# help needed with shed build



## graduate_owner (11 Apr 2019)

Hi all,
I have a 16x12 feet wooden shed with a steel box profile roof. I need to build a second shed beside it and want to use one wall of the existing shed as a common wall to both sheds. However I am not sure how to build the roof. Both sheds will have peak roofs and so there will be a valley where they join.
My issue is, how can I create a waterproof valley connecting the two box profile roofs.

Any ideas?

K


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## jimmy_s (11 Apr 2019)

I would think you would need a valley gutter made from profiled sheet with a decent lap under the existing and new roofing sheets. Thats my guess but its not my area of knowledge.


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## flying haggis (12 Apr 2019)

as Jimmy says valley gutter like this


https://www.google.com/imgres?imgurl=ht ... mrc&uact=8

but make sure the gutter sides go under the roof slope enough to stop water running back up the slope especially if the gutter fills with heavy rain or is blocked with leaves etc


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## MikeG. (12 Apr 2019)

Just to be absolutely sure of what you are proposing....The two ridges will be parallel, will they? They're not at right angles to each other? If I'm right about that, then it's a gutter between the rooves, not a valley. 

Again, assuming the rooves are parallel, your principle issue is going to be forming a decent gutter underneath the existing roof. You are going to have to get that up and under the roof sheets, which might be awkward, depending on where the lowest fastenings are and how easy they are to undo. Also, your gutter should ideally have some decent falls built in, and again, ideally, from the middle out to each end. Really importantly, it should be wide enough that you can walk along it so that you can clear leaves and other obstructions. In practice, allowing for the overhang of the roof sheets either side, this means your gutter needs to be getting on for 400mm wide.

Finally, box gutters are notorious cold bridges, and condensation from them can be a big issue. Make sure that you have a full depth of insulation below the gutter, which is easier said than done with the structure that can be in the way.


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## graduate_owner (12 Apr 2019)

The eaves of both roofs will indeed be parallel, so yes- a gutter is what I need. Would a wooden structure be suitable, with lead or self adhesive aluminium faced flashing be the way to go?
I am not quite sure how to do this yet though. If I build two separate sheds then there will be the extra cost of the wall, plus insulation so I am hoping this will be possible without creating issues further down the line

K


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## MikeG. (12 Apr 2019)

A timber structure is the obvious way to do it, assuming your existing building is timber. However, I wouldn't suggest lead for the gutter, because lead needs steps at the joins, and that gets complicated. I would make the gutter out of zinc or aluminium, because you can make it (or have it made) in continuous lengths without steps. The alternative is to make a wooden box and to line it with EPDM, but for that to work successfully, you'd have to remove the existing roof (to fit a substrate to hold the EPDM as it dresses up the slope under the roof). Forget "flashband".


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## graduate_owner (13 Apr 2019)

I was thinking of something like flashband, but not sure now after reading previous comment. I have some aluminium panels from a caravan I dismantled years ago. Might be long enough. If I have to join 2 aluminium sections, what would be the best way of ensuring a watertight joint? Could tig welding do it, seeing as the aluminium is very thin section? Or how else might two sections be joined?

K


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## TFrench (19 Apr 2019)

We've recently done some box gutters for a neighbour on our industrial estate. Used .8mm stainless in 2.5m lengths, we did the joins with a big overlap and a LOT of tigerseal. Fixed together with stainless rivets (well up the sides!) and when the tigerseal went off we painted each join with acrypol. Done a few like it and had no problems yet.


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## Hornbeam (21 Apr 2019)

What you need is a folded steel valley gutter , with legs which fit up under your existing trapezoidal profile steel roof. Is your existing roof insulated
This is not easy to fit in as the gutter will need to be around 300mm wide. Do you intend to retain the cladding on the side of the existing shed or are you going to open out into a larger space. I am asking as you need to work out what you ar going to support the side of teh new shed onto and how you will make structural attachments.
Steel is much better than aluminium for this application as it only expands/contracts by about 1/3 as much but needs a good coating or a membrane
The gutter should be insulated but slightly less than the draining roofs. This is so that if we have snow and ice, the gutter thaws out fist and you dont get overflow issues
Ian


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