Rotten joist end

[Cassie]

Hello folks, after a long period of inactivity, I’m back on the job and of course am out of my depth as usual.
You probably won’t remember, but I’ve got an 1870 house, brick built from first floor, but as it turns out ground floor is at least part stone.
I’ve just taken up some floorboards on the first floor to look at the joist ends. As I suspected, one is pretty rotten, soft and bounces. It’s on a really awkward spot in a corner with a brick wall on one side. It’s embedded into stone on the rotten end which is an external wall. The problems causing damp have been rectified-bad gutters, leaking roof, and the outside is being lime rendered in the spring to replace naff patched/cracked mish mash of all sorts. I’ll add pics below, but you’ll see an added complication is all the house wiring coming down very close to the wall. The copper pipe you’ll see is I think a dead leg from an old bedroom basin upstairs, but I’ll lift floorboards upstairs to check before removing.
I have no idea how to approach the rotten joist end. Any ideas? Many thanks! And now I’m back, I’ll be trying not to bother you too much, but will probably not be successful! Thanks all

 

[erikwoolf]

Hello folks, after a long period of inactivity, I’m back on the job and of course am out of my depth as usual.
You probably won’t remember, but I’ve got an 1870 house, brick built from first floor, but as it turns out ground floor is at least part stone.
I’ve just taken up some floorboards on the first floor to look at the joist ends. As I suspected, one is pretty rotten, soft and bounces. It’s on a really awkward spot in a corner with a brick wall on one side. It’s embedded into stone on the rotten end which is an external wall. The problems causing damp have been rectified-bad gutters, leaking roof, and the outside is being lime rendered in the spring to replace naff patched/cracked mish mash of all sorts. I’ll add pics below, but you’ll see an added complication is all the house wiring coming down very close to the wall. The copper pipe you’ll see is I think a dead leg from an old bedroom basin upstairs, but I’ll lift floorboards upstairs to check before removing.
I have no idea how to approach the rotten joist end. Any ideas? Many thanks! And now I’m back, I’ll be trying not to bother you too much, but will probably not be successful! Thanks all

View attachment 12647

We had a similar issue, our builder took out the rotten part and replaced it with a new piece of joist. The new piece was bolded on the remaining joist. It was a days job, you will need a good builder.

 

[Cassie]

We had a similar issue, our builder took out the rotten part and replaced it with a new piece of joist. The new piece was bolded on the remaining joist. It was a days job, you will need a good builder.

Thanks erikwoolf. If it had been in brick instead of stone, and not in a really tight corner, I’d probably just have sistered it myself! Problem is good builders are in very short supply and I suspect it will be one of those too small/too difficult jobs people will look at and I’ll never hear from again :/

 

[fernicarry]

The new piece was bolted on the remaining joist

Thats what I've done in similar situation. Problem is getting the space to manoeuvre new piece into the wall pocket. I was fortunate that the joist ends were above the front porch and that had no ceiling at the time (and still not...) so I had a couple of feet of empty space to play with. Yours look to be above a lathed ceiling so inevitably there is going to be damage to that since the laths will be nailed into the piece that you need to cut away.

Support from below in case the joist end is still taking some load whilst you work on it. Mine weren't particularly being so rotten the ends were essentially floating, the load instead being transferred into the front door frame! Remarkably the front door showed no signs of distress...

I had 3 distinct cases:
1. pocket wide enough to accommodate sister, no idea why it was so wide, but it worked to my advantage, just slide in new section making it long enough to overlap two feet of good wood on the existing, bed it into the pocket on slate and lime mortar and bolt it on, nothing cut away.
2. pocket not wide enough, cut back at least two feet from wall, insert new piece into wall, bed in as previous, bolt sister onto new piece and existing overlapping 2 feet on both, this approach means you need at least 4 feet of access from above so quite a few rows of floor boards to lift, I cut away the existing end with a circular saw, probably not the best HSE practice being balanced on a joist above a 4m drop with the saw at an awkward angle, think about where the saw is going to go in case of kick back, preferably not into your leg, the last bit was finished with a multi-tool
3. no access to cut away because of internal stud walls (yes, could have removed them, but...), I screwed a new piece onto the existing bringing close to but not touching the external wall and attached this laterally to an adjacent joist with a dwang (noggin) on joist hangers, this is least satisfactory but its still better than what was there before, joist hangers with twist nails are incredibly strong but it means the adjacent joist taking additional load, sum of the parts and all that

No 3. might work for you given the confined space but it might still allow a bit of deflection so might not eliminate all of the bounce.

