The knowledge and enforcement problems faced by governments in defining traditional ‘command and control’ regulation are well known. Significant legal scholarship offers alternative models of ‘smart,’ ‘responsive’ environmental regulation, emphasising the need for policy instrument mixes, including the vital role of voluntary, industry-led sustainability standards. Yet, as is being increasingly recognised, these contributions leave open the need for detailed, qualitative evaluation of instrument mixes as a complement to primarily quantitative cost-benefit analyses that predominate in regulatory impact assessments by governments. Addressing this need, this paper evaluates policy and standards for low and zero carbon homes in England during the Coalition government (2010-2015) when the ecological modernisation discourse of the previous New Labour government became subsumed by a deregulation agenda. Our study, incorporating 70 stakeholder interviews, suggests that, in supplier-driven markets such as housing in England, a ‘smart’ mix of mandatory and voluntary standards requires a strong, central role for government in setting national, mandatory standards and supporting their delivery. There is an important potential supplementary role for voluntary tools and local authority discretion, though our study highlights problems that can arise when such different instruments promote diverging roadmaps towards a policy goal.