Which foundations ?

[brewhut]

Hi

Hope someone can help with this.

I would like to build an outbuilding quite away from the house in my back garden to use as a workshop/hobby room/s.



Dimensions approx: 7.8 metre x 2.6 metre (area ~ 20 sqm)

Height: probably 2.2 metres, no more than 2.5 metres.

All sides in single brick, 3 sides are solid, one 7.8m side has 2m wide door and 2m wide window.

Approx 40 sqm of bricks needed.

The solid 7.8m side is very near my neighbour’s 5’ fence, the other sides are far away from boundaries.

There are no buildings in the neighbours, just a lawn.

Roof will probably be pent style, sloping across shortest sides (2.6m), not sure of material yet.

The floor will be concrete with a drain in the floor.

Ideally, DPC in the floor and the walls to protect from outside damp.

Garden is soil, not clay

Will be running in: power, mains water and drain.



For a building of this size and weight, what kind of foundation will be ok and the easiest/cheapest solution ?

1. Footings for walls and then later fill floor with a slab.
2. One big slab
3. A thinner slab that is deeper at the edges where the walls will be
4 Some Other?

Any help much appreciated.

 

[noseall]

1. Footings for walls and then later fill floor with a slab.

Preferably mass filled as brickies can be expensive...

 

[brewhut]

Thanks noseall, but I don't understand what you mean. I'm not a builder, so my above terminology might not be correct.

I intend to have this built by a builder/bricklayer, I haven't contacted any yet. but I was hoping to do the concreate foundation myself to save money, I'm just a DIY'er. I don't want to get it wrong. also I was going to get a cement company to deliver it....

How would I go about doing any of this ?
Depending on what I have to do, what dimensions for foundation type needed ?
Can anyone recommend somebody in Manchester area ?

Desperatly need help, I don't want it to fall in on me

 

[noseall]

Dig some trenches about 900mm deep (or down to solid virgin ground) on the intended building line.

Concrete footings will need to be at least 100mm wider than the wall each side. So, a 275mm cavity wall would need a 475mm wide foundation trench.

The walls will need to be centered on the footings.

You order concrete by volume, i.e. metres cubed. So let's say one trench was 8m long, 500mm wide and the intended concrete depth was say 500mm thick (deep) then this trench would require 2 cubic metres of concrete.

Ask for C20 or just tell the concrete people it is for trench foundations and they'll send the right stuff.

The actual finished depth of the concrete should be worked out from the intended dpc or floor level down, and measured so that it works in brick or block courses.

 

[brewhut]

Thanks noseall.

Been onto concrete people. I have 22m of trench. At 22 x .5 x .5 I need 5.6cu m of concrete. At 25 barrow per 1cu m, thats 140 barrows. That's just for the footings. I'd need 8 x 3 x 0.1 for 4" thick 2.4cu m for the floor

some companies don't have barrowing services and only wait so long

Do these figures sound correct ?

How can I make sure all the footings are level at the same height ?

Thanks again

 

[steadyonbob]

Have you considered making it from timber, say 4 x 2's or even 6 x 2's.

Much lighter and you will be able to insulate it far better.

Easier to do it your self too.

I did a timber outbuilding which is classed as "temporary" and so planning wasn't even an issue etc..

I made the corners of solid concrete about a metre down and two foot square.

then I joined the corners with rebar reinforced concrete trenches which were only about a foot wide.

I built a couple of concrete support walls at the same height as the main outer foundation ring.

So the spans for the timber floors were all ok.

The final size of the building was about 7mtr x 6 mtr and is as solid as a rock and very warm and toasty!

Bobby

 

[hotrod]

Do these figures sound correct ?

How can I make sure all the footings are level at the same height

Your figures look about right @ 5.5m³ for 22m*0.5m*0.5m. Getting it level - get some slate batten (or similar) whack it in the ground and use the top as your datum. Put a stake in every 3-4m and use a straight edge and level to make sure the tops are all at the same level. That will be the top of your concrete.