I toyed with the idea of fixing a header directly into the rubble to carry the sisters but decided that probably wouldn't get enough of a grip to be worth attempting.

Clean all the debris out of the wall pocket once you remove the rotten end. You will probably find a rotten wall plate below the joist end. Ideally the entire pocket should be packed with lime mortar to exclude any air that could carry moisture in from the warm side of the building.

New pieces that ended up in the wall were painted with creosote paint first. Use decent timber from a builders merchant, who will want to sell it to you in 4.8m lengths but should also be willing to cut it to size to make it easier to transport if needed. I jury rigged supports from several 4x2's screwed together and used a car jack to just lift the joist before working on it.

I used 12mm stud bar cut to length with an angle grinder, dogs tooth washers between old and new sections to prevent movement in the joint and 50mm x 3mm spreader plates under the nuts. 3 sets of bolts either side of the join, offset a couple of inches from top and bottom and positions alternated. There are websites with tables of sizes for where the bolts should go for this sort of exercise (link is in my other browser, I'll dig it out if wanted). I already had big 19mm spanners for the car to do it up with. All the ironmongery is readily available from SF or TS.

Its a fairly involved job so maybe worth getting a "professional" in unless you are very confident of your ability. This was stretching me about as far as I've gone in terms of structural stuff so I was a bit apprehensive, but it all went absolutely fine. My major worry was the very nice original cornice in the hallway below but it didn't appear to suffer. Just remember that if you do get in the pros they will almost certainly turn the floorboards above and the ceiling below into match wood giving you a more significant making good job afterwards. The cracking and splintering noises coming from next door when they went through a similar exercise being evidence of that... They also won't be that fussed about protecting the new wood, cleaning out the pockets and will use cement where needed not lime. I left my supports in place for a couple of weeks to allow the mortar in the pocket to go off a bit so that the new bits stayed where I wanted them when the joist load went back on.

Btw, that looks like your meter tails running past that location (the thickest 2 wires) as well as a number of final circuits. Be aware that even with the main switch in the fuse box turned off the tails will still be live. You might have an isolator close to the meter that will knock those off.

 

[Toby Newell]

Thats what I've done in similar situation. Problem is getting the space to manoeuvre new piece into the wall pocket. I was fortunate that the joist ends were above the front porch and that had no ceiling at the time (and still not...) so I had a couple of feet of empty space to play with. Yours look to be above a lathed ceiling so inevitably there is going to be damage to that since the laths will be nailed into the piece that you need to cut away.

Support from below in case the joist end is still taking some load whilst you work on it. Mine weren't particularly being so rotten the ends were essentially floating, the load instead being transferred into the front door frame! Remarkably the front door showed no signs of distress...

I had 3 distinct cases:
1. pocket wide enough to accommodate sister, no idea why it was so wide, but it worked to my advantage, just slide in new section making it long enough to overlap two feet of good wood on the existing, bed it into the pocket on slate and lime mortar and bolt it on, nothing cut away.
2. pocket not wide enough, cut back at least two feet from wall, insert new piece into wall, bed in as previous, bolt sister onto new piece and existing overlapping 2 feet on both, this approach means you need at least 4 feet of access from above so quite a few rows of floor boards to lift, I cut away the existing end with a circular saw, probably not the best HSE practice being balanced on a joist above a 4m drop with the saw at an awkward angle, think about where the saw is going to go in case of kick back, preferably not into your leg, the last bit was finished with a multi-tool
3. no access to cut away because of internal stud walls (yes, could have removed them, but...), I screwed a new piece onto the existing bringing close to but not touching the external wall and attached this laterally to an adjacent joist with a dwang (noggin) on joist hangers, this is least satisfactory but its still better than what was there before, joist hangers with twist nails are incredibly strong but it means the adjacent joist taking additional load, sum of the parts and all that

No 3. might work for you given the confined space but it might still allow a bit of deflection so might not eliminate all of the bounce.

I toyed with the idea of fixing a header directly into the rubble to carry the sisters but decided that probably wouldn't get enough of a grip to be worth attempting.

Clean all the debris out of the wall pocket once you remove the rotten end. You will probably find a rotten wall plate below the joist end. Ideally the entire pocket should be packed with lime mortar to exclude any air that could carry moisture in from the warm side of the building.

