Spreading and sagging

[Zebra]

My timber frame has bowed outwards and the joist ends have pulled away a little. There's about a half to three quarter inch gap at the main beam where the tenons have pulled out of their mortices, and similar at the ring beam.
(The timber frame is 12 feet by 14 feet, with a ring beam that sits on top of the lower storey brickwork. There's one main beam which spans the gap and supports the upstairs joists. It's about 6" x 6" and the joists about 4" x 2".)

I've never worried much about it, as I thought it was probably normal for old houses, it seems stable and not to be still moving. However, I do worry about whether I should have braced the building front to back to stop it going any further. If it were still possible to do, should I?

Also, there's a lot of bounce in the floor of the upper storey. Similarly, I've assumed it was normal and not worried much about it but at the moment, working upstairs with all the furniture out and scaffold stands up there, it is really noticeable. Also, there is a mortice cut in the centre of that main beam, which had been filled in and painted over. I had always assumed, perhaps stupidly, that the mortice was there because the main beam had been reclaimed from somewhere else when it went in. I don't know why I thought that, no evidence for it.

What if there were always supposed to be a support post in the centre of that main beam, and it was taken out some time recently? I've put in a temporary support post and of course it cuts down the movement in the floor drastically. Should I put it back, and have an oak support post bang in the middle of the living room? I can live with it if it's what the house needs. Or should I just let the floor bounce?

 

[Carol]

I thought this thread was going to be about being 'middle aged' !

 

[LadyArowana]

I thought this thread was going to be about being 'middle aged' !

Same rules apply :lol: Get structures thoroughly checked out by someone who is qualified and then rectify any defective bits.

 

[andrew gayton]

Is the joisting exposed in the ground floor rooms or does it have an underdrawn ceiling? If the former, you can provide steel strapping (say at 40mm x 5mm) to the sides of the joisting to stiffen them up and if the latter, double up every other joist with a partner joist to achieve the same. The spine beam could be helped with a flitch - but this is difficult / messy - so I would let in steel strapping to a chisled out rebate (so floorboards will go back down without a hump). Joist ends going back to the wall can be (re) secured using those (usually blacksmith made) L shaped straps that are nailed at the outer face of the plate then secured with a staple at the joist end; all of this can be painted in and not be visually intrusive. It goes without saying that you need to ensure that the outer plate is still atop the walling securely. Also, a 6mm ply diaphram on top of the joists before the floor boards go down will stiffen things up considerably whilst reuniting the joisting with the spine beam. if the gap at the plate end is causing concern, an applied rail can be used, but this is a last resort as it can appear clunky (hopefully strapping with the L shaped straps would be adequate).

I hope that this all makes sense.

The floor bounce has lead to deflection which has pulled at the plate causing a lack of restraint causing the spread.

''The knee bone is connected to the thigh bone, the thigh bone is connected to the ............ etc etc'' .



edited at 08.04 - 'more info'

 

[philpjuk100]

Any chance of usine tie bars? they seem to be in use in a lot of old timber frames,we have some in our house that look to have been here many years. Attended my GP yesterday for the results of an "MOT"and was told I was OK apart from a bit of "spreading and sagging" (body mass index?) celebrated with a pack of cream cakes from morrisons!

 

[philpjuk100]

I am NOT "middle aged! (not unless I live until I am 140!)

 

[DJH]

Depending on how exposed your spread is you could possibly use something like a floor cramp and, with a bit of ingenuity, put pressure on the joint pulling it back to close the gap as much as you can, and then drill and pin it with something like a threaded bar washers and nuts each side. Stainless would be good but it will at least stop it getting any worse...

Middle aged?? You're only as old as the woman you feel. :lol:

Doug

 

[andrew gayton]

Not advisable in my opinion.

 

[philpjuk100]

I remember as a schoolboy being taken during a science lesson to see a timber frame having tie bars fitted,the bars were fitted through the frame,side to side,large round plates and nuts were fitted each side,buckets of burning coke were hung from the bar and when the bar had expanded the nuts were tightened.We then watched as the bar cooled and the tenons re entered the mortices.The house was on my paper round and I watched the frame re bricked and thatched and a carpenter make yorkshire sliding sash windows.This started my interest in old buildings.Thought I would look at it on "google street view" and there is a block of flats there now! how could they?

