Re-levelling first floor joists - Lift vs drop joists? Do nothing at all?

[JamesSmith79]

Hi folks,

I have an admittedly crackpot idea to level the first floor in a doer upper I have. There was a significant leak some years ago in the property which caused the center to settle a couple inches but it has since been underpinned there with mass concrete etc well before me.

The issue I am having is sloping floors upstairs. The drop is up to ~70mm at worst (Probably over 4m). Under foot it actually doesn't feel the worst but as I am doing a full renovation here I thought now would be the time to sort or never at all.

 

I have looked up all options related to sistering, shims etc. One idea that was proposed to be was to make the high sides (external walls) lower as opposed to the other way around. The joists are all pocketed into the block cavity and mortered in. Then the other ends are pocketed into an internal 100mm block wall that goes up to second floor ceiling (5m or so) The idea is essentailly to cut pockets below every joists and drop the joist down. This will lower the floor and even out the slope.

 

Bar that one block wall in the middle, all the others are partition stud, so either should fall with the floor or stay on the ceiling. Both would be repairable.

 

Is this absolutely an off the wall idea or possible?

 

This is idea A, idea B is even more drastic. This 10m wide, 5m tall wall is holding the first floor joists so lifting the joists is impossible. What if a consaw was used to cut near the ground floor ceiling. Obviously using acrow/strong boys to support as we go. This would unlock the wall and joists above. Now we have an 8ft wall below and an 8ft above. Then from below we could jack up the first floor joists and wall....somehow.

 

My crude drawing. Two external cavity walls with one standard internal 5m (Both floor) block wall.

https://freeimage.host/i/FAZOkEx

 

 

[Gus Potter]

@JamesSmith79

1 hour ago, JamesSmith79 said:

I have an admittedly crackpot idea to level the first floor in a doer upper I have.

This is the great thing about BH when folk like you come up with ideas. It's not "crackpot".. it's just you asking a perfectly reasonable question. 

 

1 hour ago, JamesSmith79 said:

all the others are partition stud, so either should fall with the floor or stay on the ceiling. Both would be repairable.

Ah.. but the building has probably settled a bit and the roof timbers are used to the loads.. you need to look at all the load paths and how they might change when you drop the timbers

 

As a heads up..  it's an old roof, maybe the nails and fixings are corroded. You are going to change the load paths and change the stress pattern. 

 

While in principle your idea is good you need to look at the knock on effects. 

 

Your idea is elegant.. provide you can justify it is not overloading other parts.. call that unintended consequences. 

 

You mention "strong boys" For all on BH these tend to have a maximum working load rating of 350 kg or less.. which is not a lot! I can tell you as an SE that a lot of builders have no idea how llittle load these can carry! Always ask a builder if they know what they are doing when they mention strongboys!

Edited June 27 by Gus Potter

[ETC]

Why don’t you just lift the boards and put firing pieces on? Simpler and cheaper.

[JamesSmith79]

Thanks for the comment Gus!

 

You are absolutely correct, the building has almost certainly settled a bit. I don't believe ONLY the center went down in the last 50 years, the external walls must have settled even a fraction over the last 50 years.

 

If I went with idea A (Cut pockets under joists into external wall(s) cavity leaf so joists drop down.) I can't see how any load paths would change too much. This is on the presumption of all the partition stud walls upstairs not actually bearing anything and only this centre block ground-to-roof bearing wall.

 

Now idea B is where load paths definitely shift. This central bearing masonry wall will literally be lifted roughly 60-70mm at worst. There is a beam directly on the end of this wall in the roof so an element of the roof would raise.

 

A further element complicating all of this is two presumptions; A) That the house was ever 100% level. Were all walls always totally level? Were joists level? and B) determining where everything is right now. If the back external cavity wall is down 20mm itself as an example, then this has to somehow be factored into idea B if any lifting was to be attempted.

 

Say I could somehow calculate this, even attempting idea B would be tough.

 

Disconnecting the top half of the wall from the bottom would be the easy bit, how would one even lift? One dea would be to just put a beam adjacent to the wall under the joists and lift. This though is relying on the 2" of 7x2" on 12" centres literally lifting an 8ft wall above, not to mention the portion of the roof, the joists etc. 10m width/304mm centres is 32/33 joists for the length of the house. That is roughly 1700mm of joist end coverage width "touching" the wall. So jacking the joists would mean lifting directly 17% and hoping it will take it all. Thats not taking into account the strength of the wood, how deep its actually pocketed into the wall etc.

