How to Install Joist Hangers
Installing Joist Hangers
On most modern houses, the ends of the joists are supported on metal brackets called . Even if you are replacing the entire floor in an older house where were not originally fitted, you can still fit them using the method described below. There are several different types of hangers and each type comes in different sizes, so make sure you fit the correct joist hangers for your application.
The most common reason for installing joist hangers is when a new floor is being built, either for a new room or because the original joists need replacing. Joist hangers are typically fixed to either masonry or timberwork. In new houses the joist hangers are built into the wall, or if the house is timber-framed special hangers are nailed to the studwork. In older house where joists are fitted into pockets in the wall, by installing joist hangers the ends are kept away from potentially damp brickwork and masonry. Joist hangers also allow you to space the joists so that the joints of sheet flooring fall directly onto the centreline of a joist.
Tools for the Job
- tape measure & pencil
- spirit level
- cordless drill/driver
- trimming knife
- Allow for the width of the plasterboard by measuring up 12mm (9/16in) from where the underside of the ceiling will be, then mark a level line at this point all around the room using a spirit level. Mark out the centre spacing for the joists along this line no more than 400mm (1ft 4in) apart centre to centre. You may need additional joists close to the wall in order to support the edge of the boards.
- To ensure the finished floor ends up level, nail or a temporary batten to the wall so that the top edge is level with your datum mark. Hold the joist hangers on top of the batten at the centreline reference marks and or nail them to the wall. If using you may find it easier to mark the position before drilling the hole and inserting a . Use a hammer or percussion drill fitted with a bit specifically designed for masonry when drilling into brick or blockwork. If the hole has been drilled correctly you should be able simply to push in the wall plug for a snug fit.
- Get a helper to hold the end of the tape measure while you check the length of the joists. Measure by holding the tape across the room and checking the distance between the back plates of the joist hangers. As it is unlikely that the room will be completely square, hence lengths will vary slightly, do not just measure the first joist and assume all the others will be the same length. Deduct 4mm (3/16in) from the overall measurement and mark this on the joist before cutting to length with a panel saw.
- If you have cut it correctly, the joist should drop in without the need for hitting it with a hammer. If the joist wobbles from side to side slightly in the hanger, you can make it a better fit by wrapping roofing felt around the end and securing it in place with . Parcelling the end in felt also has the added advantage of preventing moisture from wicking into the end grain of the joist.
- Nail the joists into position through a couple of the holes on either side of the hangers. Galvanized nails have a better grip due to their rough finish and are more resistant to rust than conventional brightwire nails. Nails should be no more than half the thickness of the joist or there is a risk of splitting the timber. Do not drive them right home at this stage. Place the spirit level across all the joists and check for level, repeating this at several places in the room. If any joists are high, pull the nails and either trim a little from the underside of the joist where it sits in the hanger or reposition the hanger. When you are certain of the fit, drive home the temporary nails and hammer nails through the remaining holes in the sides of the joist hangers. To avoid splitting the wood try blunting the ends of the nails with light hammer blows.
- For any span more than 3m (10ft), nail herringbone struts between each of the joists to add extra strength and to prevent twisting. The joists are now ready to receive the flooring and ceiling, but before doing this run in any cables and plumbing work.
Tips of the Trade
- Positioning joists — Joists typically run across the shortest span of the room, but loadbearing walls must always support the ends. If you are replacing a floor the new joists should run the same way as the original joists. Consult an architect or structural engineer for advice if you are unsure.
- Spacing joists — The spacing of floor joists is always quoted as centre to centre. This is the spacing between the imaginary centreline of each joist. To gain the actual distance between joists, deduct the total thickness of one complete joist.
The chemical used in pressure-treated timber or joists can be poisonous if ingested. Wear gloves if possible and always wash your hands after work and before eating and drinking.
Lateral Restraint Straps
For extra stability to the completed floor you may want to add lateral restraint straps. These come in the form of galvanized steel straps, fitted and screwed to the wall, and are available from any good builder’s merchant. Such restraint straps are intended to be fitted at a perpendicular angle to the joists.