My garden building design - advice welcomed

[danlightbulb]

Hi all,

Im planning to build a solid garden building/workshop. The size Im hoping for is 6m long x 3m wide. 2.5m high at the tallest point, 2m at the rear.

Ive got an outline design done in sketchup which looks like this.

The floor joists are 6x2, 3m span.

The walls are 4x2.

Floor sheeting is 18mm OSB. I was thinking 12mm or 9mm for the roof and walls though to reduce weight and cost.

In my design I haven't shown the intermediate floor or wall joists. One of the problems I seem to be having is lining everything up whilst minimising cutting. For example, the floor sheets are 2440x1220, which doesn't divide evenly into 400mm joist spans. If I space the joists evenly at 400mm centres I end up with sheet ends not over a joist.

Anyone any suggestions on my initial design please?

Thanks
Dan

 

[Notch7]

bear in mind, the permitted development rules are 2.5m high from ground level to top of roof (assuming within 2 metres of boundary)

also bear in mind if you are sitting the wall frames on top of the floor joists, then your floor OSB will start at an offset position

to get your joists lining up to the OSB you need to set out the joists equally so you get spacings at 2440, then divide up equally in between

dont forget to use 50 x 25 battens externally to create a cavity before your cladding -if you are having say timber cladding, then use that on the seen sides of the structure and a cheaper finish on the sides facing the boundary fence -box sheet metal or rendaboard

 

[^woody^]

You are better off designing in sections equal to the size of an OSB sheet - 1200 x 2400 panels if metric with a central strut.

Design the floor and roof with joists at 600 centres, if possible, to match the wall panel struts

Then you make each panel up and just bolt them together.

 

[danlightbulb]

You are better off designing in sections equal to the size of an OSB sheet - 1200 x 2400 panels if metric with a central strut.

Yeah thats what Im saying - the timber lengths are metric i.e 2.4m, 3.0m, 3.6m. But the sheet materials are 2440x1220 so aren't directly compatible for spacing.

 

[danlightbulb]

also bear in mind if you are sitting the wall frames on top of the floor joists, then your floor OSB will start at an offset position

I was intending to sandwich the OSB between the floor and wall joists i.e build the floor first complete with full OSB coverage and then lay the walls on top. Is it better to have the walls directly on the floor joists and put the OSB in the middle of it all? I'll need extra joists then around the edges otherwise will be unsupported.

 

[^woody^]

Yeah thats what Im saying - the timber lengths are metric i.e 2.4m, 3.0m, 3.6m. But the sheet materials are 2440x1220 so aren't directly compatible for spacing.

Seriously?

You just fit the timber around the edges of the sheet and one down the centre!

Or you trim the sheet if metric units are essential - but I doubt they are.

Or if you want to do it better and use CLS, you work to the 1220 width and 2400 height and the 2440 height of a sheet allows for overhanging a horizontal top or bottom plate

 

[danlightbulb]

Seriously?

You just fit the timber around the edges of the sheet and one down the centre!

Or you trim the sheet if metric units are essential - but I doubt they are.

Or if you want to do it better and use CLS, you work to the 1220 width and 2400 height and the 2440 height of a sheet allows for overhanging a horizontal top or bottom plate

What do you mean 'seriously'?

Im trying to get a good design that minimises cutting particularly of sheet material or every single timber joist.

A 2440 x 1220 sheet will not fit perfectly into a 6mx3m footprint. To avoid cutting sheets I would have to make the building either 2440 wide or 3660.

Lets say I did make the building 2440 wide. Well now I have to cut 560mm off every single 3m long floor joist.

If I don't have uniform spacing it will take ages to cut various bespoke length noggins or cut bespoke width pieces of insulation board to fit.

The wall panels aren't so bad, Im going to have to cut most of the sheeting anyway as 3 walls are 2m high and only one is 2.4m high. Its more the floor joists Im trying to even up the spacing on.

 

[big-all]

i would find out what lengths off cladding are available from the source you are using then form a plan off what you are happy with joints along the length wise and work out iff you are happy wit a say 2" timber half way along covering the joint from top to bottom and same 2x1" tile baton on the corner this can boost the coverage length by say 120mm 'not a lot but then helps stretch a say 4.8m board to sheet material at 4880[2x2440]
you also need to keep in mind the all round roof overhang and the say 75mm extra required as 3m at a slope will be perhaps 3050-75 dependent on actual angle

 

[big-all]

dont think finished width, think finished frame width otherwise you will make it more difficult the cladding will be what ever it is as i say above boosted a bit at the corners by the 2x1"tile baton

 

[Notch7]

Im trying to get a good design that minimises cutting particularly of sheet material or every single timber joist

You don’t need to

you set your joists so they are at 2440 ctrs, starting at one end.

you lay your OSB perpendicular to the joists, if the joists are set to 2440 ctrs, then you can lay 2 full sheets straight down, cut the last one down to suit the 6.0m floor.

 

[^woody^]

Lets say I did make the building 2440 wide

You don't make the building 2440 wide. You stated it will be 3m wide so that's what you make it. All you do is work in units of 1220 wide panels

A panel is 1 strut at each side and then one in the centre. You work to the board dimensions not 600 or 400 spacing.

LIkewise for the floor, assuming the span they required distance for their depth, you space the joists according to the panel width/length not 400/600 centres

 

[danlightbulb]

Ok that makes sense for most panels but to reach my desired length of say 6m or width of say 3m, I will then need to have some odd sized panels with a lot of cuts at the ends.

Especially the floor, 3m width is 2x1220 panels plus a 560mm wide panel to get to my required width.

Instead of 3m, am I best going for multiples of 1220 so 1220 + 1220 + 610 = 3050?

 

[big-all]

ideally you would work it out to be efficient material wise
in my case a 10x12ft shed with a 30 degree pitch and 150mm overhang needed 6x 18mm x6x4ft panels for the roof plus 3x4x2ft off cuts to give a roof around 13ft 6x 11ft 6 with the floor being an exact 12x10 so 3 full sheets with 3 off cuts from the roof = 3 boards so 6 for the roof and 3 for the floor so 9x 18mm ply this actully was more expensive than the txg 5" shiplap to clad the shed

 

[Larry1990]

Having nearly done one, If you are using 8x2 OSB 18mm, which is great for the roof and floor, keep in mind that they are 590mm wide and not 600. I tried like yours to be close to the sheet size but end up cutting. It's not too bad if you take your time with a straight edge or use a fence on your circular saw. A mitre saw and stand is also a great investment if you are worried about accurate and uniform cuts.

 

[^woody^]

Instead of 3m, am I best going for multiples of 1220 so 1220 + 1220 + 610 = 3050?

Unless you are physically constrained by the site or require specific internal dimensions, you would build to a size that gives the least amount of cutting, not work to an artificial size and create lots of unnecessary work and unnecessary waste.

But as the big man alludes to, take account of the cladding and roof too as you don't want to be saving on the structure at the expense of waste or additional cost on the cladding or roof covering and finishing.

But generally, all comments should be standardised in multiples of 600mm, so if it does mean trimming 20 or 40mm of a board, that's 2 minutes and insignificant waste of a bit of board.