Within EBC Annex 61: Business and Technical Concepts for Deep Energy Retrofit of Public Buildings (IEA 2015) strategies are developed to increasepaceandquality of deepenergy retrofit (DER) projects in the public sector. Annex 61, Subtask A’s target is to assess accomplishedDERprojects to defineand find optimized measure bundles from both energy-efficiency and economical perspectives in each of the participating countries. Based on general assumptions defined by the Annex 61 team, modeling studies for different types of buildings and different climate zones have been done. The following scenarios and assumptions for all national case studies have been defined. Scenario 1 (baseline) represents the pre-1980 standard to describe the building envelope and systems before any renovation addressing the consumption of site energy, heating, and electricity. Scenario 2 (base case) is the country-specific “business as usual” retrofit; in this case, the retrofit is initiated by a general repurposing and only consider sminimumrequirements by the national building code. Scenario 3 has to achieve approximately 50% energy reduction relative to the baseline (Scenario 1), and Scenario 4 aims to achieve the current national “dream energy standard” (which can be the national definition for net zero energy buildings[WDBG2014], Plusenergy Standard, PassiveHouse[PHI2015a], etc.). Targets tobe reached in all scenarios are based on the site energy demand, including all kinds of energy use, such as domestic hot water (DHW), heating, cooling, lighting, household electricity, plug loads, and others. The results of the modeling will be different U-factors for the thermal envelope and specific HVAC and supply systems. For each component, the investment costs are calculated and a 40-year life-cycle cost analysis is prepared, considering the global costs and benefits for energy- and non-energy-related measures. To decide between different scenarios, the incrementalenergy-related costs and benefits of each scenario are compared to each other. In this paper, the modeling results of Austrian and German case studies are presented. The Austrian modeling project is a multistory housing block with four floors and 24 flats in the city of Kapfenberg, constructed in 1960–1961. The total site energy demand (DHW, heating, and supply and household electricity) of Scenario 1 is 155 kWh/m2yr (49 kBtu/ft2yr) and has been reduced in Scenario 4 to 71 kWh/m2yr (23 kBtu/ft2yr), achieving the Passive House standard (heating energy demand of 15 kWh/m2yr [5 kBtu/ft2yr]). Measures from Scenario 2 and 3 focused only on the reduction of transmission losses (e.g.,improvement of insulation, change of windows) and the reduction of infiltration losses, as these measures enable the achievement of the required energy use intensities (EUIs) in a cost-efficient way. To achieve the Austrian dream target (PassiveHousestandard[IPHAn.d.]) in Scenario 4, the implementation of mechanical ventilation with heat recovery is necessary, which means higher investment costs (higher costs for energy saved) from the cost point of view. The German modeling project is a compact (Building envelope area inm2/building volume inm3 [A/V]: 0.38) multistory office block with three floors and 1680 m2(18.083 ft2) netfloor area in the city of Darmstadt, Hesse, constructed in1962 and situated in ASHRAE Climate Zone 5. The building was refurbished in 2012 and allowed the calibration of the modeling using the performance data (Scenario 4). The total site energy demand (DHW, heating, supply and household electricity) taken as the baseline was the consumption collected from the utility bills: 236kWh/m2yr (75 kBtu/ft2yr) heating and 20 kWh/m2yr (6 kBtu/ft2yr) electricity. Compared to average EUIs for German office buildings <10,000 m2 (<107.639 ft2), the heating consumption is 12% over average, and the electricity consumption is 18% below average. Typical for office buildings of that size and age is that air conditioning was only in use for the IT server and the restrooms, but not for the office spaces. Following the requirements of the German national building code for refurbishment of the building stock in Scenario 1 leads to a reduction of 39% of primary energy including plug loads, or 41% final energy for heating. In Scenario 2, the standards for new buildings were adopted with significant reduction of thermal bridges and air leakage and a 67% decrease in primary energy and 72% decrease in final energy for heating. Scenario 4 considered the Passive House standard for building stock and depicts exactly the situation after the refurbishment was accomplished, with 76% primary energy savings and 81% final energy for heating savings. Scenario 4 actually achieved 48 kWh/m2yr (14kBtu/ft2 yr) heating site energy after refurbishment. Because of the improved airtightness of the thermal envelope, the minimum requirements for indoor air quality required the implementation of a mechanical ventilation system with high-efficiency heat recovery but without cooling. The assessment of the lifecycle cost analysis showed the best net present value (NPV) is for Scenario 2 (adoption of building code for new buildings) while the second best is Scenario 4 (cost-optimized Passive House scenario). The main difference between the two scenarios is that Scenario 2 has only a cheap exhaust air system and Scenario 4 has a costly ventilation system with heat recovery. The added insulation for Scenario 4 has almost no impact onthe NPV because the delta costs are refinanced by the energy savings.This paper describes the baselining and modeling process; describes the economic assumptions made for energy prices, maintenance, and other operating costs; and considers the investment costs and the cost optimization process.