A Rather Compromised Joist

[Mark451]

Greetings all, I first started reading this forum a couple of years back - around the same time I bought an old house as it happens.
Strange coincidence that.

Apologies for a lengthy first post but I've tried to provide all relevant info.

I've been debating what to do about this charming little gift from the past left waiting for me under the bath.
Looks like that dreaded primordial insect, the Lesser-Spotted Sawtoothed Joist-Nibbler, has struck again...

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• Mark451
• 20 Jun 2013
• 1

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• Mark451
• 19 Jun 2013
• 1

Untitled

• Mark451
• 19 Jun 2013
• 1

Relevant area in 3D to scale, easier to see the situation

Location:
1st floor Bathroom joist notched to accommodate a deep trap on bath waste, not an uncommon issue I gather. 100yr old terrace, the original large rear 1st floor single room subdivided back in the days of plaster & lath to create two smaller rooms, one being the bathroom. History unknown but estimated age of sanitaryware just removed including the problem bath trap, 30-40 years - so I assume the joist's been in this state for at least that long.

Joists:
7"x3"; spacing 390mm centres, span: 4m, passing under stud wall 1m from one end

Damage:
95mm wide x approx 80% of cross-section removed.
Approximate centre of 4m span
Timber otherwise sound & dry

Loading:
Under bath inline with centre of bath, so subject to fluctuating loads. Also inline with the toilet base, not to mention a pedestal basin (not shown) between bath and toilet - and I was surprised at how heavy that was, when I pulled it out. All in all, a fair bit of weight bearing down, although some of it is distributed across adjoining joists via the floorboards. Stud wall across joist may be helping to support it.

Symptoms:
There's been some flexing of the ceiling beneath along the joist line, but as it's papered, unless you're deliberately looking under certain lighting conditions there's not much to be seen, the ceiling basically appears fine but no doubt the plaster underneath is cracked appropriately. All previous advice has been to leave the ceiling alone - it's black ash plaster and considering what happened to Pompeii in AD79, I have no problems at all not provoking it.

I've been told not to worry unduly about the notching by a former surveyor as it's clearly been like this for many years, and the loading pattern isn't about to change (bathroom layout to stay as is, no tiled floor or other serious weight to be added)

I'm not entirely convinced & for peace of mind alone would rather do something about it now, while the bathroom's apart and empty and the opportunity is available. It might have been like this for decades without much drama but obviously it's structural vandalism and in the worst possible place along the joist; every time I took a bath I'd never quite be able to stop contemplating a sudden unplanned trip to the ground floor at 9.81m/s² in a sort of low-budget log flume simulation.

Solution:
I've searched extensively online for info - clearly there's more than one possible solution. Not surprisingly, I'd prefer the least painful or destructive option.

Access to the rear (as viewed in the 3D image) of the joist is poor (plumbing)
Apart from lifting some boards I'm clear on the front face to apply reinforcement, no pipes/cable to contend with. New trap's well clear of the floor, ironically.

I've been thinking along the lines of a steel plate sandwiched against the joist with ply, ie. a flitch type arrangement. The Bower Beam joist end repair plates out there, which can also be used to splice, caught my notice too - a supplier of the Bower product suggested using their largest (1000mm) plate as a splice. A local engineer can supply cut and drilled steel plate to any dimension and pattern, but as a non-specialist I have no guidelines for arriving at an appropriate design: eg. overall span of reinforcement, materials spec, pattern/spec/distribution of fasteners.

I did see on an older thread here [a similar problem] mention of a useful-sounding guide, but the link has expired: //www.diynot.com/forums/viewtopic.php?t=149477

All opinions gratefully received

 

[pred]

In the event you should take a nose dive as in a log flume, would it be possible to site a camera on a movement switch to catch the the moment for prosterity..

The only thing I could suggest is bolting a piece of 4"x2" or similar to either side so as to sandwich the joist.

 

[freddiemercurystwin]

Just sandwich it in between two joists of the same depth. extending 400 each side of the cut and bolted with a couple of lengths of 10mm studding.

 

[pred]

http://www.google.co.uk/imgres?imgu...bPLCUcfSNIPSPMnngdAI&ved=0CGQQ9QEwEA&dur=1786

 

[Mark451]

Cheers Pred and Freddy

I've only got access one side, so presumably I could use a more substantial length on just the one face. Sistering I believe the term is.

I'd be happy to record the event for posterity (posterior, maybe) but a 14st bloke riding a steel Kaldewei in his birthday suit - you can't 'unwatch' things once you've seen them, unfortunately. YouTube would ban it, believe me. So it would have to go on Wikileaks...

 

[freddiemercurystwin]

If you can't get to each side then that would have to do. But if you've no access to both sides how will you do the bolts up?

 

[tony1851]

It'll be the floorboards doing most of the work, transferring the load to the joists either side of the damaged one. Don't make a meal of it, just bolt a second piece of timber to the side as the others have suggested.
I'd go for a 6x2 about 4ft long, 3 or 4 1/2" coach screws each side.

 

[Mark451]

Hi Freddy's twin

The difficult [rear] face is free to one side of the notch, but on the other side I can only go about 160mm clear before I run into plumbing and extra timberwork which was added to support the pipework, so unfortunately a reinforcing plate wouldn't do a lot of good that side.