New pieces that ended up in the wall were painted with creosote paint first. Use decent timber from a builders merchant, who will want to sell it to you in 4.8m lengths but should also be willing to cut it to size to make it easier to transport if needed. I jury rigged supports from several 4x2's screwed together and used a car jack to just lift the joist before working on it.

I used 12mm stud bar cut to length with an angle grinder, dogs tooth washers between old and new sections to prevent movement in the joint and 50mm x 3mm spreader plates under the nuts. 3 sets of bolts either side of the join, offset a couple of inches from top and bottom and positions alternated. There are websites with tables of sizes for where the bolts should go for this sort of exercise (link is in my other browser, I'll dig it out if wanted). I already had big 19mm spanners for the car to do it up with. All the ironmongery is readily available from SF or TS.

Its a fairly involved job so maybe worth getting a "professional" in unless you are very confident of your ability. This was stretching me about as far as I've gone in terms of structural stuff so I was a bit apprehensive, but it all went absolutely fine. My major worry was the very nice original cornice in the hallway below but it didn't appear to suffer. Just remember that if you do get in the pros they will almost certainly turn the floorboards above and the ceiling below into match wood giving you a more significant making good job afterwards. The cracking and splintering noises coming from next door when they went through a similar exercise being evidence of that... They also won't be that fussed about protecting the new wood, cleaning out the pockets and will use cement where needed not lime. I left my supports in place for a couple of weeks to allow the mortar in the pocket to go off a bit so that the new bits stayed where I wanted them when the joist load went back on.

Btw, that looks like your meter tails running past that location (the thickest 2 wires) as well as a number of final circuits. Be aware that even with the main switch in the fuse box turned off the tails will still be live. You might have an isolator close to the meter that will knock those off.

^^^ That is exactly how to do that.

Apart from the circular saw roulette...

 

[Cassie]

Thats what I've done in similar situation. Problem is getting the space to manoeuvre new piece into the wall pocket. I was fortunate that the joist ends were above the front porch and that had no ceiling at the time (and still not...) so I had a couple of feet of empty space to play with. Yours look to be above a lathed ceiling so inevitably there is going to be damage to that since the laths will be nailed into the piece that you need to cut away.

Support from below in case the joist end is still taking some load whilst you work on it. Mine weren't particularly being so rotten the ends were essentially floating, the load instead being transferred into the front door frame! Remarkably the front door showed no signs of distress...

I had 3 distinct cases:
1. pocket wide enough to accommodate sister, no idea why it was so wide, but it worked to my advantage, just slide in new section making it long enough to overlap two feet of good wood on the existing, bed it into the pocket on slate and lime mortar and bolt it on, nothing cut away.
2. pocket not wide enough, cut back at least two feet from wall, insert new piece into wall, bed in as previous, bolt sister onto new piece and existing overlapping 2 feet on both, this approach means you need at least 4 feet of access from above so quite a few rows of floor boards to lift, I cut away the existing end with a circular saw, probably not the best HSE practice being balanced on a joist above a 4m drop with the saw at an awkward angle, think about where the saw is going to go in case of kick back, preferably not into your leg, the last bit was finished with a multi-tool
3. no access to cut away because of internal stud walls (yes, could have removed them, but...), I screwed a new piece onto the existing bringing close to but not touching the external wall and attached this laterally to an adjacent joist with a dwang (noggin) on joist hangers, this is least satisfactory but its still better than what was there before, joist hangers with twist nails are incredibly strong but it means the adjacent joist taking additional load, sum of the parts and all that

No 3. might work for you given the confined space but it might still allow a bit of deflection so might not eliminate all of the bounce.

I toyed with the idea of fixing a header directly into the rubble to carry the sisters but decided that probably wouldn't get enough of a grip to be worth attempting.

Clean all the debris out of the wall pocket once you remove the rotten end. You will probably find a rotten wall plate below the joist end. Ideally the entire pocket should be packed with lime mortar to exclude any air that could carry moisture in from the warm side of the building.

New pieces that ended up in the wall were painted with creosote paint first. Use decent timber from a builders merchant, who will want to sell it to you in 4.8m lengths but should also be willing to cut it to size to make it easier to transport if needed. I jury rigged supports from several 4x2's screwed together and used a car jack to just lift the joist before working on it.

