Cities require a change in the design of medium and high-density housing to increase green infrastructure (GI). GI provides ecosystem services: including better air quality, removal of carbon dioxide, urban heat island attenuation, biodiversity, attenuation of stormwater runoff, and space for people to have social interaction and engagement. However, GI requires investment by developers. To be worthwhile, such investment must make developments more attractive to residential buyers, increasing their interest to buy. To date, no research has explored if that is the case, and if so, to what extent, by disentangling how such interest may arise. This paper explores the causal process and assesses to what extent investments in developmental GI influence people's Interest in apartments for sale in developments, which is expected, in turn, to influence their willingness to pay for an apartment. This is done by developing a causal structural model and testing it in two experimental studies carried out on random national samples of apartment speculators in Sweden in 2021 (n = 421) and in 2022 (n = 401), under two different property market conditions. Using an innovative research design with virtual reality, 5 versions of a courtyard in a medium density residential development were developed. One of these was then randomly shown to each research participant. The experiments showed that investment in the GI had a positive effect on the assessment of the courtyard, which increased the interest in the development and the apartments for sale. The increased interest from investments in GI should thus motivate developers to such investments.