Mortgage finance has become highly sophisticated at measuring the risk of the borrower to the lender. Credit scores, debt-to-income ratios, loan-to-value ratios, automated valuation models, mortgage insurance, and capital requirements all attempt to answer the same basic question: What is the probability that this borrower will fail to repay?
There is another question that receives far less attention: What risk is the mortgage transaction creating for the homeowner?
For millions of American households, buying a home creates the largest concentrated investment position they will ever hold. The household borrows heavily to acquire a single, illiquid asset in a single neighborhood and often depends on that asset for a large share of long-term wealth.
In most areas of finance, that degree of concentration would immediately raise concerns. In housing, we treat it as normal.
Homeownership has a diversification problem
A new homeowner may put most available savings into a down payment while simultaneously taking on significant leverage against one property. If that property declines materially in value, the consequences extend beyond an investment loss.
Negative equity can inhibit mobility. A job loss becomes more dangerous. Refinancing becomes harder. Selling may require bringing cash to closing. And when declining home values coincide with economic weakness, the homeowner’s housing loss can arrive precisely when the household is least able to absorb it.
That interaction between leverage, concentration, and economic stress is one reason housing downturns can be so destructive. But it also creates an opportunity. Instead of asking only how much equity a homeowner should contribute to protect the lender, housing finance can begin asking how the transaction might protect both sides.
Diversification can change mortgage credit risk
Our published diversification research examined more than one million Freddie Mac mortgages and asked what could happen if individual-property housing exposure were partially diversified. The results were striking.
Expected credit losses were roughly 29–30 basis points for conventional mortgages, compared with about 5–6 basis points for a diversified zero-down purchase structure.
Those published results establish the economic potential of housing diversification. They should not be read as independent validation of the specific Index implementation now under development, which remains subject to legal, regulatory, operational and model review.
The broader implication is nonetheless important: a structure designed to improve the homeowner’s financial position may also improve the credit characteristics of the mortgage. Those objectives do not necessarily conflict.
For decades, the standard response to a borrower with a small down payment has been to add protection for the lender through mortgage insurance, government guarantees, higher pricing, or other credit enhancements. Those approaches can work, but the borrower often pays for the protection.
Diversification attacks the problem from a different direction: reduce the underlying economic risk itself.
An index can provide the hedge
One potential implementation uses a diversified housing index.
A homeowner whose property underperforms a broader housing benchmark could receive economic protection against some of that relative decline. In exchange, the homeowner could share some future appreciation above the applicable benchmark. The objective is not to eliminate homeownership risk or guarantee a return. It is to transform a portion of an extremely concentrated housing position into something more diversified.
Modern automated valuation models, digital servicing, housing indexes, and increasingly sophisticated capital-market infrastructure make this much more practical than it would have been twenty years ago. The same framework can potentially be applied across several areas of housing finance.
For a purchase mortgage, diversification may permit greater leverage without simply transferring more risk to a guarantor. For a home-equity loan or HELOC, it could allow a homeowner to obtain additional liquidity while reducing exposure to severe housing-price outcomes. For existing homeowners, it may create a way to reduce housing concentration without selling the home in which they live.
The homeowner benefit goes beyond downside protection
The case for diversification is sometimes framed too narrowly as protection against loss. Its broader benefit may be stronger risk-adjusted wealth for the homeowner.
Households do not maximize financial well-being merely by maximizing the expected appreciation of one asset. A dollar of expected wealth that comes with less catastrophic downside exposure can be more valuable than the same expected dollar embedded in a highly leveraged, concentrated position.
Diversification could allow homeowners to retain meaningful participation in housing appreciation while reducing exposure to the outcomes that are most financially damaging. It may also improve household resilience.
A homeowner with protection against a severe housing loss may be better positioned to sell during a downturn, relocate for employment, refinance, withstand temporary income disruption, or avoid the progression from negative equity to default. That is why the potential social benefit extends beyond investment theory.
Reducing catastrophic housing exposure may also reduce catastrophic foreclosure exposure.
The lender economics may be compelling too
A homeowner-centered product will not scale unless the economics also make sense for lenders and capital providers. Here again, the interests may align. Our published work suggests that diversification can reduce expected mortgage credit losses from roughly 29–30 basis points for conventional loans to approximately 5–6 basis points in a zero-down diversified structure.
For lenders, materially lower underlying credit risk can support greater flexibility in high-leverage and home-equity lending without requiring proportionately greater credit exposure. That could create several sources of value.
Financial institutions may be able to serve borrowers who fall outside conventional credit boxes. They may be able to generate more attractive risk-adjusted economics on home-equity lending. And they may gain access to homeowners whose equity is currently difficult to monetize responsibly.
That last point is important.
There is an enormous amount of homeowner equity in the United States, but traditional lending standards make much of it difficult to access. A mechanism that improves the risk characteristics of higher-CLTV lending could expand the addressable home-equity market rather than simply redistribute existing originations.
Technology is making a new architecture possible
Mortgage underwriting is becoming increasingly digital. AVMs are improving. Artificial intelligence is entering both origination and risk management. Capital-market platforms can connect borrowers, originators, and institutional investors with much less friction than in the past.
The industry has spent years using technology primarily to make the existing mortgage faster and cheaper. The larger opportunity may be to use that technology to change the economic architecture of the mortgage itself. A digitally originated mortgage does not have to be economically identical to a mortgage designed decades ago.
Once housing exposure can be measured, indexed, administered, and settled systematically, financial institutions can begin engineering the homeowner’s risk rather than merely underwriting around it.
Housing finance has solved only half the problem
The modern mortgage industry is very good at asking: How do we protect the financial institution when a homeowner buys a house? The next generation of housing finance should ask a second question: How do we protect the homeowner as well?
That change in perspective could expand responsible access to homeownership, make home-equity lending safer, reduce the financial consequences of housing downturns and improve household risk-adjusted wealth. Most importantly, it may make borrowers safer counterparties precisely because they themselves are financially safer.
For decades, diversification has been one of the most fundamental principles in finance. It may be time to apply it to the largest investment most families will ever make.
