Pepper, Liberty, La Trobe, FirstMac, Resimac, AFG Home Loans, RedZed - the whole spread of non-banks - are all APRA regulated now, at least when it comes to macroprudential policy and the use of more handbrakes on questionable residential lending.One vital, if final, detail in a long list of measures set out by the Australian Prudential Regulation Authority on Friday is directed at making a gutsy and vibrant non-bank mortgage funding sector conform to restraints equivalent to those imposed on authorised deposit-taking institutions.ADIs funding "warehouses" (licks of wholesale lending to non-banks, to sustain new business) must "ensure that the lenders' mortgage lending standards are consistent with industry-wide sound practices," APRA decreed on Friday. "A number of ADIs provide warehouse facilities to other lenders, allowing them to build a portfolio of loans that will eventually be securitised [via the bond market]" APRA said, in bland but accurate terms."Warehouses", a jargon word, describes a pillar of the non-bank mortgage funding model. Australia's Big Four banks are all active funders of these warehouses.This form of institutional lending is an imperative for each large bank, since the warehouse funder gets a leading role in the fee-heavy work of selling mortgage-backed securities to onshore and offshore investors.Any foreign bank under APRA's watch in Australia will also have to toe the line. Foreign banks with a yen for this mortgage risk and not locally regulated may be called on to take over a share of this funding.Whether non-banks are filling any void in the supply of investment property loans is arguable. Pepper Group, for instance, recently told Banking Day that bond investors were vigilant scrutineers on each deal's asset quality and the cash flows that ensure bonds are repaid.Still, mortgage-backed deals have flowed pretty freely from non-banks to the debt capital market since early March and the five principal non-bank lenders - Pepper, Liberty, La Trobe, FirstMac and Resimac, in no particular order - seem to be faring well.APRA said it "has been monitoring the growth in warehouse facilities" and "would be concerned if these were growing at a materially faster rate than an ADI's own housing loan portfolio."There's no real data on warehouses, but the market share of non-banks is static, if the all-banks APRA measure of housing credit relative to the RBA's aggregate for all housing credit is any guide.??APRA may thus be imposing a clamp on a risk among non-bank lending choices it can only guess at, rather than show is on the rise.