Laying a footing for an outside staircase

FredAt · 18 Apr 2010

Hello All,

I am in the process of preparing the ground to install an external staircase. The staircase is a lightweight affair with aluminium spindles and recycled plastic treds - very light, so light that I brought it home in the boot of my car. The height of the stairs is 1.6m and the landing is just over 1m square.

I am in the process of building the footing for the stairs and need some advice on how I go about this. Local conditions require that I go down to around 70cm below ground in order to ensure that the footing is frost free. It needs to be around 30cm square. My question - can I get away with simply putting in a form and pouring in concrete or do I need to reinforce the concrete.

I do a lot of DIY work but am a relative newbie when it comes to concrete. I'd much appreciate any advice.

r896neo · 18 Apr 2010

What formwork do you need? just dig the base of the hole to the right size. I would imagine you will be fine without the steel. How deep/thick are you proposing for the concrete?

FredAt · 19 Apr 2010

By form all that I meant was this - at my local builders I can buy a polystyrene form -30cm square and 200cm long to be cut to size - to place in the hole when I pour the concrete.

As to depth - as I said given the local conditions in order to ensure that the footing is frost free I need it to be 60 cm or so below the surface.

So are you telling me that I can simply pour in the concrete and let it set?

r896neo · 19 Apr 2010

You only really use a former when you are above ground and you need to shutter the concrete. I.E big raft foundations.

For foundations you want all sides of the concrete to be touching solid virgin ground, if you dig an oversize hole and then put a former in it you have to back fill around it and the backfill provides no strength to stop the concrete settling once set.

Just dig your hole to the 30x30 size and pour in your concrete and let it set. There is no real science to it, but make sure you do it on a warmer day. At least 5C and rising.

When i said what depth i meant how thick will the concrete be i.e. 300x300x??

noseall · 19 Apr 2010

Dig a hole and fill it with concrete to the required level.

Simples.

FredAt · 19 Apr 2010

Well I suppose it will have to be 300 (w) x 300(L) x 600 (D) - 600(D) to ensure it does not move due to ground heave in a particularly severe winter. Or am I misunderstanding the ground heave issue somehow?

noseall · 19 Apr 2010

Jack does not effect the ground in the UK as deep as you are assuming.

It will however have an effect upon the uppermost part of the concrete should the temperatures fall to about minus 8 and stay there for the 7 days whilst the concrete cures.

Otherwise, in sunny April, you do not need to worry about frost and frost cover. If there is a risk of frost chuck a sheet over the hole.

Clay heave is another matter....

Static · 19 Apr 2010

Got any big trees near it ? and are you in clay soil?

FredAt · 20 Apr 2010

Ummm.... I guess the fact that the forum says that I am based in Argyll is a bit misleading. I moved out of there and now live in Luxembourg. Our winters are continental - i.e. longer and colder (at least in theory). Last winter the temperature dropped to -15 and stayed there for nearly two weeks. That said, I have a temperature guage inside the pit I made for my drainage pump. The pit is covered with sand to a height of 40cm and the temperature has never dropped below 2.5C.

There are no big trees in the neighbourhood and the area where I need to dig has largely sand and stone - the back fill used by the builders when they filled up the trench around the house. At a depth of 70cm I have hit a layer of silty soil. From my experiences with the drainage pump I know that the soil is very well drained with no excessive retention of moisture.

noseall · 20 Apr 2010

FredAt said:
Ummm.... I guess the fact that the forum says that I am based in Argyll is a bit misleading. I moved out of there and now live in Luxembourg.

A little bit misleading!

Are there no builders in Luxembourg that can advise.......?

FredAt · 21 Apr 2010

Clearly, you don't know Luxembourg. Building work in Luxembourg is controlled by a Portuguese mafia. Besides people think that everyone out here is a billionaire. Cross the border from Belgium, Germany or France and everything is 4 times more expensive. Advice? Forget it! The rule is pay and get shafted which is why I am doing nearly everything myself.

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Laying a footing for an outside staircase

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