 

[andrew gayton]

Thankfully, opc based pressure grouts have fallen by the wayside also. :wink:

 

[middi]

It is quite normal in older timber framed buildings to see gaps at tenoned and pegged joints. These gaps will become evident as soon as the green oak from which they were built from begin to shrink. Also the natural stresses coupled with expansion and contraction of the frame will play as substantial part in contributing to " wide gaps" at oak framed joints. The standard procedure, especially on newly constructed old barns, would have been to periodically " re-hammer" the tapered oak pegs in their respective holes as this would have retightened the joints.
To a certain extend this procedure was also applied to oak frame dwellings, but less effective, mainly due to the extra " cladding" preventing either access to the pegs, or, due to this cladding the " pulling toghether" of joints very difficult.
These gaps at the oak joints were so prominent at the early stage of their construction ( especially at eaves heights level and therefore roof spread) and it is quite common to still find wattle and daub or haired limed plaster in these gaps.

As long as the wood and pegs are still in good condition there should not be too much need for concern, however, should there be evidence of decay that may compromise the structural integrity of the joint ( and therefore the entire building) remedy action needs to be taken.
The quickest and best solution is retaining straps, especially constructed, lapping and retaining the wood joints ( with through S/steel bolts) in their present position. Attempting to pull the joints together is a complete waste of time as it will never be achieved unless the building is stripped from it's enveloping fabric. Also, whilst this strap nees to be bolted, coach screws should not be used as these tend to come loose with susequent frame movement. ONE bolt should be used at each end of the strap and into sound wood in order to allow for a " swivel action" of the strap and therefore prevent wood split when the inevitable movement of the frame occurs.

Middi

 

[andrew gayton]

the joy of offset pegging.

 

[DJH]

I think I may not have expressed myself clearly earlier. What I was getting at is that any joint made under tension is much better in my view than one that is not...

Doug, under tension here.

 

[Zebra]

Thanks all. OK, I can strap the joist ends to the plate and to the spine beam.
What about the support post in the middle of the beam to stop the bounce?
Sorry Andrew, I'm not sure I understand this bit:

I would let in steel strapping to a chisled out rebate (so floorboards will go back down without a hump)

Would the rebate be on the top of the beam? And what size steel would go in it?
Perhaps I'm overreacting, the building is not falling apart. But a bow has developed in the back wall over the years, and this is why the joists particularly on the back side of the spine beam, have pulled out. But they are stable .
Edit: there aren't any pegs on these joints unfortunately....

 

[Flyfisher]

One of the main A-frames in our roof suffered from many years of water ingress from a leaking dormer and the result was that the corner joint into the wall plate (roof plate?) had partially come apart. To make matters worse, the wall plate itself was jointed close to this point, so the integrity of the whole area was badly compromised.

However, it had been in this condition for many years and nothing had actually collapsed, so after various discussions it was decided to stabilise the whole joint, but not to try to pull it back together.

The photos below show how I did it. Only the metal strap on the inside of the wall plate will be visible when things are properly reinstated (the ceiling beam itself was boxed-in, and this will be reinstated).

I will admit it was a pig of a job though, because nothing could be welded in place because of the fire risk, so it involved a lot of measuring, cardboard patterns, partial assembly, clamping, tack-welding, disassembly, full welding, reassembly etc. I seem to remember it took me the best part of a week, with plenty of tea, kitkats and pondering . . . but it hasn't fallen apart yet and the roof is still standing!

This is the outside view from the scaffolding:


This is the view from the attic above the main beam:

 

[andrew gayton]

Thanks all. OK, I can strap the joist ends to the plate and to the spine beam.
What about the support post in the middle of the beam to stop the bounce?
Sorry Andrew, I'm not sure I understand this bit:

I would let in steel strapping to a chisled out rebate (so floorboards will go back down without a hump)

Would the rebate be on the top of the beam? And what size steel would go in it?
Perhaps I'm overreacting, the building is not falling apart. But a bow has developed in the back wall over the years, and this is why the joists particularly on the back side of the spine beam, have pulled out. But they are stable .
Edit: there aren't any pegs on these joints unfortunately....

Hello,

The centre post could be dispensed with if the joisting and spine beam is stiffened up as mentioned above. Yes, the rebate would be on top of the beam - 75mm x 15mm strap let in would stiffen up the beam yet still allow some flex. If you do have underdrawn ceilings, I would put in partner joists. if you do this, be aware that the floor is probably 'dished', so the partner joisting may need to be in two lengths (overlapped, cut and jointed) if the joisting is exposed, then you will need to provide strapping.

