Are these plans for foundations ok? With pic

[Danturboc]

Following on from my other thread regarding a garage.
Ive decided to build a single Concrete block garage with pillars. I have drawn up this diagram to show what I think I need to do:



The plan Is 22ft x 12ft garage, Dig down 1 metre deep for foundations and 450mm wide, fill upto 750mm then block work just past ground level then a damp course. Does this sound ok? Don't think I need steel in there do I?

The ground is clay/soil. I haven't planned on doing the foundations across the main doorway for the garage is this right also?

Any info appreciated.

 

[^woody^]

What is that thick brown area?

Is someone working in metric and someone else working in imperial?

You might want to draw the plan in proportion too, it's confusing.

You don't need any steel

 

[oldbutnotdead]

If you're in good clay you might not need to go down as much as a metre and 750mm of concrete is a bit overkill as well (though does make the first course of blocks easier). And no there's no need for foundations across the door opening (but run them 300mm or so into where the opening will be to spread the load a bit)

 

[noseall]

As Wood says, strive to finish the foundation concrete at a pre-determined (metric) point below your intended DPC height. Think either 75mm or 225mm increments. Use trench pegs as a guide.

 

[Danturboc]

Thanks for the replys

The brown area is just the ground around it. The measurements are like that for no reason really, just how they came out. I can convert them if you want. I will get another diagram drawn up and will also get some pics of the ground for you to see too.

I thought 750mm would be ok for the depth of concrete, would 500mm be better? Also why 75 or 225 increments? Is that the size of the blocks? How much higher above the ground does the Damm proof corse need to be, just a blocks worth?

 

[oldbutnotdead]

Concrete isn't cheap- up here around £140/cu metre delivered. Depending on what subsoil you have, a strip foundation 225 deep x 450 wide can be perfectly adequate for your needs. And as for how deep the trench is- skips to dispose of spoil aren't free either and if you're digging by hand you'll notice the difference, trust me .If I believed your drawing (where the door is in the long side) you have about 14 linear metres of trench. I suspect the door is in the short side so actually you'll have more like 18 linear metres. At 450mm width, every 100mm depth of concrete is 0.8 cubic metres so your 750mm fill will cost you £850 (actually be more like £600, you'll get a better rate for 5 cube and above in one hit). Up to you ultimately (and as said it depends what the subsoil is like, nearby trees, any drains etc).

Your DPC wants to be 150mm above ground level- that may translate (since most gardens aren't level) to 150 at one point and 200 at another. Your DPC will be between a course of blocks- assuming you're using the usual sort of blocks that people build garages from then each course of blocks is 225mm high (215mm for the block, 10mm for the mortar). So if you want DPC at (say) 175mm above ground level, the top of your foundations at that point need to be 50mm or 275mm or 500mm or 725mm below ground level. Ish.

 

[Danturboc]

Yes the door is at the front on the shorter side. I do plan on putting a small side door and a small window in to on one of the longer sides but I don't think that affects the foundations.

I only said 750mm depth of concrete just from what I have read off here on other people's similar projects. Do you think I could get away with a shallower trench then or will I only know that once I start digging?

I understand the dpc level now. It makes much more sense.

I have allready had 4 skips now to clear the rest of the garden! Expensive!

Well I'm glad none of you have said to just get the professionals in to do it, I'm sure I can do this myself as it doesn't seem like rocket science.

 

[oldbutnotdead]

You'll only really know for certain when you start digging the trenches. You could do worse than phone your local council building control dept and asking them- they'll know what sort of subsoil exists in your area, your project is small enough (as long as it is more than a metre from neighbours and house) to not require building regs and ours up here are v helpful. There's a load of info about foundations in Part A approved documents (http://www.planningportal.gov.uk/buildingregulations/approveddocuments/parta/
as well as stuff about how far apart buttresses should be, where openings should be relative to corners/buttresses etc etc

And yes its definitely DIY doable- there are traps (like setting the trenches out so you get 90 degree corners, getting trench bottoms and foundation tops level ish) and it is hard work. Enjoy

 

[^woody^]

You need to weigh up the cost of filling the trench with concrete, right up to just below ground level, with the cost of concrete a strip at the bottom or part way, and then paying for blockwork and the labour of working in a narrow trench.

