Each manufactured home must be designed according to the federal Manufactured Home Construction and Safety Standards at 24 CFR 3280, commonly called the HUD Code. The HUD Code stipulates, at §3280.506, that the home shall be designed and constructed to conform to one of three thermal load zones. The appropriate thermal zone value used in design is dependent on where the home will be initially installed. Homes designed and constructed to a higher Thermal Zone can be installed in a lower Thermal Zone (a home designed to a Thermal Zone 3 can be installed in a Thermal Zone 1 or 2). However, a Thermal Zone 1 home cannot be installed in either a Thermal Zone 2 or 3 area.

The Uo value zone is determined from thermal zone map above. The Uo value is the overall coefficient of heat transmission of the manufactured home based on the respective thermal zone location and an indoor design temperature of 70 oF, and is defined in units of BTU/(hour)(square foot)(oF). The overall Uo value for the home thermal envelope design must not exceed the values as shown on the above map. The design Uo value for Thermal Zone 1 is 0.116 BTU/hr·ft2·oF, for Thermal Zone 2 is 0.096 BTU/hr·ft2·oF, and for Thermal Zone 3 is 0.079 BTU/hr·ft2·oF.