Dom's workshop build

[MikeG.]

My PT has never moved since I built the workshop, which shows it is in the right place, and not in the way. I have room in the main part of the workshop to have an 8x4 sheet of ply on stools, and to be able to work all around it.

You might have seen I overhung my roof at the rear by about 3 feet. This forms a really useful storage area, and eventually will have a proper base and racking. The more stuff you can get out of your workshop, the better. Dust extraction is obvious, and timber racking too. I'm watching a chap in another thread building a small set of shelves, and really struggling just through lack of space. He has to take it out to turn it around. You really don't want to go to all the trouble of building a fine new workshop and then find yourself struggling to move in it.

 

[MikeG.]

Three rooflights at £350+ a time will pay for an extra 1200 or 1800 on the length of your building..........and further, they're a nightmare to keep secure. At least with windows you can put an internal shutter in, or some bars. Your proposed building is very small, and will be well serviced by 2 windows (mine is fine with just one). Windows cost you wall space, which means less storage. I suggest you keep to one window for each side of your 2-bay workshop, forget the rooflights, and just make the whole thing a bit bigger.

 

[DomD]

Oops forgot to attach the plans: done now.

Three rooflights at £350+ a time will pay for an extra 1200 or 1800 on the length of your building..........and further, they're a nightmare to keep secure. At least with windows you can put an internal shutter in, or some bars.

If I am using uPVC windows and doors with rated locks I wonder what that means for insurance? I will need to look into it online. I guess I won't do rooflights then. The three windows at the moment are for: main area large window, window to allow long cuts on mitre saw, window in electronics area for laser cutter fume extraction and airflow when soldering. The two latter are going to be small, so hopefully shouldnt inflate the price too much.

I will definitely do an overhang and as I said maybe a small 'extension' at the front for bikes and dust.
Dom

 

[MikeG.]

I'd do away with the window for the long cuts on the mitre saw, and build something yourself. It only needs a top-hung hatch on the outside and a sliding hatch on the inside. That should be a lot stronger and safer than a window, and much cheaper too.

 

[DomD]

I'd do away with the window for the long cuts on the mitre saw, and build something yourself. It only needs a top-hung hatch on the outside and a sliding hatch on the inside. That should be a lot stronger and safer than a window, and much cheaper too.

Oo thats a good idea: I can also make it seamless as I think three windows on the front may be a bit much.

I am beginning to draw up my plans in CAD am wondering what sort of joist and rafter sizes will be needed for the 20'x12' size - I also want to use some of the joists for sheet material storage so will that mean any increace in size?
The walls I am just using 16'' on with 47mm x 100mm treated timber. Is it worth using C24 for everything or shall I stick to C16 for the walls?
And is there any way of calculating the required lintel size? My biggest opening is the 1200mm doors.

Thanks

 

[MikeG.]

Just use 145x47 at the moment for both joists and rafters.....and have a look at mine with the missing joists and a structural ridge, used to make the loft accessible internally. Don't worry about the timber strength rating, and your wall studs can be at 600 C's if you double up the top plate.

 

[DomD]

Just use 145x47 at the moment for both joists and rafters.....and have a look at mine with the missing joists and a structural ridge, used to make the loft accessible internally. Don't worry about the timber strength rating, and your wall studs can be at 600 C's if you double up the top plate.

Wouldn't 600C's for studs and joists mean cutting off 2cm/4cm of each standard 2x4 piece? Wouldn't 610C's make more sense (or 16")?

Also sorry for repeating a previous question but does exterior grade ply act as a vapour barrier similar to OSB? Hoping to clad the inside with it and dont want to put down two layers of sheet material.
Thanks

 

[MikeG.]

I'm not following. The length of your studs is irrelevant to their spacing. You'll be cutting all your studs anyway. And yeah, metric or imperial isn't an issue.......set out stud spacing according to your sheet sizes. Don't make assumptions about your sheet sizes, either. Some ply is metric, some imperial. Some OSB is metric, some imperial, although I think imperial is commonest.

