Curtain wall
Assembly U-factor, pressure plate isolation and system selection.
Curtain wall →← Technical guides
Performance
Thermal breaks and energy code basics
A thermal break is a low-conductivity barrier — usually polyamide strips or poured-and-debridged urethane — separating the exterior and interior aluminum of a frame so heat cannot pass straight through the metal. Energy code regulates the whole assembly U-factor and solar heat gain coefficient, not the glass alone, so frame conductivity, glass makeup and spacer type all count toward compliance.
What is a thermal break, and what does energy code require of glazing? For architects and owners specifying assembly performance.
01
Why aluminum needs a break at all
Aluminum is an excellent conductor. An un-broken aluminum frame is effectively a thermal short circuit through the wall: the exterior face pulls the interior face toward outdoor temperature regardless of what glass is installed. That is why interior mullion faces sweat in January in buildings with perfectly good insulated glass.
The thermal break interrupts that path. What differs between systems is how much it interrupts it, and whether the break also carries structural load.
02
Break types
- Poured-and-debridged
- Urethane poured into a channel in the extrusion, then the metal bridge is milled away. Economical, common on American-profile storefront, adequate for most standard code paths.
- Polyamide strut
- Glass-reinforced polyamide strips crimped between two extrusions. Structurally stronger, more consistent, and available in deeper profiles for higher performance.
- Multi-chamber polyamide
- Deeper isolators with internal air chambers and often foam infill, typical of European-style systems. Delivers the best U-factor and condensation resistance available in aluminum.
- Insulated pressure plates
- On curtain wall, the exterior pressure plate is itself a conduction path. Isolated or insulated plates matter as much as the mullion break.
03
The three numbers that matter
Specifications and code compliance turn on a small set of assembly values. Quoting glass performance alone is the most common specification error on commercial glazing.
- U-factor
- Rate of heat transfer for the whole assembly — frame, glass and spacer combined. Lower is better. Code prescriptive paths set a maximum by climate zone and assembly type.
- SHGC
- Solar heat gain coefficient: the fraction of solar energy admitted. Controlled mostly by the low-E coating and its surface position. Lower values cut cooling load; on north elevations the tradeoff is daylight.
- CRF / CRFf
- Condensation resistance factor, reported separately for frame and glass. This — not U-factor — is the number that predicts whether interior surfaces will sweat at design conditions.
04
Meeting code without over-specifying
New Jersey commercial work follows the state-adopted energy subcode, which offers prescriptive, trade-off and performance compliance paths. The prescriptive path caps assembly U-factor and SHGC and limits the window-to-wall ratio; the trade-off and performance paths allow a glassier facade if other assemblies or systems compensate.
The practical consequence for a glazing scope: the specification should state the required assembly U-factor, SHGC and, where condensation is a concern, a minimum frame CRF. It should not simply name a glass product. A system that hits the glass number and misses the frame number will still fail the assembly calculation.
Where condensation complaints are the driving issue, specify frame CRF explicitly. Upgrading glass on a poorly broken frame moves the sweating from the glass edge to the mullion face and solves nothing.
Related questions
Will better glass fix condensation on my window frames?
No. Condensation on frames is a frame conductivity problem. Improving the glass raises the glass surface temperature and leaves the metal cold, which typically concentrates the sweating on the mullion face.
Do all commercial storefront systems have thermal breaks?
No. Non-thermal storefront is still manufactured and is still legitimately used in unconditioned spaces such as parking structures and vestibule interiors. In conditioned space it will not meet code and will sweat.
Is European-style framing required to meet code in New Jersey?
No. Standard American thermally broken systems meet common prescriptive paths. European-style multi-chamber systems matter when you need a high-performance target, an aggressive window-to-wall ratio, or best-available condensation resistance.
Where this applies
Services this guide relates to.
Storefront systems
Thermally broken storefront profiles and where non-thermal is acceptable.
Storefront systems →Weatherproofing & silicone
Air leakage at perimeter joints undermines assembly performance.
Weatherproofing & silicone →More guides
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