Base slab specification for small outhouse

[akist]

I want to build a small outhouse, attached to the annexe, to house boiler, hot water cylinder (maybe), water filters, water softener, storage, and whatever else can go there to save space inside the annexe.

My current idea is a single brick structure, about 2m tall, with a small inclined flat roof, approx 2m x 1m in area. It only needs three walls because it backs up to the side wall of the annexe.

I have asked the builder to build a 2m x 1m concrete base and then build off of that. What thickness should this slab be to be man enough to take the weight of the bricks plus the items inside?

I have counted 351 bricks, taking into account the door, each brick is 2.25kg (according to the bathroom scales), and the mortar which I estimate to be half a brick for each brick, so altogether, 1200kg. Assuming a washing machine, and a 170lt hot water cylinder, say another 500kg of user load, so total about 1700kg.

Could someone please tell me what is the right concrete slab thickness I will need to ask the builder to make? He will try to get away with the absolute minimum and I would like to have an idea.

 

[Tigercubrider]

I'd insulate it if I were you. The boiler and hot water cylinder will loose a lot more heat if you don't.
The floor, walls and roof.

 

[conny]

As Tigercub says, polystyrene insulation, (minimum 100mm), under the slab and is the slab going to be re-enforced with rebar?
Not a builder but I would think a minimum of at least 100mm but safer with 150mm.
If your builder is the type to skimp on quality I'd look for a different builder.

 

[akist]

Considering this slab will be built right up to the side wall, how do I ensure that it does not move away from it? I can tie the walls with wall starters or wall ties, but the base is floating, and it does not look a great idea.

I drew a sketch

 

[hansPulesh]

Just out of interest, are you going to build directly on top of the slab or will you also have footings under the walls too?

 

[akist]

No I will build straight on it, that's the current idea. The builder wants to avoid unnecessary work, in this case digging extra.

 

[Notch7]

Considering this slab will be built right up to the side wall, how do I ensure that it does not move away from it? I can tie the walls with wall starters or wall ties, but the base is floating, and it does not look a great idea.

I drew a sketch

You cant stop differential movement. Use wall starters and silicone the joint -is all you can do

The problem with making a raft / slab is dealing with the dpm arrangement -its tricky to form the dpm / dpc detail.

 

[akist]

The problem with making a raft / slab is dealing with the dpm arrangement -its tricky to form the dpm / dpc detail.

Thanks for the comments

I had not thought about DPM/DPC but if it is easy to add it then I will.