garden wall building project; costs and methods?

[Jim Walsh]

Dear all, I have just demolished a section of garden wall at my property that was being pushed over by some self seeded trees that should have been removed years ago before they bacame a problem. The demolished section was about 15ft long and is around 6ft6in high at one end, reducing in a graduated fashion to around 3ft at the other (on account of the slope of the land).

I arranged for quotes to re-build from a few bricklayers, but was a bit shocked at the prices; all are around £1200-£1300. Is this way over the top? When I have watched briccies working on a major construction, it seems that they can throw up a wall in no time at all, but most of the chaps who have visited me are saying its a 3-4 day job!

I am now considering DIY, but to make the job as easy and quick as possible, I think I will use large conrete blocks rather than bricks and then render the wall afterwards (part of the existing brick wall is rendered anyway). I want the wall to be the thickness of two courses, but rather than actually building two separate courses, could I just use the blocks on their sides? I wonder whether there are any strength implications to this, since the blocks are far easier to break with a force from above when laid on their sides than when in their normal orientation. Would I be running a much greater risk of cracks caused by settlement if I use the blocks on their sides?

Thanks, Jim

[adder1969]

As it's so high I guess you'd need proper strength calculations for both the wall and the foundations. and/or go way over the top with the strength.

[Christian McArdle]

It would be much easier and less labour intensive just to buy blocks of sufficient width. Although 440x215x100 is the common block size, you should be able to find 440x215x215 in stock at a builder's merchant and they will order you some if they don't have any.

Don't forget to read up about how to design walls and their foundations. The wall needs to be designed, not just thrown up. You also need to decide on whether you want aerated or dense concrete. Personally, I would just use aerated, especially as it will be rendered, so appearance is less important. The only advantage of dense blocks is really just resistance to surface damage and better appearance. In terms of structural strength, they're just fine. They are also slightly less likely to kill you if the wall falls down.

Many of these blocks, such as the Celcon Standard 440x215x215 I would use for this application, can not only be used externally, but are also suitable for use in foundations, too.

Christian.

[Phil L]

Tell planning about it if it's that high or you could end up having it removed, a garden wall fell down a few weeks ago and killed a child and many arses have been kicked and bollocks removed as a consequence.

It *is* a 3-4 day job.

Or you could just use the trench blocks which are 2 feet long, ten inches wide and nine inches deep, they're similar to thermalite and are easily cut, carried and laid, they cost more than normal blocks but the wall is completed in half the time.

[Darryl Bailie]

The BRE Good Building Guide (GBG 14) recommends that for walls of this height in sheltered locations they should be 300mm in height. Once you get to this thickness the orientation of the block makes little difference. It also recommends for stability reasons that the minimum density of block should be 1500kg/m3. In any case I wouldn't recommend rendering lightweight block as I have seen the face of the block shear off leaving you with a really awful looking wall. The foundation should be 550mm wide unless you live in the north of Scotland and 275mm deep. If you do not live in a sheltered urban area then a simple wall will not have sufficient strength. This assumes that you have good firm soil to build off.

In answer to your question though. A 200 mm wide wall form from block on side is 3 times stronger than a 100m thk wall. A wall formed from 2 leaves of 100 block with no ties between the leaves is twice as stronger as 100mm. A wall collar jointed 200mm thk wall (blocks tied at each coarse) is just less than 4 times as strong as a 100 mm wall.

Darryl