First attempt at footing a wall

[Xereyeus]

I've just dug the trench for a wall between my neighbours garden and my drive. There are two slopes to cope with - one parallel to the wall and then a slope at the base of the drive slope from my neighbours garden. At this point I will have to turn the wall into a retaining wall. Could anyone give me advice as to how far I'd have to go with a DPM against the wall, does this go under the concrete footing (I assume not but it's a clay base when you get to about 60cms down) and advise me about the steps in the footing I will have to put in for the slope of the drive?

Any help appreciated.

 

[r896neo]

It's a little hard to visualize what you mean with it turning into a retaining wall etc, which is probably the reason for lack of responses.

Don't put the dpm under the footing, and if you are using it behind the wall make sure the wall is strong enough to cope with the reatined height and also you need to consider drainage such as weep holes and gravel back fill..
As for the steps, try and keep them divisible by brick or block sizes. which makes laying the first courses much much quicker. When pouring you want to extend the higher step by a foot onto the lower one if that makes sense?

So peg out the top level and then when you drop down to the next level place another peg at the same height as those on the previous level but place it a foot beyond where you have cut the step. The steps can be formed with shuttering Literally a bit of timber spanning the trench like a dam then a couple of pegs to hold it in place. Or you can just do it roughly as the concrete starts to firm up simply keep raking it back up and make sure to tamp it as you do it.

 

[Xereyeus]

Thank you Neo..

The retaining part of the wall is only about 5ft in length and the main part of the wall itself will not be more than 1m high with decorative railings on top. I am corresponding the steps with the pier gaps, spaced according to the railings and I understand about the overlap - I think it has to be twice the step height or 300mmm whichever is the greater.

My questions are thus:
Do I put the steps in the middle of the stretch between piers or just behind where I think they will be? I understand about the brick length but am I making a mountain out of a mole hill by putting the steps the same height as the foundation depth?

I've found the sewer/waste water pipe and am wondering whether I back track and rebury it (I can move the step back if the above question is yes I can make little steps) or I can 'lintel' it. However, I haven't a clue how to do this and there doesn't seem to be a lot out there on the web, explaining how it's done.

Any help appreciated!!

 

[r896neo]

you can put the steps wherever you want to be honest as it's all continuous concrete footing so there it's largely irrelevant.

From a practical point of view you may find it easier to put your steps away from a pier because the levelling up around the step is marginally less work to do on a normal run of stretcher bond etc than it is at the base of a pier.

How long is the wall? have you considered expansion joints as these can often be best hidden on the back side of a pier.

As for lintelling over the sewer pipe it is as easy as it sounds however can be much more of a problem if the pipe does not run perpendicular to the wall. not sure what you mean by back track but obviously as i'm sure you know you can not fill an area back in to bury it.

What angle is the pipe at relative to the wall, or another way to put it, how long is the section of pipe in your foundation?

 

[Xereyeus]

OK I guesses I probably couldn't put the soil I've dug out back in, though it is flint, soil and clay. Unfotunately the pipe is diagonal across the trench and at the moment only about 2cms of it can actually be seen as the next step is directly above it, hence I wouldn't have found it is I hadn't been trying to be totally accurate on the foundation depth.

Thus it is not as straightforward as it seems and hence I am trying to search out information.

 

[r896neo]

ok, what i was trying to get at is how long a run of pipe is through your foundations? Even if you haven't actually exposed that much it is probably pretty near the surface.

So if you use the bit you have exposed as a guide to where the pipe runs how long is the section under/in your footings?

 

[Xereyeus]

The pipe is diagonal across the trench and at the moment barely 1cm is showing at the bottom left corner of the 10 inch step. The pipe goes diagonally under the step and I would expect that given the angle, approximately 27 inches or 69cms is underneath the undug area.

Hope this helps.

 

[RedHerring2]

AFAIK, the bottom of the footings must be below the invert of the pipe, i.e. the bottom of the pipe. This is to avoid the footings (and the wall above it) from bearing any weight on the pipe and the footings exerting any sideways pressure on the pipe.

 

[r896neo]

As redherring says, you need to be at least level with the bottom of the pipe and that's why i was asking the distance because the easiest thing to do will be to stop the footing short of the pipe on either side and then put a couple of 3 ft concrete lintels (4x6 inch) bridging over between the two sections of footings.

It may be easier to cut your lower step deeper to allow for the 6inches depth of the lintel. Also i would make an expansion joint somewhere above this bridge in case of any relative settlement.

 

[Xereyeus]

Is it possible to draw a diagram because I don't understand what you mean? Also what do lintels look like - I don't want to go and get something for a doorway when I need something for drainage. Are you saying I put the lintel directly on the earth I haven't dug out, which forms the step?

I will try and post a photo.

 

[RedHerring2]

Your footings, either side of the pipe must be at least as deep as the bottom of the pipe, for safety you could go 50-100mm deeper.

A pre-stressed concrete lintel accross the footings above the pipe and the wall built off that.
Something like this:
http://www.tbsmerchants.co.uk/cgi-b...0mm_Prestressed_Concrete_Lintel_65x100mm.html

If you're doing a double skin wall, use two lintels side by side.
There is a right way up for these lintels.
They are the same depth as bricks so will not upset the brickwork levels.

 

[r896neo]

sorry it's a little hard to imagine. Just think of a bridge, treat the pipe as the river and the concrete on either side as the land. the concrete is not joined in any way it is 2 seperate pieces. you leave the area directly around the pipe clear of concrete and then simply use the lintels to jump the gap and form the bridge.

You can simply use the same lintel as for a doorways as they are not at all expensive.

 

[Xereyeus]

A small caveat is that a pillar for one of the railings was to be sited just before where the pipe gap is. Thus do I put the lintel into the first course of bricks of the pillar? I'm assuming that I shutter and fill concrete in the footing parallel to the pipe, with a given gap between, then put the lintel over.

 

[RedHerring2]

The lintels can extend into the pillar brickwork. For convenience, try to locate it/them so that they do not upset the brickwork layout, i.e avoid having to use cut bricks.

 

[r896neo]

Also as mentioned just behind this pier may be a good place for an expansion joint in case there is any relative settlement of the two footings.