The article deals with the composite reinforcement use in the foundations’ construction under difficult geological conditions and aggressive groundwater. The pile foundation of a two-story cottage was calculated using two types of reinforcement in the pile cap: traditional metal reinforcement and composite fiberglass. The modern regulatory documents requirements governing the calculation of structures with composite reinforcement were taken into account. The use composite reinforcement has been revealed not to give a significant advantage in the pile foundations cost, it is effective when the structure is used in aggressive environments: the resistance of fiberglass reinforcement plays a crucial role in combination with special concretes.