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Workshop Build - Floor height

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David Murray 104/06/2018 16:50:24
20 forum posts

Hi All

Having had to sell all my projects previously to buy and renovate my home, I've just got a small corner of the garage setup as a workshop and started building a 2" Clayton. The carrot to the new house is that there is enough room for me to build a 4m x 2.5m workshop in the garden. I've been busy putting a new fence up and now knocking down the brick wall where the workshop will go and my mind is starting to think about groundworks. My plan is to build a 4" thick concrete base to build the workshop on and then 3x2 floor joists at 18" spacing.

The question is how low do I go ....... Should I dig down 7" so the floor is level with the surrounding ground, but the timber will be below the surrounding ground. Or do I only dig 4" down and then have a 3" step up to get into the workshop - I am thinking about having to get the mill, lathe and any projects I manage to build in and out of the workshop.

All thoughts/ideas/experience greatly received.



Journeyman04/06/2018 17:06:29
816 forum posts
142 photos

David, You havn't said what sort of structure the workshop will be, wooden shed, brick or block, pre-cast etc. Whichever it will be I would consider making the slab thicker and re-inforced and do away with any sort of wooden floor. I am not up to date on modern building methods but you could even have insulation under the slab, most likely will also need some form of damp proof course. Machinery will be easier to site and more stable on the solid floor. You can apply suitable finishes to the top surface or even polish the concrete to get a good smooth finish. Consider the site for water/damp it may be that the top of the slab should be raised well above the soil level. When in doubt consult a local builder perhaps.


Edited By Journeyman on 04/06/2018 17:08:16

Bazyle04/06/2018 17:28:01
5462 forum posts
206 photos

Allow for a longer gentle slope outside the door. You also want the door to open clear of the outside paving and but against some sort of lip at the bottom. so will need a bit of a step anyway. Then you also want clear run off for water both off the door and off the paving. I suggest a cast concrete channel carefully dimensioned and sloped so that a piece of 4x2 drops in when you need the gap filled.

Since you are starting from scratch build the walls on their own brick stub walls on their own foundation. Then cast the concrete base with a 4in insulation filled gap between it and the walls and also on its own 4in layer of insulation. You then have a solid insulated floor with no cold bridge ideal for machines. The stub wall can be a 2 in wall using paving on edge then 6x1 in boards can form the wall studs bridging across the paving to the slab giving a 6in insulation opportunity.

BTW for all groundworks you dig down to remove all topsoil, anything with organic matter. Over time organic matter will decay and leave a void so you have to get down to subsoil. (ok not essential for a shed but still good practice)

larry phelan 104/06/2018 17:32:03
818 forum posts
17 photos

My workshop,and sometime garage was built on a 6" slab with insulation underneath,the surface being polished.

The builder thought I was mad going to such lengths but it,s hard to beat a smooth floor when you need to move stuff around. Damp proof underneath,of course. Floor ends up just slightly over ground level,so no problem getting machines in or out. Roof height might be worth thinking about though,more important than you might think,to go by some early posts. Sometimes that extra few inches can make all the difference.

David Murray 104/06/2018 19:00:02
20 forum posts

Hi All

The shed will be timber construction - mainly due to cost. I used to use a detached garage with a concrete floor and that was painfully cold on the feet in winter - hence why I was planning a concrete slab with 3x2 floor joists with insulation under the floor, probably covered in 30mm OSB or similar I was also thinking of putting a gravel filled trench around the slab to help water drain away and down. Roof will be a pent roof as I am limited to a maximum of 2.5m high

colin hawes04/06/2018 19:23:10
515 forum posts
18 photos

My wooden workshop is at least 12 years old and has a concrete floor with gravel under it and a damp proof plastic membrane between. There is a small, shallow, ditch around it that drains away any water to a lower level. I have an old carpet on the floor and it is always dry. The concrete is about 3" thick and supports my heavy machines adequately. Colin

Brian Sweeting04/06/2018 21:54:13
442 forum posts
1 photos

I'm not an expert but as it's timber have the concrete rising above the surrounding area to prevent water pooling around the base timbers.

