Garden party wall footings - help with calculations


Postby Koth » Thu Mar 27, 2014 11:21 pm

Hi All

I would like to build a smallish wall as a project. It will be the first time for me to have a go at building anything.

The wall is 5m long and will be 1.5m to 1.8m tall. It'll be constructed with 100mm blocks. I am planning on incorporating a few piers and tying the ends into an existing garage and an existing party wall with wall starters.

After lots of internet based research I think I have a fair understanding of what is required but I need some help with some good quality information sources if possibe please. For example, every piece of information that I come across regarding footing size contadicts the preceding information. Can somebody please offer a link to a good web page that illustrates the proper formula for calculating this?

Also, I'd like to see some text that describes proper rules for positioning the piers, max/min spacing of piers, proximity to ends of the wall etc.

Would also like to be pointed in the right direction of quality information explaining how to estimate the quantity of materials to use please?

Sorry, one more, the footing will be stepped due to the garden being on a slope, any particular rules of thumb to be aware of in this situation would be helpful.

I have been able to find many articles on the above but still feel slightly uncertain due to the apparent lack of consistency in the information that I am reading.

ATB
Koth
Koth
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Postby welsh brickie » Fri Mar 28, 2014 3:15 pm

its best to excavate 600mm deep for the foundation, a minimum of 300mm wide and 150mm thick.
you need to overlap the foundation at each step by 450mm, so each step will be 300mm thick. Piers can be as many as you want, but for this length 4 is enough, 1 at each end and 2 spaced equally apart,
Calculation of the concrete is length times breath, times depth so 5m x 0.3 x 0.150 will give you square metre of concrete allow a bit more for the steps.
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Postby Koth » Fri Mar 28, 2014 7:24 pm

Thanks for this.

Few more questions please.....

I am using wall starters at each end, is there still a need to construct pillars at each end also?

I was planning on each footing step being a fair distance apart, say 0.3m, and not resting on top of each other with an overlap. Is this a no-no?

Cheers
Koth
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Joined: Thu Mar 27, 2014 10:45 pm


Postby welsh brickie » Sat Mar 29, 2014 11:47 am

if the starter strips are secured to a solid structure then no you don't need pillars at each end,
And you must overlap each step by a minimum of 450mm
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Postby Koth » Sat Mar 29, 2014 7:38 pm

Diolch yn fawr

I've dug the footings today and got away with not stepping them so straight forward now, 600mm deep at the shallowest end of the slope and gradient wasn't as bad as I thought so not much deeper at the other end.

Mixing concrete seems straight forward but I have come across some literature that suggests that footings are stronger if the mix is semi-dry then tamped down with a wooden post when levelling. Opinion? Any advice?
Koth
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Joined: Thu Mar 27, 2014 10:45 pm


Postby welsh brickie » Sun Mar 30, 2014 1:27 pm

no its not true, and its easier mixed wet than semi dry as it sticks in the mixer, If you cut wooden stakes hammer them in the ground and level them first, pour your concrete then use a rake to level the concrete, then use the head of the rake and tap the concrete, it will bring the water to the top and create a flat smooth surface, if you can see each wood peg the concrete will be level, take your time, concrete takes at least 2 hours before it starts to harden
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Postby Koth » Sun Mar 30, 2014 7:31 pm

Ok great stuff.

I'll be pouring the concrete next weekend, if there's lots of rain this week can I still pour the footings if they are holding water?

Do I lay the first course of blocks on cement? Or on concrete in the same way that curb stones are layed?

Thanks for your continued interest.
Koth
Posts: 4
Joined: Thu Mar 27, 2014 10:45 pm


Postby welsh brickie » Mon Mar 31, 2014 10:26 am

it does not matter if it rains, wait 24hrs before starting the blockwork lay the first course dry to work out the bond, then useing a string line bed the first block, at one end and the same at the other a pull the line tight giving you a guide to work to, Take your time
welsh brickie
Posts: 1891
Joined: Sat Apr 12, 2008 7:54 am


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