L-shaped shed - is it possible?

[Nesmy]

Hi folks,

I'm just about to build my first very own shed. First I wanted to buy something already built, sit it on top of paving slabs and call it a day. However I live in a very windy part of Scotland at the top of a hill which doesn't help the matter. I would like to build a shed that will last at least 20 years. The plan is to use either 2x3's or 2x4's and 11mm osb on both sides with waterproof membrane on the outside and some 100mm insulation between the boards. There are 2 parts of the idea I struggle with and that is roof and the base. I have already acquired roughly 25 sqm worth of paving slabs which are around 3cm thick free of charge. The problem with soil is that it tends to soak up water and get very soggy - sometimes to the point where your feet leave an imprint in the sod. Furthermore, this is Scotland - it rains all year round. How do i avoid moisture entering my shed? Also the ground is a bit slanted, from one edge to the other there is about 15cm difference in height.

I have made a rough sketch that is attached to this post outlining shape of my plot (marked in black) and shape of my planned shed (marked in blue).
That's where the second problems presents itself - in order not to lose 6sqm worth of a shed I need to build it in a L shape. Walls seem pretty straightforward however I have no idea how to make a pitched roof shaped like that. Any guidance would be amazing.
I would like Eaves to be at around 2 metres and no part of the shed can be higher than 2.5 metres within a metre from the property boundary.
In total, I'm planning to store around 2 tonnes worth of items within that shed so it should really be quite solid.

If it comes to my skills - I feel quite competent in DIY within the house - I laid tiles, remodeled bathroom and the kitchen, laid carpets. I didn't do much work on the outside though. I have a decent set of tools but I'm no builder - my daily occupation is being a nurse


Any comments, ideas, anything - greatly appreciated.

 

[PaulUszak]

Hi.

So with respect - competent DIYing isn't going to help. Your problem isn't the roof question, which is only symbolic of your true problem.

Your true problem is the 6m length of wall. The 3.4m length too probably. The shed is going up a hill in Scotland. Has it ever gusted to 100mph? You can look that up. Probably has. An un-braced DIY OSB wall is simply going to be blown over or sucked off (wind sucks as well as blows). The obvious solution is to make the 1.4m wall structural, either cross braced or utilising diaphragm action of the OSB sheets. Then prop from it to the (approx) 6m mid point. Similarly prop from a structural 1.8m wall. Note: diaphragm action is cleverer and more efficient, but still not a common form as it's harder to design/build. It means there's no frame (no chassis) and if you then mess with the OSB you'll weaken the structural integrity. Like cutting holes in a monocoque. As in windows and doors especially.

The 2T of 'stuff' doesn't really help unless you can design/guarantee it's contribution to the sideways stability. And keeping the roof on. Further, the 2T is actually categorised as live load, which means it can be removed and thus contributes nothing to the shed's stability. You mustn't design this on that basis unless the 2T is absolutely un-removable - as in a huge pile of solid concrete. The shed must be safe (to others) as well as funky looking. Err, if the ground is so wet, what's to stop the 2T going through the floor?

Then there's snow loading. Does it snow on hills in Scotland? Snow's heavy, and it can simultaneously gust real hard whilst there's an existing snow load on the roof. That's makes the loads combine, but translates to even more wood for the build.


It's all tricky and I'm overly conservative, but. I would view it as quite ambitious to DIY a 6m x 3.4m open space made of wood on a Scottish hillside and expect a 20 year service life. Sorry. But see my sketch of your sketch...

My daily occupation was being a Chartered structural engineer
Thanks for the nursing.

 

[big-all]

general comments structure to one side
sheet material comes in 8x4ft sheets [2440x1220mm]
timber comes in metric but in inches reduced to the nearest 100mm as in 2.4/2.7/3/3.3/3.6etc up to around perhaps 5.4m
you need to find out what sizes are available in pressure treated in your area and plan accordingly to save waste and keep the roof line below 2.5m assuming the same as england ??

 

[Notch7]

the roof line below 2.5m assuming the same as england ?

