Bowed suspended floor

[DamonCav]

Hi all, So I have been looking into having out floor leveled, in our 1905 converted flat. We are on the second floor, and there seems to be a large bow on the floors. From the research i have done, it would seem that the best possible course of action is to lift the existing floor boards, check to see what has caused the Bow. As it could just be age of beams or something worse. Then depending on what’s the problem, repair. From my limited research is if teh bow is just age related, I could get away with just having the joist sistered, to level them up. I have take a few measurements, from the center of the room to the exterior walls, it seem to be difference of 40mm. This difference run all the way through to the next room. There does seem to be drop on the joining wall with the flat next door, which is about 1cm down. So my question is what would you advice be on best course if action, and also how long and big do we estimate the work to be. room size is 4.2m by 5.8m

 

[Cubist]

Please clarify; does the floor concerned merely slope from one side to the other OR is there a section of the floor that is lower than all the sides - in other words it has a genuine dip.

There are different treatments for these two conditions and there are issues and options within each that will have a potentially dramatic effect on the work content, timescale and cost.

 

[DamonCav]

In bow’s from the exterior walls inwards. So there is a dip of around 40mm. Where is room bows downwards from the side exteriors side walls to middle of the floor. Not sure if i have answered correctly. If i place a level line across the floor. the floor away from teh exterior wall is 40mm lower than the height of the floor at the exterior wall.

 

[Cubist]

To confirm my understanding, the floor slopes down by 40mm from an exterior wall to an internal wall.

Is this slope uniform along the full length of the room? And in which direction do the floorboards run; parallel to the external wall or at right angles to it?

Is this internal wall a brick structure that continues down through the flat below yours to the ground?

What is immediately behind the internal wall? A hallway between the rooms of your flat or a stairway to your neighbours flats above and below?

Sorry for the additional questions but I'm trying to assess the level of difficulty involved in rectifying the problem.

 

[DamonCav]

To confirm my understanding, the floor slopes down by 40mm from an exterior wall to an internal wall.

Is this slope uniform along the full length of the room? And in which direction do the floorboards run; parallel to the external wall or at right angles to it?

Is this internal wall a brick structure that continues down through the flat below yours to the ground?

What is immediately behind the internal wall? A hallway between the rooms of your flat or a stairway to your neighbours flats above and below?

Sorry for the additional questions but I'm trying to assess the level of difficulty involved in rectifying the problem.

 

[DamonCav]

I would say yes it is fairly uniform across the room. It is not wavy. So starts at a point and gets worse as we go along. I hope the diagram helps. I did take other points of measurement to test that it is dropping along the walls.

 

[Cubist]

Thank you for the diagram above. This is helpful and its possible to say that levelling this main floor should be possible BUT there are several issues that you need to carefully consider before proceeding.

1. Sistering the joists - would not be advisable or perhaps even safe.
   1. The sistering approach would need to employ an additional timber of at least 50mm x 150mm cross section dimensions for each joist beneath the floor. These new timbers would add considerable extra weight to the floor which could induce further sinking of the floors structure, induce cracking of the ceiling in your neighbours flat below and could threaten the floor with collapse in part or whole.
2. The better approach, and the one that adds the least extra weight to the floor, would be the use of 'firrings'.
   1. Firrings are ostensibly long wooden wedges that are installed directly above each joist to add extra height where it is needed.
   2. These are cut from a single piece of wood, the same length as the joist, with the start of the cut set at 35mm and reducing to 0mm at the end to form the wanted long wedge shape.
   3. Cutting the needed firrings is best conducted by a joiners shop using suitable industrial equipment.
3. Your floor seems to also have a low section adjacent to the exterior wall and between the high spots (0mm) at the returns into the room.
   1. This too can be handled with firrings to level up this side of the room.
4. Given that the room in question opens on to a hall or passage that connects to other rooms the floor will at present run contiguously through to those spaces without hindrance. This presents the first major problem because in levelling the one floor we are discussing here any method you might choose would create a 35mm high step at the threshold into/from this room.
   1. Clearly this would pose a trip hazard;
      1. Either the new floor height must be continued into the hall/passage area and the adjoining rooms,
      2. Or, the trip hazard must simply be accepted.

Regardless of method there are other considerations that must be borne in mind.

