boarding a ceiling to uneven joists

[Dan53]

I need to board a bedroom ceiling (5mx4m), but the joists are not all level. Two in particular have dropped by about an inch. This is because they're partly held by timber 4x2 diagonal eves which have also dropped slightly due to small amount of rotting.

The joists are secure, as is the roof. One option is to try and lift the supporting timbers up to get joists aligned, but this would involve pushing up supporting roof timbers (acros?) - very, very heavy, and everything has settled down. Lifting up may be opening a can of worms.

I can't just board over as it is - you'd notice a definite bulge. What's the best way of levelling the joists / boards? French relatives in the building trade say over there they never attach boards directly to joists, but to specifically designed batons which automatically ensure boards are horizontal. I've never come across anything like that here.

It's looking like a faffing job. All advice welcome.

cheers

 

[freddiemercurystwin]

Just counterbatten under the higher joists.

 

[Burnerman]

About the only thing you can do is to pack all of the other joists undersides with laths of the same thickness as the bulge - about 1"? Slaters laths are available in a variety of thicknesses but it will take you a while to get them perfect, and a table saw would come in useful here. No way would I be going down the jacking up route, but thats just my opinion!

 

[Dan53]

agreed, don't want to jack up!

Counterbatoning / packing seems the only option I can think of. It's awkward since lower joists drop more at one end than other, i.e. each baton will need to be packed out to its own specific thickness to ensure they create an even horizontal plane.

What's the standard size for batoning used for this kind of job?

Cheers

 

[Dan53]

Will check out slaters' lathes. Thanks for the suggestion

 

[freddiemercurystwin]

Alternatively fix battens say 38x75 to the sides instead of the bottom of your existing joists.

 

[dextrous]

There is an alternative. Use a bit of board adhesive on the ceiling joist and prop the boards up with long bits of straight timber across them and screw 'til they're just tight. After a couple of hours or so, when the adhesive will have gone off, tighten them up.

It's just a variation of straightening out of true stud walls, but a bit harder.