Too, have the floor joists at the standard building 16" centres, check your tape measure and you will see a mark every 16". This will make finding them easier later on if you want to screw something down.

Clive Foster05/06/2018 09:44:59
2365 forum posts
76 photos

Waterproof chipboard tongue and groove underflooring boards make a perfectly satisfactory and more than adequately warm floor when laid on top of a concrete slab with an insulation layer included. I used the good quality green stuff which has proved non-dusty. Well up to supporting industrial style machine tools too, Bridgeport, Smart & Brown 1024, P&W Model B 12 x 30 being the major heavyweights. Stands up to the odd welding mishap well. Generally tools don't chip if dropped, which is nice. Use the spare bits for shelves and cold work bench tops. Slightly rough finish is great for stopping stuff rolling off but isn't so rough as to prevent deliberate sliding.

Was told the brown equivalent is dusty, so I didn't use it.

Put up over 12 years ago so I don't recall how deep the insulation layer was laid. Basic floor is re-inforced concrete with total depth of around 9". Overkill but its not going anywhere. Stub walls up to timber frame. One brick above entry "patio",which is at highest point, so taller round back. OSB both sides of 4 x 2 timber frame, insulation between, I used fibreglass Celotex or similar sheet would have been easier. Shiplap outside painted with Sadolin has proved durable and smart. White emulsion direct on OSB inner walls keeps things bright. I had the height to put a flat ceiling in under a pitched steel sheet roof. Insulation under both. Cheap over-makes / second hand double glazed household windows and doors help keep it warm and damp free. Needs heating only at snow time and foggy, dreary winter days.

Fit plenty of electrics. I used ex-industrial metal clad distribution boards rather than ordinary sockets. Cheap, real cheap 'cos I had them!


Zan05/06/2018 11:23:14
185 forum posts
13 photos


Go for a thicker slab with at least 50 mm insulation preferably 100 mm. Be sure to bring the Dpm up to cover the edges of the slab or damp will penetrate try to get a good layer of clean rubble under the slab. It will be warm and a lot more solid for machines. I use perforated rubber mats on the floor, stops small dropped components rolling too far, is warm and the dross falls in the holes and not underfoot. Insulate the walls with king span more expensive than rock wool, but better. Line it with 12 mm flooring chipboard stood on end then it's so easy to screw anything onto the wall and its solid

My workshop has plastic cladding, air gap, breathable membrane, Osb, 4 x2 timber and the chipboard. Very very warm and dry Any timber must be at least 4" above ground level, with a ramp at the door. Will be a problem getting machines in, but you won't be doing that very often

Lastly the dpm top edge must be covered, the external cladding should be positioned so it's overhanging the slab with an air gap if possible   An internal dpm must be fixed to the insulated frame before fitting the inner layer of chipboard. My 3 X 3 ( inside) extension cost about 1500 2 years ago


Edited By Zan on 05/06/2018 11:27:30

Bazyle05/06/2018 13:26:52
5462 forum posts
206 photos

I have just googled shed planning turning up


and this doesn't seem to mention the max area permitted for sheds anymore, apart from the 'half size of house' bit. It used to be restricted to garage size in wood, or twice garage size in 'non-combustible' when next to boundary.
Has there been a relaxation recently ?

pgk pgk05/06/2018 15:01:40
1911 forum posts
288 photos
Posted by Bazyle on 05/06/2018 13:26:52:

I have just googled shed planning turning up


and this doesn't seem to mention the max area permitted for sheds anymore, apart from the 'half size of house' bit. It used to be restricted to garage size in wood, or twice garage size in 'non-combustible' when next to boundary.
Has there been a relaxation recently ?

