To mitigate noise impact to residents around airports in the US, the Federal Aviation Administration has a Residential Sound Insulation Program. An aspect of this program is the estimation of the building Noise Level Reduction. A commonly used method of measuring Noise Level Reduction uses a loudspeaker outside the house and microphones inside. This measurement technique has a few limitations such as likely noise disturbance to neighbors, effects of flanking path and interfering noise , and inability to identify the sound isolation weaknesses of the house. Two changes are proposed. First, disturbance is reduced by moving the loudspeaker inside the house and measuring the sound outside. Reciprocity ensures that the result will not change, in principle. Second, a microphone phased array outside the house and a state of the art processing method, Robust Adaptive Functional Beamforming, are used to improve the dynamic range of the method and to pinpoint the acoustic leakage paths of the house. A preliminary test was conducted using a two-bedroom house at a university research center. The expected benefits were observed.