Where rear access is a problem I was considering coach screws through the front as opposed to coach bolts for those areas.

The Bower beam plates all specify coach screws [M10/40mm]

 

[Mark451]

Hi Tony1851, thanks for the suggestion, a lot more straightforward than what I've been contemplating.

Yes, I thought the floorboards would be playing their part.

I thought about a means of spreading the load of the bath feet off the problem joist but the next joist back lies directly beneath the stud wall so it'd be difficult to get anything resting directly on it.

- Mark

 

[tony1851]

Mark;
If the notch is under the bath, could you do something like this?
A piece of well-bolted steel angle would transfer the compressive force across the notch.
Perhaps move the bath nearer to the wc if needs be?

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• tony1851
• 20 Jun 2013
• 1

 

[Porque223]

Perhaps raise the joist until it has a much deflection as some of the distant joists, bolt a plate to the bottom surface under the notch, fill the notch with wood (probably with the grain aligned at right angles to the joist grain) and then lower the joist
which now puts the bottom plate and the remaining wood in tension (like the bottom fibers of the other joists) and puts the added wood in compression.
But, the beam loading diagram as far as tension, compression and shear forces will vary depending on several factors
http://www.google.com/imgres?imgurl...4XDUcCkI9fd4AOmpYCoCw&ved=0CEoQ9QEwCQ&dur=875

 

[Mark451]

Sorry didn't reply earlier, was out scrounging a bath

@ Tony - many thanks for taking the trouble to sketch that idea, simple=elegant compared with my own side reinforcement. The notch is indeed under the bath; I've 300mm to the right to play with remaining in the bath's 'footprint', to the left it'd foul the one floorboard I'd need to keep for the bath feet, but that could be worked around.

I like it, worth some thought. Get where you're at re: resisting the compressive force on the top of the beam, it's a shame the ceiling prevents adding an equivalent flange along the bottom of the beam to conteract the corresponding tension.

The bathroom dimensions are pretty modest so I'm keeping the bath in the corner to maximise the space.

 

[rjm2k]

Perhaps a modification of Tonys idea might be better, turn the angle 180 degrees clockwise and bolt it to the side and the top of the joist to effectively box in the top and side. Additionally, you could pack the gap with a bit of timber, if it's flush enough it should help to stop some movement but I'd be careful not to need to hammer it into place!

If you needed to put boards down you could even shallow notch the top of the joist to let the steel sit flush .

It's not great, but at the end of the day it's probably been like that for ages!

 

[Lower]

Just sister it either side with the thickest material you can fit that is the same height as the joist and make the sisters as long as you can fit. Bond the sisters to the joist, coach bolt or screw and then fill and pack the cut out in the joist with a non compressible material that is well bonded into place.

Then stop worrying about it. The floorboards will be spreading the load nicely to the other joists, and as you say, its been like that for 30 years+.

 

[Mark451]

Thanks also to Porque 223 and rjm2k

I see the different ideas all circling the same problem...

@ Porque - I see what you're saying, your scheme would require both intervention through the ceiling and also applying an upward force to counter-deflect the joist before packing and reinforcing it, both of which I've ruled out, and as you say there are several factors at play which go into realms of engineering beyond my expertise if not my appreciation.

TBH there's not a single true 90° angle or level surface in the whole room, let alone the rest of the house, and if the joist has deflected slightly, it's not immediately apparent. At the other end of the room (RHS on the image) there is a perceptible slope to the floor; I added new pipe boxing using a water level to get the top dead level, but to meet the floor it's about 20mm deeper at one end... As for the top of the doorframe, you can roll marbles down it and the 1st floor and ground floor ceilings curve up to meet the party wall {opposite wall from the bath}, almost as if the building has been bent up at the party wall. Settlement over time maybe, or a Friday afternoon special during original construction? All of which drove me mad as a former draftsman when I digitised the house, trying to reconcile surfaces which just wouldn't align

Since puchasing this place I've subsequently been told that a building like this (Edwardian UK brick terrace) was in all likelihood thrown up with an original life expectancy of 50 years, and here a lot of them still are, twice that down the line. The previous occupants of mine were here for 50 years no less and it was sold 'in need of modernisation' - the brochure certainly told it like it is on that point...

If anything, now that the bathroom is stripped of all the heavy stuff, there is a very slight gap under the problem joist which suggests to me that the ceiling has, very slightly, been pushed down when the joist was loaded, and with the load removed the joist has sprung back slightly while the ceiling has to an extent remained deformed.

So I'm basically happy to lock the joist in position with no load on it.

@ rjm2k - thanks for the suggestion. Like you say, it has to have been like that for ages.

The supplier of the bower beam plates also sells various pourable structural resins (epoxy based), and I'd speculated about boxing in the notch and filling it with some - if it was a relative of Araldite, it would resist compression well, completely fill evey volume in the notch and bond to the surfaces well. But per litre it's not cheap and wouldn't dispense with the need for mechanical reinforcement

The suppliers have some interesting stuff to tackle defective structural timber, worth a look - I am no affiliate of the site concerned but if I'm breaking the rules by posting the link here, moderator please remove:

http://www.timber-repair.co.uk/order_diydoc.htm

Regards -
Mark