The purpose of this paper is to give an overall view of the varied peacetime applications of underground air-raid shelters in Finland. The practical and economic advantages which can be attained by making double use of subsurface space are especially examined. The additional costs which stem from providing for peacetime use are normally only 10 to 50 % of the costs for the corresponding above-ground alternative. Also other significant advantages can be achieved. The best way to obtain these advantages is to design shelters primarily for peacetime use provided that their conditioning for crisis use is possible within 24 hours. INTRODUCTION During the post war period in Finland a considerable number of subsurface air-raid shelters have been constructed and a great emphasis has been placed, especially in the last few years, on their most appropriate peacetime use. The Finnish Civil Defence Act also requires peacetime use to be provided for. The purpose of this paper is to give an overall view of all-round peacetime applications in Finland. The practical and economical aspects are given special examination. Also future tendencies and main restrictions brought about by legislation and regulations are reviewed. All cost estimates are given at the Feb. 1980 price level. SUBSJRFACE ROCK SHELTERS IN FINLAND According to the Finnish civil defence legislation, public air-raid shelters for more than 1500 persons must always be underground i.e. excavated rock shelters. Shelters of this size fulfill the needs of civil defence for a group of blocks or for a whole district. Smaller shelters constructed in basements of buildings are cheaper only if the immediate construction costs are considered. Due to the possibility of their efficient peacetime use, larger underground public shelters become economically very feasible when we examine their total costs over a long period. It is also noteworthy that their protective capability is much better than that of those incorporated in residential buildings. At present there is room for about 2.04 million persons in various shelters, which is 44 % of the whole population. This is one of the very highest percentages in the world. In Helsinki the coverage is 86 %. In underground rock shelters there is currently roan for about 120.000 persons and accommodation for a further 50,000 is under construction. For example in Helsinki there are altogether 27 rock shelters to accommodate 77,000 persons. This is 23 % of the total number of shelter places in the city. Underground shelters represent a considerable investment. When evaluated at the 1980 price level, shelter investments total FMK 700 million, including those under construction. FMK 20–40 million are used annually for rock shelter construction. In Helsinki, rock shelter investments total FMK 300 million. These shelters contain 54000 m2 net floor area for peacetime applications, of which over 90 % is in efficient use. PEACETIME USE FRAMWORK The following factors establish the main impediments to peacetime applications: the Civil Defence Act, the Building Decree, the Fire Prevention Act as well as psychological and practical aspect. The Civil Defence Act requires shelters to be conditioned for crises use within 24 hours.