House / Building structural question ?

[hammerswinger]

Hi,

Ok I'm a bit confused with this so I'll try my best to describe what I mean.

A house has 4 elevations, Front, Back, & Two sides.

From what I have been told by a structural engineer & the building control officer the corners of each elevation must have at least 3 bricks (approx 660mm) in each direction to give stability to the structure. Most of the time there is more than 3 bricks but I believe 3 is the minimum.

On the estate where I live there are houses that only have 1.5 bricks at the front corners, like in the photo below.

I'm guessing that the corners must be some sort of pier that is classed as self supporting and enough to stabilise the gable end wall.

Can anyone explain this to me and maybe point me to a diagram of how this is constructed as I'm confused as to how it can work, especially with a cavity?

Cheers.


View media item 61935

 

[jeds]

Building regs approved documents are only a guide. It is entirely possible to build a house with much smaller piers than 3 bricks. You just need to justify it structurally. As for that house, bear in mind it was built well before the current approved document.

 

[stuart45]

The top half of the house could be 6 inch blockwork or timber studwork.
Many houses were built in the 60's with crosswall construction, as shown below. This allowed for the use of larger windows.
These were normally timber up top, with the weight taken on the crosswalls.

Untitled

• stuart45
• 31 May 2013
• 1

 

[^woody^]

If a structural engineer has told you that a wall needs a three brick return, then get a different one who knows about structures

A three brick return is not required as in most cases the walls are braced by lintels and floor/ceiling joists

If anyone can point out some domestic two/three storey homes that have failed purely because of lack of a return pier, then I'd like to see them

The easiest illustration of the principle, is to take a piece of card, stand it on edge and push it. Then bend the car into an L shape and try again

 

[tony1851]

A three brick return is not required as in most cases the walls are braced by lintels and floor/ceiling joists

I can agree with that to a point, and most inspectors have this genetic
attachment to '3-brick returns'.

But there are some instances where less than this doesn't work. An example would be a small, single-storey extension with patio- or bi-fold doors and a light, short-span roof. Vibration from doors could loosen bricks in a narrow return.

 

[^woody^]

Vibration from doors could loosen bricks in a narrow return.

Yes but that is a design issue and not related the structural stability of the wall

If the designer designs as a whole and not as a series of components, then the building works, and any deficiencies in one component can be countered by another

The only logical reason I can see for any return, is to give somewhere to hang the curtains when they are open

 

[hammerswinger]

Hi,
Thanks for the reply's.

The house in my picture looks very similar to the one in stuart45's picture so I guess it will have been built the same ...."Cross Wall Construction".
I was just trying to get my head around how the house I pictured only has a brick & a half return but I'm being told I have to have a minimum of 3 bricks, but as woody has pointed out, you don't need a return of that size if you design around it.

I'll ask the next question regarding the brick returns in my house & what the SE has advised shortly.

Cheers.

 

[tony1851]

Vibration from doors could loosen bricks in a narrow return.

any deficiencies in one component can be countered by another

Ahh yes, I understand now. If the footbrake on my car doesn't work any more, I can always rely on the handbrake for an emergency stop. Brilliant.

 

[hammerswinger]

OK here we go....

I've posted about this before on the forum but as that topic is a couple of years old I may as well start over again.


My house looked like this

View media item 61955
(The red line represents the two 5.5 metre 254 x 146 x 43 UB's that we now need to install.)



It now looks like this

View media item 61956
The structural engineer has calculated the steels, I asked about knocking back the returns (original cavity wall of house before extension) that the steels will sit on so that the returns would not project into the room so much. This is when I was told that I could reduce both sides to leave the minimum of 3 bricks (665mm)

The calcs the SE has produced show the steels bolted down to a 440 x 100 x 215mm pad stone.

Without having to introduce steel pillars into the wall or anything like that do you think the returns could be reduced further?


Cheers.

 

[tony1851]

In the absence of a moment frame (aka goal post) you do need something substantial to support the steels. This is not just to support the vertical loading but also to provide some lateral stability. Unfortunately these do project into the room; I would have thought three bricks a minimum. Having a steel column each side would not save that much space and would cost a lot more.

On a recent job, a client asked for a flush wall, so we built the piers outside each wall (it was a detached) and ran the beams on to those. They were tricky to design and detail, but the client preferred it that way.

(btw bolting the beams down to the pads is a waste of time).

 

[catlad]

I would not be happy to go less than three bricks with that size of opening, how do you know the strength of the foundations on each corner of your house for a start, without pushing it to its so called minimum.

 

[hammerswinger]

Hi,
Thanks for the advice....Looks like it's 3 bricks then

You're not the 1st to say that bolting down the steels is a waste of time, but I'm assuming that if it's shown on the calcs it will have to be done, unless the BCO is happy to overlook it.

Actually while looking at the calcs I've just noticed that there are 2 padstones shown at each end of the steels, one on the outer leaf & one on the inner, how can that work?
The steels are 146mm wide, the padstone specified is 100mm wide so how could you sit the steel on that & bolt it down?

I would have thought that there would be one padstone block that spanned the cavity and sat on both the outer & inner leaf with both steels sitting on it?


Cheers.

 

[tony1851]

Why not ask your SE to explain exactly how you bolt a steel beam with a flange 146 wide on to a padstone 100 wide? You've paid him, so he should at least explain it!

 

[hammerswinger]

Yes I will, I hadn't noticed that detail in the calcs.


Cheers.

 

[hammerswinger]

Ok, contacted the SE who said that it was common practice to specify 2 padstones so as not to bridge the cavity. After explaining that the part of the wall where the padstones would be sitting would now be internal he still maintained that 2 padstones was common practice but said that the padstone could be solid and bridge the cavity if we wanted.

I asked if the steels really had to be bolted to the padstone as a few people have said it's a total waste of time, he said it was common practice to do this as it stopped the steels rotating....I wouldn't imagine that was likely to happen given their size & weight.

I asked if the 2 steels could be bolted together instead of bolting them down, he said they could be bolted together but they will still need to be bolted down.....I can’t really argue the point of bolting the steels down as he’s the expert.

The builders that will be doing the steel work for me are saying they have never bolted the steels down on extensions like mine, and they have done a few houses exactly the same as mine, I've been to see one of them and it is exactly the same type of house.

Is bolting the steels down a common thing?....It's just I can foresee a right carry on with this, you would have to pre drill the padstones and what are the chances of getting the hole on the steel to match up exactly....that's going to be fun with a 237 kg lump of steel isn't it.


Cheers.