Specifying thermal breaks in a coastal climate

In a hot, humid climate the argument for a thermally broken frame is usually made on cooling load. That is real, but it undersells the case. The more immediate benefit is surface temperature.

An unbroken aluminum frame tracks the outdoor temperature closely. Inside a conditioned building in August, that puts a cold metal surface into air near its dew point, and the frame sweats — staining finishes, wetting sills, and eventually feeding mould in the reveal.

Every Fortwell frame and vent uses polyamide struts, which hold the interior face far enough from the exterior temperature to keep the frame above dew point across normal operating conditions. The published U-factor range follows from the same detail; condensation control is what an occupant actually notices.