maximum opening in an external wall

[davphi338]

Hi,

Does anyone know the max. opening that is allowed in an external wall. i.e I plan to knock through my kitchen and dining room and build an extension onto the rear. I want get an idea of how much of the existing walls can be removed. I think there is some form of rule as to the maximum overall size of the openings with respect to the length of the wall but can't find any details.

 

[noseall]

there are no pre-set parameters.

there are rules governing what is acceptable before the need for a structural engineer is required, but otherwise, if you can prove it will work then fill ya boots.

you can remove the entire back end of a house provided all relevant structural requirements are met.

generally speaking you could remove 1.8m of wall leaving a 675mm nib (to the outside wall) and not have any probs. otherwise consult an s.e.

 

[davphi338]

Hi,

Thanks for the reply but after a bit more research and talking to a structural engineer it seems the max. opening you can have in an external wall that provides buttressing to the side walls is 2/3rds the total length of the wall in which you are creating the opening. This is to provide lateral support to stop the house falling down sideways. I was told there are ways around it but it involves using a steel framework in a goal post like affect and involves a lot more work.

 

[noseall]

2/3rds is usually enough for most people.

 

[^woody^]

Hi,

talking to a structural engineer it seems the max. opening you can have in an external wall that provides buttressing to the side walls is 2/3rds the total length of the wall in which you are creating the opening.

Ask how this applies to a garage or double garage etc

You can have as big an opening as you like.

The opening can run from inside face to inside face across the room, so that there is just the thickness of the external walls at each end - and if you cantilever the supports, then you don't even need any corners

Talk to an different engineer - one who knows engineering stuff maybe?

Otherwise follow the guide in Part A of the approved documents

 

[Shytalkz]

Ah an SE uber-obsessed with lateral stability....2/3 involves very little effort on his part, calculations-wise, that's all viz less effort for same fee. It *doesn't* always involve a goalpost at all.

Woody is tallking sense (dudududududuhhhhhh )

 

[June1]

I agree, definately get a new Structural Engineer. I design my own selfbuilds and extensions and my structural engineer never has a problem. Its all down to cost and time.

Have you seen houses in mags and on the tv with the whole rear wall removed and replaced with great big glass doors, all thats left are the side walls.

I would ring a few SE and ask how quick they can turn the work around and give them a quick idea of what you want, they maybe able to give you a ball-part figure on their costs (they vary a lot!) I had a difference in prices for a small job between two SE before, one of £200 the other was £1500!

 

[Shytalkz]

Send me some drawings and I'll give you a idea of fees if you want.

 

[davphi338]

Hi,

Thanks for the replies. It was actually the structural engineer from Building control that has put the restriction on. My plans were passed but with conditions, and that was the formation of the additional openings did not provide enougth lateral support (buttressing). The length of the rear wall is 9.9m and they have said I can have max openings in that wall of 6.6m (2/3rds) and this includes the patio doors that are already there.

When my plans were drawn up the structural engineer simply left a 550mm pillar inbetween the dining room and kitchen to support the RSJ. I now have to add an additonal 1.7m of wall to reduce the openings which is why I asked if there was set rule on the max openings. Its not too big a problem because the I have added 600mm on one side of the kitchen wall and 700mm on the other and this can be hidden within the kitchen units. I just woundered why B.C would insist on having the 2/3rds restrictions.

 

[Shytalkz]

Complete horlicks. There are set dims in BRegs which are "deemed to satisfy", but they are not cast in stone. It just needs a (sensible, not LA type) SE's input.

 

[^woody^]

Hi,

When my plans were drawn up the structural engineer simply left ....

Then get the engineer to sort this out with the council - he has either not done the calcs properly, or the calcs are OK and the council needs to be put right

Then we venture into the area of Part L1a, and area of permitted openings and SAP calculations