With a laser set a standard datum level to work off (arbitrary, but normally something like 1 metre above the highest point on the floors). Mark the datum in each room on the wall opposite the door, and on the landing. Doors, skirtings and architaves off. Lift floor. Set up the laser in the doorway - you need to work towards the laser starting at the furthest point away from it. Screw sistering timbers (3 x 2 or 4 x 2 will often do on terraced houses) to the sides of the existing joists starting at the far corner of the room and working towards the doorway and laser. To set the sistered timbers a marked lath is used (say 1.2 metre long accurately marked with a line, using a try square, at the 1 metre PLUS THICKNESS OF THE FLOOR (say 22mm) up from the bottom. This rod is used to set the sistering timbers at the right height. Screw the sistering timbers to the sides of the joists at 400 to 600mm centres. These new timbers will subsequently carry the floor. When the rooms are done, do the landing. Refloor the area. Refix the architraves and skirtings. Trim the bottoms of the doors to match the new floor levels - allow a 4 to 6mm gap beneath (more if a thick carpet). Don't try to do this by messing about with packers or wedges - it takes longer, is a less flat floor and stacks of packers have been known to shiftMy mate said he will have a go at straightening the floor himself.
Not sure how difficult that is. Anyone had a similar issue to resolve upstairs and how did you tackle it?
With a laser set a standard datum level to work off (arbitrary, but normally something like 1 metre above the highest point on the floors). Mark the datum in each room on the wall opposite the door, and on the landing. Doors, skirtings and architaves off. Lift floor. Set up the laser in the doorway - you need to work towards the laser starting at the furthest point away from it. Screw sistering timbers (3 x 2 or 4 x 2 will often do on terraced houses) to the sides of the existing joists starting at the far corner of the room and working towards the doorway and laser. To set the sistered timbers a marked lath is used (say 1.2 metre long accurately marked with a line, using a try square, at the 1 metre PLUS THICKNESS OF THE FLOOR (say 22mm) up from the bottom. This rod is used to set the sistering timbers at the right height. Screw the sistering timbers to the sides of the joists at 400 to 600mm centres. These new timbers will subsequently carry the floor. When the rooms are done, do the landing. Refloor the area. Refix the architraves and skirtings. Trim the bottoms of the doors to match the new floor levels - allow a 4 to 6mm gap beneath (more if a thick carpet). Don't try to do this by messing about with packers or wedges - it takes longer, is a less flat floor and stacks of packers have been known to shift
A word about stairs: the going of the stairs needs to be fairly constant. In fact there is a requirement that a tread should be within 6mm+/- the height of the preceding/following tread. If your new floor ended up =, say 25mm above the level at the top of the stairs, on a 12 tread staircase you'd have to raise the height of the treads using thin plywood or MDF s"skins" fixed to the top of the treads to give a progressive change. In fact this would mean something like 22mm on the top tread, 19mm on the tread below, 16mm on the tread below that (so far all standard plywood thicknesses), then 13mm, 10mm (9,5mm), 6mm (6.35mm) and 3mm respectively (so a transition over 7 treads). The rest of the treads would remain as was. This transition is a lot safer tham having one or two non-standard steps near the top and is much less of a trip risk
I have undertaken this task a few times as part of my "day job", and that is more or less what I do. It is a lot of work, but with a laser it is well within the capabilities of a keen, competent DIYer
Not all the floor is slopping. Its confined to the landing area and part of the floor the other side of the landing wall in the bedroom (see pic above with lots of cut floorboards in a row, first post, first page).
Thanks
As earlier (and obvious from the video walkthrough!), those floorboards run under the wall, I don't know what @JobAndKnock thinks, but would it be better to take the wall down and rebuild?
View attachment 277687
Better to take the skirtings, etc out, then a part of the floor, do the levelling work and make good. Taking out a stud wall completely is potentially an awfully messy procedure, especially on an older house. As that stud wall runs in line with the joists it may well be necessary to take the floor out piecemeal in the vicinity of the joist, inserting solid strutting as you go between the joists adjacent to the wall in order to carry the weight of the wall
Shimming is a PIA to do and is almost possible to do right, and it will always tend to have issues, such as the shims moving in service. It is a complete and utter bodge. Sometimes you just have to take the hit and do things a bit better.
BTW, self levelling can be contained by a temporary "dam" of, say, 2 x 1 softwood lath screwed to the edge of the landing ans the joint siliconed. It might even be better to add a permanent fascia (say a rip of painted 8mm MDF or the like with the top set to the required floor height at it's top edge) before putting down the SLC