Concrete base advice

[morgen]

Hello all,

I'm hoping to get some advice in preparation for creating a concrete base. The initial purpose for the base will be for parking/carport, but in the longer term I'm hoping to construct a garage so ideally I'd like to over-engineer things a bit to really last.

The size of the base will be approximately 4 x 7m and it will have up to 4 cars on it (the cars are small; old mini, Morris Minor, and similar). In terms of the final finish the smoother the better to make the use of trolley jacks easier.

From what I can gather around 20cm will be deep enough for the main base; of course things will be different in the future if I need to create foundations at the perimeter.

In terms of layers, what would people recommend in terms of damp-proof membrane, sharp sand, hardcore, metal reinforcement for the concrete etc?

Any advice would be really appreciated; I'm hoping to do most of this myself, but if I get anyone in it would be great for me to be more informed. If a garage one day does go on this base, will that mean that I should think now about specific regs?

Thank you!
Morgen

 

[Ian H]

Mine garage is about that size.

It’s on a 150mm thick slab which itself is on some 300 DPM (Visqueen). I put that straight on very solid ground. It’s got a full layer of (I think) A142 mesh and the corners were doubled up.

 

[oldbutnotdead]

The size of your potential future garage would probably put it in building regs territory.So what you might be wise to do is put in a building notice for the size of garage you plan to build with proper foundations (trench to whatever local conditions dictate or raft if that's your preference), get BCO to do the usual inspect the trenches etc before the concrete goes in then do the foundations/slab or raft, get them to come and have another look and then build your garage whenever you like in the future. They'll nag at you every year or so- just tell them no you haven't finished it, cash flow, dog ate the plans, whatever- but the file will always exist. Come the actual garage build they might try and squeeze another Notice fee out of you if you've left it 10 years but at least they won't be insisting on exposing the foundations to check they're suitable.
Slab- 200mm is plenty, 100mm would do for most garage loads. 100mm well compacted hardcore, blinding layer of sharp sand (25-50mm), DPM- leave enough spare at the edges so you can lap it into the wall- then concrete. Hard work but very DIY-able, you'll get a reasonable surface by levelling with a batten then rough floating. Once you put some floor paint down it won't be mirror flat but it will do.

 

[Leofric]

If you have concrete strip foundations and ground bearing floor contained within walls, garage floor construction specification in my experience is 150mm thick concrete on Visqueen 2000 dpm on 50mm sand blinding on 150mm well compacted and consolidated hardcore ( subject to ground conditions )