Creaking and cracking floorboards?

Creaking floorboards are very common for us to find when conducting a snagging survey in new build houses. The location of where it occurs can often move through the settlement process or disappear altogether after a short time. Having said this, a large amount of the houses we inspect months or years after completion still have squeaking and creaking floors.
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The most common reason for floors creaking are:

• The floorboards have not been glued down fully / at all or have the incorrect fixing holding the floorboard down to the joists. In the case of chipboard floors, incorrect nails will become loose and often they may have used an insufficient quantity of fixings. It is generally speaking best to screw rather than nail down floorboards which accounts for the most common annoying squeaks encountered.
• Ideally the top of the joist should have glue applied and then the tongue and groove joins are glued together. All of the joins of the floorboards should be spaced so the joins rest on the joist, where as a final measure they should be nailed or screwed down. If nailed then they should be ring shanked to avoid them dislodging and creating that gap between the floorboard and joist which is a common reason for the creaking.
• The floor joists need to be absolutely solid and of the correct size to prevent movement across the span they are bridging.

It is important that joists are fixed solidly at either end of the room and spaced at the correct centres (usually 400mm) and cannot move in their wall sockets or joist hangers. The tail of the hanger should be firmly built into the wall and the joist firmly fixed into the hanger. Only an intrusive investigation would identify if this is the cause of the noises experienced. A joint acoustic study at the University of Salford with the NHBC identified the loudest noise came from these sides of the wall: either due to the junction between the joist and block work party wall / external walls or where it meets the plasterboard wall/ceiling lining.

​In an attempt to prevent vibration from the boards travelling through the room below, builders have resorted to resilient bars which essentially create a floating ceiling separating it from the plasterboard underneath where the noise is bridged. To achieve this, 
insulation is installed between the timber joists with an acoustic mineral wool, then the resilient bars are affixed to the timber joists. Then several layers of acoustic grade plasterboard are packed in with a layer of acoustic membrane.

Whilst a slight creak can be easily solved by accessing the fixings under the carpet, often customers encounter a cracking noise which indicates an issue with the strength of the joist rather than movement in the floor board.
Cracking noises (like a pencil snapping rather than a creak) often requires more intrusive structural remedy such as installing noggings, which provide more rigidity to the joists.​