Alternative to piers every 3m?

[Pallatrax]

Hello,

We're building an extension on a building notice, and expect to get to dpc on Tuesday after pouring the foundations this morning and planning to take the weekend off. Everything is going so well despite the rain while excavating!

Part of the extension comprises of a single-skin garage, and my builder wishes to build block piers every 3m (wall will be made from conventional 4" concrete blocks).

The roof is a lean-to and the span over the garage 2.6m, but It is the throat into the garage which is where the main issue lies and my reason for hunting to an alternative to a 4" obtrusion into the space.

I understand building it in 6" is ok, but I've not run this passed BC yet.
Length of wall is 5m, though I'm not sure the cost vs saving 2" is worth it...

Any ideas?

Thanks in advance
Tom

 

[^woody^]

Reinforce alternate bed joints

 

[tony1851]

Reinforce alternate bed joints

How would that reduce the tensile stress due to wind load?

 

[^woody^]

Try blowing a reinforced wall

 

[tony1851]

With reinforcement in the bed joints, it will only be reinforced horizontally.
But it also needs to be reinforced vertically as well if it is to be adequate against wind load.

 

[^woody^]

Err no. Horizontal reinforcement works in the horizontal plane which stop the wall buckling or deflecting in wind loading

Do you think that one 100mm pier in the OP's 5m panel will resist wind load better than a whole reinforced panel?

 

[tony1851]

Err no. Horizontal reinforcement works in the horizontal plane which stop the wall buckling or deflecting in wind loading

Incorrect. The half-brick wall acts like a slab, and has to be reinforced in both directions if it is to be effective against horizontal wind pressure. This is basic stuff.

Where's Ronny?

 

[^woody^]

The half-brick wall acts like a slab

What does that mean?

A wall is a vertical panel and nothing like a horizontal slab, and not even at all like a mass of concrete in terms of how it behaves

I'd get a refund from the place you learnt your "basic stuff" if I was you

 

[tony1851]

The half-brick wall acts like a slab

What does that mean?

A wall is a vertical panel and nothing like a horizontal slab, and not even at all like a mass of concrete in terms of how it behaves

What I meant by that was that the wall is subject to horizontal wind load and the cracking patterns would be similar to that of an insitu reinforced concrete slab except, of course, it is vertical rather than horizontal.

Obviously, very few brick panel walls are built with vertical reinforcement, but the applied bending stress due to wind load has to be accounted for. As you will know, although brickwork is very good in compression, it is poor in tension.

In the absence of tensile reinforcement in the vertical direction, the only way the brickwork can counter the applied tensile stress is by a combination of its own dead weight, and the load the wall is carrying - such as a roof.

Assume the OPs garage is, say, 2.3m high, you wouldn't build a free-standing boundary wall 1/2 brick thick this high, because it would blow over. It would blow over because the tensile stress caused by the applied load of the wind would exceed the (low) permissible tensile stress in the brickwork. But in the case of the garage, there is the dead load of the roof giving some pre-compression, and there are also the piers which, if spaced at reasonable intervals, increase the effective thickness of the wall.

The OP has come up against the 'deeemed-to-satisfy' povisions of Approved Document A. If he wants to do away with the piers, he is at liberty to do so, but the Council will want structural calculations to prove that the garage wall will satisfy the requirements for structural stability under wind load.

Unless the roof is fairly heavy, and the wall in a demonstrably sheltered location, it will be difficult to proof compliance without some form of strengthening.

 

[Pallatrax]

Hi Tony/Woody,

Thank you for your comments, and getting stuck in!

The wall is very sheltered due to the proximity of the neighbours house, and the roof will be tiled with clay double romans and constructed from 200x50 rafters - so there is substantial weight.

I'm struggling to see how horizontal reinforcing would help at all?

But, perhaps there is an option for me to run these vertically (if necessary when considering the lack of wind, and mass of roof) on the outside/inside before applying render?

Can anyone link to this reinforcing you speak of?

Thanks
Tom

EDIT:

How about A142 mesh tied in with tall ties and rendered over? I'd imagine that would put up a lot more resistance than a couple of piers and I'd only loose, what, an inch..?

or

I imagine carbon fiber strips aren't cheap, but surely the soil in this diagram is acting on the wall in a similar way to horizontal wind loads https://www.google.co.uk/search?q=w...tion-waterproofing%2Freinforcement%2F;403;526

 

[tony1851]

Hello Tom,

Reinforcing the bed joints as W suggested would do no harm, but it wouldn't address the problem of 'vertical spanning' of the wall.

On a wall of that thickness, there is no viable way of reinforcing it in the vertical direction. Applying mesh to the wall and rendering that over would almost certainly not be acceptable to the council.

You might get away with a 6" solid concrete block wall. The problem is that building inspectors vary on how they approach strictly structural issues.
Inspectors are rarely engineers but some have instinctive feelings for what will or won't work. If your inspector feels happy with a 6" wall, then go for it. But my guess is that he would ask for structural calculations to prove adequacy.

Looking at the probem another way; could you widen the opening on the other side, eg by taking out a side skin of the house wall?

 

[Pallatrax]

Hi Tony,

Thanks for your reply.

I'm surprised by your reaction to the mesh idea. It was a bit out of left field I grant you, but with the roof holding the top of the wall, and the base unlikely ever to move, I though the aim of the piers was to stop the wall buckling - ie bending before failing. Surely the mesh would solve this problem in an unconventional way?

It is only the throat into the garage which is narrow and determined by the house which stops as the garage starts. The walls are old rubble filled jobbies, so it simply isn't worth touching them. Once into the garage room isn't an issue, and moving back the doorway just decreases the overall length which I don't wish to compromise.

So its good old piers, 6" blocks (maybe), or some other hair-brained idea I'd have to convince my inspector to go for!

Issue really lies in that we're building up to dpc (or wish to!) on Tuesday, and I need to decide very soon what and how we're proceeding...

Thanks
Tom

 

[^woody^]

So let's see. A 5m wall, restrained at each end by buttressed returns is going to be pushed or pulled in what location by wind loading? Now consider restraint top and bottom.

And this force is trying to bend the wall how?

And having a continuous strip of horizontal reinforcement to resist the force trying to bend the wall will do what?

I take it you don't know how sails work?

This is even more basic than basic stuff, and does not need convoluted text to try and justify the point

 

[Pallatrax]

Hi Woody.

I don't understand how it can go anywhere to be honest, but if it needs additional support or strength then so be it.

I'd like to get my head around it though and come up with a solution which meets my needs.

Can you please explain whether the concern is with the wall failing in the middle (for arguments sake), or being pushed over - or both?

If it were a free-standing wall it would obviously fall over before it broke in two, but this is restrained, as you know...

Thanks
Tom

 

[theoldun]

Sorry Tony, but the woodenhead wonderloaf is about right in this instance, providing B.C, agree.
O.P. If you want to cover your ar*e stick a 150mm wide block in footing for section in question.
Regards oldun