Best size timbers for shed roof?

[Cmoran]

I’m constructing a shed at the moment with 20’ bays was going to put 7x3 timber on roof and make the cleats 1’ long but some people are saying I’d need 9x3 for that span. They are lot more expensive and I need to decide today what are people’s opinion?

 

[puppet]

You can still see a dip on some 9×3 so 7x3 will be too weak.

 

[gatepost]

Min 9x3 I would think,

 

[bigw]

Make your cleats bigger still to give as much support as possible, 9x3 timbers too.

 

[Sharpy]

9 by 3 I'm afraid, unless its a steep pitch then you can reduce timber size. Remember that timber today is grown quick and doesn't have the same strength of much of the stuff from 50 years ago.

 

[Wilber32]

I’ve just put in 9 x3 for 20foot span. 7x3 for 15

 

[Cmoran]

Ok thanks folks

 

[Warp Land Farmer]

Why not consider galv purlins?

 

[farmerdan7618]

Got 9x3 on 20' span here, wouldn't want them any smaller.

 

[BredRedHfd]

Try and source Scandinavian. English treated is utter utter carp

 

[Fendt516profi]

Make your cleats bigger still to give as much support as possible, 9x3 timbers too.

Make your cleats 20ft, called z purlins

 

[Tarw Coch]

. Remember that timber today is grown quick and doesn't have the same strength of much of the stuff from 50 years ago.

I helped a mate take down a shed in the autumn, reckon it would have been at least 50 years old.
The timbers were still better than new today and you could still smell creosote on them

 

[Lewis]

What would be a direct replacement for a 9x3 20ft timber to Z purlin? And approx cost difference? See they do different thicknesses.

As I've a possible job to roof between 2 lean to's which is 22ft wide so think Z's would possibly work best as can only get 20ft or 24ft wood purlins .

 

[Cmoran]

I’ve ruled out z purlines as any sheep locally that used them they just rotted away in 15 years. I’ve gone for 9x3 timber

 

[YELROM]

What price are 9x3 timbers and do they need to be a certain grade
We are looking at putting up a shed with 20' bays

 

[Cmoran]

What price are 9x3 timbers and do they need to be a certain grade
We are looking at putting up a shed with 20' bays

I’m in Ireland and a local sawmill is €40 inc vat

 

[Sid]

I’ve ruled out z purlines as any sheep locally that used them they just rotted away in 15 years. I’ve gone for 9x3 timber

Spot on, Zs are a no no in livestock housing

 

[OGB]

treated 9x3 or reduce span with purlins... could use engineered rafters / timbers, section would not need to be so significant. But down to individual circumstances and cost

 

[Sid]

Could Z purlins be powder or plastic coated?

Timber has gone very expensive now

 

[betternextyear]

My advice, use 9 by 3 and buy them 3 months before you need them and store inside to dry out. You will make a better job using dry purlins. Our local supplier only has wood at about 40% moisture which is difficult to work with. You can then not worry about them warping.