Footings for a small brick garden office

[Tony K]

Hi

As part of our SB I am going to build a very small home office for myself in the garden. External footprint of the building will be 2m x 1.6m. 

It's far too small to need building regs, but I want to make it using brick walls, probably single skin with insulation and board on the inside. I'll damp proof it like a proper building, and it will ultimately have electric and heating inside. 

In terms of footings, how deep and wide should I be aiming for? Its clay soil, but a full 1m deep seems a tad OTT.

Any ideas?

Ta

[markc]

No need for real `footings` an insulated slab would be perfect for this

[Tony K]

7 minutes ago, markc said:

No need for real `footings` an insulated slab would be perfect for this

 

Thanks. What sort of thickness would you propose, and would you bring the edges down a little deeper than the centre?

[markc]

Tony, Bringing the edges down to form a ring-beam makes insulation difficult.

If i was doing a similar build i would excavate as for a ring-beam but level the top of the hardcore, sand blind, DPM, 75-100mm insulation and then a 75-100mm slab on top.

Maybe overkill (i do it often) but it would be nice and warm and last for ever.

 

I would be interested to hear other peoples suggestions

[Tony K]

8 minutes ago, markc said:

Tony, Bringing the edges down to form a ring-beam makes insulation difficult.

If i was doing a similar build i would excavate as for a ring-beam but level the top of the hardcore, sand blind, DPM, 75-100mm insulation and then a 75-100mm slab on top.

Maybe overkill (i do it often) but it would be nice and warm and last for ever.

 

I would be interested to hear other peoples suggestions

 

Cheers Mark.

I'm not familiar with insulated slabs really. I presume the insulation sits under the whole thing, including the walls and can take that weight without becoming compressed?

Is there a depth of excavation for the hardcore you would use (edges and centre)?

Thanks

[Declan52]

The depth of your concrete will be determined by the ground make up. If it has to go 1m because the ground is poor then that's how deep it has to go. If you don't then you risk the concrete cracking and walls and floors cracking.

If you go for a timber build you wouldn't need any proper concrete foundations due to the lighter weight of the structure. You can build it like a deck resting on a few concrete blocks sitting on some concrete pads. Would be a hell of a lot cheaper.

4*2 timber for the frame with 100mm insulation on the inside of the studs would mean a larger internal space. Easy to insulate the floor as well. 

You can clad the building in everything from shiplap to slate lath to Siberian larch. All depends on the budget.

 

[Tony K]

1 hour ago, Declan52 said:

The depth of your concrete will be determined by the ground make up. If it has to go 1m because the ground is poor then that's how deep it has to go. If you don't then you risk the concrete cracking and walls and floors cracking.

If you go for a timber build you wouldn't need any proper concrete foundations due to the lighter weight of the structure. You can build it like a deck resting on a few concrete blocks sitting on some concrete pads. Would be a hell of a lot cheaper.

4*2 timber for the frame with 100mm insulation on the inside of the studs would mean a larger internal space. Easy to insulate the floor as well. 

You can clad the building in everything from shiplap to slate lath to Siberian larch. All depends on the budget.

 

 

Thanks @Declan52 

I had originally planned to do exactly as you suggest, it's really just an aesthetic choice on my part to go for brickwork on the outside. 

Perhaps I'll just talk myself around to using timber instead. 

Cheers

[Temp]

5 hours ago, Tony K said:

As part of our SB I am going to build a very small home office for myself in the garden. External footprint of the building will be 2m x 1.6m. 

 

That's quite small. The table I'm using for my computer would fit in but it would probably have to be assembled inside unless one whole wall was a door. Plan the layout carefully and think about reflections off the computer screen as it will be hard to rearrange things later.

 

4 hours ago, Declan52 said:

4*2 timber for the frame with 100mm insulation on the inside of the studs would mean a larger internal space.

 

I assume you mean between the studs. That's what I did. Outside clad with ply (for anti racking) then membrane, battens and weatherboarding. Inside lined with plasterboard or painted plywood.

 

As for the electrics..  You should get an electrician to do it (and he will notify the BCO under Part P) but can probably save some money if you lay the cable yourself. There are several different options depending on the exact set up. 

https://electrical.theiet.org/media/1695/electrical-installations-outdoors-a-supply-to-a-detached-outbuilding.pdf

I went for figure 3.. An underground cable from the CU in the house to a so called "Garage CU" in the outbuilding. This was laid in conduit but probably no need. The Garage CU has two ways (one for  power and one for lighting). An earth rod is installed near the outbuilding connects to the garage CU. 

 

You might consider making the eaves high enough so you can attach a sun sail and sit outside under that in summer?

[Conor]

When I built my 2.4m x 3.6m block brewshed, I laid 300mm trench, filled with concrete and couple layers of block on flat to bring up to floor level. Laid 100mm of eps inside on a dpm, and poured 75mm of concrete to floor level. Then built walls up with block on edge. Simple timber flat roof with GRP.

You could probably get away with shallower founds but you'll still need 100mm EPS and 75-100mm concrete for a half decent floor.

 

Electric cable (extended a ring from an external socket using armoured cable) and water pipe came up through a 40mm duct in the slab. Waste pipe out the side to a simple soakawway.

 

If I were doing it again, I'd build it out of timber stud and clad it! Would have made it a lot faster build and walls would be easy to take electrics through and to insulate. Reason for block was to satisfy the planning guidence of "mostly non combustible material" when building an outbuilding within 2m of a boundary.

[Tony K]

Thanks all.

 

23 hours ago, Temp said:

 

That's quite small. The table I'm using for my computer would fit in but it would probably have to be assembled inside unless one whole wall was a door. Plan the layout carefully and think about reflections off the computer screen as it will be hard to rearrange things later.

 

 

Yeah it's small, but so is the house and the garden. Every inch of every part of the whole thing has been planned meticulously, and the office is no different!

 

5 hours ago, Conor said:

When I built my 2.4m x 3.6m block brewshed, I laid 300mm trench, filled with concrete and couple layers of block on flat to bring up to floor level. Laid 100mm of eps inside on a dpm, and poured 75mm of concrete to floor level. Then built walls up with block on edge. Simple timber flat roof with GRP.

You could probably get away with shallower founds but you'll still need 100mm EPS and 75-100mm concrete for a half decent floor.

 

Electric cable (extended a ring from an external socket using armoured cable) and water pipe came up through a 40mm duct in the slab. Waste pipe out the side to a simple soakawway.

 

If I were doing it again, I'd build it out of timber stud and clad it! Would have made it a lot faster build and walls would be easy to take electrics through and to insulate. Reason for block was to satisfy the planning guidence of "mostly non combustible material" when building an outbuilding within 2m of a boundary.

 

Cheers. Right now the only thing I need to think about is whether to dig out foundations for the office at the same time as the house footings. If even a brick office would only require fairly shallow footings then I can afford to forget about it for now and make a decision later. 

[Conor]

14 hours ago, Tony K said:

Thanks all.

 

 

Yeah it's small, but so is the house and the garden. Every inch of every part of the whole thing has been planned meticulously, and the office is no different!

 

 

Cheers. Right now the only thing I need to think about is whether to dig out foundations for the office at the same time as the house footings. If even a brick office would only require fairly shallow footings then I can afford to forget about it for now and make a decision later. 

If you have a digger on site, do it now, it'll cost you nothing. Get the area you are thinking of using roughy excavated down to the subsoil level, backfill with rubble or subbase or any other type of stone. It will mean you can use the area in the mean time and will be a doddle to dig out in a years time to do your founds.