Q for Mike - Workshop Foundations

[Norty Raskel]

Hi Mike,

You may remember this is my workshop, it was already here when I moved into the house and has served it's purpose.

However, it's 6x3m, which leaves me with 2.8m internal working width which I find too restrictive. I'm planning to build a new workshop on the same site and utilise the current wasted space between the workshop and the boundary, something along the lines of this:

(bold number are internal measurement, others external based on 300mm wall thickness)

Now because I intend to build close to the boundary and with a pitched roof I'll need PP, but by keeping below 30m2 footprint and build with brick and block (not only for flammability, but aesthetics also) I'd hope not to involve the building inspector.

The current workshop is built off a 100mm slab, if Building Control are not going to be involved could I extend that slab and lay the walls directly off it, or would that be bad practice?


Thanks
Jon

 

[Mike G]

You can't extend concrete. There will always be a join. If it were thicker you could chemical-anchor reinforcing rods into the edge of the existing, and these would be encapsulated in the new giving you a good mechanical link. However, it would still be a line of weakness in terms of damp penetration. However, 100mm isn't really thick enough even for that.

I'm afraid I would break up the existing and start from scratch. With that size of slab it will need to be 150 thick, and you could maybe thicken up the edges to take the weight of the walls. You do know that there are lots of boards which look like timber but aren't, and which fulfill all the fire resistance criteria for building near a boundary? You could easily build this timber framed.

 

[Norty Raskel]

Thanks Mike,

I thought that would be the answer, even if I had hoped it wasn’t.

Yes, I’m aware of the likes of Cedral cladding, my main motivation for going the brick and block route was aesthetics, (I think Mark’s workshop looks great). The workshop is close to the orangery and will be very visible considering the amount of glass that makes up the orangery, I just feel brick would be more in keeping with the house than timber clad. If it was further down the garden, it would definitely be timber framed.

Having said all that I haven’t yet gone into great detail of the cost implications of brick over timber, so this may yet influence my decision.

If I went brick/block would the foundations still need to be 1m deep, (assuming no Building Control input) I hit firm solid ground at 0.5m.
Thanks
Jon

 

[Mike G]

As you will be your own building control, the depth of footings are going to be down to your own judgement. If you are on solid ground all round at 600 deep, with no tree roots or organic matter in the excavations, then you are below the frost line and should be OK-ish. However, there is always the matter of clay heave and shrinkage, and a hot dry summer or a soaking wet winter could lead to some movement. The deeper you go the greater the peace of mind.