Jamb Extensions

What is a Jamb Extensions?

Definition of Jamb Extensions in Construction
Pieces of wood or vinyl, sized to accommodate varying exterior wall thicknesses. An increase in exterior wall thickness has become customary, due to the additional insulation required for the exterior walls of a residential home or commercial structure to adequately comply with the new insulation requirements. To increase the insulation rating of the exterior walls additional insulation is required. This insulation is generally achieved by the installation of a heavier batt insulation within the walls as well as rigid insulation sheathing on the exterior of the structure. This application of additional insulation causes the walls to thicken requiring additional jamb width at the openings. This additional jamb width can be achieved with jamb extensions that are applied to the perimeter of element that is being installed within the exterior walls. In some instances the jamb extensions are delivered as separate pieces of wood, vinyl , aluminum or other material to be installed in the field. In other applications, the manufacturer of the door, window or other construction element to be installed within the exterior walls will attach the jamb extensions on the units prior to shipment to the project site. This is a decision that needs to be made by the construction manager and the individual suppliers.