Garage Foundations

13 Sep 2009
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United Kingdom

I'm thinking of building a brick block garage 6.5m length x 4m width with apex tiled roof and 2.5m roller shutter door. It will be an artist studio so will be double skinned with insulated cavity (50mm?), door and couple of windows, electrics etc. As photos show , the back alley road level is higher than my grass/garden.. 1st stage is to sort out the existing foundations to bring me level with back alley!

Does this sound right?:

1.Knock down existing containing wall, dig down 1m, 600mm wide.
2.Concrete part fill 300mm thick.
3.Thermalite foundation block 440x215x300 ..Probably 3 courses to bring me to grass level.
4.Use existing common brick for facing + cavity + inner block (fibolite?) bring me up to back alley level.OR do away with the facing brick and 300mm wide block all the way (but visually wouldn't look too good)
5.Hardcore/sand/dpm/foamboard/steel mesh/150mm concrete slab.

I'm not a professional bricklayer but a competent diyer with some bricklaying experience. Is the above procedure correct or a bit over the top or under adequate? Any advice is helpful. Thanks!
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Double the foundation concrete thickness thus halving the time spent faffing about laying blocks in trenches. ;)
Why not sketch, and scan a section view, with dimensions - footings/trench depth to FFL - of what you propose?

At a min. you should always work to a basic drawing of the ground plan.

I presume that the conc. panel fence is to go?

I thought about making concrete fill thicker, but cost does seem to be lot more than me laying trench blocks. Maybe i can reduce depth to 750mm then 2 courses of trench block instead? Yes the brick wall with wooden fence attached is to be knocked down. Drawing above is an idea of my intentions although i do wonder if i should tart up what's already there, add new slab + concrete sectional garage instead, but then i'd have to mess around building inner stud wall and insulate etc as needs to be warm and dry.
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I've just dug down and the existing retaining wall is sitting on 2in concrete and appears to be clay only 10in down. Because of the clay, is it really neccessary for me to dig 1metre down or can i start foundations shallower?

Still undecided as to what to do regarding foundations. Ideally i'd prefer not to dig new trench footings which would mean to knock existing retaining wall + about 30 ton soil rubble skips/diggers etc!

Can i keep existing retaining wall, build another 2 courses brick up and lay raft foundation reinforced slab 6in thick within. This is what i was going to do if having a prefab sectional garage. I would then use celcon lightweight block (maybe 8kg) to build the garage single skin(or ideally double). This would be 'weight wise' equivalent to a prefab. Can always put on light weight roof instead of tiles to help keep weight down.

Any further ideas appreciated as i'm in limbo deciding whether to flatten eveything!!!!

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