I used 12mm stud bar cut to length with an angle grinder, dogs tooth washers between old and new sections to prevent movement in the joint and 50mm x 3mm spreader plates under the nuts. 3 sets of bolts either side of the join, offset a couple of inches from top and bottom and positions alternated. There are websites with tables of sizes for where the bolts should go for this sort of exercise (link is in my other browser, I'll dig it out if wanted). I already had big 19mm spanners for the car to do it up with. All the ironmongery is readily available from SF or TS.

Its a fairly involved job so maybe worth getting a "professional" in unless you are very confident of your ability. This was stretching me about as far as I've gone in terms of structural stuff so I was a bit apprehensive, but it all went absolutely fine. My major worry was the very nice original cornice in the hallway below but it didn't appear to suffer. Just remember that if you do get in the pros they will almost certainly turn the floorboards above and the ceiling below into match wood giving you a more significant making good job afterwards. The cracking and splintering noises coming from next door when they went through a similar exercise being evidence of that... They also won't be that fussed about protecting the new wood, cleaning out the pockets and will use cement where needed not lime. I left my supports in place for a couple of weeks to allow the mortar in the pocket to go off a bit so that the new bits stayed where I wanted them when the joist load went back on.

Btw, that looks like your meter tails running past that location (the thickest 2 wires) as well as a number of final circuits. Be aware that even with the main switch in the fuse box turned off the tails will still be live. You might have an isolator close to the meter that will knock those off.

Thanks so much fernicarry for this very comprehensive response. I indeed think it’s beyond my confidence level (but that can always change after so many rejections from builders!) At least now I have the advice on how to do it when I find someone game, and I’ll definitely be looking over his or her shoulder as I suspect there will be more joists requiring attention. You’re right about the electrics. The old consumer unit was upstairs, looped supply from next door, and it’s been a bit of a mammoth (expensive) fandango to get everything routed down to a new CU with new supply in floor below. Still a bit of an ongoing saga I think it might have to be option 3 because the wall almost abutting the rotten joist is brick rather than stud. I work in a and e, so at least I have friends in case of circular saw mishaps

 

[Toby Newell]

Not sure I would actively volunteer for such a job, but you are in Devon anyway.

You could cut back, butt joint and overlap sister, with noggin (dwang! you learn something every day) for good measure. Having direct support at end would be best otherwise joist wants to rotate. So option 2. Maybe it's because I am a tradie but no way would I use a circular saw for this, super sketch. I would use my Fein and a hand saw. Never owned a recip saw that might might work. Circ saws are number two most dangerous tool after table saws (and any metallic pointy thing you poke live cables with)

I never use joist hangers myself but I guess the joists I work on are very often, bent, bowed and skewed all at once and I fit a lot of noggins! Twisted wire nails are great but screws great for tight spaces (I use screws) old boys (no insinuation ) frown on screws as they see them as weak in shear but this is largely based on Taiwanese and Chinese crap from the 1960s to 1980s. These days high quality engineered screws are just as good if not better (esp in clamping force and pull out), most can take 30° bend. It's true that a good nail can take a 90° bend (but would work harden and fail under stress cycles) but slightly moot as by then pull out would probably be more of an issue. In fact Simpson Strong Tie (market leader in hangers ) in their technical documents quote the highest load rating when using their own high performance torx screws. Not to say square twist nails are bad, just that screws are ok. I have fitted several hundreds of noggins, and thousands of boards, almost all with screws now. No one appears to have died yet. (Although maybe that is survivor bias and they are all dead)

I find that a tight fit is best for load transfer in noggins. For carriage bolts, in addition to belt and braces of dog tooth washers for twist and square washers (a must) I add a line of MS polymer adhesive inbetween and construction screws at the end past the bolts. But everything fern says is spot on and as per regs.

Also, I use bitumen flashing primer (blackjack etc) then wrap the end in Bitumen flashing tape, I find this gives a 1mm or so cushion which helps to seat the joist and reduces the possibilty of grit or a rough surface from penetrating through any coating. Bedding the end in lime makes sense as breathable and more flexible.

 

[fernicarry]

Toby, how do you attach noggins? Do you screw through from the opposite face into the end of the noggin? I usually prefer screws due to their easy reversibility and my inability to aim a hammer straight.

 

[Cassie]

Not sure I would actively volunteer for such a job, but you are in Devon anyway.

