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PostPosted: Wed Sep 06, 2017 11:00 am 
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Hi, another question, I have a Lean-To Conservatory W 5.3m x Projection 4.5m which I want to change the roof to a light weight tile roof. The conservatory as 6 x 2 timber rafter space at 700mm. A builder told me to put new 8x2 rafter in space at 400c but can I just add extra 6x2 rafter so spacing will be 350mm or double up the rafter, as this is going to be light weight tiles. Many thanks


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PostPosted: Thu Sep 07, 2017 5:01 pm 
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ust to start the correspondence, your builder is likely technically correct, you have a long horizontal span for 2x6, unless you use top grade wood and doubling the number for a 350 spacing it would be below his standard. Likelyhood of snow weight or someone taking it as a proper tiled roof, chancing climbing on it, hence flexing and strength factor will be in the standard calculations.
Also the bearing area the rafters sit on, is also important factor.
A forum Builder will be more specific!



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PostPosted: Thu Sep 07, 2017 5:35 pm 
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8 X 2 @ 400mm centres appears to be correct in span tables for a flat roof, 4.48m is the max span for 8X2 (got no figures for a pitch below 22.5°).

6 X 2 will span roughly 3.7m for pitches between 22.5° & 45° and 3.2m for a flat roof, (all @ 400mm centres).

Just doubling up the 6X2 is not going to do the job as they will still be @ 700mm centres.

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PostPosted: Mon Sep 11, 2017 4:50 am 
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ayjay wrote:
8 X 2 @ 400mm centres appears to be correct in span tables for a flat roof, 4.48m is the max span for 8X2 (got no figures for a pitch below 22.5°).

6 X 2 will span roughly 3.7m for pitches between 22.5° & 45° and 3.2m for a flat roof, (all @ 400mm centres).

Just doubling up the 6X2 is not going to do the job as they will still be @ 700mm centres.


Hi, thanks for replying., 700 center is what it is now, we where going to add more 6 x 3 timber between making it 350 center. The roof is 10 degree pitch, can I used 6 x 3 at 400 center?


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PostPosted: Mon Sep 11, 2017 5:20 am 
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Hi, is it 6x3 or 6x2 as in your 1st post? (rigidity is more about depth than width).


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PostPosted: Mon Sep 11, 2017 9:29 am 
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aeromech3 wrote:
Hi, is it 6x3 or 6x2 as in your 1st post? (rigidity is more about depth than width).


HI, I got 6x2 in now but need to change as I want to put a light weight conservatory roof on, so I would like to used 6x3 400 centre., I also did ask if I could double up the 6x2 as that's what in now. Hope I am a little clearer. thank for replying.


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PostPosted: Mon Sep 11, 2017 11:36 am 
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I would think you would be ok with doubled 6 x 2's

you will probably find your roof will have a degree of deflection from its self weight.

It also may not cope with a full snow load, but bear in mind the snow load is a 1 metre depth of snow.

Im guessing you are talking about the lightweight tiles used on conservatory roofs?, you will also have the weight of insulation and plasterboard, but thats a lot less weight than clay tiles

The pitch is so low that really flat roof span tables will apply not pitched roofs

Ive certainly built conservatories with glass roofs with rafters around the 160 x 58mm section for a 4.5 metre or so length.



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PostPosted: Mon Sep 11, 2017 12:46 pm 
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Notch1 wrote:
I would think you would be ok with doubled 6 x 2's

you will probably find your roof will have a degree of deflection from its self weight.

It also may not cope with a full snow load, but bear in mind the snow load is a 1 metre depth of snow.

Im guessing you are talking about the lightweight tiles used on conservatory roofs?, you will also have the weight of insulation and plasterboard, but thats a lot less weight than clay tiles

The pitch is so low that really flat roof span tables will apply not pitched roofs

Ive certainly built conservatories with glass roofs with rafters around the 160 x 58mm section for a 4.5 metre or so length.


I find a supplier for c24 6x3 but the person who answer the phone was not sure about the minimum span, as for the pitch I was told its 10 degree there's 60cm different in height to the back wall and front of the conservatory roof.


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PostPosted: Mon Sep 11, 2017 12:51 pm 
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600mm high over 4500mm length is about 7.5 degree pitch


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PostPosted: Mon Sep 11, 2017 1:10 pm 
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Notch1 wrote:
600mm high over 4500mm length is about 7.5 degree pitch


Wow, thanks, that's even lower, do you think c24 6x3 would be OK, 8x2 make it too low at the front.
Thanks


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