Ply is usually way more expensive than OSB, which is why I suggest the latter, but ply is OK if you want to use it. Be cautious of the cheap stuff, and in particular watch out for sheathing ply, where finding something flat can be a real struggle. They can also delaminate. But if you've got a source of decent ply at a better price than OSB, then that's fine. It isn't as good a vapour barrier as OSB, but it's good enough for a workshop. It wouldn't be good enough if you were regularly doing a "wet" activity in the space.

 

[DomD]

I'm not following. The length of your studs is irrelevant to their spacing. You'll be cutting all your studs anyway. And yeah, metric or imperial isn't an issue.......set out stud spacing according to your sheet sizes. Don't make assumptions about your sheet sizes, either. Some ply is metric, some imperial. Some OSB is metric, some imperial, although I think imperial is commonest.

Ah sorry '2x4' sounded like I meant studs but I was actually referring to sheet material (which is usually 4x8, my mistake). All sheet material in my area is rounded off imperial (e.g. 2440x1220) so I think 610 spacing would work well - as long as that is enough to support the load of the roof.
Thanks

 

[DomD]

I am having second thoughts about using the concrete as the floor: on one hand, it would be nice to be able to do occasional welding on it but I think floor insulation is going to be a pain if not on top of the poured slab. I also don't really want to have to step up.
Are there any good methods of isulating the bottom of the slab and sides or shall I just use PIR over it?
Insulation is important as I plan to heat it year round.
Thanks

 

[MikeG.]

You can insulate under a slab. It just means a little more digging, that's all.

 

[RobinBHM]

I built my 18 x 9 shed on pads

I made 12 concrete pads, 4 rows of 3. I then used 4no 120mm x 78mm I beam steels I then used 4 x2 joists, which allows space for 70mm insulation. For me it saved moving so much ballast down the garden. Perhaps not as solid as a concrete base, but still very solid and means a suspended timber floor which is knider on the feet.

 

[DomD]

You can insulate under a slab. It just means a little more digging, that's all.

So can I confirm this is what you are suggesting, with the PIR (kingspan) right up against the earth under the slab. This will insulate the bottom of the slab but from looking online most heat is lost throgh the sides. Also, will the kingspan be fine under the weight of 150mm concrete?

I built my 18 x 9 shed on pads
I made 12 concrete pads, 4 rows of 3. I then used 4no 120mm x 78mm I beam steels I then used 4 x2 joists, which allows space for 70mm insulation. For me it saved moving so much ballast down the garden. Perhaps not as solid as a concrete base, but still very solid and means a suspended timber floor which is knider on the feet.

Definitely an option but I think I am pretty set on a slab now especially as I have some heavier machinery.
Dom

 

[MikeG.]

......... will the kingspan be fine under the weight of 150mm concrete?.......

Yep.

 

[DomD]

I redrew (once again) the floorplans: this time going to the full horizontal width of my area (14ft):

Some notes about this design:

1. There is no space allocated for a planer thicknesser yet, maybe it would work well just below the sheet material storage?
2. I see a lot of small workshops with a big table saw cabinet; is there any point in this rather than a 'roll out station' (or rather do you think the practicality outweighs the space costs)?
3. I feel like the mitre/cross cut station may be a bit too large; is there anything I could move around so it maintains its cutting length if required but another tool/machine could be used in that area?
4. Is there any point of having a 'proper' dust collection system in this size an workshop or will a cyclone and shop vac on wheels suffice?

As you can see I went for the seperate room and think this is what I will stick with just due to the risk of dust.

Ply is usually way more expensive than OSB, which is why I suggest the latter, but ply is OK if you want to use it.

I will think about this: I much prefer the look of plywood and really dislike the look of OSB, I know it can be painted but it still doesn't hide the texture. If I were to use plywood it would be WBP B/BB external grade stuff that apparently is less likely to delaminate.

This is my BOM so far for the base:

The subbase type-1 costs loads but I guess there is nowhere else where I will be able to get the amount of hardcore required (and deliver it). Other than that the concrete and pump are very rough estimates based on what I can find online.

