Joist cantilever balcony regulations

[dobson156]

Hi,

My house has a Juliet balcony which is constructed from the internal joists that then extend out of the house acting as a cantilever on the external blockwork.

This balcony needs some work and I'll basically be rebuilding all of the box section it and re-treating and then weather painting the joists.

Are there any UK regulations about cantilever distances when built this way? I've had a google and all of the resources I've found have been for the US market.

the joists are 2x8s and I'll be replacing anything i am not keeping with C24 2x8 timber.

Cheers

 

[freddiemercurystwin]

Do you mean you're planning on replacing the cantilevered bits of the joists?

 

[dobson156]

Nope, I am hoping to keep the existing joists, but replace the boxing around it, as that was exposed the elements. Just wondering if there were any regs about this stuff.

 

[freddiemercurystwin]

Not really, it's good practice to provide some ventilation to the voids inside. Does it have a waterproof layer on top? Always a bit tricky ....

 

[dobson156]

It had ventilation from below. As I said, I am rebuilding it, so happy to add in better ventilation.

It and a DPM between the joints and the deck that went over the top of it. This will be reinstated. But I was tempted to give it a few coats of either weatherproof paint and/or bituminous paint as well.

What I really want to know what the safe cantilever spans are for 2x8. I can get regs for the USA for that, but don't seem to be able to find any for the UK.

 

[freddiemercurystwin]

I've always worked on the rules of thumb that about 1/3 of a joist can cantilever.

 

[dobson156]

Thanks for all your help!

Just to clarify that, if a 2x8 c24 joist is 6ft long - you could have 4ft inside the interior of the property, and 2ft extending beyond the exterior wall?

 

[freddiemercurystwin]

Yes, approximately, assuming it was adequately secured within the building.

 

[dobson156]

Great, thanks. That's very helpful. The current size is 18" out from the wall, and I am tempted to extend it to 24" so it's wide enough for a chair an small table. That's still a fraction of 1/3 of their overall length. I'll probably offer up some drawings and photos to this forum before I proceed just to be on the safe side.

Cheers.

 

[mikeey84]

I'd be careful if you are extending it, in case a neighbour who doesn't like you shops you into the planning dept

 

[dobson156]

haha it was my neighbours who suggested the idea!

Although they might be playing the long-con to get me in trouble.

 

[noseall]

The current size is 18" out from the wall, and I am tempted to extend it to 24"

Balconies are one the most contentious and scrutinised aspects of a planning application. Be careful.

 

[^woody^]

BS 8579:2020 will apply for the design.

There are special requirements for the fixings and proximity to edges too - see NHBC guidance.

Fire resistance and external spread.

Building control will be looking for the above, plus any specialist engineers design.