Removing sagging in ceiling joists

[iandandav]

I have an old terraced house Im renovating. Ive pulled down the sagging bedroom ceiling (plasterboard) and can see that the reason is that the old joists have bowed over the years.
What I wish to do is to remove the bend before putting up new plasterboard and also make the timbers strong enough for a floor. This will just be for storage and not a loft conversion.
What are the options? Note that the joists are nailed to the rfters and not on the top of the wall.

A few solutions came to mind can you advise on the best approach?

1) I thought about new joists, expensive and time consuming. If I went with this option can they simply be nailed onto the rafters like the old ones?

2) Strengthening the old joists by nailing another similar sized joist above or at the side of the old one and screwing/nailing them together?

3) Using a metal strip screwed on the sides of the worst affected joists (probably about 4 of them) in the region of the bend.

4) Use of struts screwed between the joist and rafter to take some of the load of the joist (diagram below). This would be near the crossmember (purlin?) which would mean that the rafters were not under too much force.

What is the usual procedure to solving this problem?

 

[masona]

How much is it sagging in the middle?

Look like the ceiling binders is missing however I don't know the size of the room.

 

[Deluks]

How long are the joists, and is there no support from the room below?

 

[iandandav]

Room is 427cm. The joists would be a couple of feet shorter as they dont span the entire room. The diagram is not to scale the sagging is probably about 10cm. Part of the problem is that one of the sagging joists has a 2ft split along it.

The diagram is an over simplification, below is more representational but not to scale.

 

[iandandav]

What are ceiling binders?

 

[Deluks]

Binders are long joists, usually from 4x2, that sit on top of the ceiling joists and running in the other direction. They are to stop the joists from sagging or twisting. They work because they join each joist to it's neighbour, so each joist can be thought of as being held up by the one next to it.


http://www.woking.gov.uk/planning/building/guidance/pitchedroofs


Your second pic tells a different story altogether from the first.
New joists fixed alongside the current ones would be best bet. Assuming your existing ones are 4x2, you could bolt or screw some 6x2 alongside them for a loft floor (storage only) if the area to the right of the wall is ok, then you only need lengths to span the saggy area. A proper job would be to take it all the way across, but note that you can join 2 lengths together if they are both resting on that wall.

6x2 £2 a metre, bolts 25p each, or a fivers worth of 90mm screws. cheaper if you shop around. Not expensive if you are prepared to have a go (and have a drill)

 

[iandandav]

Yes there are no ceiling binders. Wouldnt ceiling binders hinder the laying of a floor? Or are the binders removed and their function taken over by the floor boards?

 

[Deluks]

Yes there are no ceiling binders. Wouldnt ceiling binders hinder the laying of a floor? Or are the binders removed and their function taken over by the floor boards?

Yes, the floorboard would add strength. some noggins between the joists would be useful though. (short lengths of timber cut to fit between the joists)

You could run a binder just past where the split area is, and butt your flooring up to it. No point in flooring right up into the eaves anyway, it's too tight for useful storage.

 

[masona]

What you could do is sister/double the joists from the top of the wall to wallplate and rebate on both side to override the sagging by dropping the new ceiling joists down very slightly, in the real world is full length wallplate to wallplate as mentioned.

 

[iandandav]

The joist doesnt meet a wall plate but is nailed to the bottom of the rafter (diagram above) Should I do the same with the new joist? If so it would have to be nailed through the old joist to the rafter or I could place it on the other side of the rafter, in which case there would be a gap between old and new joist the thickness of the rafter, meaning that they could not be screwed together.

 

[masona]

What is the room height and is it possible to take a photo in the loft?

 

[iandandav]

What is the room height and is it possible to take a photo in the loft?

Ill take some pics tomorrow