Development on existing sites, especially in large cities, often comes with additional costs and challenges compared to conventional greenfield development, despite urban development often selling for above-average values per square foot. As a result, the evidence suggests that brownfield sites take longer to build out and have a 'higher' attrition rate during development, yielding fewer homes overall - though it should be noted that constructions periods can vary for multiple reasons and drawing clear conclusions is challenging.

Analysis of consent and site-level data from H1 2025 (as a proxy for the current state of play for development) shows that brownfield sites take 8 months to progress from being granted planning permission to starting construction, compared to 6 months for a greenfield site. Construction also tends to take longer, with brownfield sites taking around 23 months on average to complete, compared to 18 months for greenfield. And the gap is growing: across the data we analysed, construction times have doubled for brownfield sites since 2020, compared to an increase of 50% for greenfield sites.

Brownfield sites also have a higher attrition rate, where homes granted consent fail to be built out. Between 2020 and H1 2025, the rate of attrition of was on average 8% higher on brownfield sites than on greenfield, likely due to the greater complexity and more marginal viability that the former typically face. Long build-out times and a higher “attrition rate” highlight how relying too heavily on brownfield sites can lead to a slower rate of delivery and more schemes potentially failing to deliver any homes at all, thus risking overall housing supply.

In addition, the NPF4’s focus on ‘Town Centre First’ essentially now requires developers to demonstrate existing use of a building is no longer viable, and thus a change of use, such as residential, would be viable and desirable, adding an additional layer of complexity to bringing forward brownfield sites even when other policy is supportive of delivering more homes on such locations. A brownfield-first approach therefore risks loading development onto sites that are more challenging and take longer to deliver, and have a higher risk of falling foul of obstacles that prevents housing delivery.

With a complete reliance on allocated sites and an excessive focus on brownfield sites, NPF4 will struggle to reverse the shrinking flow of planning consents thus leading to less developer activity in the short term. On the contrary, the new framework risks excluding too many viable and deliverable sites from the overall supply of new homes, and threatens to push the weight of housing delivery onto too few sites with often limited viability and higher risk of development failure. It is therefore unlikely that NPF4 will help increase the volume of housebuilding to the levels required for Scotland to seriously meet the challenge of the housing emergency and to help grow its economy.

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