Residential Wall Over 9m

[Prime Design]

Hello all,

My company is primarily involved in industrial design, however a friend of the company director is having an extension built so we've been given the work.

Part of the extension works means that one of the walls becomes longer than the standard 9m without buttressing. The client doesn't want to put a brick buttress in because it ruins the "flow of the room", and Approved Document A doesn't give any information on alternatives. The architect responsible for the design suggested we build a steel column into the inner leaf and cavity of the wall which would then essentially act as a "new" section of wall, as the column would be classed as a vertical restraint.

Is this something that is standard practice? In terms of assessing the stability of the wall, is this just wind loading calculations? Carrying out calculations isn't an issue, it's just making sure we are calculating the correct things, as I said, we usually focus on heavy industry i.e. petroleum, mining, steelmaking sectors.

Thanks for any advice.

 

[MotorCity]

I am trying to picture this wall with all of its leafs and cavities and potential buttresses. You also mention the wall is "longer" than the standard 9m. To me, that means we are talking about the horizontal length of the wall, not the height. Is that correct? Can you post a sketch? Given enough money, anything is possible......even a wall 9m tall.

 

[hokie66]

Like MotorCity, I took the "over 9m" as the height, and immediately thought of steel solutions. If it is length, why should that matter? Where does the "standard 9m" come from?

 

[Prime Design]

The wall is indeed over 9m long. I've attached a very simplified version of the architects drawings. The drawings are not my property so I can't attach the full official drawings.

This is the building approvals comments on the length:
[li]Please submit an assessment of the stability of the
existing two storey side wall, which may now exceed 9.0m without adequate
buttressing.[/li]

The 9m is to do with lateral restraints on wind loading. It is part of the government "Approved Document A" for building control.

Thanks

 

[hokie66]

The extension seems to be single storey. By "existing two storey side wall", I would assume that means the north wall, and the 9m could be either horizontal or vertical, depending on whether there is a floor abutting that wall.

 

[Prime Design]

From conversations with the architect it is horizontally the issue occurs.

 

[hokie66]

But your sketches seem to indicate the problem is in the extension, while the approvals comment is about the side wall of the existing.

 

[Prime Design]

I realise the drawing makes it confusing as it doesn't show the full ground floor plan.

There is an internal load bearing well that acts as a buttress/lateral restraint in the double storey wall. So without the extension it's fine. However with the extension added to the second storey wall it produces a length over 9m between walls perpendicular to the wall, so that makes it it laterally unrestrained i.e. no buttress.

Building control guidelines state for two storey residential properties there must be a full wall height lateral restraint. There is in the existing two storey wall from internal load bearing walls. The extension creates a 9m horizontal span that is unrestrained laterally

 

[HouseBoy]

It seems to me that the existing second floor is restraining the existing portion of the wall and I would expect that the new roof could be made to provide horizontal support for the 4 meter portion that is new.
Of course I am assuming that there is a second floor about the dining area.
I'm wondering about the apparent infilled portion that appears to be being built on top of an existing half height wall. Perhaps that is a hinge there and that could be a problem. Much will depend on how the wall is actually built.
It seems to me that something could be installed there (like the steel column that was mentioned). You might also want that there if there is a need to pick up a header from where the original rear wall is being removed.

I'm not aware of a limit on the length of a wall without perpendicular buttressing. As long as it can span vertically, why not?

 

[BAretired]

Building Approvals comments seem to be referring to Table 3, below.

BA

 

[hokie66]

It is probable that only those accustomed to dealing with those prescriptive provisions can be of assistance. The provisions in the table which BA provided are presumably for unreinforced masonry walls.

 

[BAretired]

That could be, hokie. I have not studied the entire document thoroughly, but any way you slice it, the existing south wall has been almost completely removed. It will take some thought to render the building adequate to resist E-W wind.

BA

 

[JoshPlumSE]

You're providing engineering calculations for this structure, right? If so, then you should be able to demonstrate whether the wall has adequate lateral capacity to resist wind and seismic forces regardless of the length of the wall.

Or, is this a project where the architect (or contractor) took on the project assuming they could entirely use prescriptive provisions and got spooked when the city / plan check pointed out some ways in which this doesn't conform.

A 190mm wall is pretty thin. But, 290mm is pretty thick. Certainly you can come up with a design in-between that would work by engineering principles.

 

[Prime Design]

Thanks for the responses everyone.

@HouseBoy, we do plan to carry out a site visit to fully assess the interior of the property. The architects drawings aren't the greatest, the floor plans only show new and not existing. They're putting a steel beam in across the dining - living room kitchen area so might be we can incorporate a steel post to pick that up to act as a horizontal support.

@JoshPlumSE, this is indeed a job where the architect has taken on the project and not had a structural input until local building authorities got involved.