Replacing joist without taking up floor

[lsx]

Hi

I’m a long time lurker but have finally decided to ask something.

I’ve got 5 joists which are suffering from rotten ends. I understand why they’ve become rotten (blocked air bricks, bridged dpc etc)

Two of the joists don’t span the full length of the room, they’re just over a metre in length… one end sits on a bearing on the side of the chimney breast, the other end sits in the front wall. Because they’re small (although 7”x3”), I’m going to replace these first. I’m trying to do this without taking up any of the floorboards as they were sanded/waxed a few years ago and I’d like to avoid damaging them.

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My thoughts are I could use a multi tool to cut the top of the joist around the clasp nails holding down the floor. And then tap the nails out of the floorboards from below after removing the joist.

My question is whether it’s realistic to be able to replace a joist like this with the floor still down? I’m wondering if I’d need to support the floor somehow (maybe with an acrow) while the joist is removed? Also is it a bad idea to use a reclaimed joist rather than a new one?

Thanks for any advice :)

[big-all]

not an option i am afraid---- remember joists sit in captive pockets on walls off a greater length than wall to wall distance
you may manage short lengths as easy to manage by manoeuvring but full length need a clear path and spare room side to side and up and down for ease off operation
now not saying its not possible but would suggest holes in outside walls and at least a few planks lifted would be a minimum requirement and perhaps 4 times the time cost and effort as a trade off

you will only ever know by working out a plan for
A removal
B working out the path for getting timbers under the floor
C working out the path to final position
a will be easy as cuttting timber is an option

[dewaltdisney]

Have a look at sistering the joists, this is where you screw a new joist to the existing increasing the strength and loadbearing. You may have to fathom out those cable runs but not too difficult possibly. I do not see a need to fix the floorboards to the added joist sections although you might need to butt them up tight tp the boards to stop any creak.

DWD

[Grendel]

What sort of access do you have to get timbers under the floor? That’s going to be your biggest problem as you may have to cut a hole in the exterior wall to feed the joist in. Other than that it’s not an impossible task. In restoration we had to do similar occasionally where the fabric of the building had to remain intact . The downside was that it took much longer and thus was more expensive. For these joists if space is limited metal plates could be used . We did that too , cutting away the rot and bolting on stainlesss steel angle plates which went into the wall. If you go with your original plan cut some shallow wedges to drive between the joist and boards to give a gap to get the saw blade in . You can cut all the nails but replace one joist at a time , that should eliminate the need for propping , just keep people off the floor . The props would more than likely be an extra impediment anyway for manoeuvring your timbers into place . At the end of the day it’s your call as to wether the time and effort is going to be better than taking up the boards and refinishing.

[stevei]

It sounds feasible but in practice there will be many problems for you to deal with: access being the main one. I would lift the boads as carefully as possible, marking each one for position on the floor. Have a look online at floor board lifting tools. A specialist tool for the job will save you damaging the boards and be time saving. You may find that removing the skirting at each end will make things easier. With the boards lifted you will be able to fit strutting to the new joists to stop bounce, herringbone strutting be the best as this transfers weight more efficiently to the adjacent joists. Check to see if you can get away with lighter joists which will save you money. They tended to be belt and braces in the old days.

[dewaltdisney]

I rather thought that this is an underboard repair as the Op does not want to rip up the floorboards as stated in his original post above.

DWD

[stevei]

If I was doing the job, I would lift the boards.

[lsx]

Sorry it's taken me an age to reply. I've been thinking (slowly!) about what you've all said.

The advice you've given has been really helpful.

On a couple of points...

Unfortunately it's not realistic to slide in joists from the front of the house as they sit behind a massive lintel/feature in the front wall. See the course below the airbricks.

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And although I would consider taking the floor up if I absolutely had to, I'd like to avoid this to keep the missus on side. Here's the floor above the short joists I need to replace.

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My preferred option is to replace each of the two short joists using a pair of sisters. So say the existing joist is approximately 1.25m long, I would cut two pieces of timber approx 1 metre in length each. One piece would slide into the wall pocket, the other piece would sit on the chimney bearing. The two pieces would sit side-by-side spanning the gap, overlapping by approx 80% of the span and would be bolted together with coach bolts.

What do you think?

The other option of replacing with metal plates sounds interesting. What has been your experience with using these? I was thinking you would need to trim the bottom of the joist so the plates fit into the existing pockets?