You could cut back, butt joint and overlap sister, with noggin (dwang! you learn something every day) for good measure. Having direct support at end would be best otherwise joist wants to rotate. So option 2. Maybe it's because I am a tradie but no way would I use a circular saw for this, super sketch. I would use my Fein and a hand saw. Never owned a recip saw that might might work. Circ saws are number two most dangerous tool after table saws (and any metallic pointy thing you poke live cables with)

I never use joist hangers myself but I guess the joists I work on are very often, bent, bowed and skewed all at once and I fit a lot of noggins! Twisted wire nails are great but screws great for tight spaces (I use screws) old boys (no insinuation ) frown on screws as they see them as weak in shear but this is largely based on Taiwanese and Chinese crap from the 1960s to 1980s. These days high quality engineered screws are just as good if not better (esp in clamping force and pull out), most can take 30° bend. It's true that a good nail can take a 90° bend (but would work harden and fail under stress cycles) but slightly moot as by then pull out would probably be more of an issue. In fact Simpson Strong Tie (market leader in hangers ) in their technical documents quote the highest load rating when using their own high performance torx screws. Not to say square twist nails are bad, just that screws are ok. I have fitted several hundreds of noggins, and thousands of boards, almost all with screws now. No one appears to have died yet. (Although maybe that is survivor bias and they are all dead)

I find that a tight fit is best for load transfer in noggins. For carriage bolts, in addition to belt and braces of dog tooth washers for twist and square washers (a must) I add a line of MS polymer adhesive inbetween and construction screws at the end past the bolts. But everything fern says is spot on and as per regs.

Also, I use bitumen flashing primer (blackjack etc) then wrap the end in Bitumen flashing tape, I find this gives a 1mm or so cushion which helps to seat the joist and reduces the possibilty of grit or a rough surface from penetrating through any coating. Bedding the end in lime makes sense as breathable and more flexible.

Thank you Toby. I’ve just got in from work and had a look at the 3 options again while looking directly at it. Given the rotten end is in stone which I think will be more difficult to create a new hole in the right place, and as you say to avoid twisting, I think now option 2 is probably the better one. I’ve got plenty of room to work further along the joist and away from the scary electrics. Propping from below is in a hallway so that’s achievable. Joist hanger could be difficult to attach to the wall-either in stone or the crumbly bricks, so good to hear of an alternative. Interesting view on nails v screws-your experience here is very useful. My gut would have gone with screws, and it sounds like this is right. My biggest concern is the tight space between the joist and the parallel brick wall. Grazed knuckles are anticipated! I’d definitely prefer bedding in lime because of flexibility. Need to find a builder who knows what blackjack is

 

[Toby Newell]

Thank you Toby. I’ve just got in from work and had a look at the 3 options again while looking directly at it. Given the rotten end is in stone which I think will be more difficult to create a new hole in the right place, and as you say to avoid twisting, I think now option 2 is probably the better one. I’ve got plenty of room to work further along the joist and away from the scary electrics. Propping from below is in a hallway so that’s achievable. Joist hanger could be difficult to attach to the wall-either in stone or the crumbly bricks, so good to hear of an alternative. Interesting view on nails v screws-your experience here is very useful. My gut would have gone with screws, and it sounds like this is right. My biggest concern is the tight space between the joist and the parallel brick wall. Grazed knuckles are anticipated! I’d definitely prefer bedding in lime because of flexibility. Need to find a builder who knows what blackjack is

You are very welcome. Yes, nails are very difficult to fix in many situations, banging them also isn't great for surrounding lime plaster. I try to reserve my banging for knocking in noggins. There is a caveat to using screws though, there is a massive difference in quality, although recently quality has increased a lot accross the board. I have AB tested dozens of different screws and currently have about 5,000 in multiple tool boxes. Forget builders special Turbo golds... best bet is to stick with Spax. Forgefix znd Timco are other good brands I use. Spax are the most spendy but highest overal quality. Another tip, always go for torx (t star) headed fixings, I haven't used cross heads for years, torx heads are 10x better for torque and reduced cam out, also buy good bits! I use Spax, Wera or Wiha. Roberts (square drive) are good but not v common in the UK (popular in N America)

People who complain about price of fixings are pretty dense imho, a bit like using ungraded or C16 timber... saving 5p per screw doesn't seem so smart when whatever you have fixed fails I am old enough to have lived through the time when screws were mostly finest slim threaded Chinesium, through to the shiny shiny look its Gold and has a Turbo... to the modern screws that out perform nails almost all of the time.

All builders should know what Blackjack is...

