Many housing policies aim to increase supply and reduce prices through rezoning, relying on the assumption that increasing allowable densities automatically accelerates the rate of housing supply. However, the existence of landbanking (land hoarding), where land able to be profitably developed for housing is withheld from the market in anticipation of future gains, undermines the logic of such policy changes.

We expose major limits of the static housing supply model behind these policies by looking at the degree to which landbanking behaviour is consistent with model predictions. To do this, we assemble a new dataset of home sales and landbanks from the annual reports of Australia’s top eight publicly-listed residential developers from 2001 to 2018 and use complete state-level planning approvals and lot production data in Queensland, Australia.

In contrast to the static model prediction that landbanks serve the function of inventories, and are hence minimised, we find that (1) over 200,000 housing lots, or 13 years of new supply, are held by the eight largest housing development companies, and eight years of these landbanks are held in housing subdivisions that are approved and already for sale, that (2) the amount of zoned supply in a region is unrelated to the rate of new housing supply, and that (3) housing developers routinely delay housing production to capitalise on market cycles. Dynamic incentives to maximise total returns, including capital gains in the option value of undeveloped land, could be related to this observed behaviour.

许多住房政策旨在通过重新分区来增加供应并降低价格，这是基于以下假设：允许的密度增加会自动加快住房供应速度。但是，土地储备（土地ho积）的存在会破坏这种政策改变的逻辑，在土地储备中，能够为住房谋利的土地可以被有利地开发，而这些土地却被市场预期未来的收益。

通过查看土地储备行为与模型预测的一致程度，我们揭示了这些政策背后的静态住房供应模型的主要局限性。为此，我们从2001年至2018年澳大利亚排名前八位的上市住宅开发商的年度报告中，收集了一套新的房屋销售和土地储备数据集，并使用了澳大利亚昆士兰州的完整州级计划批准和批量生产数据。

与静态模型预测的土地储备起到库存功能并因此使其最小化相反，我们发现（1）八个最大的房地产开发公司拥有超过200,000个住房地块或13年的新供应量，而八个这些土地库中有数年存放在已批准且已经出售的住房细分中，（2）一个地区的分区供应量与新住房供应的速度无关，（3）住房开发商通常会推迟住房生产利用市场周期。旨在使总收益最大化的动态激励措施，包括未开发土地的期权价值中的资本收益，可能与这种观察到的行为有关。