Building regs for window opening near corner of extension

[Billjg]

Hi, is there a minimum distance between the corner of a building and a window opening for a single storey extension? Basically, how close can I get a 1200mm wide window to the corner of the extension according to building regs.

Thanks,
Bill

 

[tony1851]

If it's a normal-height window, about two bricks from the corner.

If you are doing this through Building Control, the inspector will probably ask you for a three-brick return. That's not because it's structurally necessary- it's because most inspectors are dim.

 

[noseall]

Any less than three bricks (@100mm cav) and you are looking at a fairly stubby return for curtains etc.

You need a minimum of two bricks to prevent the lintel bearing from interfering with the cavity. Some S.E.'s will factor in an even greater bearing than the standard 150mm.

On our current job the S.E. is asking for 250mm end bearings on the extra heavy duty lintels we are installing. This would compromise the cavity according to Tonys two brick return.

Ho hum.

 

[Billjg]

It is going through building control, the window is 900 (h) x 1200mm (w).

The window is to be cut out but not built in so will require a concrete lintel on the block work and a single leaf steel on the brick work I believe. I think 150mm ends for each lintel should be fine.

Is the distance from window opening to corner the internal or external measurement?

 

[tony1851]

The requirement for a return is to provide a degree of lateral stability, in particular against the wind load on the flank wall of the extension.

The distance is an external measurement.

A return wall 900 high (ie the height of the window) x 2 bricks wide will easily provide sufficient resistance moment to counter the applied moment caused by the wind.

If the window is only 1200 wide, there won't be much load on the lintel and 100 bearings on both skins would be OK.

 

[tony1851]

On our current job the S.E. is asking for 250mm end bearings on the extra heavy duty lintels we are installing.

If he's asking for 250 bearings, how wide is the opening?

Even Catnic, with their heavy-duty fabricated lintels only require 200 bearing.

Either this is another ar$e covering exercise by your client's SE, or the SE doesn't know his job/can't be bothered to do proper calcs.

 

[noseall]

On our current job the S.E. is asking for 250mm end bearings on the extra heavy duty lintels we are installing.

If he's asking for 250 bearings, how wide is the opening?

Even Catnic, with their heavy-duty fabricated lintels only require 200 bearing.

Either this is another ar$e covering exercise by your client's SE, or the SE doesn't know his job/can't be bothered to do proper calcs.

Bear in mind these are CX EXTRA heavy duty fellas.

The floor load is directly above both openings and is a 6m span.

The openings are both less than 2m.

The SE is pretty good (Mike Abbott) and is respected at Staffs building control.

Floor, roof and wall loads amount to 51.5kn.

 

[tony1851]

Floor, roof and wall loads amount to 51.5kn.

Factored or unfactored?

Either way, I wouldn't say it's an unusually heavy load.

As a matter of interest, is the beam bearing on brick/cavity/brick or is it brick/cavity/aac block or 225 brick? Just curious.

 

[ban-all-sheds]

The requirement for a return is to provide a degree of lateral stability, in particular against the wind load on the flank wall of the extension.

The distance is an external measurement.

A return wall 900 high (ie the height of the window) x 2 bricks wide will easily provide sufficient resistance moment to counter the applied moment caused by the wind.

If the window is only 1200 wide, there won't be much load on the lintel and 100 bearings on both skins would be OK.

Ah.

So would this not work:

Grey are the existing house walls. And just realised I've not shown the external width of the return at the top - it'd be about 600mm.

The 2100mm opening is about the same in height - patio doors.

 

[noseall]

As a matter of interest, is the beam bearing on brick/cavity/brick or is it brick/cavity/aac block or 225 brick? Just curious.

105mm brick - 110mm cavity - 3.5n fibolite block.

 

[tony1851]

As a matter of interest, is the beam bearing on brick/cavity/brick or is it brick/cavity/aac block or 225 brick? Just curious.

105mm brick - 110mm cavity - 3.5n fibolite block.

Assuming 51Kn was an unfactored load, on reflection I think he's about right. It's the inner skin that is the weak side. Technically it could have been slightly less, but not much - and of course I don't have to take the responsibility!

 

[tony1851]

Grey are the existing house walls. And just realised I've not shown the external width of the return at the top - it'd be about 600mm.

The 2100mm opening is about the same in height - patio doors.

As the projection of that part is only 2.1m from the original wall, the wind load on the 600 return will be quite low. Even with a 2100 door height, that could be shown to work.

If you ensure that the (flat?) roof is adquately tied by straps to all the new and existing walls, the roof then acts like a rigid diaphragm, and will help to spread the wind load around all the returns; each return then plays a part in sharing the horizontal load.

 

[ban-all-sheds]

Thanks.

(flat?) roof

Yup.

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