I have no idea how I will get the hardcore and sand up to the site: I guess just bit by bit in a wheelbarrow? Has anyone tried the double wheeled wheelbarrows? Might help as this is the slope I need to get it up (from an upstairs window!).

Finally, any reccomended tools for the job? I use bosch wireless tools so am thinking about the wireless circular saw but not sure as of yet about mitre saw or nail framing nailer.

Thanks, Dom

 

[MikeG.]

£10 will buy you one bag of cement and a wheelbarrow of sand. That's seriously unrealistic. You'll buy sand and ballast by the bulk bag, for about £45 each.

Mortar is mixed at the site of the sand, and then barrowed across to where you need it. No other way works at all. And don't ever buy anything other than a builder's wheelbarrow. Again, nothing else works. If you are laying the bricks yourself, you'll do well to use more than a barrowful of mortar in the morning, and another in the afternoon, and pushing that down your garden is no hardship. In fact, if you're sensible, you'll use half a gauge of mortar at a time, and leave the other half in the mixer to rejuvenate with a bit of water.......so you'll only be pushing half a barrowful at a time.

Depending on your ground conditions, you may well not need anything below your slab other than sand blinding (to protect the DPM). Hardcore or Type1 /2 are for consolidating soft or wet ground, or for building up levels. If you don't have those conditions, then don't use it. As soon as spring arrives, you should dig yourself a trial patch in the area of your workshop, and see what the soil conditions are like. Ideally you'll remove the topsoil and bed directly onto the top of the subsoil, and if that is firm enough, just put an inch of sand over everything.

 

[DomD]

£10 will buy you one bag of cement and a wheelbarrow of sand. That's seriously unrealistic. You'll buy sand and ballast by the bulk bag, for about £45 each.

Ok, just checked and yes, for two courses a bulk bag each looks like enough; not sure why I put 10 there, didn't even search it. I will probably be laying some myself but also have some help from a bricklayer friend so can check the details with him.

Depending on your ground conditions, you may well not need anything below your slab other than sand blinding (to protect the DPM). Hardcore or Type1 /2 are for consolidating soft or wet ground, or for building up levels. If you don't have those conditions, then don't use it.

That would be good as it could take quite a few full days to move all that type 1 up the hill (and adds ~£300). I will definitely check.

Dom

 

[mindthatwhatouch]

Also I stuck some celotex under the concrete slab. If you go down that route.
Roof covering wise I can recommend the metal tiling system I used, (decra or equivalent) really don’t understand why you don’t see more of it around.

What would be the layering of that? Did you do hardcore->sand->celotex->concrete
Yes to that order.

I am worried the heat would just be lost through the sides of the slab if I do that, not sure if it is worth it for the extra digging required. Put an upstand of celotex around the perimeter.

 

[MikeG.]

.........Put an upstand of celotex around the perimeter.

That's not possible without either a strip footing, or a stepped slab/ raft edge ("toe").....and the latter requires a structural engineer.

Celotex can't be left exposed to the elements, so it needs to be behind a skin of something. That skin needs something to stand on.......thus the foundation. The whole point of this technique of mine is to make the build simple enough that novices can build it, but of course, there are alternative designs available to those up for strip footings, cavity masonry work, vertical DPM's lapping with the DPC, and ground bearing slabs. Something as seemingly simple as an upstand of Celotex around the perimeter of the slab has fundamental implications for the entire design, and for the ability of 95% of the population to build it.

 

[DomD]

.........Put an upstand of celotex around the perimeter.

That's not possible without either a strip footing, or a stepped slab/ raft edge ("toe").....and the latter requires a structural engineer.

Is the heat loss from the sides of the slab substantial enough to justify the insulation on top of the slab?

I am currently CAD framing and wondering how the interior room would be done, this is what I have at the moment:

How would the interior room frame be attached to the main frame and how would this interact with the internal OSB (/ply)? I assume it cannot be recessed into the OSB as this would breach the vapour barrier?

Thanks