How much weight can my loft bear?

9 Feb 2023
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United Kingdom
Hi All,
I would like do to a semi-conversion of my loft to use it as an office space/man cave (tv, desk, etc.) and to store some boxes, and as any house owner does sooner or later, I worry that the ceiling will sooner or later come down for the weight (or worst, I will come down with the ceiling, maybe during an important work call).

I added two images to show how the loft joist are laid and to show where they sit.

I measured the joist and they are 3x2" and 30 cm apart.

On one side the joists are divided into two runs of 3.6 meters, the joist starts supported from a wall at the center of the property.

On the other side, the joists are a single run of 7.2 meters, however, they are supported by two walls, so from one end of the property there is a wall supporting it at 2.6 meters, then a space of 2 meters before another wall, then another 2.6 meters to the other end of the property.

There is also a ceiling binder at 2 meters from the center and 1.6 meters from the outer wall on both sides.

Also, the loft is boarded directly on the joists with 18mm tongue and grove chipboard (unfortunately not all tongues are in the groves) and there is laminate on top.

I was hoping to have an opinion on the general structure of my loft, to know whether it can take some load for the uses described above and whether it's suggested to reinforce it.

Ideally for my peace of mind, I would also love to know the actual weight I can put around but I have no idea how to calculate that, does anyone have any idea how to do that?

Thank you very much in advance for the help!



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IF it can be done, (and I don't know because I am not a builder/joiner etc), then if your loft supports are like the first picture, then I think it is going to take a major re-construction of your roof system.
Those diagonal supports will need to be removed to create the floor space. New, alternative methods of support will have to be designed, calculated and verified by someone such as an architect/structural engineer. I would imagine that, possibly, planning permission would be required and also building control by the local council.
I certainly don't think it is a DIY job unless you have previous experience of such work.

PS Just because it is boarded out with 18mm T&G chipboard, (possibly/probably done by the previous owner), doesn't mean it is done correctly and is safe.
The issue isn't that your ceiling will collapse if you turn it into a man cave - it won't. However, your floor would need considerable strengthening in order to comply with building regulations (plus of course all the other regs related to heat loss, means of escape etc etc).

Floors are designed for 1.5kN (around 150kg) per square metre, while loft storage spaces are designed for 0.25kN (25kg) per square metre.

It's unlikely you will load up your man cave with 25kg on every square metre, and any boarding, binders etc will help spread the load from your hairy arse over a few of the joists at least.

The potential deflection of the joists could cause cracking of the finishes too, although this isn't particularly any more likely than walking around in the attic looking for Christmas decorations etc...
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I would like do to a semi-conversion of my loft to use it as an office space/man cave (tv, desk, etc.)
The problem is (...and why you see the answers given above), in the eyes of building control you are creating a habitable space.
If you are creating a habitable space, a whole raft of building control measures come into place, with the most important related to fire safety and evacuation.
For your safety and the safety of your family, we can only recommend complying fully with the regs.
For you to meet these regs, there isn't a huge difference in effort, to create a full loft conversion.

If however, your loft was only for storage, it would not be classed as a habitable space.
In which case you could look at strengthening the loft joists, along these lines:

Post in thread 'Strengthening Loft floor'
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Taking your worst case of 3.6m span and assuming C16 timbers the the max load on the ceiling (dead load and live load) would be in the order of 20kg/m2 in order to keep the deflection within the 10-11mm allowed but strength wise its OK by roughly a factor of 3. If you loaded it to its max allowable strength then 60kg/m2 would be in order but deflection would be 3 times the allowable limit. C24 timbers improve the situation by about 25%. The foregoing calcs are based on standard timber design codes which have several FoS in them so the actual tends never to be as bad as the theory.
There was some research done by Arups some time ago, which found that even in offices, floors were not often loaded up to the domestic loading of 1.5kN/m2.
I suspect there is a case for the regs to be changed to accept slightly lower loadings in loft conversions (say 1.0 - 1.25 overall) on the grounds that the area of floor close to the eaves can't be loaded to the same extent as the rest of the floor (if at all) due to the low headroom.
On the other hand, if half a dozen teenagers decided to have a party up there ? :unsure:
Putting the building regs to one side (not that they should be ignored) the moment you start using a loft space for more than just occasional walking around / dumping stuff the realistic prospect is that the plaster skimmed ceilings in any rooms below will likely crack. Had it exactly here where regular loft visits in an already boarded out loft on 3 x 2 joists during moving in and substantial storage was fine, but the moment more than one person was up there whilst we did a lot of subsequent building work to vault part of a ceiling and all the ceilings below are cracked,. I expected it and it's just a quick filler / paint job now the build work has finished but it was probably where two people were stood in the same place for certain periods.

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