When i bought this farm i got local planning officer to come down re sheds/greenhouses and he nicely pointed out that my predecessors planting of trees around the extended garden he'd created had been in 'illegal' existence for long enough to gain immunity such that I now had a 3 acre garden I could happily cover half of with whatever i wanted subject to things like heights near boundaries etc. I should have made my shed bigger. That was 7yrs ago


Samsaranda05/06/2018 16:45:06
965 forum posts
5 photos

David make sure any timber of the construction is well clear of the ground level to prevent water damage, my workshop outer walls, which are wood, stand on 9 inch high blockwork. Internal floor is concrete much more practical and stable for the machines.

Dave W

David Murray 106/06/2018 08:52:51
20 forum posts

Thanks for the ideas everyone.

I am now having a dilemma! Leave the floor concrete or wood! I suppose I could put the machines in and then if find it is cold put a wooden floor in later between them.

As it happens I am demolishing a 6ft high double brick wall to make way for the shed so I suppose I could lay a couple of courses of brick on top of the foundation slab and then bring the wooden walls down on top of them.

steamdave06/06/2018 10:36:38
455 forum posts
35 photos

My workshop was a single garage with a concrete floor. When I moved here, I first laid a DPM, reaching up the sides to just above the final floor level. Then 2 x 2" battens in a 4 x 2 ft matrix. The 'holes' were filled with 2" polystyrene foam slabs and the whole lot was covered with flooring grade T & G chipboard. To cap it off, the floor was covered with industrial grade vinyl flooring.

I have had some heavy machinery standing on it with no problems. It is warm and comfortable to stand on and also it is easy to keep clean. 15 or so years on, I don't regret getting a hard-wearing, comfortable floor, even though it may not have been the cheapest solution at the time.

If you use a wooden floor, you need to seal it in some way to prevent oil ingress. The vinyl (non foam backed) is an easy solution. Choose a light colour so that when you drop a small screw or the like, it can be (relatively) easily seen.

The Emerald Isle

Jon Jones06/06/2018 10:45:39
2 forum posts

Try looking at this forum for ideas on workshop constructio. some good ideas, methods and construction logs.

their sub-section - workshop builds. Gives thje rules on size and distance from boundaries and heights as well to comply with planning and Building regs if you need to.

ChrisH06/06/2018 11:58:34
878 forum posts
29 photos

Dave - if you were wondering what a 'polished floor' meant for concrete, it means a floor that has been power-floated. You can hire power floaters by the day. The trick is to wait until the concrete has nearly gone off so you can walk on it but is still a wee bit soft so a little of the 'fat' will rise to the surface when troweled. Then go over and over it with the power floater, maybe adding a little water spray if it's too dry, until a nice flat polish is achieved.

It's well worth the extra effort, you get a nice flat smooth floor. The snag is that there is usually a long wait until the concrete is ready. Lay the concrete at the wrong time of day and you can be power floating at 2-3 am! Not really neighbour friendly. Perhaps get a builder/ground works guy to do it, he will know the right sort of time frames and can plan the job accordingly.

That's how I've seen it done, no doubt someone else will point out where I'm wrong!


Edited By ChrisH on 06/06/2018 11:59:20

Emgee06/06/2018 17:14:07
1701 forum posts
225 photos


Polishing the concrete is well worth the effort especially if you have a big area the power float is the way to go, but if a small area it can be done by hand with a steel float but with a lot of manual effort.
I used a floor paint on mine when the concrete cured sufficiently and sweeping up dust and swarf is a simple task.


Jon06/06/2018 21:01:48
997 forum posts
49 photos

Had same problem David in the winter the cold comes through the floor and up your bones.

Easty fix for little is the cheap 3mm rubber matting should do that for £30 region.
Its easier and quicker to warm up, what used to take 4 hrs now takes 1hr.

Over time even thick board will wet and or bellow at any centres, more so with heavy machines on top stick with thicker concrete you wont regret.
Boards good for the walls though on battons, just make sure the shelf brackets are made specific spreading the load 1"x1"x1/8" good for 1/4 tonne spaced accordingly around 2ft. (3 over 4ft)

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