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When I bought a steel patio kit, I thought I would put one of its square hollow section (SHS) steel posts on the existing balcony so I ordered it in two and half meters. However, I have changed my mind and would like to make the patio larger and put the post in the ground. Therefore, I need a post that is five meters long.

Is it okay to extend the existing post instead of getting a new longer one? What is the best way of doing it? I thought welding would be the way to go but I am not sure as I couldn't find any information or instructions on the internet around how to do it best. The existing post is 100x100x3mm and powder-coated. The extra length that I can get for extension will be galvanized and in the same size or possibly thicker, i.e., 4mm.

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    A lot will depend on the load being supported by the posts, how many posts and other factors. I would think that you would get more strength if you could put something inside the two 1/2 posts for a couple of feet to give it rigidity around the joint, but I have zero experience welding or doing very much with steel posts (and nothing of this size) so just a comment from me. May 6, 2022 at 5:11
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    I think you are better off drawing your design and asking about using a 15' post in the highlighted portion. You don't see a 15' post very often. How are you planning on lateral supports for the post? Decks over a certain height typically have cross bracing between the posts. Steel jack posts are engineered and designed to be extendable - I've seen 12' not sure about 16'. May 6, 2022 at 5:50
  • If at a stress point(where it might bend), I would usually add internal/external support to the welded section. Most square hollow tubes come in different sizes that fit inside or outside of the size your tube is. If done by a master welder, support might not be needed, weekend welders support won't hurt.
    – crip659
    May 6, 2022 at 13:51

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If you can obtain an extension that would go over the existing leg, or even inside it snugly, so the overlap is at least 300mm, it's a start. I would then fashion a piece of hardwood to fit snugly into both, an interference fit, minimum 400mm long. Probably no need to screw top and bottom if the fit is snug. Welding after that won't affect the internal wood enough to make a difference, and may not even be necessary.

Then, if possible, use plastic square section down pipe to slide over the whole leg, to obtain a nice finish - I guess white would be good. Presumably the foot will be bolted to whatever it stands on, for extra stability. If not, make sure it will be.

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  • White may look good on your house, but what if the rest of the kit and the trim on the OP's house is black? Or red? That's why we don't do any sort of decorating advice here...
    – FreeMan
    May 6, 2022 at 11:38
  • @FreeMan - that's why I included 'I guess'. It's pretty obvious that OP doesn't have to take my advice - any of it for that matter! The idea was to cover the whole leg, while making it even stronger, and obviating its painting. I doubt if OP would have used red legs to matcch the (perhaps) red trim, but who knows...
    – Tim
    May 6, 2022 at 14:38

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