Roof overhang limits

[Mad Moose]

I have enjoyed many hours reading loads of posts here over the past week. About to start groundworks for my new workshop. First time build of a bespoke structure - my only previous experience is putting up prefabbed sheds 6'x8' / 8'x10'. So my concrete pad should be getting poured next week. The footprint of the workshop will be 4.8m x 4.2m which will be huge in comparison - I am so excited!

The roof will be single plane pent with 1:40 fall (2.4M at front down to ~2.3m at the back internally). Boarded with T&G 18mm OSB and covered with EPDM. My question relates to how big I can have my overhangs. Planning on using 6x2 timbers at 400mm centres for the rafters so front and back are straight forward enough to create - but not sure about any limits. Thinking specifically about the sides, how wide can I make the laddering on each side. Hoping to get 60cm to allow some protection from rain and to have some storage for timber under the eaves. once I understand the constraints I will know the size of the roof and how much EPDM I need to order.

I can guarantee that there will be lots more questions as I get started. I use the University of YouTube extensively but there is no substitution for the ability to get answers to specific questions from wise and experienced woodworkers.

I plan to document the whole thing and will post on here if anyone is interested. Currently trying to learn to use SketchUp to do the design and get a clue as to how much timber, how many sheets of OSB, insulation etc. I need to be buying and work out just how much is is going to cost - or more realistically working out what the initial budget needs to be. . .

 

[Jameshow]

If your using 400mm centres why not make it 400mm overhang seems obvious to me...land a joist on the wall? One bay out each side. Noggins every 1.05m

Just my inexperienced thoughts!

 

[Bingy man]

I have enjoyed many hours reading loads of posts here over the past week. About to start groundworks for my new workshop. First time build of a bespoke structure - my only previous experience is putting up prefabbed sheds 6'x8' / 8'x10'. So my concrete pad should be getting poured next week. The footprint of the workshop will be 4.8m x 4.2m which will be huge in comparison - I am so excited!

The roof will be single plane pent with 1:40 fall (2.4M at front down to ~2.3m at the back internally). Boarded with T&G 18mm OSB and covered with EPDM. My question relates to how big I can have my overhangs. Planning on using 6x2 timbers at 400mm centres for the rafters so front and back are straight forward enough to create - but not sure about any limits. Thinking specifically about the sides, how wide can I make the laddering on each side. Hoping to get 60cm to allow some protection from rain and to have some storage for timber under the eaves. once I understand the constraints I will know the size of the roof and how much EPDM I need to order.

I can guarantee that there will be lots more questions as I get started. I use the University of YouTube extensively but there is no substitution for the ability to get answers to specific questions from wise and experienced woodworkers.

I plan to document the whole thing and will post on here if anyone is interested. Currently trying to learn to use SketchUp to do the design and get a clue as to how much timber, how many sheets of OSB, insulation etc. I need to be buying and work out just how much is is going to cost - or more realistically working out what the initial budget needs to be. . .

I see no issues with a 600mm overhang given your 6”x 2” joists I’d treat any exposed timber with a suitable wood preserver eg sika 5 star complete as any rain driven by the wind will find any weak points. You can work out how many sheets of plywood/ osb to buy as they are 8’x4’ or 2.4 x 1.2 .. good luck

 

[Mad Moose]

Thanks for the input guys - much appreciated. I have dimensioned the workshop to utilise full sheets and minimise cutting - hence the long walls are 4.8m by 2.4m.

 

[Jake]

You'll have some small cuts with that - wood panel sheets tend to be 2440 x 1220 not precisely 2.4 x 1.2 (although plasterboard and insulation are the latter, and chipboard and plywood T&G floor is 2.4 x 0.6).

 

[HOJ]

Planning on using 6x2 timbers at 400mm centres for the rafters

I know its a workshop, but worth looking up the span tables for your roof timber lengths @ 6" x 2" (Regularised C24 will be 145 x 44mm) is fleet.

 

[rob1693]

If they're osb3 tg4 dimensions are 2400mm x 590mm , it's what I used on my workshop walls and roof

 

[Fergie 307]

I know its a workshop, but worth looking up the span tables for your roof timber lengths @ 6" x 2" (Regularised C24 will be 145 x 44mm) is fleet.

No mention of which way the joists are going, ie are they spanning 4.8 or 4.2?
Seem a bit light to me, especially for a low pitch pent roof.
My shed has 8x2 spanning 4m at 600 centres, that is on either side of a 15° pitched roof.

 

[Mad Moose]

You'll have some small cuts with that - wood panel sheets tend to be 2440 x 1220 not precisely 2.4 x 1.2 (although plasterboard and insulation are the latter, and chipboard and plywood T&G floor is 2.4 x 0.6).

Thanks for the heads-up on the oversized OSB panels. I will adjust the concrete bas accordingly. I could use the extra 40mm of height to tap the OSB down over the edge of the concrete to ensure runoff.

 

[Mad Moose]

I know its a workshop, but worth looking up the span tables for your roof timber lengths @ 6" x 2" (Regularised C24 will be 145 x 44mm) is fleet.

Thanks for the input - I was going for 6x2 on the basis of 'The DIY Guy' on YT. His build was 4m span and he says 6x2 at 400 centres was more than enough. Granted, mine is 4.2 span - so I have checked the span tables (here) an maybe I need to be looking at C24 7x2 (47x175).

Best to do it properly first time - but 8x2 (Fergie 307) seems like overkill. . .or maybe not. . .

Cheers.