3615 Dodgy floor

We have a bedroom floor which bows slightly when I walk on it and have had various views from "leave it alone - it's stayed up 50 years" to "it's not safe to walk over without supporting struts".

It's composed of 1 metre long hollow bricks held between H bars which just aren't really solid enough, with a layer of cement on top.

If we decide to do something about it the options seem to be to put a couple of extra beams underneath at right angles to the existing beams or a reinforced cement floor, tied into the walls, on top.

Anyone had any experience with this sort of thing?

Thanks

Category
Building/Renovation

Well, I'm not going to disagree with any of the advice you have been given!!

If the floor is a bit springy, well that is a characteristic of a steel structure, it will spring, but it will basically not collapse - thus if the floor is solid enough to not give you problems with the tile grouting breaking up (which is untidy), then your least cost option is just to leave it well alone. If the floor has bowed, so that furniture doesn't stand up straight without bits of wood under some of the legs, if you can live with that - fine, leave it alone!

But if the grout is breaking up, or the floor is nowhere near flat, you might sensibly choose to intervene. If the space below his floor is unimportant - a garage or something - then retrofitting one (or perhaps two) big steel beams at right angles to the existing steel beams is a perfectly good solution, and not excessively costly. However, if the space below is something you want to turn into accommodation, a couple of RSJs on show are going to look pretty naff.

If you want to have the space below looking smart, than your only option (other than scrapping the existing steel structured floor entirely, and restructuring from new with either timber or larger section steel), is to regard the current structure as "shuttering", and lay a new reinforced concrete floor above it - as you say - supported off the walls. This requires some precision steelwork design, and means the existing floor must be propped while this slab is laid, and you would need to accept a minimum thickness of 10cm (say for a 4m span - more if it is a larger space), thus you would lose this 10cm off the ceiling height.

Clearly laying a new slab on top of the existing structure will destroy any pavimento which exists, so you will have to do a new tiling job. In my experience the cost of laying a new slab on the existing structure is unlikely to be any less expensive than demolishing the floor and starting from scratch, and if ceiling height is an issue it avoids this snag as well.

One failure which can occur with floors structured on relatively lightweight steel beams is that the beams rust away at the junction with the walls. If this has happened it is really only sensible to scrap the floor entirely.

Ask your geometra for quotes for any alternative you want to consider before you decide.

...I was going to ask what your Geometra's advice was.

I have assumed that these alternatives came from the geometra, since they are all perfectly valid alternatives, and I thought it was helpful to point out the pros and cons of each potential solution.

Thanks for the information. Sounds like you know about these things Relaxed.

These options didn't come from any geometra. Our experience with geometras so far doesn't lead us to hope for useful or impartial advice from that quarter. Two geometras walked over the floor on their way to have a look at the leaking roof (one said the roof problem was too small a job for him to be bothered with and the other one said we need a new roof for €25,000) and neither spotted it as a work opportunity, which I think tends to support the "no problem" view.

However I'm a bit concerned that some of the bricks between the bars are cracked and I can't help visualising a particularly heavy friend going straight through when he visits. Perhaps fortunately the floor hasn't been tiled and it occurs to me that putting wooden floorboards on the cement surface (at right angles to the metal bars underneath) would at least spread the weight and perhaps even counteract the bounce to some extent. Sound sensible?

By the way if anyone can recommend geometras or builders in Lunigiana I would be very grateful.

Thanks

The only advise i would give over the net is spend a few hundred euros getting a structural engineer to come and have a look. One practising as a structural engineer. Expensive, but normally good advice backed up with a good proffessional indemnity policy.

If it looks bad, it normally isn't as bad as it looks, but you shoudl check it out anyway.

Regards

Andy

The advice to get a structural engineer's advice is very good - but possibly you will regard it as a bit of a gold-plated option!
Your floor seems to be getiing more dodgy by the day - at first it only bounced, now you are worrying about people falling through it. Frankly, this floor sounds to me a pretty weak specimen - let me explain how builders and clients (not structural engineers) go about specifying a floor.
There are various sizes of H section steel, the one typically used for up to 4m span assumes that the extruded clay slabs (tavelloni) for a floor will be 70 or 80cm, not 1m. Of course, it is cheaper to do it with the standard H beams and longer tavelloni (you use less beams), and the floor is necessarily weaker, but if the client or builder are saving money this is what you get. You have probably also got some pretty sketchy reinforcement mesh in an thin screed on top of the structure (solaio) - if there is any steel mesh at all!
You say some of the tavelloni are broken - this must mean that you can see the unplastered underside of the floor, so (at least at the moment) the space below isn't a "room", so the extra larger RSJ s under the floor sounds like a potential solution.
As to boarding it, that would certainly mean that nobody could fall through the floor - but it wouldn't stiffen it at all.
When you get a geometra involved, if you do decide to do something serious about this floor, the geometra will probably engage a structural engineer to tell the geometra how big any "remedial" beams should be - so my advice is to find the geometra first, and avoid paying the structural engineer twice!