Lean-to Bike Shed

**jimbouk** · 18-03-2022, 03:53 PM

Re-purposing this thread into a build thread

Will keep the questions coming but this should save everything being spread around multiple posts!

The space & base:

This is the rear garden behind the garage, got a gate behind where the photo was taken to get the bikes in and out. Garage is 'up' with the floor line where the power socket is. Weed matting and stones have been put down on the left and rear (from photo) edge where the drainage ditch was kept (original level was a bit lower).

The space (including wood surround) is 2.77m x 1.755m. The intention is to hang bikes on the garage wall, and a pent roof running down to the left fence.

Will obviously lose some length due to cuts so expect the door to be slightly large to make up for it.

Shopping list:
Bought:

Concrete paint: No Nonsense Trade Floor Paint Grey 2.5Ltr - £19.99
Sleeper screw: Timco In-Dex 10150INH Flanged Hex Index Timber Screws Silver Ruspert 10 x 150mm 10 Pack - £14.89
Concrete bolts: Easyfix Bright Zinc-Plated Carbon Steel Concrete Bolts M8 x 80mm 10 Pack - £6.29
Wood screws: Spax Wirox TX Self Countersunk Woodscrews 5 x 70mm 100 Pack - £11.29
Flashing: Bostik Flashband Grey 10m x 225mm - £21.49
Wall bottom: Treated Incised UC4 Sleeper Green 100 x 200 x 2400mm x2 - £83 .88
Walls: Sterling Zero OSB3 FSC 2400 x 1200 x 9mm x 5 - £178 .14
Roof: Sterling Zero OSB3 FSC 2440 x 1220 x 11mm x2 - £80 .50
Wood treatment: Barrettine Wood Protective Treatment 5L Clear - £24.28
Wood cut end treatment: Cut End Wood Preserver 1L By Barrettine - £16.50
Angle brackets: Stainless Steel Angle Bracket 60 x 40 x 60mm x10 - £26.90
Wall/roof frame: Wickes Treated Kiln Dried C16 Timber - 45 x 95 x 2400mm x 12 bought - £113.40
Roof felt: IKO Black Shed Felt - 10 x 1m - £20.00
Truss clips: Sabrefix Truss Clip Galvanised DX275 95mm x 44mm 20 Pack - £8.79
Shed wall to brick wall sealant: No Nonsense Builders Silicone Brown 310ml - £6.99
Wood primer: Leyland Trade Wood Primer Undercoat 2.5Ltr - £22.99
Damp course: Capital Valley Plastics Ltd Damp-Proof Course 1968ga Black 30m x 100mm - £4.29

Decided:

Wall/roof frame: Wickes Treated Kiln Dried C16 Timber - 45 x 95 x 2400mm x 13 left to get

Unknown:

Felt tacks: think I have some in garage
Exterior paint (colour...)

Running cost: £660.61

Original post:

Hello,

I've got a shed base (poured concrete, wood surround) behind our garage ready for a bike shed. I'm hoping to use the garage wall as one of the shed walls to maximise space rather than just dropping in an off the shelf shed with gaps around.

I've been trying to read around on the job but most of the instructions for building a shed are on a wooden base, e.g. https://thecarpentersdaughter.co.uk/...e-a-shed-base/

Part of me just wants to build the 3 walls, fit them to each other, the base and the garage wall and be done with it (and the roof

). Does that make sense?

I'm sure I'll be back with more questions, will look round the other shed posts on here as well. Cheers!

**jimbouk** · 18-03-2022, 04:45 PM

Just seen this one from https://forums.hexus.net/home-garden...new-shed.html:

Originally Posted by Saracen999

I'm not expert, but my approach to a concretebase was to get the shed clear of touching it. A good base, which essentially decent quality (as in outdoor-rated, properly treated base of 2x4, with the 4" side vertical (i.e. givig a 4" ground gap) and then a heavy sheet of watrproof ply (I think it was 3/4" or about 18-20mm,might have even beem a inch thick) provide the base on which the whole shed sits. The actual shed skin was about 1/2" or 15mm (yeah, I know 30mm <> 1 inch) thick, whick pretty much ensures it won't warp/shrink and therefore leak.

