Garden Room - Steel Beam Help Please!!

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RobinBHM

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Why not just go for planning permission, you've always got your hands tied if you try to work with PD restrictions, and have to engineer a solution that may cost more in the long run, and will always be a compromise, I wouldn't build anything on this scale without it, and certainly not without a SE design input.

A couple of hundred extra mms would make all the difference.

2.5m isn’t much, because that’s from ground level.
 

johna.clements

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I would be mostly worried about the wind as others have noted. When it is windy and a door is open (or the glass breaks) there will be quite a large upwards load. Bolting to a 20 to 30 kg concrete block will not weigh enough to hold the steel post down. You need a structural concrete pad.

I would also concerned about how the RSJ will react with one end supported by a stiff steel column and the other end by more flexible timber. The two M20 bolts will not provide a moment connection so the joint will rotate slightly as the timber compresses shedding more load onto the timber. This could result in the doors jamming. Why not have a second column at the other corner, then the corners match. And then make the RSJ longer may have to be slightly bigger for the increased span.

How are you going to put the RSJ up on the timber studwork. If you had to columns it may be easier to erect and fix the RSJ. When you have the goal post up you can build the rest at your leisure. If you put it on the studwork you have to stop whilst the steel is erected then continue with the roof.
 

morqthana

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The trouble with going for PP is the old "it's easier to ask for forgiveness than permission" thing.

A couple of hundred extra mms would make all the difference.

2.5m isn’t much, because that’s from ground level.
Hence my Q about maybe digging down a little, say so the FFL of the building is at ground level.

And if he gets on OK with the neighbour, and the high point of the pent roof is 4m from the boundary, the edge nearest the neighbour is under 2.5m, and the neighbour isn't going to complain, JFDI is an option. Any subsequent hassle he can claim an ignorant misunderstanding that he thought 2.5m applied to the height nearest the boundary, but with nobody on the ground kicking up a fuss the council have to justify public interest in pursuing it, and they are so short of funds I doubt they would be able to do that. We're talking a small garden shed here, which at its highest point would be 4-8" too high, not a house built without PP. If nobody tells the council they won't even know.
 

Churchy00

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Presumably you can't get it more than 2m from the boundary?

Could you dig down a little more than 270mm?
Nah, must be almost at the boundary. Digging down more is still something I'm contemplating. I'm even considering a wooden framed floor...which I steered clear of up to now as it consumes a fair bit of the 2.5m height allowance when you take into account the raising above soil level, joist height and Egger protect boarding (or something similar). That's why I'm favouring an insulated concrete slab...but this makes it difficult for the steel post anchoring.
 

morqthana

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OK, so the high point is 3m-ish from the boundary - same principle applies. If you could have the high point as you want, what would be the height of the low point at the boundary?

As for the steel post, what if you welded it to a reinforcing mesh in the slab before the pour?

Another idea - a bit radical and more expensive:

The building only needs the walls supported - the floor joists are only for the floorboards. Structurally there is no reason why you could not excavate deeper, construct a masonry wall to take you up to ground level and thence the walls of the building, so that you step down as you enter the building and have plenty of headroom.
 

RobinBHM

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The trouble with going for PP is the old "it's easier to ask for forgiveness than permission" thing
If planning is refused, permitted development will still be intact.

I would rather get planning than worry about planning enforcement.
 

morqthana

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But what he wants is outside the limits of PD. My theory is that if he's not totally taking the p**s, i.e. only a little bit too high, and his neighbour isn't going to complain, enforcement action is extremely unlikely given the requirement for it to be in the public interest and the lack of funds available to the council to chase after minor breaches where there isn't really any public interest at stake.

I know what I'd do.
 

woodwind

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But what he wants is outside the limits of PD. My theory is that if he's not totally taking the p**s, i.e. only a little bit too high, and his neighbour isn't going to complain, enforcement action is extremely unlikely given the requirement for it to be in the public interest and the lack of funds available to the council to chase after minor breaches where there isn't really any public interest at stake.

I know what I'd do.
Yes, but he might want to sell the house in the future!
 

Kriggi

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I haven't read through the whole thread so apologies if my solution has already been suggested. When we had a similar construction created the steel guy came up with a neat solution that means the fixing is completely concealed. Unfortunately I don't have any pictures of the steel without the bricks on as the brickies got there before me.
 

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MikeJhn

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Please take this advice from an old retried Chartered Structural Engineer, your current design although a commendable effort is flawed, spending a few hundred for a professional design would be money well spent, ask you local steel fabricators who they use, but on quick look you will end up with steel goal post and concrete foundations.
 

Terry - Somerset

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The cost per square meter for a reasonably well specified garden office or extension seems to be around £1400. Probably a bit less for largely self build, somewhat more for higher spec or if location/access are issues.

Your 15 sqm will cost in the region of £21k based on this. Ask yourself - how likely is it that a professional design could save (say) £1000 (5%) through better design and appropriate material specification.

Although it always pains me to spend more money than I need to, and I would find the challenge of good self design motivating, I think I would reluctantly pay the professional.
 

morqthana

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Yes, but he might want to sell the house in the future!
a) One of those useless indemnity policies will calm any buyer.
b) If he doesn't move for 4 years it's too late for enforcement action.
c) If he ticks the "right" boxes on the questionnaire, WT* is going to take the trouble to measure a the height of a small shed when looking at a house and start worrying about PP vs PD?
 

RobinBHM

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a) One of those useless indemnity policies will calm any buyer.
b) If he doesn't move for 4 years it's too late for enforcement action.
c) If he ticks the "right" boxes on the questionnaire, WT* is going to take the trouble to measure a the height of a small shed when looking at a house and start worrying about PP vs PD?
Yeah, I can’t see a surveyor picking up an outbuilding slightly outside PD height constraints
 

MARK.B.

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My neighbor recently had a complete new roof on the kitchen extension with pitched roof and concrete tiles , the ridge beam(maybe that's not the correct term ) was a rsj .What interested me was seeing him pick up and carry a 150mmx100mm rsj that was 6 metres long by himself ,turns out that the beam was made from some sort of plastic material. He used a Structural Engineer who did all the calcs and stuff to make sure it was safe etc. I am in my sixties and had no problem lifting it up . The Bifold doors had the same plastic rsj over them and the door frame fixed through the top with screws . Might be an option for you in your build.:)
 

baldkev

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In terms of fixing down, get wall plate straps and add an extra bend, so it is cast into the concrete layer ( i didnt draw the dpm, obviously you'll need one and the insulation barrier between screed and walls )
The straps fix down onto the sole plates of the studwork to add resistance to lifting as they'd have to break the straps or through the concrete. Using 18mm ply on the outside of the timberframe glued and screwed is a good idea, with tyvek, spacer battens and insect mesh etc, then cladding or render.
The steels should be galvanised after fabrication and ideally wrapped with insulation. The 90 x 90 5mm posts would be perfect, but to echo above, get a structural engineer and consider planning. Not only can you go a bit higher, but you could go a bit bigger on footprint.
You will need foundations.
 

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baldkev

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Nah, must be almost at the boundary. Digging down more is still something I'm contemplating
The ffl needs to be 6" above exterior ground level, with a dpm. If you cut corners, then if, or when, you run into problems with the council / building control, they'll have more leverage to make you rip it down.
Seriously, get an engineer and apply for planning. You'll sleep easier and if you sell later, its all legal
 
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