I think Scotland has a different PD rule -something like 2.5m max near the boundary but can be taller further away.

(Its from memory and I cant be bothered to look it up, so could be talking bollards!).

 

[Notch7]

I live in a very windy part of Scotland at the top of a hill

Eek

My daily occupation was being a Chartered structural engineer

consider the wise comments from the pro!

I have built a garden cabin and combined shed in my garden which is 6m x 5m -but its in a sheltered garden in Sussex.

I used 4 x 2 studwork, 18mm OSB outside, 18mm mdf inside. 100mm insulation in walls, 125mm in roof.

I built a flat roof with a lanterns -it was a real struggle to get under 2.5m.

if you build with a flat roof it may help your wind load problem as the flat roof designed correctly will help to brace the walls.
you might be best to built with 18mm sheathing plywood, it will give you far more structural stability for lateral restraint.

Dont underestimate the power of wind loading on a 6m x 2.4m wall panel.
nor the weight of snow on the roof (for my region, I think calcs are based on 75kg per sq metre)

you cant build on paving slabs -in your location you will need the walls bolting to a foundation -maybe you could do a series of concrete pads, put down some steel beams and build off that.

 

[mattylad]

Have you got lots of stone lying about on this hill?
You may be better off building stone walls.

 

[PaulUszak]

Or, you could go Mad Max. 6m ~ 20'. Assuming access, you could buy a used 20 foot shipping container. Haven't looked up the pricing, but times are hard and a deal may be possible. It does mean that there will be no structural issues as long as you stick it on level ground. Some type 1 can help. It's rigidity will spread the weight across the soft ground like a tank track. And it doesn't have to look bad either. Cover it with a surplus camo net or pea nets and grow stuff over it. Or paint it pretty. New ones are air tight (as we sadly know) so no water ingress. I think that I'd remove the doors/ a door and add my own wooden entrance. Have the door(s) on the leeward side. Insulate internally. Such is common on construction sites as temporary offices/ stores.

Others should weigh in here, but a free standing container isn't a permanent built structure so building/ planning regulations may not apply; reference all those trailers in fields along motorways used for advertising.

People actually use them to build family homes. When the Corona thing gets bad, you can use it as a bunker to safe guard your stock of loo paper and canned tuna fish. And whiskey.

 

[Tigercubrider]

I was going to mention shipping containers. You get a lot of bang for the buck.
Remember to allow either for access with a truck or a long reach crane .
If you're in the sticks then talking to farmers might help.

Also farmers will know a reasonable welder who might be able to join the two together in a weatherproof way. You can buy containers that are doors at both ends, but it's probably cheaper to site them and get busy with an angle grinder

 

[PaulUszak]

Lastly, this is what you can do with (ply)wood in an even harsher environment

 

[Nesmy]

Hi all,

Sorry it took me a while to reply. I was trying to reply at around 3am today but my draft wasn't saved and so I have given up and decided to do it at home.

Firstly, PaulUszak and others, thank you for your amazing contribution.
I thought that the idea of a shipping container is brilliant and cost effective as well. I even think I could coerce my wife into agreeing for a frickin' shipping container in the back garden. The issue is however that there is no good access to my back garden. For something of a size like that it would have to be lifted above my house and dropped into the garden which I can't seem to imagine happening. My house is a mid terrace. There are 3 terraced units of 4 houses each placed into a rough shape of a triangle.

Scottish Regulations relating outbuilding such as sheds are stating no outbuilding should be higher than 2.5 meters within a meter of a property boundary and 4 meters for all the other areas. Furthemore outbuilding cannot take up more than 50% of the curtilage. So, Notch7, you were correct.

PaulUszak, I'm not quite sure whether the gusts of wind were over 100 mph since it's quite hard to measure, based however on a website showing wind forecast and looking into past 3 months, theres high 30's and low 40's gales almost every week.

As the property had an old nasty fence around it I decided to replace it. I'm planning to put up a fence with 4x4 fence post buried deep into postcrete. Could that possibly shield the shed from some of the winds?