[big-all]

looking at the picture again
the inside sleeper wall has obviously been strengthened with a lintel to take the weight off the ends i assume 4ft away allowing the half the joist strength to be removed for i assume a large window with lintel above
working on that principal then much smaller timber section perhaps 4x2 would be sufficient and easier if it can be worked in more like a splice/sister as dwd says


but just a thought wait for others to comment

[Grendel]

Big-all I don’t think it’s a sleeper wall as such , the area looks to be more like a cellar of some sort . There looks to have been a lath and plaster ceiling at some point .
Sistering will require the pockets enlarging to make space for the new timber and the old hole filling in. Using metal is on perhaps a little more expensive in materials although there’s no real need to use stainless steel as we did in restoration it’s just that our architects specified it for everything. Galvanised is more than good enough and even mild steel well painted can be fine. It may require a little bit of work to enlarge the pocket depending on how tightly the joist are fitted. We often found that joists were packed on slate which we could remove easily to allow sliding in the new steels. Joist hangers are another option that minimises the amount of cutting into the brickwork . If you need to trim the bottom of the existing timbers to fit in an angle plate then that’s not a huge task as such , there have been times when I’ve had to cut a slot in a beam from underneath in order to insert a steel plate into the beam itself.

[big-all]

your the expert on this one so will bow out and say "what grendel says "

[lsx]

So the house has a full-length cellar split into two rooms. At the back of the house you can exit the cellar at ground level, but at the front ground-level is mid-way up the wall.

I've added the approx position of the joists on to the photo of the front of the house. The ones that have rotten ends are the red ones.

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There used to be a lath and plaster ceiling, but I've removed most of this as I'm looking to insulate the ceiling before winter comes.

Some of the joists are packed on small pieces of stone to adjust for the varying dimensions on each joist.

Here's a better photo of what I've referred to as the chimney. It's not actually a chimney breast until the floor above.

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I have a trim router I was thinking I could use to create rebates on a joist for metal plates to sit into.

I was considering the kind of sistering where you chop the joist at some point back from the wall, remove the old joist from the wall pocket, insert a new piece of timber into the wall pocket then bolt sisters either side of the join. I'm not sure how using metal plates compares in difficulty to sistering for a first timer?

[Someone-Else]

Just saying................ after a few years of being here, we found we had a rotten joist in the kitchen..............

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So we opted to have the floor taken out, much easier. (I know you said you have a nice floor, but we had a nice kitchen, taking the floor out was easier and better) and we now have a trap door. (Just need to get sound proofing.)

[dewaltdisney]

Just stand back a minute and think this through. Much will depend on the loading on the floor, especially if there is a partition wall sitting on a span (I doubt this) It does not look like the joists are only supporting the floor, and that they do not appear to be supporting anything but that. Therefore your issue is the rotting ends of the joists and whether these might fail in the future. I was thinking originally that it would be easier to chop out the joist sockets to accommodate the sistered joist. if this is too difficult then I would consider 10mm Mild steel angle about £50 for a 1.5m length screwed under the joist to give it support see https://www.themetalstore.co.uk/product ... NzU5ODczMQ..

Sees if Grendel sees this and look for his comments, he knows this work best on here.

DWD

[Grendel]

So the house has a full-length cellar split into two rooms. At the back of the house you can exit the cellar at ground level,
I have a trim router I was thinking I could use to create rebates on a joist for metal plates to sit into.

I was considering the kind of sistering where you chop the joist at some point back from the wall, remove the old joist from the wall pocket, insert a new piece of timber into the wall pocket then bolt sisters either side of the join. I'm not sure how using metal plates compares in difficulty to sistering for a first timer?

If you have access to the cellar at the rear then that should make life easier getting materials down there. I see what you mean with regards to the sistering and I’ve done it that way myself as well both with timber and with metal plates. The timber first , pros are it probably being a bit cheaper and possibly easier to source. Cons , it should really be treated and any timber going into the wall I’d wrap with dpm material. The rot probably occurred because the joist are pretty much at ground level and are liable to become damp. Timber can be a bit more awkward with regards to drilling. The joists are probably around 16” centres so perhaps 13” or so i between take off the thickness of the new timber and you’re left with a space nearer 11” . You”ll need an angle drill ideally to get the bolts in straight although there have been times when I’ve had to drill the holes at an angle. We normally used all thread for bolting.
Metal plates are probably dearer but I some ways easier . They can be the angle that dwd mentioned and probably would be better if the joist is supporting something else. Whether you chop it into the timber is up to you really . If you are replacing the ceiling then perhaps do so or pack down to take the plasterboard if height isn’t an issue . If the joist is just supporting the floor then simple flat plates would be more than adequate , think big long gang nail plates , and they can be screwed or bolted. You’ll probably still need an angle drill but you’ll have more room to play with.
By the way The Metal Store that dwd linked to are decent enough , I’ve used them in the past . Helpful if you have questions , quick delivery and no mistakes that I’ve noticed . Not expensive I felt and they gave me a free tape measure to boot..