Repairs: floors and flooring

Problem 2: Undersized floor joists

The floor joists in older properties, especially pre-1880 or thereabouts, are frequently undersized when compared with modern building standards. To make matters worse, occupants now tend to have more furniture (in the case of dwellings) or more boxes and filing cabinets (to store records in case of future litigation) in the case of commercial properties.

Joist hangers are sometimes retrofitted to provide support for new doubled-up joist timbers inserted midway between the original joists to help redistribute the floor load.

But a steel angle shelf is a means of providing added bearing surface to the existing joists at the same time and may be preferred, especially if there is a risk of hidden joist end decay. This can be used in a similar manner to that shown in Problem 1, Solution 2.

Cost sequence - First floor joist repair/support

Assumes first or second floor joists can be improved with no special access requirements.

Assumes that screw-jack support can be installed from the ground to first floor with no requirement for special/additional reinforcement apart from timber spreader plates.

For first floor joist repair:

  1. Screw-jack supports installed at 2m centres to about 1.5m back from the joist ends/wall with timber spreader plates taken across ground floor and at ceiling level to provide temporary support to the floor.
  2. Break out ceiling finish up to 1m from the existing wall/joist bearings.
  3. Floorboards and floor covering to be carefully removed 1.5m or more away from the floor above to expose top and bottom of the joists. Carefully set aside for reuse.
  4. Carefully cut away decayed joist ends. Allow for removal of any decayed waste joist ends within voids in the wall.
  5. Plate up decayed joist ends and allow for new sections of timber, say 1.3m in length bolt fixed along side the origianl joists with minimum no. 4 bolt fixings (assumes use of engineering stud bolts, washers and nuts on each side).
  6. Minimum stud bolt size: M15
  7. Sleeve PVC damp-proof course material across the joist ends to prevent any contact with damp solid wall surfaces.
  8. Slide in steel angle shelf with minimum 75mm bearing edge for the new joist ends.
  9. Assumes new supporting stud bolts are socketed into the wall at 400mm centres, secured in resin fixings with steel angle shelf bolted in place. (Fixing positions will need to be adjusted to fit around assumed 400mm joists centres.) Structural engineer to calculate/verify fixity method, if any doubt as to masonry support capacity. Not included in this costing.
  10. Replace skirting boards and floor boards above and screw back down onto floor and allow for any flushing off and any tidying up.
  11. Remake repaired ceiling finish below. Allow for 12.5mm plasterboard with joints set and flushed. Allow for 2 coats matt white paint to entire ceiling of assumed area 25m2.

First floor joist repair - cost £1,400

Small works pricing

Since the original price estimating in 2008 the economic turmoil of the last few years has caused some disparities in pricing - if you are reviewing these figures in the London area they may look laughable - if you are located in Hull they might still look a bit expensive. Please treat them with caution and of course always consider obtaining more than one quote against which to test prices. Reference to the BCIS or a small works pricing book such as Spons or Laxton's will help assess costs and the hourly labour rates upon which they are based.