Thoughts about this floor - uneven joists

[SimonH2]

We have a house where the previous owner built an extension - 4mx5m approx living room. When I first looked at the house I knew the floor wasn't "right" - there's part where you can feel a slope under your feet. But like a lot of other issues, the benefits (house is the right size, garden big enough to satisfy SWMBO and the grandkids) outweighed the downsides - he was also "poor" at plumbing, and rubbish at plastering.
Anyway, this year we've got to this room for re-decorating (cue disagreements between myself who does everything (extra sockets, lights, etc, etc., vs SWMBO who likes to just slap on a coat of paint). I had in mind replacing the Weetabix floor with proper floor boards - I was brought up with traditional floor boards where it's relatively easy to lift a board or two for access to services, I hate these big sheets of chipboard, especially when overlaid with click together cardboardlaminate.

There's been several jobs (wiring and plumbing changes) I've wanted to do, but couldn't because I couldn't get under this floor without disassembling (and then re-laying) all the cardboardlaminate - and it's been driving me nuts.

I got as far as lifting one corner sheet last night, and this is what I found :

According to the tables I've found online, the joists are only just large enough - 8"x2" with 4.1m span, no idea of timber grade but I assume building control must have signed it off (or did they ?) But in this corner in particular, there's holes drilled every which way - you can't see the end joist (off to the right in the last picture) where there's at least two holes drilled diagonally and nowhere near the centreline But just these bits show that the joist tops aren't level.

I don't know if it's just this end run of sheets where the joints aren't over the joists - the next run does have joints where they should be, I haven't uncovered any more yet. For good measure, I can't get the furniture out of the room so can only do one half of the floor at a time.

I'm thinking that without a lot of work cutting variable thickness shims (I had an idea last night how to make a jig for that), regular (120 or 150mm wide) T&G boards are going to accentuate the problem. I suppose I could just deal with the ends and leave the middle as it is (lets the boards follow the contours of the joists) - but I know I'll always feel that uneven floor

Any thoughts ?

 

[Deleted member 174758]

All I'll say is that his work has a certain je ne sais quoi about it - that and if you were to lay plywood or chipboard over it at least a lot of the dips could be taken out with self-levelling compound before the finished floor went on top. Not sure about the fall on the floor - it might just be one joist, as by convention "crowned" joists are always installed crown uppermost on the grounds that when loaded it will flatten the crown out. In bad cases it's not unknown for a power planer to be used to kiss the crown and reduce it a few millimetres. To be sure what is going on I think would take a laser level and a home made staff or at least a long level - a 1 metre level isn't really long enough (the black level looks like a Stabila brickies level and they come in lengths up to 1m) and can create a misleading impression, you really need a 1.8 or 2m level (or failing that strap that level onto the top of a piece of straight, planed 3 x 2 2m long CLS to extend it). Even a taught string line can work to check straightness (if not level)

If you intend to plank that and get it perfect the shimming might also prove to be an exercise in frustration. But forget about the shim machine - plywood comes in 3, 4, 6, 8, 9.5, 12.5,15, 19mm, etc ex-stock from builders merchants and even DIY sheds and can be readily ripped into shim width stock then crosscut - all with a small circular saw (fitted with a rip fence), whilst thinner shims are could be just graduated plastic horseshoe packers, like those we used for door frame installation:

That's a Broadfix one - they come in 1, 2, 5, 6, 10 and 12mm from builders merchants (or SFX/TS) and can be used in conjunction with plywood shims.

 

[SimonH2]

Thanks.

I did wonder if he'd laid any joists upside-down - or perhaps they were all straight and some have sagged due to differences in grain.
I do have a 5ft level - there just wasn't room to use it with just the one (part) sheet up. I also have a mate with a self-levelling laser gadget so I might just tap him up for a loan of that.
As to the first suggestion, I'm looking to get rid of the "no access for maintenance" sheet material. Otherwise I'd just be leaving the weetabix in place (but screwing it down properly)

 

[SimonH2]

Bit of an update ...
Yes, the floor will be coming up for levelling. Borrowed a laser level from a friend and walked around the room with a stick. 1 1/2" variance overall - though I need to double check the level. But a good 1/2" between adjacent joists in the middle of the floor - that was the bit I could feel just walking around.

For good measure, I put the heavy rad that's in the background onto a dolly to wheel it around. Moved it out of the way, pushed it back to the wall, let go and ... it rolled away from the wall

 

[Deleted member 174758]

Are you going to sister the joists with 4 x 2 CLS or the like?

 

[SimonH2]

I wasn't planning on doing. Just find the highest spot and pack everything else up to match. I'm hoping my mate's level is a little out and there's a bit less needed.

 

[Mr Chibs]

Just bend the spirit level to match the floor... much more simple.

 

[Deleted member 174758]

I wasn't planning on doing. Just find the highest spot and pack everything else up to match.

That can work with sheet materials, but it is slow and it can go wrong (e.g. if the packers shift), so it's not the best way to proceed. For floor boards, though, it is an awfully labour intensive way to go and using (bought-in) packers is not only potentially more expensive, but I feel it doesn't give you the guaranteed flat, solid surface you need to install floor boards properly.

 

[Deleted member 174758]

I'm hoping my mate's level is a little out and there's a bit less needed.

It might be a couple of millimetres out, but probably no more than that. Best way to check is to put a couple of pencil marks (small, faint) on each of the walls of a room about 5ft apart, then put your 5ft level on to see if they match (but bear in mind that levels can be out, too, but at least they can be verified by switching end to end)

 

[SimonH2]

A further update ... this room is the gift that keeps on giving

Firstly, I did check my mates laser level, and it's within about 2mm across 4m. Did that by working from one side to the other and noting the level difference between two points, then moving the level to the ledge on the other side of the room and doing the same thing.

I've now had more boards up to do more of the wiring. I think I can see a "slight issue" here

Might explain why the floor slopes up at the edges.

He also seems to have had a random position generator for drilling holes - they are every which way (including diagonally) except where BRs permit.

I'm adding some extra bolts (concrete screws) to the wallplate which seems to be an "interesting" shape. I don't think there's a problem there, but they are a doddle to add, I've some left over from a previous job, and I've taken a bit of strength out of the wallplate to get the conduits in.
Having fed some cables across the room, there seems to be 2 sets of noggins. The first is about half way across the room (to the right in this picture), and then there's another set about 3/4 across - and I assume that at the other end the joists are sat on the flange of structural steelwork, but I've not lifted any boards there yet. It's a 4.1m span with 8x2 joists - so from this end, hanger, 2m span, noggin, another 1m, noggin, another 1m, sat on steelwork flange (I assume).

Given that these hangers at this end don't provide any rotational control (they just hang from the top of the wallplate, and there's mostly a clear gap all the way down between hanger and wallplate), would you say the noggins are sufficient ?
And should I be worried about the holes, or work on the principle that the sizing tables for joists are "fairly conservative" ?

But replacing the floor is now put back to next year. Need to get all the chasing out filled in and the walls decorated so we can have the room back for Christmas. That'll be a nice look - bare Caberfloor and a rug in the middle So just the new pipes for the rad to get in, then screw the boards back down and try to forget what I've seen for now