My first roof build

[JimWoodwork1975]

Hi, I'm building myself a small workshop and I'm looking at the roof construction, I've attached my initial plan and I'd like to ask some questions if possible?

1. Is the pitch suitable for the span - I'm trying to get more headroom as I'm 6'4". I know I have to keep the structure under 2.5m
2. Are the bottom rafters overkill?
3. Am I right in saying C24 treated would be best?
4. I've drawn this using 2x4", would I get away with 2x3's?
5. Over hang the rafters or just the boards?

 

[MikeG.]

1- Yep, depending on what you are planning to put on top, 14 degrees is fine.

2- Do you mean joist, or ties? Rafters are the pitched (sloped) timbers. If you don't want them, then the ties, or at least most of them, can be designed out.

3- No. C16 would be perfectly OK with these small loads saving some money. Saving money is always good. :lol:

4- No. In fact, you'll struggle with 4x2s because of the insulation and airgaps.

5- Overhang the rafters by about 6 inches.

There is something seriously amiss with your drawing. The section shows a span of just under 3m. The roof plan shows a span of a tad over 2m. Which is it? The answer to that affects the design greatly.

Your spacing is odd. 500 just won't work with the sheet materials you'll be working with. 400, 450 and 600 are the typical spacings. You can stick with 500 if it suits you.

 

[AJB Temple]

Is there a reason for making it L shaped? If you can make it square then your internal space will be a great deal more flexible for a workshop, especially handling sheet materials and placement of machinery.

 

[JimWoodwork1975]

⁹

1- Yep, depending on what you are planning to put on top, 14 degrees is fine.

Great thanks.

2- Do you mean joist, or ties? Rafters are the pitched (sloped) timbers. If you don't want them, then the ties, or at least most of them, can be designed out.

Horizontals so the ties cheers, just leave the end ones out?

3- No. C16 would be perfectly OK with these small loads saving some money. Saving money is always good. :lol:

Good, cost is key, isn't it always...

4- No. In fact, you'll struggle with 4x2s because of the insulation and airgaps.

What size would you recommend?

5- Overhang the rafters by about 6 inches.

Cheers.

There is something seriously amiss with your drawing. The section shows a span of just under 3m. The roof plan shows a span of a tad over 2m. Which is it? The answer to that affects the design greatly.

Always better to mess up the drawings instead of the build

It's the 2m which probably means I can leave all the ties out?

Your spacing is odd. 500 just won't work with the sheet materials you'll be working with. 400, 450 and 600 are the typical spacings. You can stick with 500 if it suits you.

600 then, less rafters, less expense.

Thanks very much. =D>

 

[JimWoodwork1975]

Is there a reason for making it L shaped? If you can make it square then your internal space will be a great deal more flexible for a workshop, especially handling sheet materials and placement of machinery.

Garden shape and 40m pine tree is the short answer. Yes ideally I'd do the square, cheers fella.

 

[owen]

A lot depends on what you are covering the roof with? I'd be a lot more inclined to go 400mm centres rather than 600, sheet materials will have a lot less say over it and it generally just feels a better build quality.

 

[JimWoodwork1975]

Thanks, was looking at 9mm OSB3 and Felt.

 

[owen]

9mm will sag awfully at 600mm centres. Drop to 400mm centers and use 12mm

 

[MikeG.]

...........Horizontals so the ties cheers, just leave the end ones out?........

No, it's more complicated than that. If we take out the ties, then we need to prevent the roof spreading in another way. It's easy, and there are a number of ways, but it isn't just a question of leaving out the ties. First job is to give us a properly drawn drawing with correct dimensions. :wink:

 

[MikeG.]

Thanks, was looking at 9mm OSB3 and Felt.

9mm will sag awfully at 600mm centres. Drop to 400mm centers and use 12mm

No! No, no....... 18mm OSB for a roof. And you'd best look at EPDM instead of felt.

 

[JimWoodwork1975]

...........Horizontals so the ties cheers, just leave the end ones out?........

No, it's more complicated than that. If we take out the ties, then we need to prevent the roof spreading in another way. It's easy, and there are a number of ways, but it isn't just a question of leaving out the ties. First job is to give us a properly drawn drawing with correct dimensions. :wink:

Yeah I'm on it now lol

 

[JimWoodwork1975]

9mm will sag awfully at 600mm centres. Drop to 400mm centers and use 12mm

See I'm thinking what will fit together and your thinking will it work? That's why I'm the one asking the questions lol Cheers.

 

[JimWoodwork1975]

OK, V.2 using 2x2" timber at 400mm centres.

 

[owen]

Thanks, was looking at 9mm OSB3 and Felt.

9mm will sag awfully at 600mm centres. Drop to 400mm centers and use 12mm

No! No, no....... 18mm OSB for a roof. And you'd best look at EPDM instead of felt.

I was thinking 18mm osb but a lot of sheds use 12mm on massive spans, so on 400 centres I thought it would be ok? Isn't EDPM a bit overkill for a garden shed if the roofs pitched? A good quality felt would last just as long wouldn't it? Only time I've used EDPM before is on flat roofs and I have to say it is bloody good stuff.

 

[MikeG.]

.......... Isn't EDPM a bit overkill for a garden shed if the roofs pitched? A good quality felt would last just as long wouldn't it? Only time I've used EDPM before is on flat roofs and I have to say it is bloody good stuff.

No, EPDM is going to last 10 times as long as any felt, and is a cheap product. It's the plastic trims which are expensive, so don't have them. And this is a workshop, not just a shed, so well worth looking after properly.

 

[MikeG.]

......OK, V.2 using 2x2" timber at 400mm centres.

For the rafters? No. If 4x2s weren't big enough...... :lol:

 

[JimWoodwork1975]

OK so the plan looks like;

EPDM
12mm OSB
2x2 (C16) Rafters
2 inch insulation (also for walls and floor)
400mm centres
Approx. 6 inch overhang.
I think I will put in Ties/ceiling joists because they will clear even my lofty nut.

I really appreciate everyone's help, cheers. Build pictures will follow.

 

[JimWoodwork1975]

......OK, V.2 using 2x2" timber at 400mm centres.

For the rafters? No. If 4x2s weren't big enough...... :lol:

Lol, but my current shed is 6ft wide, all the framework is 2x2 and there aren't any rafters, apart from those at the ends of course..? Although the pitch is steeper and the roof covering timber looks like shiplap about 9mm thick...

Simple this game is :roll:

 

[owen]

You'll need an airgap if you're using 2" of insulation so you want at very least 3x2s

 

[owen]

.......... Isn't EDPM a bit overkill for a garden shed if the roofs pitched? A good quality felt would last just as long wouldn't it? Only time I've used EDPM before is on flat roofs and I have to say it is bloody good stuff.

No, EPDM is going to last 10 times as long as any felt, and is a cheap product. It's the plastic trims which are expensive, so don't have them. And this is a workshop, not just a shed, so well worth looking after properly.

Fair enough