replacing floor joists

Replacing floor joists Begin by taking up all the boards fixed to the joist. lf the joist is in an upper storey, you will need to free the ceiling below by pressing gently on top of the ceiling to push the fixing nails down. One way of finding these nails is to push a very thin blade under the joist and move it along until the nails are located. If the ceiling is made of lath and plaster you will probably have to cut a large area, if not take down the whole lot. lf the replacing floor joists joist is supported at its end on joist hangers, or fixed to the top of a wall, it can be lifted clear. The new joist, which obviously should be of the same size as the old, can then be dropped into place.


Should the joist be resting on wall plates, withdraw any fixing nails, then once again remove it and tit the new joist. lf the joist is built into a slot, get someone  to hold it while you saw through it near its ends. Lift the main body of the joist away, then pull out the short stub still in the slot. You cannot push a new joist back into these slots, so they will have to be bricked up and joist hangers mortared  into the brickwork. An electric cable may have been passed through a joist you are replacing. Disconnect it- having turned the supply off at the mains first- from the nearest connection and draw it clear. Bore a 19mm diameter hole in the new joist 50 mm from its top to accommodate the cable.  Timber floor surfaces Floorboards, nowadays, are often tongued and grooved (‘t and g’) so that as shrinkage of the timber occurs over the years there will not be a gap for dirt and draughts to pass through.


replacing floor joists

But this was not always so: in the last century, and occasionally in this, boards without tongues and grooves – ‘square-edged’ boards – were fitted.  Warped floorboards Warping can cause boards to curl up at the edges, making it difficult to lay floor coverings. It this is not too pronounced, overlaying it with hardboard will be a sufficient cure. Alter- natively, you can sand the boards flat again with a floor sander, using a course abrasive belt. Normally when sanding boards you should work along – not across – their length, because crosswise sanding causes score marks that are difficult to remove. Work at an angle of 45° to the side of the boards. lf you mean to seal the boards and leave them uncovered,  treat them along their length in the normal way first with a medium, then with a fine abrasive.

floor joist repair

floor_joist_repairFortunately, joists do not develop as many faults as floorboards, but defects can occur, especially if unseasoned wood was used in the first place. A joist can twist out of true. A symptom of this would be that a floorboard would be seen to be twisted, but could not be nailed down flat. Or a joist can be attacked by woodworm or dry rot. The floor will seem weak or unstable if this is the case. If you suspect a weak floor you should always lift a board or two to discover what is wrong, it must be stressed that floor joist repair is a major undertaking,  and not to be embarked upon lightly. They involve a great upheaval, especially on upper floors, for your work will almost certainly damage the ceiling below. Since each joist carries every board in the room, a large part of the floor, if not the whole lot will have to be taken up, which will mean the room will be unusable, as will any room below if you interfere with its ceiling.

A joist might be damaged along part of its length — a tendency for the floor to sag or feel unstable at one point is an indication of this, in such a floor joist repair case, saw out the damaged section as detailed below, buy a new length of timber of the same size, and bolt it to the cut ends of the old joist. If a joist is twisted or bowed it is often possible to straighten it by fitting struts between it and the joist on each side. Should all the joists be twisted, struts of fairly strong timber, 25 mm thick, and almost as wide as the joists are deep, will have to be fitted between each of them. They are cut to a length equaling exactly the spacing between the joists, and are fixed by skew—nailing. If this remedy does not work, the joists will have to be replaced.