Building a balcony, or 'high decking', how to design and size it?

We're planning to build a balcony/decking outside an upstairs bedroom and need some pointers on how to go about designing it as regards sizes of beams, depth/type of piles required, etc.
It will be mostly rather less than a full floor height from the ground as the ground slopes up slightly, we are also aiming to add a staircase which will probably only have a 4ft or 5ft drop.
The balcony will probably be either 3 x 3 metres or 4 x 2 metres (with 2 metres projection). Thus we will need two posts to support the outer corners and RSJs (probably) to support the decking/floor of the balcony.
What I need some help with is the sizing of RSJs (either two 2m ones and a 4m one or three 3m ones) and the sort of footings/piles we need to support the posts.
I *think* the most suitable supports for the posts would be screw piles of some sort or other but I'm willing to look at alternatives. Does anyone have experience of this sort of thing?
Then where do I find out what sort of size of RSJ is needed, no wall load on them, just some 'floor' and people.
Any help such as pointers to sites with information would be most welcome.
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Chris Green
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On 13/01/2019 13:48, Chris Green wrote:

Just in case it's not impinged on you, planning permission and building regulations seem likely to be relevant so - depending on your local authority's willingness to engage informally - you might want to start by what tends to cause them least problems.
https://www.planningportal.co.uk/info/200130/common_projects/11/decking
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Robin
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[snip]

Yes, we're aware that planning and regs apply. The above site is totally useless, all it does is tell me that decking more than 30cm high requires planning permission which we knew already. There's nothing at all about balconies or outside stairways.
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On 13/01/2019 15:25, Chris Green wrote:

True. But it is not a big step from being told that building regs. are relevant to Approved Document K which Owain has already cited. FTAOD that explicitly states that it applies to external steps and balconies where part of a building.
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On Sunday, 13 January 2019 14:03:06 UTC, Chris Green wrote:

Regulation K2 (a) (b) prescribes various situations where guarding should be provided to areas where people have access: this can include both internal and external areas. It states that any stairs, ramps, floors and balconies and any roof to which people have access shall be provided with barriers where it is necessary to protect people in or about the building from falling. Approved Document K2 (3.3) is quite specific in commenting that horizontal rails for guarding should be avoided and any construction should be such that a 100mm sphere cannot pass through any opening in the guarding.
https://www.labc.co.uk/sites/default/files/labcpd0914_techg_balconies.pdf
See also https://www.designingbuildings.co.uk/wiki/Railings https://www.designingbuildings.co.uk/wiki/Stair_design (although this is not an authoritative source)
As far as RSJ and foundation piling is concerned, that's structural engineer territory. If you're anywhere near central Scotland or Milan, I can suggest one :-)
Owain
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On Sun, 13 Jan 2019 13:48:14 +0000, Chris Green wrote:

I would treat it an an internal floor for design - doing the same job but outside.
Not sure why you need RSJs at both ends; should be enough (I think) to have a beam parallel to the wall on two uprights, then have joists running from this to wall hangers along the wall, then planking parallel to the wall.
No reason not to go for 3 RSJs though, if that makes you more comfortable.
Anyway <http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2010/ Part6/section4/appendix.htm> might be of some help.
Someone with a link to an online tool will be along shortly. :-)
Cheers
Dave R
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On Sunday, 13 January 2019 14:03:06 UTC, Chris Green wrote:

Rule of thumb for joist sizes. (Imperial dimensions) For 2"joists at 16" centres. Depth of joist in inches is equal to span in feet plus 2" So a 12 ft span would need a 14" deep joist.
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There does seem to be a rash of balconies in the planning applications around here of late. I'd imagine that As it will need planning consent there must be guidelines around somewhere. Brian
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The main issue with balconies seems to be if they might overlook neighbours' properties thus invading their privacy. Since our neighbours are several hundred yards away behind huge trees that isn't going to be an issue for us. Also as it's going to be at the back of the house appearance isn't really going to be a problem, no one can see the back of our house unless they're on our land.
However I think getting building control in might well be quite useful in terms of getting things 'done right'.
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