Proposed workshop build

[DomP]

I'm a longtime lurker on here but this is my first post.

I'm planning a workshop of roughly 7 x 4.5m, I'm thinking of a raft type foundation, 3 courses of brick then studwork framing clad internally with osb, insulation and then wrapped externally in membrane then either corrugated sheet or feather edge. My question is if I'm going to 2.5m at the eaves what size section of treated cls should I use for framing if I'm going for 600mm centres on my uprights? I was thinking 50×120mm, any help or thoughts much appreciated. Dom

 

[DomP]

One other consideration is a large beech tree that sits central on our land and is near to where I'd like to site my workshop, how close can I sensibly go to it or what measures can I take to safeguard my concrete pad? Felling it is not an option at this point

 

[Jameshow]

One other consideration is a large beech tree that sits central on our land and is near to where I'd like to site my workshop, how close can I sensibly go to it or what measures can I take to safeguard my concrete pad? Felling it is not an option at this point

Plenty of reinforcement in the pad? And thicker too say 300mm.

Others will be along with more concrete advice!

 

[DomP]

300mm, wow I wasn't banking on that. Ive looked at resiting it but this area makes most sense other than the tree situation

 

[DomP]

Any thoughts on this? I'm keep to proceed with my plans but the realisation that a large beech tree is going to cause me issues has stopped me in my tracks. Repositioning is an option but doesn't work so well with garden layout or the contour of the land as its not an overly flat site.

 

[Seascaper]

I'm a longtime lurker on here but this is my first post.

I'm planning a workshop of roughly 7 x 4.5m, I'm thinking of a raft type foundation, 3 courses of brick then studwork framing clad internally with osb, insulation and then wrapped externally in membrane then either corrugated sheet or feather edge. My question is if I'm going to 2.5m at the eaves what size section of treated cls should I use for framing if I'm going for 600mm centres on my uprights? I was thinking 50×120mm, any help or thoughts much appreciated. Dom

Hello,
Reference your workshop dimensions - if you buy 4 x 2 in bulk to can get a discount it comes in 6m lengths so that the length of the building may be better belong 6m, something that can be considered. Your timber yard will give a better discount if you ask for whole lengths of 6m 4x2. Work out the roof pitch to save wastage.
I built such a workshop and went for a portal frame building, so that it is a completely free open space, that is, no roof trussing. With a portal frame building of this size you would need one large central support frame floor to roof apex made from something like 8 or 10 x 2 bolted together with metal knee plates at both eaves and apex.
The advantages are enormous when using long lengths in your workshop.

Start of with 4 to 5 courses of bricks on to a trench type foundation about 1ft wide, damp proof membrane and bolt 4x2 wood to bricks and build up from there.
For the floor get some sheets of metal reinforcing steel, raise of ground and then pour concrete over and smooth. If you want it reasonably warm put some sheets of 2 inch polystyrene on ground before you por concrete. Remember to have fun doing it....

Regards

 

[DomP]

I want to maximise the permitted size allowed without planning and without it being a long narrow space so I initially thought along the lines of 7x5 given that the internal space would then be nearer to 30m². I've no close neighbours and rural so I'm not too fussed on being strict to actual size as a few around us have just done as they please with outbuilding builds.

 

[pauljhaigh58]

Hi have you considered ground screws you won’t have problem with roots and can get closer to the tree than with a concrete pad

 

[DomP]

Hi have you considered ground screws you won’t have problem with roots and can get closer to the tree than with a concrete pad

I need a concrete pad due to a 250kg planer thicknesser and motorbikes that will be occasionally stored/maintained in it. I'd also like to have 3 courses of brick or a block wall to get above splashback

 

[Jameshow]

Hello,
Reference your workshop dimensions - if you buy 4 x 2 in bulk to can get a discount it comes in 6m lengths so that the length of the building may be better belong 6m, something that can be considered. Your timber yard will give a better discount if you ask for whole lengths of 6m 4x2. Work out the roof pitch to save wastage.
I built such a workshop and went for a portal frame building, so that it is a completely free open space, that is, no roof trussing. With a portal frame building of this size you would need one large central support frame floor to roof apex made from something like 8 or 10 x 2 bolted together with metal knee plates at both eaves and apex.
The advantages are enormous when using long lengths in your workshop.

Start of with 4 to 5 courses of bricks on to a trench type foundation about 1ft wide, damp proof membrane and bolt 4x2 wood to bricks and build up from there.
For the floor get some sheets of metal reinforcing steel, raise of ground and then pour concrete over and smooth. If you want it reasonably warm put some sheets of 2 inch polystyrene on ground before you por concrete. Remember to have fun doing it....

Regards

6.0m? Most timber is 4.8 around me unless you pay extra!

What are you putting in the workshop ?

