This paper discusses how simplified thermal and ventilation tools could be used during thefeasibility study of buildings to demonstrate the advantages of natural and low energyventilation strategies. The paper focuses on local authority library buildings in South-EastEngland and two simplified tools were used; one using a dynamic thermal simulation andventilation method and another based on the admittance method. The prediction of both toolswere compared with measured temperatures from an existing library that has a knownoverheating problem. Having gained confidence in the tools' predictions, the dynamicthermal simulation and ventilation tool was used to modify the design of a proposed librarybuilding at the feasibility stage, as a way of demonstrating how the design of the buildingcould be change to benefit from natural ventilation. The paper concludes that using the resultsof user-friendly dynamic thermal simulation and ventilation models, local authority engineerswould be able to adapt the concept of the building to low energy design principles. The needto develop simple adaptable and accurate tools for natural ventilation applications for avariety of building types is highlighted.