Steel Box Profile Roof on Log Cabin workshop

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Established Member
12 Oct 2020
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East Sussex
Evening all.
I am in the process of building a large log cabin workshop/store, and luckily managed to obtain a second-hand cabin.
We had to dismantle it and in the process the roof wasn't salvageable, so now looking at roofing it.

It's 8m x 5m (with a 0.5m overhang at the front), with a central ridge pitched roof.
The roof structure is simply a ridge beam and 2 purlins each side, with the front, intermediate and rear apex trusses supporting them, so the roof will sit on those and supported by the tops of the side log walls.

To roof it conventionally with boards, insulation, more boards and then something like felt or EDPM would be a) quite costly and b) take a bit of time and extra labour; so I'm thinking of using insulated steel box profile sheets.
These will easily span from the ridge, via the 2 purlins to the wall (just over 3m) without additional support, and will be quick and straightforward to fit (I think!).

My only concern is the eaves detail.
If I leave the underside steel sheet and insulation overhanging the walls, then I'm concerned about creating a cold bridge and the resulting condensation inside around the edges.
I can cut back the underside steel sheet and insulation level with the log walls, so there is only the "corrugated" top steel sheet protruding beyond the logs, but then I guess I'd need to scribe some form of barge board to go at the top of the log walls and fit the underside of the corrugated top sheet to seal off the exposed foam insulation, which sounds like a right pain!

Also, I'd like a large overhang (say 250mm) to keep the weather off the logs, but then not sure how to fit the guttering.

Has anyone done this before and have any tips/ideas?
Many thanks.


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Good thinking re the cold bridge.

How about cutting the lower
Steel sheet and parting the insulation.

As it's the eves it dosent matter.

Then use the offcut sheet and insulation as your eves?

Use a bit of 2x to separate them?
Instead of trying to remove the insulation from the overhang, use a metal cutting blade in a circular saw to cut a line across the underneath of the sheet, just through the flat backing sheet, where it sits over the wall and some mastic to help seal the sheet for any uneveness to the wall. Trying to remove the foam and then having to finish the bare metal that's just been exposed is well pointless imo. The foam won't peel off it will have to be sanded off.
As the for guttering 'industrial trimline guttering' and any associated brackets to suit the overhang are required.
I,ve just completed my build in a similar fashion.
I purpose made 3 trusses(6x2 rafters) for mid and quarter positions on the 9m length and fitted 6x3 purlins(3 runs each side)flush top and bottom between the trusses with the gable studding kept down 6" to overshoot the purlins before trimming off .
wallplate straps were screwed the bottom of all the joints,across the purlins after the purlins were side stitched with 100 screws and galv wire nails just to be sure
the purlins were set at 90 degrees to the rafter with the bottom ones furthest out point plumb with the side studs externally and the rafter tails trimmed flush as well .
this left virtually no gap between the wall plate and the purlin but i ran the foam gun along externally just to ensure no cold air ingress .
my sheeting was ordered to suit so was already back cut on the bottom sheet .Care was needed with the rafter length to ensure a tight fit along the ridge from both sides ,i foamed this above too before fitting the ridge .
I then fitted a 7x 1 1/2 facia along the outside to take the gutter and 12mm t&g sheeting then fitted from the top down after fitting a vapour barrier.
To get a fixing point between the rafters for the facia ,it is necessary to fix a 2x1 treated lathe at the required height on the bottom purlin externally using a straight edge up the face of the exernal stud work.adjust the lath until it touches and fix in place .
I got gable trims sent with the roofing sheets and put plenty of foam on the ends ,left to set ,trimmed flush and trims fitted .
rockwool insulation internally covered with 11mm osb .
my only weak point is the single skin roller door .
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As above create a thermal break in the bottom sheet with a saw cut then mastic up or use a rubber T shaped strip to fill the cut.
You can reduce thermal bridging by one or more shallow cuts through the steel liner sheet which rests on the wall plate
Order the roof sheets the length you require including the overhang but remember if you have put a thermal break cut you will have reduced the strength of the panel so keep overhang sensible
Alternative approach would be a built up insulated construction, where the liner sheet wouldnt go all the way through the wall section
If you have to cut panel at all do it at the ridge where any messy cut will be covered by the ridge flashing
Easiest way to attach eaves line gutter is you fit a strap to the crown of the profile which sticks our over the top of the gutter, bend down the front face of the gutter and returns under the gutter supporting it. They are standard available parts

See this post for any details
I should have said that panels are avai;lable with foam cut back, this normally 60. 100 or 150mm. You will need some cut back or the foam and liner at the eaves to fall into the gutter properly. Most panels are factory cutback to allow end lap joints
I am rather late to you question!
I have a similar cabin but not as a workshop (Home office) 10m X 3m. As I was concerned about appearance, I went for Fibre cement slates, see below, which can be used down to 15 degree slope. I found them easy to fix and cut. The ridge flashing is aluminium. Insulated with rigid foam membrane etc. One other benefit is no "rain on roof noise".


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