So I guess the intention is that the treated 2x4 wood makes contact with the ground and deals with the moisture so the floor and the bottom of the walls do not? And air can flow under the floor (although inside the actual shed it's still as sealed/ventilated as you make it). The wall cladding would then not touch the floor either even if it was slightly proud of the wall frame at the bottom to cover the base (is that a good idea?).

**Ttaskmaster** · 18-03-2022, 07:32 PM

It makes sense to me.
I think the bigger issue would be ensuring you have a weatherproof seal all around the sides and roof, as it's right against the house wall. We have a similar entry-way thing* on the side of our house, but whoever built it forgot to include lead cladding over the roof joint!

I like The Carpenter's Daughter site, though. Very good find!

*No idea what it should be called - Wooden house extension in front of the front door, bigger than a porch, it's basically another full-size room with a second room and toilet off to the side. Most fitting term I could find was a barbican!

**TeePee** · 18-03-2022, 09:14 PM

The major thing to think about with a wooden structure is moisture.

If wood surround means the formers used when pouring the concrete slab, which are in contact with the soil and potentially your shed, then they will wick moisture. Placing your shed timber in contact isn't the greatest idea. You can remove those and simply deal with the concrete base.

In the US, timber framing on a concrete slab is the normal method of house construction. Typically there is a purpose designed membrane between the wood and concrete for air, moisture and insect sealing. For a shed, you probably don't need to worry about any of those things.

What you should focus on is thinking about where the water will go. Use overhangs, so that your pressure treated bottom plate doesn't end up sitting in a pool of water. Ideally your sheathing can overhang the edge of the concrete preventing that surface from collecting water.

**jimbouk** · 18-03-2022, 09:43 PM

Cheers both.

Yes I've considered the roof to wall join - might need to call in the builder for that one. Not sure I want the cost of lead but after a bit of reading it seems you can just chip out some mortar, feed in the felt and re-mortar on the join. Won't be the prettiest thing in the world but I won't be able to see it!

Re the floor. The wood looks a bit more sturdy than just throw away boards and are round all 4 sides including against the wall. But on two sides it goes down to drainage space so wouldn't want to rely on them for load bearing. One side is level with and butting up against decking and the other is against the garage wall. Will take another look at the two exposed edges and decide whether to keep our remove or just to treat and try and keep the water off.

Aiming for a single slope away from the garage wall for the roof. Will have some overhang all round and is a fairly sheltered space so hopefully all the water will stay away! Guess I could gutter if feeling keen and feed it down into the ditch.

Will try and grab a decent picture on the space on the weekend

**ik9000** · 19-03-2022, 03:53 PM

rain splash zone IIRC is typically taken as 150mm above concrete. If you can tolerate a step-up into your shed use driveway paviors/frost resistant bricks to raise the timbers off the ground. This allows under-floor ventilation so the floor panels should last longer too without worries about damp going underneath and not being able to dry out. Set back the supports so the shed overhang shelters the bearings of the shed onto its supports and prevents direct wetting.

Treat all exposed timbers ideally start with pressure treated wood and then give all cut ends with 2x coatings (or a good soaking) of end grain preservative such as ensele (others are available)

After that has dried coat all the wood with decent preservative-finish coat for external use. Some include stains too if you want a particular colour etc. Depending how long you want the thing to last consider only using fixings that are suitable for external use - these will be more expensive. You probably don't need stainless, hot-dip galv is probably sufficient, just be consistent and match the fixing materials to the brackets etc.

NB to allow for mastic joints between the timbers and your brick wall, and use some slotted galv or stainless tie brackets to restrain the panels back to the masonry but allow it to move vertically as the timbers and brickwork will want to expand/contract at different rates. Any roof flashing should similarly be lapped and jointed to allow for movement.

