The ends of the floor joists that sit into your house walls will have rotted over the years and dropped slightly. You may need to have a closer inspection as to the extent of any rot and what state the joist ends are in. The main cause is usually water or damp getting the joists wet and then drying out over long periods. Packing the joists with slate to raise them to the original level is often the easiest cure if the joists are fairly decent.Otherwise it could involve bolting a fresh length of joist to the original and socketing it into the wall ensuring the end of the new length is wrapped in Damp Proof Membrane first. At worst you may have to replace the joists concerned. If it is a ground floor that's affected and you can get access under the floorboards then it may be an option to support the floor halfway across the span with two pillars of brick or blocks and a piece of joist running at 90 degrees to the rest of the joists as well as packing the ends.
Another thought,if it is on the ground level it could be the 4"x2"wallplate sitting on the sleeper wall rotted away as most of them didn't dpc in those days.
Lifted a couple of floorboards (ground floor) to reveal that parts of sleeper wall had been demolished in places to insert ducted air heating system, obviously done when house was built in 1979.Inserted wooden wedges between joists and sleeper wall to support floorboards. Really bodgy job by builders 'Leach' I think. Springiness has virtually disappeared.
No,you don't have to unless it's going into the walls and providing you've got a good air flow and it's never a waste of time if you do treat it.
Try not to get your timber from diy superstore they tend to be more dearer.Best place would a timberyard or Wickes do treated timber which don't cost a lot more.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local