Bouncy floor - repair or replace

[John Davison]

Floor

• John Davison
• 10 Jun 2016

Floor

• John Davison
• 10 Jun 2016

Floor joists

• John Davison
• 10 Jun 2016

Hi, we recently purchased a 1800s stone built house. The walls are approx 18 inches thick rubble filled stone. In the main bedroom we have lifted the carpet with the intention of restoring the wooden floorboards - however, the floorboards are in a very poor state and have been damaged by various installations and changes of the centuries - most of the t&g is broken and the edges of 50% or more of the boards have been damaged where they have been lifted. We are now planning to replace the floorboards, however we have a bigger issue to deal with first...

The floor joists in the room are well undersize - they are approximately 3x6 over a 4.3m span at 400mm centres with no central beam and only a small number of noggins - this leaves the room like a trampoline. At some point in the past someone has attached new 2x1 beams and packing to the underside and created a level ceiling in the lounge underneath, but upstairs the floor is significantly bowed - at least a 4 inch drop in the middle of the front wall compared to the edges. I've lifted the floorboards upstairs and the joists appear to be in quite good condition - there is no sign of compression or rot at the ends so either the building has settled and the floor has just sunk or there is something else going on I can't see. The joists are sat in tight wall pockets.

At the moment I am considering either taking everything down, replacing the joists with C16 treated 45x220mm and enlarging the existing pockets, adding 2 rows of noggins and fitting a new ceiling and floor directly to the new joists. A joiner has quoted us £3000 for this, looking at the suppliers I believe I can get the materials for about £1200 (this includes replastering the entire room and the bedroom and lounge ceilings which are to be replaced and the new flooring.)

Does anyone have any less 'destructive' methods for strengthening the floor? I have considered adding additional joists inbetween the current ones to level the floor and take the weight - this would mean I could keep the downstairs ceiling in place but I would either have to use masonry hangers to support the new joists or cut new wall pockets. I have also considered sistering but don't want to have to open up the current wall pockets any more than necessary.

Does anyone else have any ideas why the floor has sunk in the middle? The back (internal) wall of the room seems level, it is just the front wall of the property where the floor seems to drop so dramatically, and there is no sign of collapse in the timber or the pocket, and the wall seems stable below with no sign of cracking or failing to indicate something more structural going on?

Thanks for your advice.

 

[oldbutnotdead]

Have you got a bay window in the front wall underneath the bedroom (where the sag is)?

 

[John Davison]

Yes we do but the ceiling line looks ok- no obvious sign of failure.

 

[vinn]

If you lift the boards its possible to add new sistered in joists but it would probably require the calcs and direction of a SE for sections etc.

Thing is, if you add 70mm depth with the 220mm joists then its 70mm best dropped and lost in the room below.
But you have to carefully weigh up the knock-on effects of raising or lowering a first floor before doing anything.

With ref. to perhaps what oldbutnotdead was asking - all external building openings will have been linteled with timber and the ends might be rotted. If you have a two story bay the "Bressummer" beam will need examining.

I'd suggest that if there's any possible way of keeping and using your old flooring materials then I'd do it.

 

[John Davison]

Thanks for your reply Vinn. The bay window is only single story, but it may have a wooden lintel, or several through the thickness of the wall. Any movement seems to be quite historic and settled but it does mean those central joists are that few inches lower.

I'm fortunate that I can add the depth to the lintels within the existing floor the ceiling level due to the sag so the rooms will still feel the same size, it's just the best way to go about it that I'm trying to get my head around! I've checked with my joiner, a SE and the span tables and everything seems to agree with either 9x2 or 8x3 joists at 400mm centres over 4.3m span. I'm not sure about sections for sistering though but I assume it will be less!

Any more thoughts welcome as this is going to be a tough project to get right!

 

[oldbutnotdead]

Interesting. Given the age of the place (1800s you say) the bay was quite possibly added at a later date. If the masonry is in good nick, no sign of rot or worm in the joists, pockets well formed etc. then I'd be trying very hard to retain the existing joists. I think that if you sistered 6 x 2 to the existing joists (don't open up the pockets to get the sisters into the wall, just cut them flush with the walls and fix them to the existing joists, coachbolts and those throwing stars should give you a nice rigid coupling) and set the top edge of the 6 x 2 so you get a level floor upstairs then that would stiffen things up quite nicely as well without major disruption. I'm not sure how BCO would look at it though, some might regard it as structural work, must use 9 x 2, hangars etc etc.

 

[vinn]

I viewed your photos and the floor boards look to be in good condition - they aren't original but they could be sanded down and finished to suit.
If all the boards are lifted then its ideal to belt sand them individually on a bench - any that are too disfigured can be flipped over.
When lifting boards mark the boards for same place replacement.

Is your cottage detached?
Is it rendered?

 

[John Davison]

Hi, the cottage is in a terrace but the joists run front to back so no party wall issues at least! The front was cement rendered until about 8 years ago when it was removed and repointed by the previous owner. I'm going to try and save as many boards as possible but some have got lifting damage on both sides so I can't even turn them over well, they are also quite bowed so I don't know well they'll take to a flat floor!

 

[theprinceofdarkness]

It is very possible that the stonework has changed its shape when the bay was knocked through. My 1800 stone cottage has got a 2" drop across its back extension. Also where I have exposed the original rear wall stones as a feature, you can see that at a height of about 5' a tapered courses of stone had been built in to get the courses horizontal again. i.e. the wall settled while it was still being built. I would put a horizontal string across the front above the bay and see if the blocks have dropped, giving a kink to the courses. Should be interesting to look at the roof line also.
FWIW I have found really old beams to be more bendable then the timber table say. A 10" X 4" sagged 3mm with my weight on it, a modern 9" X 2" = 0! (or less then the thickness of a pencil line).
So as I see it you have two main problems, one is the out of plumb (upstairs), the other is the spring. Another smaller problem is the sagging ceiling downstairs.
I would remove the floorboarding (label each bit, because the room might not be square). Prop the ceiling to raise it a few mm. Then sister in new joists, using a decent glue and loads of screws (pre drill the holes in the new bit). So where the level allows it use 9" X 2"s (say centre 4 or 5) and cut them down so they are tapered. Fit with the uncut surface downwards. If the old ceiling is lathe and plaster, you will not have access to the full joist depth then go for a suitable size (8 or 7 X 2?). It will be a massive job what with fiddling around pipes and cables and resetting the skirting boards. I am not sure that noggins spread much load sideways, they are just to stop the joists twisting. One problem with sistering is that the floorboard fixing holes are now over free air, so new holes will be required.
My bedroom floor is 32mm T&G with one blacksmith made nail in the centre of each board (circa 1805). Try matching them! I left the floor alone, its like walking over a drum, the room rattles from the change in air pressure, and the furniture needs packing to get it to stand upright.
Frank