Installing the Floor & Ceiling Joists
Taking measurements from the existing first floor level, the height of the new floor joists is worked out. The tops will be the same height as the existing first floor less the thickness of the flooring itself. The level is marked on the back wall and the centre line of each joist marked out along this line. Small slots are then cut in the brick work at this point with an angle grinder so that the joist hangers can be fitted. These are wedged tight and, where necessary packed with off cuts of slate.
On the opposite wall, the end wall of the new extension, the level for the joist hangers lines up perfectly with one of the mortar joints in the block work and they are easily fitted. With these hangers in place, the timber joists are cut to length and fitted into the hangers.
Some of the joists have to be set back from the original back wall. To do this, a pair of timbers is cut to span between the full length joists. These trimmers are then used to support the ends of the shorter, trimmed joists. The joists are fixed to the trimmers with screws driven in at an angle. Short lengths of timber are cut and fitted between the joists approximately half way along their length. These noggins give extra rigidity to the floor joists by preventing any lateral movement.
It’s not long before all the floor joists are in place. Normally, the ceiling of the room below would simply be fixed direct to the underside of the floor joists. However, on this job, the set up is a little different. The large steel over the opening between the old room and the new extension could have been boxed in. But, this would draw attention to it. On this project the ceiling is to follow right through from the underside of the steel. This will mean that the ceilings are at different levels but it will give more continuity.
The finished height of the new ceiling is marked out on the flank walls. At each end of the room, a string line is then fixed between the walls at this height and fastened with small battens nailed to the block work. The ceiling joists will be notched onto the steel work at either end of the room. The underside of these joists will be the thickness of the ceiling above the string lines.
Each joist is measured and cut to length. The size of the notches required at each end is then marked on the joists and the rebates cut out. One by one, the ceiling joists are cut and fitted. The rebate sits over the bottom flange of the steel. Once each joist has been fitted and aligned, it is wedged tightly into position with a short length of the same timber. This is packed tight between the top of the ceiling joist and the underside of the top flange of the steel.
With the two sets of joists in place you can begin to visualise the shape and size of the new rooms better. The contractors are now ready to start the final lift of brick work to take the extension up to roof level.
If you live in the Hertfordshire area and are looking for a professional building contractor, you can get in touch with G L Smith and Sons via their website: http://www.glsmithandsons.co.uk/
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