 

[Toby Newell]

Toby, how do you attach noggins? Do you screw through from the opposite face into the end of the noggin? I usually prefer screws due to their easy reversibility and my inability to aim a hammer straight.

It depends fern. Any way I can get them in, often from both sides at angle, one at top, other at bottom to reduce twist. You can screw from top too but have to be careful not to split, you can pilot drill. I do sometimes screw from end if I can get to it (in addition) but remember that can split as you are going into end grain and also it doesn't stop twist, so I would still screw each side. Spax or Forgefast decking screws with reduced head can help but they are only 60mm. For the sides I often use Spax wirox 4.5x 70, 80 or 100mm. The key to noggins is to make them tight as the wood will shrink. Measure, add 3 to 5mm, then retest and slowly creep back on the mitre saw, you want 1 to 1.5mm over as joist will move and you can knock in. If joists are canted you can add a fraction of a degree of bevel to the end. It helps to have a nice mitre saw. I have the Festool KS60 Kapex. I only ever use C24 timber from proper local yards, eg Champion, Hitchcock and King, Travis Perkins are normally pretty good nationwide, always pick up in person so you can sort yourself. I would say at a good yard 80% of joist is usable, at Wickes maybe 20% is usable. You can use twisted bananas, they are still graded the same, but it makes life much harder. C16 is weaker so you have less leeway, also if you order online from Wickes or B&Q you can get some appalling undersized boomerangs, whenever Ive been forced to rush to Wickes to get timber I have had to sort through an entire stack to get a few useable joists.

And yes, I have several kilos of unused cut clasp nails, good riddance to them! An average sized floor uses about 1,000 fixings. Let's say you hold your nail for 4 hits, then the punch for 2 hits, thats 6x1000 = 6000 hits. If you are 99.99% accurate that still means you will smash your hand on average 6 times per room. After the third or fourth time when you smack your swollen, bruised and bleeding knuckles with your 21oz Estwing you often ponder your life decisions...(as you quickly circle the room shouting **** very loudly in your head)

 

[CliffordPope]

I am old enough to have lived through the time when screws were mostly finest slim threaded Chinesium,

You must be very young then! I remember when proper screws were steel, made in England, with traditional slotted heads, and available in a range of thicknesses from very thin size 2 for delicate work up to size 14 or much more more for heavy work.
There were grades of steel for different requirements for strength or rust-resistance, and of course brass or bronze too.
But using nails or screws in woodwork was always regarded as a bit of a bodge, a substitute for a proper joint.

 

[Cassie]

You are very welcome. Yes, nails are very difficult to fix in many situations, banging them also isn't great for surrounding lime plaster. I try to reserve my banging for knocking in noggins. There is a caveat to using screws though, there is a massive difference in quality, although recently quality has increased a lot accross the board. I have AB tested dozens of different screws and currently have about 5,000 in multiple tool boxes. Forget builders special Turbo golds... best bet is to stick with Spax. Forgefix znd Timco are other good brands I use. Spax are the most spendy but highest overal quality. Another tip, always go for torx (t star) headed fixings, I haven't used cross heads for years, torx heads are 10x better for torque and reduced cam out, also buy good bits! I use Spax, Wera or Wiha. Roberts (square drive) are good but not v common in the UK (popular in N America)

People who complain about price of fixings are pretty dense imho, a bit like using ungraded or C16 timber... saving 5p per screw doesn't seem so smart when whatever you have fixed fails I am old enough to have lived through the time when screws were mostly finest slim threaded Chinesium, through to the shiny shiny look its Gold and has a Turbo... to the modern screws that out perform nails almost all of the time.

All builders should know what Blackjack is...

Very interesting, thank you. Using cheapie screws seems to be a fools errand-I only want to do this once!

 

[bobby spray]

Thats what I've done in similar situation. Problem is getting the space to manoeuvre new piece into the wall pocket. I was fortunate that the joist ends were above the front porch and that had no ceiling at the time (and still not...) so I had a couple of feet of empty space to play with. Yours look to be above a lathed ceiling so inevitably there is going to be damage to that since the laths will be nailed into the piece that you need to cut away.

Support from below in case the joist end is still taking some load whilst you work on it. Mine weren't particularly being so rotten the ends were essentially floating, the load instead being transferred into the front door frame! Remarkably the front door showed no signs of distress...

