Couple of questions

[Joe1975]

I am stewing over how to build a small workshop (16x8ft). I want to avoid a concrete floor but want something sturdy enough to take the repetitive knocking of hand tool woodworking. The ground is about two foot of soil on top of a chalk bed. I am hoping to build something that will last 30yrs or more, and remain level of course.

I have already built a studio in the garden. I dug nine large holes down to firm chalky soil (approximately 20”) and back filled with hardcore (4”) reinforced concrete (5”) and blocks stacked and concreted until above ground level. They are not going anywhere, but it was a lot of work by hand and, due to the spacing, the floor is a little springy. Not an issue for the studio but not what I want for a workshop floor.

I have a few ideas. The floor will need a lot more supporting points. I will be use 5”x2” joists due to overall height restriction of 2.5m.

Option 1: Use six oak railway sleepers llllll coated in bitumen and resting on a shallow bed of hardcore. This should provide the largest area of support. Concerns include; difficulty getting them all level, warping over time, eventually rotting.

Option 2: Use 600x600 concrete slabs on a bed of hardcore, timber frame raised with single blocks on top of slabs. This will involve the least digging and won’t rot. Concerns include, slabs cracking (especially if blocks are towards the edges)

Option 3: dig lots of relatively small, but deep, holes and use postcrete to cement oak beams in place. Bolt the joists to the posts. Concerns includes; over fiddly, potential movement, lots of bags of postcrete.

Which option would you go for and why? Any other ideas?

 

[Spectric]

You could localise your issues, with handtools I know you need a heavy solid workbench so why make the whole floor that solid. Just make an area really solid with concrete on which the bench can be built and then build the rest of your floor around it. If just looking at a really solid bench then you could make the legs from something like 6 by 6 post and sink them into the concrete so the bench just cannot move.

 

[HOJ]

In view of your caveat that you expect it to last for 30 years, why limit its life before you start, any timber near the ground will rot prematurely, (needs to be at least 150mm clear)
Why not seek planning permission and build in a way that will provide capacity for your future 30 year needs, even though they may not be apparent now, maybe for the inclusion of machines etc.
Its a massive compromise to build anything off piers or posts with a height limitation of 2.5m, adding to fact you will always have a step or two to negotiate to gain access as well as limiting headroom.

 

[Jameshow]

I would go for no2.

The oak dosent really add anything tbh.

I'd paint the underside of the floor beams with bitumen paint for best protection.
Moisture won't get in and any that does will be drawn out by the timber structure above.
I might dig down so the floor is level with the ground.

 

[Blackswanwood]

If you haven’t seen it already this may help …

Thread 'Build a shed Mike's way, without concrete'
Build a shed Mike's way, without concrete

 

[Joe1975]

You could localise your issues, with handtools I know you need a heavy solid workbench so why make the whole floor that solid. Just make an area really solid with concrete on which the bench can be built and then build the rest of your floor around it. If just looking at a really solid bench then you could make the legs from something like 6 by 6 post and sink them into the concrete so the bench just cannot move.

Good idea, if I were to use concrete I could probably get away with just doing half the floor area. It’s a small workshop so will need to be able to move the bench from time to time.

 

[Joe1975]

In view of your caveat that you expect it to last for 30 years, why limit its life before you start, any timber near the ground will rot prematurely, (needs to be at least 150mm clear)
Why not seek planning permission and build in a way that will provide capacity for your future 30 year needs, even though they may not be apparent now, maybe for the inclusion of machines etc.
It’s a massive compromise to build anything off piers or posts with a height limitation of 2.5m, adding to fact you will always have a step or two to negotiate to gain access as well as limiting headroom.

Thank you, good thoughts. If my woodworking requires some heavy machines in the future I will have to relocate, and I have a plan for that should it happen.
I’m looking for the simplest (and cheapest) build, having just built a studio and injured my back in the process.
I’m surprised that oak sleepers (especially if painted with bitumen) would rot under a shed in less than thirty years.

 

[Scruples]

I have a shed, the same size as your space. I would have liked a bigger area but was stuk with using an old single garage base.
I had a very small wall built around the wall, then laid a 19mm ply base on 5x2 at 600 centres. then, stud wall walls lined with 25mm insulation with 11m ply on the inside and plastic cladding on the outside. Double doors at one end and a side door, stable door, for access from the kitchen.
The roof was pitched from OSB and had a thick felt covering and then felt tiles over that. the roof, too was insulated behind 11mm ply. Good storage in the roof space.

I designed the interior as a corridor with units down one side with shelves and cupoards over, and made a workbench from pine and a hardword top.
I have a table saw, bandsaw, drill press with a Makita thichnesser stowed away for occasions use.
Tools are all over the wall above the bench or in cupboards.

It was built in 2011, when I retired, from my own plans, and cost me around £8,000 for materials and a carpenter for a week. I still like it and feel good having a space where I can leave a project on the bench and not have any problems with the management...