First floor ceiling sagging in a Victorian house

[whoisthedaddy]

Hi All,

I am hoping for some advice. I am in the middle of renovating a Victorian terraced house and decided to remove the first floor ceilings as I thought the lath and plaster ceiling was sagging badly.

Once I had removed the lath and plaster (nice job - NOT!) it became clear that it was the joists that were sagging and not the plaster dropping.

Ideally I would like to replace these joists with new 6 x 2 timber but I am a little confused. The joists are not attached to the rafters but to the wall plates. it looks like they are nailed downwards into the wall plate. (In a modern roof the joists attach to the rafters to stop them 'pulling the walls apart' - well that was my understanding?).

The roof does have purlins front and back but whilst these take some of the weight I can't see how they stop the 'spreading' load.

My question is therefore can I (and how do I) change these for modern timber safely?

I have put some pictures up for explanation but am not sure I have got it right yet!

Untitled

• whoisthedaddy
• 18 Jul 2011
• 1

Untitled

• whoisthedaddy
• 18 Jul 2011
• 1

Thanks
Lee.

 

[RedHerring2]

I'm only a DIYer, but IMHO, you don't need to replace them, just add additional joists to stiffen them up.

Several ways to do this:
sister new ones to the old ones, some or all. But you may want to straighten up the old ones before fixing the sisters.
Additional binders accross the top, possibily fixed to other support, again, possibly straightening up the old ones.

 

[whoisthedaddy]

Yep I did think about those options but the sag is quite pronounced (around 5" to 6" in the middle).

The sistering I don't think is an option as most of the joists aren't nice and square and therefore aren't easy to bolt through.

The other piece of advice given to me from my Dad! (which I think is what you are thinking too) was to put a beam at 90 degrees to the joists (cut into the end walls of the terrace) and then fix the joists up into it. This didn't seem a bad idea except that the underside of the joists aren't really nice and square to accept plasterboard.

I thought both of these solutions might be considered a bit of a lash? Whilst cutting in a support or sistering it seemed around the same sort of workload to just replace all the joists with new ones provided the roof didn't come in as I took them off?

Thanks
Lee.

 

[tim00]

1. What is holding down/fixing the in-situ wall plates? Google Simpsons Strong Ties.
2. Eye-ball the elevations from outside, or drop plumb bob's to determine any roof spreading. Or even a level and straight edge against the bed room exterior walls.
3. What future use for the loft do you have in mind? This is a key question, eg. the beam binder proposition could interfere with or aid future plans. Also: wiring, lighting, trap access support, and section of new joists etc.
4. Are the rafters set at the same centres on both sides of the ridge?
5. Are any valleys or hips involved?
6. If new joists are tied into the rafters (best bet) then the old joists could be propped to that level.
7. Some of the old joists are in two pieces scabbed together and /or held by flimsy binders. Twisted joists are irrelevant for plasterboarding and skimming.
8. As a matter of interest, cut back the plaster,say 25mm ,at top of the walls to enable p/b to be "slipped in".

 

[tim00]

Also: Do not remove or interfere with the in-situ joists and their fixings. Leave well alone.

 

[whoisthedaddy]

Thanks for the reply Tim,

in answer to some of your points...

1. I don't know what is holding down the existing wall plate, there are no straps as such. I can't see any fixings at all but guess there are some going down into the brickwork from above.
2. I have no reason to suspect the roof is spreading - I have only just bought the place and the homebuyer survey didn't pick up any issues with this.
3. The loft will continue to be just a loft, I did toy with putting a room up there but the headroom isn't brilliant so have knocked this idea on the head.
4. Yes, the rafters are at the same centers both sides.
5. There is a small hip at the rear of the property (over what used to be the third bedroom - now the bathroom)
6. Sounds like a good idea, what is the best method of propping the existing ones to the same level (coach bolts / steel rod with washers & nuts ?)
7. Agree - but they need to be about level.
8. Not sure I understand this one - sorry?

Also, very tempted to agree with your do not touch but what are your reasons?

Thanks in advance
Lee.

 

[tim00]

1. then there are none. merely bedded in mortar.
2. be certain - go look.
3.
4. good, new joists will tie-in easily. pre-drill and screw/bolt everything -least disturbance possible.
5. examine it, int. and ext. for movement. Eye ball your hip line and your ridge line for straight/level.
6. Once the new joists are in, simply noggin or pack across in 2/3 places and pre-drill and screw thro the old joists to level and firm them up.
7.
8. where the wall meets the underside of the joists - dont butt the boards to plaster but to brick.

caution - there is no need to disturb the in-situ joists or their fixings. Also, dont go putting any weight on the old joists, wait until the new joists are in before going onto the joisting. Think about trimming out your access trap.

 

[whoisthedaddy]

Thanks Tim for all advice.

I will look at everything again later today from a fresh viewpoint but after you have pointed it out I think I'll leave everything as is and just add the new joists tying the originals to them.

Last question, Do you think 6" x 2" C16 (or would 4" x 2" suffice?) will be sufficient?, the maximum span is about 3.6m and I'm looking at 400mm centers.

Thanks
Lee.

 

[RedHerring2]

170mm X 38mm or 170mm X 47mm according to 2005 Timber Tables.

that's about 7"X 1½" or 7" X 2" in old money.

But if you are using 170 X 47mm you could go to 600 centres.

 

[tim00]

Just to be sure that you understand: the key part of tieing-in is to fix the new joists across the loft width to tie-in to the rafters where they sit on the wall plates, ie. fixed to the rafters, creating in effect, a truss. All the new joists must also be pinned to the wall plates.

 

[whoisthedaddy]

Tim, Thanks again for the comprehensive reply.

Having looked again in detail today I think I am going to have trouble fixing the new timber joists to both the wall plate and the rafters. I may be able to fix a screw through the new joist at an angle into the rafter or at worst drill a pilot hole and put a coach bolt through. The maximum span is 3.35m

I think it worth remembering that my aim here is to build a structure that can effectively support the existing joists and give me something strong enough to hang the ceiling from. I am a master of over engineering and although I want to do a proper job I also don't want to spend more time and money than is absolutely necessary.

I did think of using 5 or 6 lengths of 7"x2" at approximately 600 centres (the existing rafters are more like 400 so only every third one will line up!) and sitting these on the wall plates. (Not sure how to fix yet to stop them wanting to tip over? Noggins will help!).

Over the top of these new joists I could then fix one or two cross members at 90 degrees to the joists so that these cross members run in the direction of the purlins. These cross members could then be used as a support for the dips in the existing joists by using threaded rod, washers and nuts to bring them up. The bottom of the cross members is above the top of the existing joists and they will sit directly above where it needs supporting. (The other solution was to put the new joists near to the existing ones and simply bolt through but it seemed to me that this would put a sideways load onto the new joists which isn't efficient.

I hope I have managed to explain this clearly. 1 drawing would probably clear it all up!. What do you think?

Thanks
Lee.