1. The room must be emptied of any furnishings and valuable fittings must either removed or protected during the period of the work.
2. All skirting boards and floor length architrave around doorways must be removed.
   1. This can result in damage to the plasterwork and decoration and perhaps also the loss, through damage/destruction, of the skirting and architrave mouldings themselves.
3. All the floorboards would have to be lifted and de-nailed if they are to be re-used and stored while the firrings are installed over the joists.
4. Any new materials needed for the floor would need to be transported and stored indoors ready for use.
5. Two to three elapsed weeks assuming a team of two people would be required to complete the work and restore the decoration.

Cost of materials would depend on whether the extant floorboards could be re-used but a new hardwood floor for that area would start at around £3-4K and a minimum spend of £1-2K for the firrings timber and incidentals.

 

[DamonCav]

Thank you for the diagram above. This is helpful and its possible to say that levelling this main floor should be possible BUT there are several issues that you need to carefully consider before proceeding.

1. Sistering the joists - would not be advisable or perhaps even safe.
   1. The sistering approach would need to employ an additional timber of at least 50mm x 150mm cross section dimensions for each joist beneath the floor. These new timbers would add considerable extra weight to the floor which could induce further sinking of the floors structure, induce cracking of the ceiling in your neighbours flat below and could threaten the floor with collapse in part or whole.
2. The better approach, and the one that adds the least extra weight to the floor, would be the use of 'firrings'.
   1. Firrings are ostensibly long wooden wedges that are installed directly above each joist to add extra height where it is needed.
   2. These are cut from a single piece of wood, the same length as the joist, with the start of the cut set at 35mm and reducing to 0mm at the end to form the wanted long wedge shape.
   3. Cutting the needed firrings is best conducted by a joiners shop using suitable industrial equipment.
3. Your floor seems to also have a low section adjacent to the exterior wall and between the high spots (0mm) at the returns into the room.
   1. This too can be handled with firrings to level up this side of the room.
4. Given that the room in question opens on to a hall or passage that connects to other rooms the floor will at present run contiguously through to those spaces without hindrance. This presents the first major problem because in levelling the one floor we are discussing here any method you might choose would create a 35mm high step at the threshold into/from this room.
   1. Clearly this would pose a trip hazard;
      1. Either the new floor height must be continued into the hall/passage area and the adjoining rooms,
      2. Or, the trip hazard must simply be accepted.

Regardless of method there are other considerations that must be borne in mind.

1. The room must be emptied of any furnishings and valuable fittings must either removed or protected during the period of the work.
2. All skirting boards and floor length architrave around doorways must be removed.
   1. This can result in damage to the plasterwork and decoration and perhaps also the loss, through damage/destruction, of the skirting and architrave mouldings themselves.
3. All the floorboards would have to be lifted and de-nailed if they are to be re-used and stored while the firrings are installed over the joists.
4. Any new materials needed for the floor would need to be transported and stored indoors ready for use.
5. Two to three elapsed weeks assuming a team of two people would be required to complete the work and restore the decoration.

Cost of materials would depend on whether the extant floorboards could be re-used but a new hardwood floor for that area would start at around £3-4K and a minimum spend of £1-2K for the firrings timber and incidentals.

Thank you very much to the detailed reply. If I did the 1 room, i would continue through to the room next door, so the full floor would be done. I gave full details on the 1 room as it is quite empty with furniture at the moment so it made it easier to get more detailed measurements. The basic measurements done to the next room past the staircase seem to start off at the 35mm as well. I assume the gap would decrease i got closer to the exterior wall.

Based on what you have detailed, it would seem that most of the work could be done by a decent DIY’er. The part which would require specialised work would be the fairings.

As a question, would you have a rough guideline on pricing for this. The assumption is that each room is 4.2m by 4.7m, the current floor boards run parallel to the staircase. So I assume this would mean that the joist run from room to room.

 

[Cubist]

I suspected as much and the problem you're seeing is not uncommon. You could reasonably expect too that the height of the floor at the far wall will be pretty close to that of the nearest external wall in your diagram. Its hard to say what the firrings might cost but the joiners shop would cut them from a wide stock plank so it should not be more than say had a days work and three or four suitable planks of a 50mm thick timber. Worst case maybe £500, but I'm guessing now.

 

[DamonCav]

Thank you, that does seem too bad.