•This paper evaluates residential house design by varying floor and roofing design.•It describes life cycle assessment and life cycle costing analysis for Australian houses.•Life cycle environmental and cost are significantly affected by floor and roofing design.•GHG and CED impacts are decreased when star rating is increased. This paper describes life cycle assessment (LCA) and life cycle cost (LCC) analysis for typical Australian houses. It reports how different roofing (i.e. roof and ceiling) and floor designs affect the life cycle environmental impacts and cost (LCEI & LCC) over the various life stages of buildings (i.e. construction, operation, maintenance and final disposal). A case study house, called Base House, was modified with 8 alternative roofing and 4 floor designs to generate 12 variant houses. Specifically, one variable either from roofing or from floor was varied at a time while keeping wall and other components as in the Base House. The four life cycle environmental impacts were greenhouse gas (GHG) emission, cumulative energy demand (CED), water use, and solid waste generation, evaluated by LCA approach. The LCC was estimated based on life cycle costing approach. The results of LCEI & LCC of each house were evaluated on a whole of life cycle basis. A number of trades-off on the houses modified with roofing and floor designs were identified based on LCEI & LCC results. For the houses modified with roofing and floor designs, the high star skillion flat roofing and mixed floor houses were the attractive trades-off.