6 meter long wall of the planned shed would be facing my house, whereas the strongest winds usually come from the sides. Could you maybe explaing what do you mean by OSB diaphragm action? Also, you mentioned cross bracing the 1.4 meter wall. I understand you are a professional and it might be obvious for you, but do I understand correctly that by putting extra timber diagonally I will strengthen the whole of the structure?

I would like to have only one pair of normal sized doors and no windows - would like to have electricity delivered to my shed for a bit of a workshop activity so lamps are not a problem.

2 tonnes worth of items - obviously not concrete slabs but moveable items of sorts. Toilet rolls are already stashed away, along with tuna and whiskey. Can't do much to avoid covid though while caring for these folk, unless my family will decide to self isolate me in there

Just today I have seen somebody mentioning in the other topic ground screws. As if make a proper base with 6x4 joists, make it even and evenly braced with the screws and then build walls and the roof on top of that. Would that make any sense at all? It would seem to me that this soultion would also ''attach'' the shed to the ground not allowing it to fly to my neighbours garden. Screws would also keep the timber off the wet soil, slowing down the rot.

I have to admit PaulUszak, your solution for a roof shape is so simple, yet never crossed my mind. Also your sketch helps to visualise your ideas.

To address your other question, yes it does snow in Scotland, this winter the biggest snowfall was about 4 inches overnight.
I don't own an oil field however, so the Norwegian megashed-skyscraper plan will have to be postponed


Thanks everybody for you contribution and hope you will manage to guide me in the right direction.


Cheers,
Nesmy.

 

[big-all]

your building is limited to 2.5 maximum if any part is within 1m you treat it as a box so iff you have an apex and any part is within the 1m its 2.5 even iff the apex is more than a metre away

 

[Nesmy]

Hi big-all, that's correct. However following the advice of PaulUszak in terms of roof apex placement, the corner of the the apex would be in a proximity closer than 1 meter from the boundary.

 

[PaulUszak]

I only suggested that ridge arrangement as it keeps the roof spans the shortest. If height is a problem, you could rotate the ridge through 90 degrees so that the falls went at right angles to how I drew them. That means though that the roof structure would have to be 4.4 times as strong, or 2.2 times deeper.

I'm going to do a quick calc to see whether the shed needs to be bolted down against wind. Can I ask then:-

1. What's the nearest city to you?
2. Are you in a town or the countryside surrounded by fields?
3. What is this hill like? Is it a small hill that a wheelchair can get up with a push, or is it actually a mountain top?
4. What is your elevation above sea level?

These are the principle factors that influence the wind load.

 

[scbk]

You haven't said what your 2 tons of stuff is, maybe you'd be best off with a concrete floor? But if it's a terraced house, have you got good access for materials

 

[Nesmy]

2 tons of stuff - A lot of garden tools, all the other tools, toolboxes, spare furniture, shelving units, car parts including a whole engine, transmission, doors, parts of the chassis, huge chest freezer filled with food. That's just things off the top of my head. I can see it go up to 2000 kilograms as we all now things are easy to pile up with time.

PaulUszak:

1) Glasgow
2) Something in between. It's a tiny town with a population of a couple of thousand. I live at the very edge of it and the town is surrounded by miles upon miles of fields. I can see sheep and cows from my main bedroom window
3) My town has two main densely populated area, one with a main road that sits lower at around 600 feet and the part up the hill, where elevation sits at around 800 feet. The road I'm normally taking when coming back home is so steep I avoid it in winter and so does everybody else - only time when it was snowing I went there was when I was testing a set of brand new winter tyres and I barely made it. Could a person be pushed on a wheelchair up on this hill? In summer tyres and non-bariatric person sitting on it I could probably make it, however I don't pose usual nurses size - 6'4", 20-something stone here
4) As above, the lowest sits at around 580, highest at around 830 feet.

Could you tell me whether I understand that correctly, If we were to turn the ridge by 90 degrees, roof ridge would sit at three meter point on a 6m wall and 1.2 meter from the wall you were thinking of bracing? Also, could you provide some more details about the membrane action?


Thanks a lot!