

Flat roof are built with timber joists and OSB sheets, which can twist and sag, supported on walls that can settle, with complicated junctions, upstands, verges and outlets.  Often there are trims or leadwork added at the point where the water should run off.  There are a couple of flat roof puddle threads on this site at the moment.

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If I did use a 1:40 furring strip at about 5 meters, a website I was on to buy at this size has it running from 130mm to 5mm. That's fine but this brings the fascia to about 48-50cm high? Does that sound to big or is that a normal sounding size for a fascia? It looks big by tape measure but I find these things hard to visualise haha. It has to be done right, but I still want a certain amount of aesthetics ??. Unless there is other ways of doing things. 

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