 

Another option would be to support the cut wall above (With a lot of stongboys!) and every x m pocket in a bottle jack into the lower wall to directly lift above. 

 

 

[JamesSmith79]

4 minutes ago, ETC said:

Why don’t you just lift the boards and put firing pieces on? Simpler and cheaper.

 

Thats absolutely an option but for a 70mm lift, surely that will make things tough with doors etc. Everything will have lost 70mm at floor at the lowest point. This just so happens to be where the doors are. There are a few doors in this masonry center wall. How would one rise those 70mm?

 

I actually thought the idea of dropping joists on one end could be cheaper and quicker but probably not. If this was easy other people with similar issues would do it. I haven't seen any example online of dropping down joist ends!

[Gus Potter]

2 minutes ago, ETC said:

Why don’t you just lift the boards and put firing pieces on? Simpler and cheaper.

Agree. 

 

From an SE view the roof will be restraining the old walls. Once you start to muck about you could break these established bonds and risk things starting to move. 

 

When working on old buildings we need to be careful that when we stengthen things we don't inadvertently cause harm. 

[ETC]

Once stayed in a hotel/b&b in Canterbury - not a level floor in the whole building - was grand.

[Nickfromwales]

3 minutes ago, ETC said:

Once stayed in a hotel/b&b in Canterbury - not a level floor in the whole building - was grand.

I stayed a good few times in the Chapter House in Salisbury, a proper steak house to say the very least.

~13th century building, and the staircase going up to the rooms was like that perpetual staircase where you seem to go down or sideways and not up! Great if you don't want a drink as just walking up the staircase to the room makes you feel like you've had 9 pints  

 

If anyone likes steak, and you're passing by there, go get some of the best beef you'll ever eat  

[ProDave]

We once tried to buy a wooden bungalow with a subsidence issue years ago.  It looked like the subsidence had stopped and it had been re roofed with a custom cut roof that corrected the previous wonky roof but the building had been left with one outside wall that had clearly sunk leaving one room with a sloping floor.

 

Our plan would have been level that floor and do nothing else, and in the longer term it would have been knock down and rebuild.  But we were outbid and it sold for more than we though it worth.

[Temp]

Would dropping the joists at the outer ends put stress on any wiring or pipe work?

[Nickfromwales]

3 hours ago, Temp said:

Would dropping the joists at the outer ends put stress on any wiring or pipe work?

I tried jacking a floor up like this before, and it was like fighting against dark matter. After decades and decades of progressive deflection, you just cannot fight natural timbers et-al back into shape over a long weekend. Give it up IMHO.

 

Furr the tops of the joists and pack & level the ceiling and re-board. Sistering the joists is my favoured method of levelling up a 1st floor bathroom floor before installing a new wet-room / level floor for tiling etc, and that is usually the best option. 

 

If the floor is say 50mm out end to end, I will sister the high end with the new timber 25mm down, and glue and screw the joists together to act as one, and then electric plane the original timber down to meet the new. Moving one end to take up the 50mm.......not whilst I have a hole in my box of holes.

[Dave Jones]

could just accidentally burn the place down and get a new one!

 

https://www.bbc.co.uk/news/uk-england-stoke-staffordshire-68414524

 

[JamesSmith79]

On 30/06/2025 at 00:15, Nickfromwales said:

I tried jacking a floor up like this before, and it was like fighting against dark matter. After decades and decades of progressive deflection, you just cannot fight natural timbers et-al back into shape over a long weekend. Give it up IMHO.

 

Furr the tops of the joists and pack & level the ceiling and re-board. Sistering the joists is my favoured method of levelling up a 1st floor bathroom floor before installing a new wet-room / level floor for tiling etc, and that is usually the best option. 

 

If the floor is say 50mm out end to end, I will sister the high end with the new timber 25mm down, and glue and screw the joists together to act as one, and then electric plane the original timber down to meet the new. Moving one end to take up the 50mm.......not whilst I have a hole in my box of holes.

 

Just for peoples information, I am looking to jack the low side or drop the high side as the joists are straight, but sloped due to the subsidence of the internal wall. 

 

Also bear in mind my property is old but not period old, built in the early 80s.

 

All that being said, you're probably right about the firring. The thought of trying to take up all the t&g boards without damage is awful though. Also it would be lovely to have the ceilings downstairs level. Although saying that you dont notice the 70mm difference...unless you get out the laser I suppose.

 

I think looking for perfection here will just send me mad

Edited July 2 by JamesSmith79

[JamesSmith79]

Hi all,

 

I just wanted to update this post with what we decided. In the end we decided to go down the route of dropping joists at the high ends. Depending on the joist run per room, it involved bringing down the level on internal block walls and the external cavity.