Any panelling you use should ideally be OSB3/OSB4 and ply to BS-EN636-3 to deal with external conditions. Note you still need to add surface treatment to the panels, the specs deal more with the glues used in the panels to make sure they can handle the humidity. The sort of tropical hardwood that could also resist external exposure without treatment generally isn't available (and rarely sustainable ergo illegal if anyone tried to do it).

**jimbouk** · 19-03-2022, 08:23 PM

Updated the first post, will use that as a build tracker and keep the questions coming here. Thanks everyone for the information so far. There is no fixed budget, but obviously I've not just handed a blank cheque to the local builder so not looking to 'waste' money. One of the reason we moved to this house was because it has a garage for my car - but it's been 8 months now and I still can't get it in due to the bikes (and some other crud I'm still to cull!).

I'm going to start from the bottom so I don't overload myself. So:

Floor bearers: "2 by 4" (45 x 95mm), 4" upright as advised sounds the best. Do I need C16 treated for this or is ordinary treated enough? 400mm spacing seems to be the norm so will go with that.

Floor: Will need to look in details at the options. Sounds like the grading is as important as the specific material though!

Floor covering: As bikes will be coming in and out then it's probably worth having something on top - I got a bunch of children's interlocking play mats which were put to good use keeping me off the ground when I used to work on my car on the drive so something similar might do the trick, else I can see if anyone is getting rid of old flooring - we put the old kitchen floor

Will get an end grain preservative and then a general preservative for the rest of it. I'm guessing taking the time and doing it all carefully before construction will be time well spent - you can pop another coat on the outside in a couple of years but complete reassembly will be a job and a half!

Re the step up - ideally this won't be too big so a bike can wheel in and out without being carried so I won't go too crazy on the floor height.

**ik9000** · 21-03-2022, 10:49 AM

Have you considered just using the existing concrete for the floor and building a dwarf wall 2-3 courses high in brick to support the timber sides? Or do the levels not work?

I imagine this lean to will fall under some kind of permitted development clause but do check with your local planning authority whether you're going to need any permission. Emphasise it's for bike storage and I think that helps motivate them to help you under their green targets etc. Don't mention it's so you can get car in garage. It's so your family can access bikes and do more journeys that way to reduce your use of the car.

Also never underestimate a fussy mortgage surveyor or future solicitor wanting to see building regs for lean-tos that rely on the main building. Pita for something so basic but not unknown for mortgages to be refused- seen it happen (though that was for a conservatory rather than a bike store)! Deal with it as % change in load onto the wall. I imagine the % will be small enough to be considered acceptable. That assumes you put vertical load onto the wall, if you frame it right you could probably avoid having to do that.

Re timbers I wouldn't use ungraded timber for this.* Not when it adjoins the house. Treated c16 minimum or c24 depending on what your local merchants stock..c24 is better timber both strength and appearance (fewer knots etc) 4*2 will probably suffice for the dimensions you give if you span the short dimension with it. If you want to go the long dimension I might use 5*2, but tbh it's the connection details that can sometimes govern depth required depending on how you want to joint everything together, and it all depends how much load you want it to carry.

Walls and roof typically need 4*2 c16 at 400-600mm centres with 11mm-12mm panelling screwed to each timber at 150mm centres or thereabouts.

*graded timber C16 etc has been assessed as suitable for structural use and assigned a strength class, with corresponding tabulated engineering properties. You can therefore use it with confidence knowing what it is good for, and if needs be an engineer can apply a full design to it. Ungraded is a lottery. It could be ok, but isn't the likelihood that it fails grading in some ways (otherwise why not sell it as the better stuff?) and at that point wouldn't you think twice about trying to use it structurally, particularly for anything intended to carry people?! I guess the flip argument is that grading assessment incurs cost and some suppliers might seek to avoid that by selling it ungraded... but then it's a gamble as to what you actually receive. Without a classification you have no comeback if it's not what you were hoping for assuming there is no set preformance/quality standard mentioned.

**ik9000** · 21-03-2022, 11:17 AM