The state of Australia's housing bubble, if any, and the consequences for the banking sector and the economy featured in a flurry of regulator commentary on Friday, with the latest official views grounded in continuing unease.APRA, the RBA and the IMF all chimed in with a fresh outline of views on the factor they all connect, to some degree, to a budding economic shock.Wayne Byres, chair of the Australian Prudential Regulation Authority, spoke at an economics forum on Friday, spelling out once more the regulator's willingness to resort to harsh measures."At least for the time being, the benchmarks that we communicated [in 2015] - including the ten per cent benchmark for annual growth in investor lending - remain in place," Byres said."Lenders that choose to operate beyond these benchmarks are under no illusions that supervisory intervention, probably in the form of higher capital requirements, is a possible consequence."Byres reminded his audience that "if capital for the banking system is our main policy item, then housing is our main supervisory focus."In a survey of recent measures, Byres said "we have lifted our supervisory intensity in a number of ways - collecting more data from lenders, putting the matter on the agenda of Boards, establishing stronger lending standards that will serve to mitigate some of the risks from the current environment, and seeking in particular to moderate the rapid growth in lending to investors."And just to be clear about it, we are not predicting whether house prices will go up or down or sideways (as the governor of the Reserve Bank said last night, they are doing all these things in different parts of the country), but simply seeking to make sure that bank balance sheets are well equipped to handle whatever scenarios eventuate."APRA's recent efforts, he said, "have generated a moderation in investor lending, which was accelerating at double digit rates of growth but has now come back into single figures. We can also be more confident in the quality of mortgage lending decisions today relative to a few years ago."Of the recent pick-up in the rate of new lending to investors, Byres said this "in itself is not necessarily surprising - with so much construction activity being completed and the resulting settlement of purchases, some pick-up in the rate of growth might be expected."Or not, if the detailed commentary in the Reserve Bank of Australia's quarterly Statement on Monetary Policy is a guide.Riffing off past cautions on the fragility of the boom in multi-unit construction, or plans for the same, the RBA said "although investor activity is currently quite strong, at least in Sydney and Melbourne, history shows that sentiment can turn quickly, especially if prices start to fall. "Softer underlying demand for housing, for example because of a slowing in population growth or heightened concerns about household indebtedness, could also possibly prompt a reassessment."Shifts in sentiment could easily reset the level of housing prices, the RBA pointed out."A widespread downturn in the housing market could mean that a more