And, as your mate is not a builder, the risk of him charging for longer than is necessary working in a narrow trench, and cocking the whole lot up at the end of it.

It's easier to square a wall when working near the top of a trench, than at the bottom, for instance.

 

[Danturboc]

Good thinking for ringing the council I will do that on Monday and see what they say.
I have read all the regulations about planning etc and as far as I can see I shouldn't need building control or planning so long as I keep it no higher than 2.5m ( if I have read it right). The garage will sit within 1 metre of the boundary but I'm sure I read that's ok at 2.5m high?

I have decided to do it all myself now rather than paying my mate to do it. Even down to digging the trenchs out my friend has said he will do it for 300 using a mini digger. But after seeing that most people just dig it by hand then I think I will do that and save myself some money. I'm all up for hardwork and it will be good excersice.

Do the blocks upto dpc have to be under ground level? Is that a rule? Or can you just fill a shallower trench full with concrete and say build 2 blocks worth up to dpc?

 

[^woody^]

You can concrete up to the point where you don't want to see it, and then start the wall

 

[oldbutnotdead]

If this is your first building project then you'll probably be better off (as Woody said) maybe having deeper fill concrete in the trench so you're not trying to set out and lay blocks 500mm below ground level- easy enough for experienced brickies with the proper kit but very time consuming and easy to get wrong for DIY. Again as Woody said you can concrete to just below ground if you want, then 1 block then DPC and away- yes it costs more for concrete but it could save you a lot of time and grief starting your walls.

Trenching by hand- depends how deep you have to go and what you're moving. 500mm in soil/firm clay is quite easy, much deeper than that and it gets really hard work (you have to make the trench wider so you can get your shoulders in it which means even more spoil to shift), plus the piles of spoil by the side of the trench get too big and unstable so you have to barrow it away. Going rate for minidigger here for 24 hours hire (from J*wsons) is £50 plus fuel, as long as you're not near anything sensitive (like yours or next doors' foundations) then they're not difficult to learn and real good fun- I'm no expert, last one I had was to fill 2 skips with random clay and rubble & trench 20m x 300mm wide x 1m deep for power cable, water pipe and comms ducting. Got it all done in a day & wasn't really sweating at the end of it Well worth getting a skip with it, by the way- again depends what your ground is like- mine is about 400mm of really nice rich black soil (which I kept) and then firm clay (which went in the skip). Remember your 18m of trench even only doing the minimum (450mm deep x 450mm wide) will still be near 4 cubic metres of Stuff.

And yeah as long as you're doing blockwork walls & something non-combustible for the roof (fibre cement sheets, fibreglass, tin) then up to 30 sq m and 2.5m to ridge no planning or building regs required

 

[Danturboc]

Thanks guys great advice!

So I need to ring the council now and try and find out how deep to dig, maybe dig a test hole just to see whats down there at the different levels. Price up the concrete and off I go.

I will get lots of pics up when this all starts and I will let you know exactly what depths etc ive decided to do.

 

[Danturboc]

Another quick question for you, the blocks upto DPC are these different blocks than the rest of them? If so which ones?

 

[noseall]

Another quick question for you, the blocks upto DPC are these different blocks than the rest of them? If so which ones?

Masonry below DPC is specific. It needs to be FL rated. Use dense 7n blocks or semi-engineering bricks or those that are suitably FL rated, below DPC.

The same blocks can be used above DPC but they are heavy and you would only be able to build a few courses at a time. Not good when you consider that an average sized block-work garage would normally get knocked off in a day by a three (2&1) gang.