Saggy ceiling joists - loft conversion

[Sparkasaurus]

Hi all,

Pulled down the bathroom ceiling as part of a refurb, moved a stud wall over a bit, then realised that a couple of the ceiling joists are sagging a fair amount (maybe 1.5 inches worst case). The ceiling was artexed so probably hard to spot.

The 70's built house has had a loft conversion about 20 years ago, so in the photo you can see the new 8 x 2 floor joists which go into steel and the old 4 x 2 ceiling joists sat below them - they are not connected to each other in anyway. The old 4 x 2 joists were maybe ok before the webbing was chopped when they were part of the truss roof. The span of the 4 x 2 (ignoring stud walls) is around 8.6 metres and they are on 600mm centres.

Could there be any issue if I jack up the sagging 4 x 2 ceiling joists and then strap them to the 8 x 2 floor joists to make them straighter and take some of the load off the stud walls ? The stud walls are only 3 x 2 in the house, including the one I just re-built, it makes me feel uneasy about them taking any load (even if it is just the ceiling).

I've read on another forum post it's not recommended to have any connections between the new loft conversion floor joists and the old ceiling joist but I don't understand why it would be an issue - they're decoupled at the moment from a noise transmission point of view but normally the ceiling would be attached directly to the floor joist anyway?.

Cheers
R

 

[George_engineer]

I'd be tempted to remove them and raise the ceiling level. That way it;s slightly light (no more 4x2s), the load is distributed and the ceiling is higher.

If you have any concerns over connection to the rafters and whether the ceiling joists (originally the bottom chord of the roof truss) are still acting as a tie, then get a structural engineer to take a look.

Do you have the calculations from the original loft conversion? Could see whether a ceiling load had been assumed, but that's a problem whether you keep the 4x2s or not.

 

[jks7492]

Not a problem to jack them up if you’re replacing the ceilings throughout, but might find you crack the plasterboard or start popping screws if your keeping the existing ceiling elsewhere.

Yes you can fix the original ceiling ties to the newer joists. The reason they’ve sagged is probably because this wasn’t done when they did the loft conversion. When you remove the internal truss diagonals, the original bottom chord of the truss loses all the action of the truss and effectively becomes an undersized ceiling joist.

 

[^woody^]

I've read on another forum post it's not recommended to have any connections between the new loft conversion floor joists and the old ceiling joist but I don't understand why it would be an issue

When a new loft floor is built, the timber and steel beams will deflect by a known amount when the floor is constructed and then loaded with furniture etc. So it's good practice to keep it independent of any existing ceiling components else the ceiling finish is at risk of cracking.

After this initial deflection and once the timbers have stabilised to internal humidity, it's potentially OK to connect the existing ceiling joists to the loft floor to deal with situations such as yours.

This assumes the loft floor has capacity for the additional loading.

 

[Sparkasaurus]

Thanks guys, I'll see if the old owner left the calcs out of interest, but seems like I might get away with strapping them to the floor joists strategically.

 

[wessex101]

When a new loft floor is built, the timber and steel beams will deflect by a known amount when the floor is constructed and then loaded with furniture etc. So it's good practice to keep it independent of any existing ceiling components else the ceiling finish is at risk of cracking.

Ordinarily yes but not with a trussed rafter roof conversion. The ceiling chords (ceiling joists) are far too slender to support the ceiling once the rest of the truss is cut away so there should have been additional support for the existing ceiling - usually by fixing to the new floor joists.

 

[^woody^]

Ordinarily yes but not with a trussed rafter roof conversion. The ceiling chords (ceiling joists) are far too slender to support the ceiling once the rest of the truss is cut away so there should have been additional support for the existing ceiling - usually by fixing to the new floor joists.

No it's just poor design.

If chords are fitted to the new joists, the ceiling would crack.

The designer should know this and design accordingly or allow for a new ceiling.