mimum distance between door and window

[patman209]

Hi all

I am replacing 4ft french doors in my rear (single storey extension) with a wider 8ft one. Making the larger opening means tht the distance between the door and the window that sits on the same wall as the door, is reduced to 300mm (600mm returns either corner). Wall is cavity filled 500mm width.

BC say that the distnce between door and window needs to be at least 600m. Anyone come across this kind of requirement before?

Thanks

 

[tony1851]

Approved Document A (Structure) stipulates various dimensions for brickwork returns, minimum widths of piers, max. width of openings and so on.
Some dimensions may not fit in easily with the layout of doors and windows, and can be modified if you are prepared to provide structural calcs justifying them.
But, 300mm between an 8ft door and a window is not very much, and I think you (or in fact an SE) would struggle to justify this. Can you not reduce the width of the doors?

 

[patman209]

Hi, I could go for 6ft width (buying offthe shelf) but was looking for a decent improvement over the current 4ft.
I will take a look at that doc, thaks for posting the one to look at,

 

[tony1851]

If you Google the Document, the diagrams and info. you need is on page 27.

 

[patman209]

Thanks tony had a quick look but couldn't easily work out the distance will take a look a bit later . Cheers

 

[^woody^]

Whether the pier is a problem or not could depend on the spread of the load from the roof and the restraint to that pier, as this is just a single storey.

Approved documents are just conservative guides, and if need be an SE could most likely prove this pier to be adequate.

Other options are to build the pier in solid brickwork with insulation and drylining internally, or reinforce the joints and building in brick cavity

I assume a big lintel across the whole lot is out of the question

 

[tony1851]

if need be an SE could most likely prove this pier to be adequate.

Would a 300 wide pier in cavity work be ok to take wind load from part of the patio door on one side and the window on the other?
Also, if it is actually 300 wide, he will have to cut bricks and will end up with 75 wide bits ...not ideal.

 

[patman209]

As the returns are 600mm each with steel lintels across the door opening and window opening I assumed the 300mm pier between the door and window would suffice.
I was going to think about putting a large steel pillar in the cavity of the 300mm pier but not sure that will suffice either now.
Going for lightweight tiles too - those decra ones on the roof.

 

[tony1851]

If you are running a steel beam across the lot, you would still need to make sure that the pier is securely fixed to the steel in some way. Remember that the patio doors will be fixed to it, and it could eventually work loose.
Sometimes people add a steel column in the cavity as you suggest (it is a wind post) but if you do that, it is possible Building Contro will ask for calcs for the post and fixings top and bottom =more expense.

 

[^woody^]

I misread it as "Wall is cavity filled 500mm width" and thought that meant the pier, but it may be still possible with a 300mm pier depending on the roof load above

Wind load is not an issue for a single story extension

This needs to be considered pragmatically in terms of how the whole wall and roof work together

 

[tony1851]

[quote="^woody^";p="2477281

Wind load is not an issue for a single story extension

[/quote]

Woody, with all due respect here, I have to disagree and say that wind load is an issue, even for single storey.

I have lost count of the number of times inspectors have asked for calcs for small central piers, or short-width returns, and it all comes down to lateral stability under wind load.

Ironically, for the typical single-storey extension like the OPs, the heavier the roof, the better.

 

[patman209]

I was actually going to go for the concrete tiles but then thought about the decra ones when BC started saying they wanted more space between the door and window

 

[tony1851]

I'm not familiar with decra tiles, but I assume they are lighter than concrete tiles.
If this is the case, you may be barking up the wrong tree because in your situation you need more weight from the roof, not less.
I suspect you are concerned about the vertical load-carrying capacity of the brick pier, but that is not the issue.

If you got to build the pier 300 wide (not adviseable), it would almost certainly be satisfactory for carrying the vertical load, particularly as the effective length of the pier will be quite small because of the window.

It is the lateral load due to wind which could potentially crack a narrow pier as brickwork is not v.good at resistting lateral loads.
One thing which does help brickwork resist lateral loads (ie wind) better is extra weight from above.

 

[patman209]

I'm going to have to call BC back and thrash something out with them . My builder says that the 300mm would be sufficient but obviously BC call the shots.
Else a smaller window but my wife insists on a decent size window above the sink!
Yep the decra tiles are lighter - about 75% lighter than concrete.

 

[patman209]

If you Google the Document, the diagrams and info. you need is on page 27.

tony I ws just reading that doc, on page 31 they have a section on major openings, with a pier that is 325mm x 325mm. The example they give is two major openings, whereas I have one, and then a window.

Could this not be applied to my situation?