Footings for Garden walls.

[Andy]

Hello Folks,

My neighbour has chided me into replacing a falling down fence with a block wall. I'm using centred brick-and-a-half piers tied into the block walling with a fixing tie system thingy from Screwfix. The distance between piers isn't quite an exact multiple of block width so I will add a 'course adjuster' block on end per course. That's the background.

I am making the footings 6" thick nominally ( wall is 39" high single thickness, pier will be about 52" high ), and 12" wide except below the pier where it will be probably 22" wide.

I have clay soil, and was thinking of pouring the concrete footings straight into the foundation trench, if the soil looks firm, but I keep seeing hardcore mentioned, though not always. What is the point of hardcore? Do I really need a layer of it under the concrete? If so how deep? Does it need 'blinding' with ballast to fill the gaps? Etc, etc.

Any ideas anyone?

Thanks,

Andy.

[Phil L]

You don't need hardcore. Hardcore is merely 'filler'...if you were filling in a large area and it was already 3ft below the level you actually required, hardcore would be used to bring it up to something like(maybe two feet deep) , then concrete poured on top (usually after polystyrene or other insulating boards and then plastic membrane, so the concrete isn't actually in contact with the hardcore) For clay soil you don't need anything other than a few inches of concrete.

Also I'm a bit puzzled as to why your piers aren't spaced at block lengths?...you do realise that the joints can be as wide or as narrow as you like?....you can lose or gain 10 - 15mm per block, meaning that you can gain six inches over a ten block long stretch.

[Andy]

Thanks Phil L: just as well I don't need hardcore then as I haven't any anyway!

The piers are not spaced at block lengths because I have to build between an existing pier ( boundary wall, running along the road ) and a garage. The distance is fixed, and at maximum allowed pier spacing ( I don't want to have to build more than necessary ) I end up with 5 stretches of wall supported by 4 new piers ( the last stretch gets attached to the garage ).

I don't want to adopt wall lengths based on block sizes then have a short stub section of wall and an extra pier right next to the garage, it'd look naff ). I could perhaps adjust the pier spacings, so they would be slightly unequal but multiples of block lengths, but some would then exceed the max allowed pier spacing ( it so happens that I'm actually just over the 9'9" limit as it is but who's going to measure? ).

It's interesting to hear what you say about increasing the joint size, I didn't want to go much away from the guidance of 10mm that is always quoted. I actually will have 2.2cm vertical joints if I don't insert course adjusters. I take it then this is no big deal? Sounds within your gain/loss of 10-15mm/block.

NB: I have built stone walls before, but they're a completely different ballgame - nothing fits properly anyway.....

Andy

[Phil L]

I understand.

No one, and I've never heard of this before, BC are only usually interested if the wall exceeds a certain height (for safety reasons) - a 3ft 6 wall is of no concern to them at all....I've seen walls built without any piers in, although I should imagine that they would be a bit rickety after a few years.

I sometimes don't bother with piers until after the wall is up, you can then either use screw in brick ties and just 'stack' the piers up, or if you know 'generally' where they will be going, leave conventional butterfly ties protuding, one on each course....I've never had one move as yet....this makes things much easier and you can simply pour the footings a bit wider for say, a two foot section, and your pier can go anywhere on that, the remainder just gets soil / paving / whatever covering it later.

Me too, backbreaking work IIRC.

[Andy]

I should have mentioned that the wall is built on a slope, each wall section is 39" high at the one end, 47" high at t'other, so I think piers are in order.

Hehe, sounds like the easy way to go. I can't build in block piers because they'd be offset piers and it will create a fair-face and a not-so-fair-face, which is a pain to come to an agreement over with a boundary wall. Anyway, centred brick piers is the way the walls facing the road are built and I like to keep things original. I can't see that I build a single-thickness wall with no piers then attach bricks to it with ties in this case - it needs to be a brick-and-a-half pier to blend in with other existing ones, so that would require tieing in half-bricks as well as full ones, a bit dodgy IMO. I've elected for a brick-and-a-half pier about 14" square, with a rebar running down the central hole for extra support. Overkill perhaps, but I've bought the bits now.

Thanks for the info,

Andy.

[meow2222]

Piers that are built into the wall rather than added on later give more stability. If you're not convinced, try it with some lego.

NT