If only light machinery then why not use piers? 400mm sq dense concrete blocks? Overcomes the roots issue?

 

[Inspector]

My table saw is 310Kg and I have a couple hundred board feet of hardwood, about 400kg, in a stack near it and that doesn't include other machines and more wood. The floor is 2x10 on 1' centres with 1" OSB sheets. There is no deflection that I can detect walking on it or looking up at from the garage below. You would put your walls directly on the wood deck and run the siding down to the bottom edge of the deck. The ground screws keeping you off the ground. There would be no spalsh back. A ramp would let you drive the bikes in and roll out.

 

[DomP]

Don't get me wrong, I appreciate your advice and will have a think on it but I'd rather a solid concrete base to work from as it gets really wet where I am so the idea a wooden floor failing once I've got an expensive structure on top doesn't appeal. Also oil and fuel getting onto a chipboard floor doesn't seem a good idea.

I'd definitely get splashback unless I have it a good 3-400mm off the deck as my current shed has shown which is why I'd like to get a few courses of brick

 

[mikej460]

Don't get me wrong, I appreciate your advice and will have a think on it but I'd rather a solid concrete base to work from as it gets really wet where I am so the idea a wooden floor failing once I've got an expensive structure on top doesn't appeal. Also oil and fuel getting onto a chipboard floor doesn't seem a good idea.

I'd definitely get splashback unless I have it a good 3-400mm off the deck as my current shed has shown which is why I'd like to get a few courses of brick

deeper eaves and guttering will take care of splashback

 

[Inspector]

I am not offended that you want to go a different route. Some of it is with the conventions you have around you.

As for the oils, fuel and some solvents on the floor. I had assumed you would be using an appropriate finish on the floor much as you would with concrete.

As Mike mentioned wide eaves and gutters go a long way to keeping walls dry.

I also would not consider the shop floor extending past the outside of the shop even if being made of concrete. Your practice of a bigger slab, then bricks on it and the wall perched on top is something never done here. I see it as asking for leaks under and through it as well as being prone to failure in earthquake regions. Except for a few areas in Canada (West Coast where I grew up) rafts or slabs as we call them are rarely used because of the cold sucking the heat out of the edges and frost heaving them. The usual practice is a footing several feet deep at least with a concrete foundation wall poured to get above ground with the house on top. Then foam insulation placed around the inside edges of the foundation with a slab poured on top of foam and vapour barriers to keep dry. Here because of the cold virtually all structures have that footing and foundation wall are deep enough for basements. Otherwise foam slabs around the outside have to go almost as deep or out horizontally 6' or more to keep the frost from heaving the place. All our walkways and driveways etc are poured after the foundation etc is made, slope away and usually lower than the floors inside.

With concrete or screw piles your structure is above the ground and a skirting placed around it to keep critters and such out from under. That would also stop splashing from getting under and with treated wood at least for the perimeter a little dampness isn't an issue. Venting dries out the space.

Construction approaches are different due to an areas history and what works there. Sometimes tradition is good and sometimes not. Thing is to keep an open mind. Good luck with your build.

Pete

 

[DomP]

Surely by the time I've got ground screws or piers and floor joists I'm going to be quite far out of the ground and losing valuable height at the eaves

 

[Inspector]

If that is a restriction then yes. A couple feet give or take, depending on the height of the ground screws, slope etc. I don't have to contend with heights. I was told for under 100 sq ft (no permits) garden sheds I can go three stories high if I like. Anything with a bigger foot print needs permits and inspections and being rural height wouldn't be an issue either. In the city they look at each build case by case if outside the general rules but someone I know was granted permits to build his shop and he has 10' high walls inside and is within 3' of the property line at most. Your rules are different and you must abide by them which can dictate/limit what you can practically do. If that means a slab then so be it. Trees won't like it but who listens to them anyway?

Pete

 

[DomP]

I was more worried about the tree cracking my pad

 

[PDW125]

The issue with that size will be cracking of any slab that is long and narrow where heave occurs. As it is only a timber structure, I would go with a thickened raft and use 300mm at the edges, then use 150mm Jablite insulation in the centre as insulation but also as back fill. Laid across the slab to leave a 300mm deepened edge all around, and then use sheets of A142 mesh to tie in to the overall slab and ring beam. Positioning a DPM may be a challenge with this as you’ll end up with it wrapped outside the concrete structure however you could also go with a DPM on top of the slab and then a floating chipboard or ply floor.

 

[Jameshow]

Also perhaps 200mm reinforcing squares in the 300mm edge beam wouldn't hurt?!

 

[MikeJhn]

I always leave my Jack hammer out of reach of the trees.

A slab of that length to width ratio will crack without heave, best to put some crack inducers into the slab and locate the crack where you want it, at the edge form a step that will take the DPM and attach to the DPC, or consider a suspended timber floor.