C24 Timber Span of 5.8 meters?

27 Sep 2016
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United Kingdom
Hi all.

Looking for some advice on loft conversion and flooring joists and would be grateful for any help.

My party wall to party wall span is 5.8 meters. Im considering using timber instead of steel RSJ's. The area would be unsupported as there are no supporting walls in between.

Im considering C24 timber at 225mm x 50mm or 75mm.

However im unsure if I can span this area with unsupported joists under building regs. Im looking to get an architect in but looking to gain as much knowledge as possible so I can discuss different options with him. Thanks in advance.
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If it's actual floor joists you are describing, 225x75 C24 won't do as the deflection will be too much; you would probably be looking at something like 250 x 75, or alternatively spacing the 225s a lot closer than the usual 400 centres. Either way this would be an expensive floor, with a lot taken off the headroom as well.
But unless I've read this wrong, why are you spanning party wall to party wall?
Usually in a loft con., the floor joists go front to back and are supported off steels at each end.
Many thanks for the reply.

I had a builder in to get a quick idea and he said we could go party wall to party wall as span from front to back is 7 meters with no supporting wall in the middle which he said would be a problem to overcome. We also have a small chimney going through the middle off the loft which would be a problem. Theres also 2 very large beams going from party wall to party wall which appear to be supporting rafters, with timbers holding up the roof, which would get in the way of RSJs.

The loft space is very high, from the ceiling joists to the highest point of the roof is 7 meters high so height may not be a problem.
Il post some pics up tomorow of the obstructions the builder mentioned so u guys can get a better idea of the layout

I've taken some photos of the loft and the structure. Please note the floorboards were placed by previous owner onto the existing beams.

From these pics would it be possible to advise of what may be required for the loft conversion? Would timber be a suitable materials or will it have to be RSJ's?

Another concern is what happens to the small wall, about 1.5 meters high they have build thats attached to the chimney? It appears to be resting on a small RSJ between party wall and chimney. As you can see loft is very high, center point is almost 7 meteres

Due to financial constraints and a very tight budget i'm looking to do about 80% of the work myself as i'm relatively good at DIY and woodwork (i've done small projects like garden decking and raised playhouse platforms in the past) and fully qualified plumber and gas man. Will be getting in a sparky mate for the electrics.

Any advice would be much appreciated.

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