by Mike G » 11 Nov 2014, 18:43
Hmmm....
Floorboards could expand without bending or breaking screws, simply by bowing the joists, or by leaning the screws over within the softwood of the joist (or a combination of both). Leaning the screws in the direction of the grain of the joists is trivially easy.
Guidelines such as this are written to cover all circumstances, not ideal ones. You may well have a perfectly sound environment for your boards, with stable temperature and relative humidity, but not all floors will be laid in such conditions. The regulations/ recommendations (whatever), therefore have to be written to cover the worst-case, rather than the everyday. Imagine a suspended ground floor with a small void, poor or no ventilation underneath, no DPM, a leaking pipe or waste, and intermittent heating above. Now, if you laid that flooring right to the walls, you could push your walls out, easily.
You can certainly, therefore, take a view on the risks of your floor ever falling into less than ideal circumstances. You may well be confident that it never will, and reduce the gap.......but I certainly wouldn't be reducing it to zero.