Can my first floor room carry a very heavy bookcase?

Kilrath

I have a large bookcase that alone weights 160Kg. When filled with books I expect the combined weight will be on the order of 430Kg. I have measured the joists. They are all 2"x10". The floor is comprised of panels of thick plywood(? - don't think it's chipboard) in 8'x4' sections. The panels supporting the bookcase are shown in yellow in the diagram below. Joists are spaced at 4' intervals. The flat has a central hallway and has rooms of equal length on each side (3.6m) and there appear to be two joists running the length of the flat, one on each side of the hall. These run from an external wall, but I have no idea where they are supported at the other end or how long they are - they disappear out of my flat and into a communal hallway (where the question marks are in the diagram).

Thoughts? Can I safely put all my books in the bookcase without them ending up in the flat below me?  So far (one quarter full) I don't see any deflections when using a spirit level.

casper_gutman

It'll be fine. A bookcase is a normal item of furniture, and an adequate floor should hold it with no difficulty.

Four people could easily weigh the same, and nobody would think twice about having four people dancing about in the middle of a room (which would be a much worse load than the same weight sitting still along the wall).

ETA: I went to check what loads floors are designed for, but the numbers are less reassuring than I'd hoped - probably about 1.5 kN/m² which is roughly equivalent to 150 kg on every square metre. While the bookcase will exceed this locally, I'd still expect the floor to be fine for a few reasons:
1) The heavy load is in one part near the ends of the joists and there'll presumably be a big area in front of the bookcase with next to no load.
2) As pointed out previously, the bookcase is right against the wall on one side of the room, nowhere near midspan for the joists. This makes much more difference than you might think. Try putting a ruler between two books and compare pushing down on it with you finger near the end or in the middle.
3) Even if you actually managed to exceed the overall design load for the floor joists (you won't), all that should happen is that they deflect in the middle slightly more than the design limit. This could conceivably mean some cracks in a plaster ceiling or a tiled floor, but most definitely shouldn't mean anything more dramatic like the floor collapsing!

TELLIT01

Joists at 4' intervals??  Are you sure as they always used to be at 16" or 18" centres.  I would certainly think twice about allowing 4 16 stone people dancing in the middle of an upstairs floor.  Nonetheless, I do agree that it shouldn't be a problem as the bookcase will presumably be against the wall, and screwed to that wall.

the_lunatic_is_in_my_head

Currently I think 10 x 2 for a 3.6m span should be 600mm apart.

Looking at the diagram it looks like the joists going across the room meet the joists running parallel with the hall, so the bookcase is basically sitting where those joists meet at right angles without knowing how they are connected, is that right? 

I’d feel more comfortable with the bookcase on the external wall as at least it’s then known the joists are sitting on the wall rather than on an unknown. 

Or maybe there’s not an external wall opposite the current diagram marking for the bookcase and we haven’t been told what the joists sit on there?

Kilrath

Thank you.  Yes - I was surprised that the joists have 4' centres - but the panels are nailed around the edges and I've drilled some 1/8" holes to test for joists in between and can find nothing. There are some cross pieces between joists, to which the floor panels are nailed with smaller nails. I worked out the layout because I have been screwing the boards down - the place was built in 1984/5 and the nails they used had worked loose and caused squeaky floors.

Kilrath

Sorry, I forgot to show the other external wall on the diagram. The wall opposite the bookcase is an external wall. Unfortunately I cannot place the bookcase on any external wall as they all have large windows and there is not enough room to either side.

the_lunatic_is_in_my_head said:

Looking at the diagram it looks like the joists going across the room meet the joists running parallel with the hall, so the bookcase is basically sitting where those joists meet at right angles without knowing how they are connected, is that right? 

I’d feel more comfortable with the bookcase on the external wall as at least it’s then known the joists are sitting on the wall rather than on an unknown. 

Or maybe there’s not an external wall opposite the current diagram marking for the bookcase and we haven’t been told what the joists sit on there?

Kilrath

the_lunatic_is_in_my_head you are correct. The joists actually run perpendicular to the way I've drawn them - I was fooled by the builders skimping on nails. Drilling a small hole I have found a joist I didn't know existed. They are indeed spaced at 24" (600mm) intervals and run parallel to the bookcase.

casper_gutman

Is this flat in a purpose built modern block or a converted older building? How well insulated is it?

Especially in an older building with less than brilliant insulation, leaving aside any possibility of structural deficiencies in the building I'd prefer to put a bookcase on an internal wall than an external one .

External walls can tend to be cooler and attract condensation. Unless they have plenty of air circulating near them this can lead to damp and mould/mildew. This doesn't provide a good environment for books (or for the hardboard backs on most modern bookcases - I've lost a couple to this issue!).