Ammonia (NH3) emissions were monitored from ten commercial layer houses in Iowa (IA, six) and Pennsylvania (PA, four) for a full year, with two different housing and management schemes. Highrise layer houses (four in IA and two in PA) stored manure in the lower levels for a year, whereas manure belt houses (two in each state) had the manure removed either daily (IA) or twice a week (PA). Dietary manipulation consisting of two levels of crude protein (CP): standard CP (Ctrl) and essential amino acids (AA) supplemented lower CP (Trt), was evaluated with the four high-rise houses in IA, two houses per type of diet. Ammonia and carbon dioxide (CO2) concentrations of exhaust air in each house were measured weekly or bi-weekly using portable monitoring units (PMUs), with each data collection episode lasting two consecutive days. Ammonia levels were measured using periodically purged electrochemical sensors. Ventilation rates were determined by calibrated carbon dioxide mass balance method, based on the latest metabolic rate data for the laying hens. There existed substantial diurnal variations in ammonia emission rate (ER) for the high-rise layer houses but less variation for the manure-belt houses. In comparison, seasonal variations in ER were relatively small. Manure handling practices and diet manipulation all demonstrated effects of various degrees on ammonia emissions rate. Specifically, NH3 emission rates during 12-month monitoring period averaged 0.90 and 0.81 g/d-hen, respectively, for the high-rise layer houses with Ctrl and Trt diet in Iowa; 0.83 g/d-hen for the high-rise layer houses in Pennsylvania; and 0.068 and 0.084 g/d-hen, respectively, for the belt houses in Iowa and Pennsylvania. The results contribute to the U.S. national inventory on ammonia emissions from animal production operations, and quantify the dynamics and magnitude of ammonia emissions from U.S. layer houses as affected by housing type, manure management, diet manipulation and geographical location.