# Roof timber sizing



## Stickystuff (11 Sep 2014)

I'm building myself a shed out of pallets and I've come to the roof! 
The idea was to keep costs down, and so far it's only cost me £9 for a few boxes of long screws, and some fuel collecting the pallets! Luckily the pallets are in the same industrial estate that I work so it's not really cost me any more then normal! 

The roof I have wanted to use 2x4s to make my main structure out of, but I don't really want to spend too much, now I've been looking and I can save myself some money by using 2x3 instead! 

Will this be strong enough to cope? 

The main structure is 3 metres wide and 3.6 deep im going to make a pointed roof and also I want to make a storage space in the roof. It won't be anything too heavy and just some toys for my daughter! 

I just wanted to make sure that it will still be strong enough. 

Anyone's help will be very much appreciated!


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## carlb40 (11 Sep 2014)

What will you be covering the roof with?
You have to take the weight of that into consideration, plus the weight of a snow load in winter. Well if it snows lol

Personally on a pitched roof such as yours, i wouldn't use anything under a 6x2. 
While you might think overkill/ expensive. It's cheaper than doing it a 2nd time if the weight of the roof and stored items etc are too much for the 3x2s.


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## Ghengis (11 Sep 2014)

I'm sure there are clever ppl on here that can do the maths for you but how about laminating the roof timbers out of the same palet timbers?


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## StevieB (11 Sep 2014)

Short answer - no! I was (am, eventually!) looking to build a carport with polycarbonate sheets on the roof with a span of 3m. It will be slightly sloped (5-10 degrees) to allow the rain etc to run to guttering. I looked at 2x4 and was advised they would sag too badly and to go for 2x6 minimum. You say your roof is pitched, so sag may be less, but the weight of your roof will be higher. You will likely need collars to tie the joists and stop them spreading. I would also be concerned about a wall plate - how have you made the shed from pallets? Pallet timber tends to be fairly rough and ready and will be in short lengths, how are you stopping the roof from pushing the walls apart?

Steve


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## PAC1 (11 Sep 2014)

According to the tables you can use 4x2 for the rafters of pitched roof of that span. But as said if flat would need to be much deeper 
The other concern are the walls if they are built from pallets of say 3 or 4 feet long there is no strength to stop your rafters from spreading and collapsing the whole thing. In which case you will need to make roof trusses. So the first question is how have you framed the walls. Have you used 4x2 or 3x2 full height uprights with the same size timber running the full length of the shed as a wall plate and base plate?


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## Stickystuff (11 Sep 2014)

I have used 1000mm x1200mm pallets approximate size they are all roughly the same size. 
The ones I have used are from USA so built with rough cut 3x2, 3 in each with then the wood spanned across all different but around 1/2 x3 in general
I would upload pics but apparently my pictures are too large(any one can help?) I'm on iPad so no idea how to change file size.

I did toy with the idea of stripping more pallets and using the 3x2 and joining each end to make a long length to make the trusses out of but the wood is too brittle and snapped even with a lightest pressure. 

Although you say not too if I where to double up on the trusses to increase the strength of the roof would that be sufficient? I have May have an opportunity to get some reclaimed 3x2 lengths at a fraction of the prices for new wood meaning I can make more to strengthen it all up? 

I initially have thought of using the wood from pallets to effectively 'clad' the roof and then just use felting to water proof it all. But I may just use chipboard or OSB if that's suitable as it will save me a lot of time stripping pallets. 

I really appreciate all of your input and experience. 
I'm certainly a newbie when it comes to wood work!


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## Stickystuff (11 Sep 2014)

I'll see if this works, this is what the construction looks like 

And this is as far as I've got


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## PAC1 (11 Sep 2014)

If all you did was fix pallets together then your walls will not resist the load from the roof pushing the wall out. What is needed is a frame full height by full width with uprights every 600mm or so. The frame will give the wall strength. Some pictures would help


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## RossJarvis (11 Sep 2014)

I would have thought 3x2 would be fine on that sort of span as long as the covering isn't elephants or something, though I would tie the rafters together with the same. Make ply fillets at the top and the joints with the ties (joists). I've just built a shed of 8' wide by 20' long with 3x2 rafters at 2' spacing. In comparison to commercial sheds this is massively over-specified. They tend to use something about 1" square with spacings of about 4', although they don't floor out the roof for storage.


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## RobinBHM (11 Sep 2014)

Euro pallets are pretty strong, put together well you could end up with quite a substantial structure. 

I would be tempted to screw some 3 x 2 around the top as a wall plate to stiffen up the structure. 

It would be worth going to see some display sheds to look at the roof members. I think budget sheds are built with surprisingly small section timbers. Maybe the middle rafters could be bigger section and the other intermediates smaller. You will definitely need some tie bars / collars to stop the roof spreading. 

Do post some more progress shots and a total spend would be interesting.....there could be some pallet workshops going up soon


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## Stickystuff (11 Sep 2014)

I see what you mean, if I'm honest the walls do flex a fair bit if you wobble them although the front wall is solid since putting the door frame in. 

I intent the make my joists/trusses in triangle shape with an over hang at each end, and possibly with a sorts of square support/section to strengthen it up and allow some storage space with a little floor boarding in.
In tween the red lines is what I would us as the storage.





I know it's a little rough but you get the idea. I would connect all the bits of wood together with a plywood or Mda panel at each join with plenty of material to cover. I would probably screw the red sections in as I think that would be stronger... Please correct me if I'm wrong.


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## Stickystuff (11 Sep 2014)

I've just posted a progress thread in the projects section if anyone is interested, 
ashley-s-free-cheap-she-d-made-from-pallets-t83401.html


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## PAC1 (12 Sep 2014)

that sort of truss would be fine. you could probably use a combination of 3x2 and 4x2. The horizontal wants to be at least 4x2.
The problem remains you need to stiffen the walls. A wall plate as suggested would help but unless your walls are stiff in length and height it will collapse.
bought sheds work with much smaller sections of timber because they make frames that provide the structural strength. A shed 3.6m long would have say two frames 1.8 long thus doubling the structural member in the centre. It would then have a strong truss spanning across at the centre point to stop the walls flexing. The roof weight is then transferred with purlins to the end walls and the centre truss. This removes any load from pushing the walls apart. Except for the centre where they have beefed up the structure.


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## Stickystuff (12 Sep 2014)

I understand what you mean with the frame in the centre to add a bit of rigidity. 
A bit like this? 






So the arrow pointing with number 1 is the frame in the middle. I used some of the pallet slats and placed on the top of the wall alike arrow number 2 but do I really need to change this to 3x2 or 4x2? It did make the walls slightly stiffer after doing so. Another thing to mention that the walls aren't all properly level...
So I know that the roof won't be perfectly level but it's not supposed to be perfect.


Also this is how I would mount the roof trusses which would mean that the walls would just be load bearing from above and not sideways(unless windy etc) the bar in the middle ties the two upper bars together which takes the sideways load off the walls right?


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