footings advise pretty please

13 Apr 2007
Reaction score
United Kingdom
Hi all.

Im currently planning on putting a garage on the side of my house. My only problem is the size of footings for the gable end wall. Its 8.2m long by around 3m high (its gonna have a pitched roof). Im thinking of doing the concrete base etc as if i was having an extension built on the side of the house, reason being because in 5 years i will be converting the garage into an extension. So, with a double skin wall, outer brick, inner block, how wide would my footings need to be. I know the footings need to at least 800mm deep and the slab at least 150/200mm thick but its just the width im having issues with.

I hope you guys and gals can help


Sponsored Links
I would beef that sucker up to 225mm thick. As for the width a 2 foot bucket should see you through.
Footing width depends on load from floors/walls above and type of bearing strata (ground) below.. if you have lightweight timber floors/walls/roof and bearing onto limestone then can get away with next to no foundations.. if you plan to put in concrete floors and dense blockwork and bearing onto peat then strip footings may not even work..
i shall beef that sucker up, lol

The footings will be going directly on to clay. It will be a garage with no secondary floors so the only load on the foundations will be 1500 bricks and 200 blocks plus the pitched roof 300 tiles ish
Sponsored Links
Will the BCO want you to excavate the footings, in 5 years time, when you want to convert to an extension, to demonstrate their suitability?

You may want to insulate under the slab if you wish to convert from garage to habitable space in the future. You will also need to consider finished floor levels as you may wish to add a screed finish to the slab when you convert.

600mm wide usually the standard for mass conc trench FD. But like said above, depends on the bearing capacity of the clay.

Ideally a Building Inspector will expect to see bottom of foundation level match the existing adjacent structure. Founding at the same level is likely reduce any potential for differential settlement.

Hope above helps.
also slab thickness.

Is the slab ground bearing? assuming it is, 150mm THK should be ample with mesh installed 50mm from top to control any cracking.
Hi and thanks for your replies guys.

I wasn't planning on informing BCO because my neighbour has has a side extension done last summer so my plan was to dig down to there footings level and match what they have. Then photograph and video the entire project so when i do convert the garage into an extension, the BCO if they ask questions have all the photographic & video evidence they need.

The garage will be 8.2m long by 2.5m wide so I'm within the area of not requiring planning permission. I will not be joining to my neighbours extension so party wall agreements will not be required.

I'm planning on insulating a proper base etc along with screed so converting in 5 years should be a simple case of a few minor alterations.

Now the steel mesh is a good point. With the dimensions i mentioned above, do you think a steel mesh would be required?? This is gonna sound silly but the garage will not be used for parking a car, simply a storage area only, so the load on the base will be minimal.

Because this area of building is new to me, i have had a company round to quote me on them installing the correct footings and base etc. If there price is reasonable i may let them crack on knowing its done correctly. If there quote blows my budget then cups of tea, bacon sandwiches and cans of carling will be required for my mate, lol

Thanks for your comments guys, its really good advice tar

If your not wanting to ever put a car in there then insulating now under the slab would be fine.

The other alternative would be to keep the uninsulated finished concrete floor 180mm below the house finished floor level. then when the time comes to convert you can simply lay 100mm of insulation and screed over the top of this which will make matching the levels easy because you can simply take a few mm out or add a few mm to the screed depth.
Good point. It just seems strange that you can pour concrete on this insulation stuff and the floor feel solid under your feet. In my head i imagine the floor wobbling like jelly.

Do you guys know of any helpful websites which outline step by step the process and materials required to do this job properly? I have found various sites but not found one site which nails everything in one hit.

Just got my quote for footings and base. This quote includes digging, material, labor, removal of waste. £2200 for footings & 1750 for concrete base which includes insulation etc. Is this good or bad?

I priced up the concrete myself and it come out at £650 (for footings, base & screed) • Removal of waste £150 • Hardcore, sand etc £150 and £0 for labor...i have good mates!! • Two bricklayers at £75 each a day (1500 bricks 300 blocks £600ish) • Timber £200 • Roof tiles £300. Im planning doing all this for under £4k. It is possible...i think!!

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links