window jamb 16 the curl spring 42 may resist being uncurled such that the curl spring 42 exerts an upward force on the carrier 40 thereby biasing the lower sash 14 toward the open position one aspect of the present disclosure is an air and debris dam 200 200 u2032 300 400 shown in fig2 9 the air and debris dam 200 200 u2032 300 400 primarily serves to obstruct airflow through the jamb channel and provide a barrier to inhibit the proliferation of debris in the jamb channel the air and debris dam 200 200 u2032 300 400 is preferably formed from a light weight cellular foam type material that is flexible and or elastically deformable yet resilient in this respect the air and debris dam 200 200 u2032 300 400 can be deformed for installation through the slot 36 in the jamb channel 26 of an assembled window 10 and then return to its original size and shape once positioned in the jamb channel 26 the cellular foam material resists the flow of air and can capture debris 50 as shown in fig6 the air and debris dam 200 200 u2032 300 400 is sized and shaped to fit generally snugly within the jamb channel 26 of the window jamb 16 several exemplary embodiments of an air and debris dam 200 200 u2032 300 400 are shown in fig2 9 referring now to fig4 air and debris dams having various geometries are illustrated a first exemplary air and debris dam 200 includes a base portion 202 having a generally rectangular prism geometry the width w and.