When policy scholars assess the effects of federalism on climate change mitigation, they often look at countries that rejected binding commitments (in particular, the USA) and find that federalism enabled sub-national entities to partly fill national regulatory voids. In accordance with a similar case study on Austria, we find the exact opposite for Switzerland, a country that committed itself to an 8 % cut in 1990 greenhouse gas emissions under the Kyoto Protocol. To reveal the detrimental effects of federalism, we focus our case study on the integration of climate change concerns into building policies, a policy field fully in the hands of Swiss sub-national authorities known as cantons. Apart from a few pioneer cantons, we found mainly federal departments concerned with integrating climate change mitigation into cantonal building policies and cantonal as well as federal actors struggling with the numerous pitfalls of Swiss federalism in their own ways. On the one hand, various federal departments tried repeatedly to facilitate a nationwide greening of cantonal building policies, and their interventions often resulted in lowest common denominator solutions that were difficult to improve once in place. On the other hand, Swiss federalism gave a few pioneer cantons the freedom to green their building policies early on, but their policies hardly diffused to other cantons. Resembling our main finding of the Austrian case study, we conclude that the 15 % emission decline in the Swiss building sector during 20082012 compared to 1990 levels happened despite, not because of Swiss federalism. This warrants caution against high hopes in assuming that decentralised or polycentric governance can fully compensate for failed national (or international) climate policies.