I had 3 distinct cases:
1. pocket wide enough to accommodate sister, no idea why it was so wide, but it worked to my advantage, just slide in new section making it long enough to overlap two feet of good wood on the existing, bed it into the pocket on slate and lime mortar and bolt it on, nothing cut away.
2. pocket not wide enough, cut back at least two feet from wall, insert new piece into wall, bed in as previous, bolt sister onto new piece and existing overlapping 2 feet on both, this approach means you need at least 4 feet of access from above so quite a few rows of floor boards to lift, I cut away the existing end with a circular saw, probably not the best HSE practice being balanced on a joist above a 4m drop with the saw at an awkward angle, think about where the saw is going to go in case of kick back, preferably not into your leg, the last bit was finished with a multi-tool
3. no access to cut away because of internal stud walls (yes, could have removed them, but...), I screwed a new piece onto the existing bringing close to but not touching the external wall and attached this laterally to an adjacent joist with a dwang (noggin) on joist hangers, this is least satisfactory but its still better than what was there before, joist hangers with twist nails are incredibly strong but it means the adjacent joist taking additional load, sum of the parts and all that

No 3. might work for you given the confined space but it might still allow a bit of deflection so might not eliminate all of the bounce.

I toyed with the idea of fixing a header directly into the rubble to carry the sisters but decided that probably wouldn't get enough of a grip to be worth attempting.

Clean all the debris out of the wall pocket once you remove the rotten end. You will probably find a rotten wall plate below the joist end. Ideally the entire pocket should be packed with lime mortar to exclude any air that could carry moisture in from the warm side of the building.

New pieces that ended up in the wall were painted with creosote paint first. Use decent timber from a builders merchant, who will want to sell it to you in 4.8m lengths but should also be willing to cut it to size to make it easier to transport if needed. I jury rigged supports from several 4x2's screwed together and used a car jack to just lift the joist before working on it.

I used 12mm stud bar cut to length with an angle grinder, dogs tooth washers between old and new sections to prevent movement in the joint and 50mm x 3mm spreader plates under the nuts. 3 sets of bolts either side of the join, offset a couple of inches from top and bottom and positions alternated. There are websites with tables of sizes for where the bolts should go for this sort of exercise (link is in my other browser, I'll dig it out if wanted). I already had big 19mm spanners for the car to do it up with. All the ironmongery is readily available from SF or TS.

Its a fairly involved job so maybe worth getting a "professional" in unless you are very confident of your ability. This was stretching me about as far as I've gone in terms of structural stuff so I was a bit apprehensive, but it all went absolutely fine. My major worry was the very nice original cornice in the hallway below but it didn't appear to suffer. Just remember that if you do get in the pros they will almost certainly turn the floorboards above and the ceiling below into match wood giving you a more significant making good job afterwards. The cracking and splintering noises coming from next door when they went through a similar exercise being evidence of that... They also won't be that fussed about protecting the new wood, cleaning out the pockets and will use cement where needed not lime. I left my supports in place for a couple of weeks to allow the mortar in the pocket to go off a bit so that the new bits stayed where I wanted them when the joist load went back on.

Btw, that looks like your meter tails running past that location (the thickest 2 wires) as well as a number of final circuits. Be aware that even with the main switch in the fuse box turned off the tails will still be live. You might have an isolator close to the meter that will knock those off.

This is a great guide and something that I have to tackle myself shortly. It appears from your username that the house I am tackling is approximately 4 miles as the crow flies from you. Strange that we should both have a rotten joist problem - must be the weather around the Gare loch!

 

[Toby Newell]

You must be very young then! I remember when proper screws were steel, made in England, with traditional slotted heads, and available in a range of thicknesses from very thin size 2 for delicate work up to size 14 or much more more for heavy work.
There were grades of steel for different requirements for strength or rust-resistance, and of course brass or bronze too.
But using nails or screws in woodwork was always regarded as a bit of a bodge, a substitute for a proper joint.

Aha, the screw fetishist awakes... yes, I remember when you could pop into Bishops in Crouch end and order ounces of your favourite treat, weighed out like pear drops and dispensed in brown paper bags...

Modern screws are much better though, the good ones at least, if maybe less attractive.

Alas, in no small part thanks to Mrs Thatcher, British Steel went from being the best in the world to non viable. We still rank up there with Japan and Sweden for the speciality stuff but the real problem was cost and the need to import coal.

For modern high performance steels sadly our high sulphur (causes embrittlement) coal isn't very good.