Doing the housing supply maths

Laurence Murphy is a top property economist at the University of Auckland. I met him last night after a presentation in Sydney where he took on the myth that planning constraints are a major determinant of current home prices in Australia and New Zealand.

He said it is very easy to demonstrate mathematically how little impact even a large increase in the rate of supply would have on prices. But when he shows this analysis to government officials, planners, and engineers who have bought into the supply-side narrative their response is often

“I see your calculations. I follow the logic. But I don’t believe it!”

So I wanted to try the ‘basic supply-side maths’ for myself on the blog to see what sort of effects radical changes to the rate of new housing supply could have, and see if I generate some of the same responses.

Here’s how the maths work. I take the number of new dwelling completions from the ABS for the past 20 years, which is shown in quarterly figures in the blue line of the chart below. Since 1995 new housing supply has been 146,546 dwellings per year on average, which is about a 2% increase in the stock annually, though this moves with the business cycle.

I then add 10% to this number every year to generate a counterfactual world where supply has been much higher over a sustained two-decade period (green line). Then I add 20% just to take an extreme scenario (yellow line). Note that in this exercise I don’t ‘elastify’ supply, which would have higher construction rates in boom periods, and lower construction in a slump. When I run the numbers for a more elastic supply that responds more to both booms and slumps I get fewer homes built compared to what actually happened! This is because when the completion rate falls, it falls faster, offsetting all of the gains from the previous boom. I show a 'twice as elastic' scenario in the next graph in red, which actually results in 8,000 fewer dwellings built in the past 20 years. ‘Elastifying’ supply can’t really be what is desired by those advocating for supply-side reforms. 

Any supply-side housing initiative should simply aim to get more homes built, year in, year out. This is what I capture in my counterfactual scenarios of 10% and 20% higher construction over two decades.

So here is the question. How many more houses would there be now in these counterfactual worlds? And what would the price impact be?

Well, if we had built 10% more new home each year for the past 20 years Australia would have around 300,000 more homes. At a 20% higher rate of completions that's 600,000 more. Sounds terrific! That must have a massive impact on prices.

Well. No.

You see Australia’s current housing stock is somewhere around  9.3 million homes. Around 8.8 million occupied, and many second homes, holiday homes, and so forth that are traditionally about 8-10% of the housing stock. These additional homes in my 20-year supercharged supply scenarios represent just a 3.2% and 6.4% increase in total stock respectively.

The price impact of a 3% increase in supply is a 3% reduction if demand elasticity is unity. That’s it. The price reduction could be less if there are countervailing income effects that lead to outbidding for superior locations.  So twenty years of supercharged supply provides somewhere between 0% and 3% lower prices, which suggests to me that focusing on the supply side is close to a waste of time. In the 20% higher housing completions scenario the effect is somewhere between zero and 6%. About the same as two and a half years of rental price growth.

To put it another way, after 20 years of a 10% higher rate of new supply, rents today would be the same as they were in early 2014.

We can alternatively look at the raw measure of the gains to the amount of floor space per person. Taking the average floor size of homes, which is about 180sqm, and adding 3%, and assigning it to the average of 2.6 occupants, to get an additional 2sqm of floor space per person.

Or we can think of it in terms of occupancy rates — the number of people per dwelling — which would be 2.51 instead of 2.6 with the same size homes under the 10% higher supply scenario.

That’s all you get for 20 years worth of sustained housing supply stimulus. And you get none of that simply from more elastic supply only.

The point is that current massive price increases, in the order of 17% per year in Sydney and Melbourne, simply cannot be explained by anything like unresponsive supply. Not only that, any supply-side effect on prices takes many decades to have any effect, and only enters the price equation via effects on rents.

If we want cheaper housing we need to reform legal structures to shift bargaining power to tenants from landlords, curb speculation through financial controls (and keep stamp duties!), and stop rewarding political parties who promise housing supply as any sort of solution to current prices.

Unfortunately, very few people actually want housing to become cheaper. Around 70% of households are homeowners, around 30% are property investors who come from the wealthier part of society, while most politicians also have a huge share of their wealth tied up in residential property. It suits all of these interests to point the finger at supply because they know it sounds attractive in a naive economic way, but won’t actually reduce the value of their housing portfolios.

As Professor Murphy explained, the consensus around new housing supply as a solution to housing affordability problems is a political construct. This unfortunate political reality is best summarised in this tweet. 

  

Politician: I'm want a new housing affordability policy Expert: So u want home prices to come down? Politician: Hell no! #Australia

— Cameron Murray (@Rumplestatskin) September 9, 2015

Dear reader I hope you see my calculations, follow the logic and believe it!