Ways to long-term storage of carbon molecules captured as CO2 from atmosphere are looked for. Timber structures act as carbon storages and timber construction is sometimes claimed as a solution to mitigate climate change. This article attempts to estimate (a) the volume of carbon stored in wooden structures of new buildings annually, and (b) the role of new wooden buildings as a compensator of human-caused annual CO2 emissions in Finland and globally. Annual share from the total CO2 emissions stored in wooden buildings is called building sink effect (BSE). The BSE was 0.61 in Finland in 2017, and global BSE is even smaller. In order to achieve a global BSE of 1%, approximately 450 million m(3) of wood products, corresponding to 85% of the global production of lumber, all structural engineered wood and construction logs, should be long-term stored in buildings. New wooden buildings have almost indistinguishable mitigative influence on annual CO2 emissions. However, timber construction is an important factor in a strategy towards more climate smart future, and substitution effects multiply the effects of physical carbon storages. Still more powerful actions, such as emission cuts or reforestation, have to be implemented to see real climate effects.