 

It has been very successful for my house and the upstairs rooms we have completed have been transformed. In the end we more or less levelled (Within 15/20mm) four rooms upstairs. The largest drop we made was around 100mm on an end of one room

 

This method is really only possible if you are completing a full renovation on a house. This is also heavy, dusty (To say the least) work that takes time and patience. There is a lot of making good required. I have attached pictures of some of the rooms!

 

If anyone wants to go down this route, here are the very rough steps that were followed:

 

Pre-requisite steps:

a) Its obviosuly imperative to set up acrows and headers along the end of each joist run you are bringing down.

b) All radiators in each upstairs room you are lowering upstairs MUST be removed/disconnected. The plumbing will drop as the floor drops.

c) Toilets will be difficult. Its likely the toilet waste will be directly through the external wall and this would have to be disconnected etc. In my case, I ignored the toilets.

d) Be VERY CAREFUL where you are working on joists above sockets, light switches etc. There will be a conduit just to the left/right so you must be accurate.

 

General steps:

a) Decide exactly what your new "level" is. This will most likely be the lowest point of the floor.

b) Map out all of the joist runs per room.

c) Use a laser to exactly calculate the drop required. This will be at the other end of the room, again depending on the joist run.

d) Mark datums on your walls on the ground floor. Using these confirm the drop previously calculated off the floorboards, now off the ceiling.

e) Once confirmed, mark your drop required below the ceiling downstairs.

f) Run a chalk line from the end of the room/end of the joist run to where you plan to drop to. This may not be the end of the room downstairs.

g) Using a tool (Oscillating multitool was cleanest for me) cut the ceiling at the intersetion tot he wall.

h) Find and mark all joists along each wall that you want to drop. Easiest method is to use the dull edge of a saw to hit against each. You want to mark the outline of where you want the joist now to be below.

I) Using a LIGHT sds drill and a 12/14mm bit you can stitch drill around this line. Its very important to come about 15mm lower/wider than needed. 

J) Using a chisel bit you can now get through the plaster/block. Its very important to try to keep the drill level as otherwise you may not take out enough material. The above 15mm rule was from experience.

K) As you go along from hole to hole, each hole will get progressivelly smaller. Its imporatant when the drop required is small (Say 10mm), the hoel should be at least double. Otherwise its impossible to drill and pack later.

L) If you are working on the inner leaf of an external wall, its important to be more accurate and try to not allow too much block to fall into the cavity. 

M) Once you are finished with each hole on one wall, make sure there is no debris left.

N) We are now ready to drop t he floor. Once again the edges of ceiling must be detatched from the wall/plaster as the lowering will simply take chunks out of the ceiling.

 

Lowering:

A) Slacken off the acrow at the edge of the room above where the most amount of drop is requied. This needs to be done very slowly.

B) Go to said room upstairs, walk around and you should hear creaking, popping etc.

C) The floor will slowly drop down.

D) At external walls its possible the floorboard edges will catch against mortar under from when the house was being built up. If so, use an oscillating tool to remove some of the floor boards along that wall. Really this might only be 10-20mm.

E) The stud walls for us were nailed to the floor boards and just had to be levered with a nailbar. In our case they stayed attached tot he ceiling/roof joists.

 

Once one wall is lowered and you are happy, you can move to the wall adjacent in the room. Once you have the room where you want it upstairs, you can tighten the acrows. Now we will go back, clean out all of the holes again as some debris might have fallen.

 

Resupporing joists:

A) A good 3:1 strong sand/cement mortar is the bed I chose for these joists. 

B) Its important to use SBR in this sand/cement also.

C) First prepare each hole you are working on with a watered down sbr to improve adhesion.

D) Pack below the joist with your semi-dry sand/cement.

E) Its very important to go slowly and use small tools to make sure you are getting the full 100mm block bed for the joists. Internal walls are easy as you have access both sides.

F) This sand/cement should be rock hard after a day.

 

Now the acrows are removed and you are finished. Now the holes above the joists must be made good. That is my next step. Also any gaps around the side of the joists at the external wall also need to be filled if even just to reduce drafts. We also have large gaps below stud walls between rooms that we are making good with 3x2/3x3 treated timber etc.

 

Still cannot believe I went this route, but at least it worked! 😅

 

Pictures below are of a pre-dropped room downstairs and a post-levelled room upstairs.