I did a mixture of the above on my last house where the 1st floor was a trampoline - the only difference being that I applied a layer of 6mm ply before floorboards and then before putting in a new ceiling to make a 'joist sandwich' as the ex. joisting was very mean (75mm x 75mm generally) this enabled me to jump up and down on the 1st floor with no bounce whatsoever.

All easy stuff.

 

[Zebra]

Sorry if I'm being thick Andrew, the rebate is along the length of the main beam? Is it 75mm horizontally and 15mm vertically? In which case that's almost the entire width of the beam. Do you have to then screw it down to the beam?
Or do you mean 75mm horizontally and 15mm vertically, ie a slot within the beam? In which case if the beam is itself dished, would you have to get a piece of steel specially made?

My ceiling is not underdrawn, not now anyway, so unfortunately the partner joist thing wouldn't work. My joists are small too, 75mm x 50mm, but the span is only 1.6m each side.

The ply floor thing is worth thinking about. It would make a bigger step at the top of the stairs, but then perhaps I could put a ply layer over each stair too - I was going to replace the 1960s treads anyway - the originals will remain underneath.

But with the floor being so dished already, would the ply allow you to screw it down?

Gosh Flyfisher, my situation is nowhere near as serious as that!

I could install a tie bar front to back to stop the spread, but do they expand and contract with the seasons at a different rate to the timber, meaning that a tie bar inserted in the summer would then contract in the winter, pulling the building together and cracking the plaster?

 

[Flyfisher]

Gosh Flyfisher, my situation is nowhere near as serious as that!

That's partly why I posted the photos. I'm not recommending it, but timber framed houses seem able to withstand some very serious problems, presumably because of their 'lattice' construction in which everything helps to hold everything else together and spread the load when things do go wrong. Collapsed sole plates are perhaps the classic example.

I'm not suggesting we should ignore such problems, but I do think there is rarely a need for panic.

I could install a tie bar front to back to stop the spread, but do they expand and contract with the seasons at a different rate to the timber, meaning that a tie bar inserted in the summer would then contract in the winter, pulling the building together and cracking the plaster?

That's an interesting point and I'm sure the basic premise is correct. However, given that it is a widely used method of repair or support I assume it's not an actual problem in practice. We certainly have various tie-bars around our house but I've not noticed any particular cracking problems - perhaps I can't see the wood for the trees

Also remember that lime mortar/plaster is supposed to be able to accommodate slight movement without cracking, so perhaps that's the reason tie-bars do not cause differential expansion/contraction problems.

I don't know the relevant data, but it should be possible to calculate the expansion and contraction figures for oak and steel over typical UK temperature extremes and determine the actual difference. I suspect it would be very small and hence no significant problem in practice.

 

[Zebra]

Well, I've hung a marker pen on a piece of string from the centre of the main beam, with a piece of paper underneath it and gone a bounced up and down upstairs, adjusting the height of the pen until it draws on the piece of paper, then measured the gap. It's around 2-3mm of deflection over a 4m span. So it's not that bad. Perhaps with the ply as Andrew suggested sandwiched between the two layers of floorboards upstairs, the deflection will be OK.
Edit: of course, a larger animal upstairs would cause more deflection. I shall have to remember when my friend the hippopotumas comes round, to encourage her to stay close to the edges of the room.

 

[Penners]

I seem to remember it took me the best part of a week, with plenty of tea, kitkats and pondering . . . but it hasn't fallen apart yet and the roof is still standing!

Proof positive of the beneficial effect of the Kit-Kat in building repair.

I hesitate to add anything to the expert views contributed above. However, I will just mention that I had a similar bouncy floor construction in one of my earlier timber-frame properties. I tackled this by adding "companion" joists on both sides of each of the common joists, bolted to the originals. These were a bit shallower than the original joists, so they also became the counterbattens to which the plasterboard ceiling panels were fixed, in the voids between the common joists.

I also stiffened up the king joist across the centre of the room by adding substantial knees in the right-angles with the support posts, at each end of it. In your case, if you're sure that the mortice in the centre of this member is a significant contributor ro the bounce, then you could perhaps add a stiffening "sandwich" of additional members, bolted on each side of that part of the king joist and extending well beyond each end of the mortice. These members could be hidden above your ceiling panels (assuming you're planning to install these).

As already mentioned above, I would deal with the pulled-apart joint y using a steel strap. I would not try to pull the joint back together - just to reinforce it in its current location.