 

[noseall]

As Hot Bod has stated, peg the trenches every 1.8m or so. This is by far the best way to set out the concrete levels.

steady bob wrote:

I did a timber outbuilding which is classed as "temporary" and so planning wasn't even an issue etc..

Planning recognise buildings and not their longevity status.

Sheds, connie's, verandas are all recognised as "structures".

 

[brewhut]

Thanks everyone for info, it's becoming clearer, slowly

Not sure what a slate baton is, but I'll ask for some. I assume it's so it won't rot ?
Can't use wood building, as I'll be using water.




Couple more points:

It will be single brick, is that 100mm depth. If so does the trench only have to be 100mm + 100mm + 100mm = 300mm wide

The other thing is: My garden is about 8" (200mm) higher than my neighbours. Does that mean I need to dig deeper i.e: 900mm + 200mm = 1100mm and make the concrete 500mm + 200mm = 700mm deep (but only for the 8m run against the fence, 500mm deep for the other 3 sides still

Aside[ I want to keep the total height below 2.5M to comply with planning not needed. Is this measurment WRT my garden height ]

Thanks in advance

 

[hotrod]

Slate batten is mainly used on roofs but it has a myriad of other uses. It is pressure treated so can be used outside but it's not essential for the purposes of setting out concrete - it's just a handy sized timber. Anything you've got to hand will do within reason.

"Single brick" usually refers to a 9" wall (i.e. a full brick length ways) but I think you're intending on building a half brick wall (i.e. single leaf)? I would be dubious about building a 100mm wall @ 2.5m height if that is what you are intending

Can you clarify how wide the wall is going to be, and its construction (solid or cavity) because this will determine how wide your trench needs to be?

 

[brewhut]

Thanks Hotrod

Here is a diagram (the number of bricks is not to scale)

The wall near the fence is 7.8M long and about 2.2M high at 1/2 brick

Not sure how heavy this is or if it can be built in one width without the expansion thingy. I can't go any bigger than 7.8 x 2.6 area (outside) and I'm trying to keep the floorspace (inside) as big as possible.

I also had the idea of blocks on the fence side to a height just below the fence, then brick on top of that. This is so it does't look a mess from my neighbour view.

Can an outbuilding of these dimensions be built safley

Any suggestions on any of this, thanks again

 

[noseall]

Because of the shape/design of the building you have plenty of inherent strength. The returns look large enough, though i would beef up the door jambs with a 225mm pillar each side

I would also be inclined to include a pillar at mid-span along the longest side.

I'm sure one of the structural bods will advise....

 

[Static]

Because of the shape/design of the building you have plenty of inherent strength. The returns look large enough, though i would beef up the door jambs with a 225mm pillar each side

I would also be inclined to include a pillar at mid-span along the longest side.

I'm sure one of the structural bods will advise....

Would normally suggest two pillars for a 7.8m long wall.. so 2.6m centres from the return walls and then do as Noseall says for the door jamb pillars..

 

[brewhut]

Thanks again all.

There isn't a structual body. When I contacted the council and told them the dimensions, building materials and positioning, they said that's ok, just build it and are the neighbours ok. It's > 15sqm and <30sqm.

Are these pillars like what you have with front garden walls and gates etc, i.e columns of bricks. If so would these stick out equally either side of the wall (birds eye view) ?

I was also thinking could it be made of blocks (440 x 215mm) without pillars, some block are 140, 190mm deep ? Also some have fair faces, so will look good. any ideas please!

Not sure if this info from Lignatite, says 140mm is ok for 8m long, 2.5m high.

Also had builder in, who said a slab with normal breeze block would be ok, no damp course, liner under concrete. No sure about this

 

[Static]

From that table 140mm wide blocks for an 8m length sure.. but you have a door way so your panels have no lateral retraint there.. so add a pillar (215x215mm like a gate end) also will stop the wall moving around when the door blows about in the wind..
You could make the whole thing 215mm thick wall and it will last a nuclear attack..