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Groundwork & Foundations Question
Double garage, trench foundations or slab ?
I'm wanting a double garage and trying to get a grasp of the project. I will be doing most of the donkey work myself due to funds. So, the garage will be detatched from the house at the bottom of my garden. It will be10m x 6m and will have 100mm insulated cavity and a pitched roof with gables at each end with a brick front and blocks/render to the other three walls, will this require concrete foundations in a trench (if so how deep?) then the floor poured seperately ? or could it all be done on a reinforced concrete slab ? Thanks.
id advise trenches 500mm wide and 600-1000 mm deep depending on ground conditions.
then a 150mm of compacted stone with a 25mm sand blinding on top of the stone then a 1200 gauge dpm to prevent any damp penetration then a reinforced concrete slab of 100mm with some m12 mesh in should do the job nicely.
hope this helps.
Answered 13th Feb 2018
Rafts are seldom used unless ground conditions dictate them and supported by a structural engineers design so I would say you will require trench foundations.
Personally I prefer 600mm wide foundations but you might be able to use 450mm wide but in either case they will need to be to a minimum depth of 1000mm.
As the garage is at the foot of your garden you may be required to dig deeper than 1M especially if you have a clay based soil and established trees / hedges nearby. If this is the case you may also need anti heave protection as well as adopting a block & beam floor with reinforced concrete overlaid (all capable of supporting garage loadings).
As the building will be about 60M2 in footprint you will require Building Control and all foundations / ground slab / B&B floor etc will need inspecting at the relevant stages. You can ask the building control officer to visit prior to excavating foundations to discuss required depth to site site conditions or have a structural engineer prepare a design & calculation package.
Answered 15th Feb 2018