My attic as been floorboarded but there is a sag where a room below has been opened out leaving 2m unsupported.
The joists are 3" x 2". I've just been next door and he's replaced these with 8" x 2" so obviously a lot less useable space and height.
Q1. What do I need under the 2m unsupported?
Q2. I intend to use the attic for a bit of storage and maybe to put a computer, desk and chair up there whilst doing projects such as digitising slides and VHS and suchlike. 8" x 2" seems an awful lot. Can't I just double up with 3" x 2" or 4" x 2" even? Total span is about 6.6m with supporting walls below at around half-way.
Depending on the construction of the roof, you may be able to put some hangers in between the roof rafters/purlins and the "ceiling joists". These could be wood or the metal strap you can buy at the builders merchants. Latter is more convenient.
This sort of thing:-
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Looks messier than extra joists but might not matter.
You can put in extra joists of same size between existing as alternative. May not be practical if ceiling has already sagged, matter of degree. Probably not practical to straighten the sag either.
If you are planning to use it for extra working space, then you will need to upgrade it to something a little closer to that expected of a floor.
The ideal way to do a floor in a loft is so that it is decoupled from the existing ceiling. Typically you stick a 1" thick piece of timber on the wall plate at the eves between the existing joists. Then you sit the new joists on these, interspersed with the old ones. They will be taller than the old ones, and hence the new floor will be well above the old joists, and the bottoms of the new joists, well away from the old ceiling below.
The last couple of photos here show what it looks like:
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So your effective span can be taken as 3.3 m or so (you would probably use two joists at that length - that meet side by side on the supporting wall)
For a 3.3m span using C16 grade timber, you would need 50x170mm cross section timbers to meet modern building regs. However if you are not worried about the floor feeling a bit bouncy (and since its decoupled from the ceiling, you need not worry about it deflecting a bit more than the building regs normally stipulate) you could drop down a bit - to say
150mm. Allowing for the spacer on the wall plate (and supporting centre wall), that would give a new floor level about 4" higher than your current one.
A simple solution is to strap a 6x2" or so beam where the wall xxxx was and overlapping both sides.
1-2" angle iron screwed or bolted[1] between each joist and beam intersection. Effectively you will hang the overspanned joists off this and transfer load to the wall either side through the tops of the other joists.
Bolt mid way between top and bottom or a number of small screws It will give you a "hump" but it's simple - highly related to what I'll be doing tomorrow...
My father did correct a sagging ceiling by jacking up a beam underneath it - he used an array of large wood and wedges, but a couple of acros would work more easily.
Expect some plaster repair work in the vicinity.
If you can support the beam underneath, the final solution will be good.
If it's well nailed or screwed, it will tend to spread the load and tie the adjacent joists together.
I would expect the beam (what size is needed?) would go into the brickwork either end.
The vendor said something to my wife about an arch being removed - it may have been the vendor's wife and I wasn't in on that conversation otherwise I might have had a closer look at the time.
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