 

Edited August 31 by JamesSmith79

[Nickfromwales]

2 hours ago, JamesSmith79 said:

Hi all,

 

I just wanted to update this post with what we decided. In the end we decided to go down the route of dropping joists at the high ends. Depending on the joist run per room, it involved bringing down the level on internal block walls and the external cavity.

 

It has been very successful for my house and the upstairs rooms we have completed have been transformed. In the end we more or less levelled (Within 15/20mm) four rooms upstairs. The largest drop we made was around 100mm on an end of one room

 

This method is really only possible if you are completing a full renovation on a house. This is also heavy, dusty (To say the least) work that takes time and patience. There is a lot of making good required. I have attached pictures of some of the rooms!

 

If anyone wants to go down this route, here are the very rough steps that were followed:

 

Pre-requisite steps:

a) Its obviosuly imperative to set up acrows and headers along the end of each joist run you are bringing down.

b) All radiators in each upstairs room you are lowering upstairs MUST be removed/disconnected. The plumbing will drop as the floor drops.

c) Toilets will be difficult. Its likely the toilet waste will be directly through the external wall and this would have to be disconnected etc. In my case, I ignored the toilets.

d) Be VERY CAREFUL where you are working on joists above sockets, light switches etc. There will be a conduit just to the left/right so you must be accurate.

 

General steps:

a) Decide exactly what your new "level" is. This will most likely be the lowest point of the floor.

b) Map out all of the joist runs per room.

c) Use a laser to exactly calculate the drop required. This will be at the other end of the room, again depending on the joist run.

d) Mark datums on your walls on the ground floor. Using these confirm the drop previously calculated off the floorboards, now off the ceiling.

e) Once confirmed, mark your drop required below the ceiling downstairs.

f) Run a chalk line from the end of the room/end of the joist run to where you plan to drop to. This may not be the end of the room downstairs.

g) Using a tool (Oscillating multitool was cleanest for me) cut the ceiling at the intersetion tot he wall.

h) Find and mark all joists along each wall that you want to drop. Easiest method is to use the dull edge of a saw to hit against each. You want to mark the outline of where you want the joist now to be below.

I) Using a LIGHT sds drill and a 12/14mm bit you can stitch drill around this line. Its very important to come about 15mm lower/wider than needed. 

J) Using a chisel bit you can now get through the plaster/block. Its very important to try to keep the drill level as otherwise you may not take out enough material. The above 15mm rule was from experience.

K) As you go along from hole to hole, each hole will get progressivelly smaller. Its imporatant when the drop required is small (Say 10mm), the hoel should be at least double. Otherwise its impossible to drill and pack later.

L) If you are working on the inner leaf of an external wall, its important to be more accurate and try to not allow too much block to fall into the cavity. 

M) Once you are finished with each hole on one wall, make sure there is no debris left.

N) We are now ready to drop t he floor. Once again the edges of ceiling must be detatched from the wall/plaster as the lowering will simply take chunks out of the ceiling.

 

Lowering:

A) Slacken off the acrow at the edge of the room above where the most amount of drop is requied. This needs to be done very slowly.

B) Go to said room upstairs, walk around and you should hear creaking, popping etc.

C) The floor will slowly drop down.

D) At external walls its possible the floorboard edges will catch against mortar under from when the house was being built up. If so, use an oscillating tool to remove some of the floor boards along that wall. Really this might only be 10-20mm.

E) The stud walls for us were nailed to the floor boards and just had to be levered with a nailbar. In our case they stayed attached tot he ceiling/roof joists.

 

Once one wall is lowered and you are happy, you can move to the wall adjacent in the room. Once you have the room where you want it upstairs, you can tighten the acrows. Now we will go back, clean out all of the holes again as some debris might have fallen.

 

Resupporing joists:

A) A good 3:1 strong sand/cement mortar is the bed I chose for these joists. 

B) Its important to use SBR in this sand/cement also.

C) First prepare each hole you are working on with a watered down sbr to improve adhesion.

D) Pack below the joist with your semi-dry sand/cement.

E) Its very important to go slowly and use small tools to make sure you are getting the full 100mm block bed for the joists. Internal walls are easy as you have access both sides.

F) This sand/cement should be rock hard after a day.

 

Now the acrows are removed and you are finished. Now the holes above the joists must be made good. That is my next step. Also any gaps around the side of the joists at the external wall also need to be filled if even just to reduce drafts. We also have large gaps below stud walls between rooms that we are making good with 3x2/3x3 treated timber etc.

 

Still cannot believe I went this route, but at least it worked! 😅

 

Pictures below are of a pre-dropped room downstairs and a post-levelled room upstairs.

 

Thanks for the comprehensive reply.