Concrete Depth Recommendations Please

[jetstream]

Have dug a Trench 1mtr deep by 600mm for the foundations of my extension, the BCO has had a look and passed it.

What i would like to know is what is the best or recommended way of filling it, depth of concrete etc. Have never done this before so totally green.

The original footing the house stands on (see pic below) is 4 brick courses below ground and 150mm concrete as can be seen in the picture below, how would the experts on here proceed please ?

 

[pilsbury]

Don't know how the experts would proceed but I'd pour concrete to the same level as the existing then brick from that.

 

[Diver Fred]

Undercut the existing footings by about a shovels length. Fill the new footings to the height of the existing and brick up from that level. But the BCO may be happy with you concreting to a course below ground level / Damp proof course - Ask.

 

[KenGMac]

i would "tie in" your existing founds to the new by boring in 2 or 3 X 20.mm rebars

Drill horizontally into the existing founds by not less than about 300.mm using an epoxy resin fit the 20.mm rebar into the existing founds and let the rebar protrude into the new concrete area by not less than 300 or 400 mm.

Why?

The rebar will assist in preventing differential settlement and a crack forming between the new and existing structures.

But as last post by wgt52 --- ASK --- your BCO

Ken

 

[Notch7]

I wouldve thought 1 course of hi7 concrete blocks, facebrickwork from there onwards.

What ever combination you do, finish founds to line up just below one of the couses.

Make sure you start brickwork a bit below ground level -you dont want a block or engineerings showing above.

 

[noseall]

First look at finished concrete floor levels (where you will be knocking through) and the existing DPC height. These are the critical points you will be working to. Ideally, the top of your concrete wants to be 525mm down from DPC, if it is your intention to use metric units externally. This allows for two courses of block and a course of bricks on the inside and one course of block and four courses of brick externally. If the ground falls away around the extension then you show facing bricks accordingly. It also sets the top of the concrete deep enough to allow a drain gully to sit on top of the concrete, should you need to. And you can knock that top course of bricks off easily should you need to when you screed into your openings.

As an aside, the job we are doing presently is a bit of a faff. Externally we have used imperial bricks below DPC and metric block/brick internally. I have deliberately finished the masonry a wee bit higher internally than externally because the concrete floor level finishes higher than the DPC. The brick courses externally are 89mm gauge with the average bed being 15mm!

 

[^woody^]

I would say "Work to the plans".

 

[jetstream]

Very true Woody, but the plans submitted for planning permission do not show details on construction, that is why i am asking !

 

[^woody^]

Very true Woody, but the plans submitted for planning permission do not show details on construction, that is why i am asking !

Lol

What about the rest of the work above foundations then?

Are you doing this on a building notice but don't know the specification you need to work to?

 

[jetstream]

Thank you woody for your quick reply !

 

[jetstream]

And a very big thank you to noseall, notch7, KenGMac, wgt52, and pilsbury for taking the time to give constructive advice in a positive way.

Both myself and my son are more than capable of physically doing the work, just don't have a background in building, this will be a long term one off project, and intend to learn as i go . . . . I do not have all the answers or confess to know everything, that is why i may seam to be asking simple questions on here.

 

[pilsbury]

Both myself and my son are more than capable of physically doing the work, just don't have a background in building, this will be a long term one off project, and intend to learn as i go . . . . I do not have all the answers or confess to know everything, that is why i may seam to be asking simple questions on here.

Seems you are in a similar position to me. Only I am very close indeed to finishing. My advice to you is to read up on everything from lots of different sources to corroborate information. This forum is also a big help.

So are you doing this under permitted development? You do have building control involved? So is this full plans or building notice? The only reason i ask is that as a total novice myself, by drawing and submitting my own full plans, it made me stop and think and build it to regs which building control will have no mercy on if it's not. That could be costly.

 

[^woody^]

Seems you are in a similar position to me

Oh no! Here we go again.

 

[pilsbury]

Oh no! Here we go again.

Keeps you “in business” on the forum.... where would you be without us?!

 

[jetstream]

So are you doing this under permitted development? You do have building control involved? So is this full plans or building notice?

Thank you for the advice, and yes i will follow your lead a draw up full detailed plans myself (when i get time). But at this stage in the game, all i am interested in is getting the trench filled and built up to DPC - I have had basic 3 view plans already passed by local council, building notice given and building control have visited site and are happy with the trench depth/width already dug out and passed it, and will return next for oversight inspection, before concrete base goes in or before if I require it.

I don't confess to know everything and don't really want to bog myself down with info overload, in fact i know very little of building at this stage, that's why i am here asking what may seam to some as simple questions, but i neither knew how to start and run a business (running 30 years now) build an aircraft from scratch, design and build 8x4 ft CNC router/lazer cutters. All i know at this stage is the ship is sailing, i know where i started from and what the destination will look like, the rest i hope to fill in as i go along.

Do you think this is the wrong approach ?