An aluminum storefront frame expands in the afternoon sun and contracts as it cools overnight. A recessed window on the same building may stay shaded and experience a smaller temperature swing. Each opening needs movement allowances that reflect its exposure.
When specifying windows, storefront, or curtain wall for a site with large temperature swings, start with the temperatures the glass and framing will experience. Those conditions help determine the clearances around the glass, the location of frame joints, and the connections to the building.
How Temperature Swings Affect Glass and Aluminum
Weather data gives the design team a starting point. Component temperatures also depend on direct sun, shade, and how much solar energy the materials absorb. When establishing the design range, consider how exposure changes from day to night and across seasons.
Glass and aluminum expand and contract at different rates. The length of the framing matters too: if two profiles of the same material are free to move and undergo the same temperature change, the longer one changes length more. Account for this movement where profiles meet and where the frame surrounds the glass.
Whether the project is a sun-exposed storefront in Arizona or Nevada, or a glazed façade in New Mexico, Colorado, or Utah, base the range on the actual site and each façade’s exposure.
Where a Glazing Assembly Needs Room to Move
The drawings should show where the glass is supported, which frame joints allow movement, and how the assembly meets the wall. These details help the system retain the glass and maintain its seals as temperatures change.
Coordinate Glass Clearance, Bite, and Support
Inside the glazing pocket, edge clearance gives the glass room to move without contacting the metal frame. Glass bite is the depth of the glass edge engaged by the framing. There must be enough bite to retain the panel throughout the expected movement. Setting blocks support the weight of the glass and help position it in the pocket.
Set the clearance and bite together. With the same pocket depth, increasing the clearance at an edge reduces the bite at that edge. Follow the system’s requirements for glass retention and blocking for the specified glass makeup. The National Glass Association’s glazing manual provides guidance on these relationships.
Detail Frame Joints and Perimeter Seals
Review the splices between aluminum sections and the perimeter joints where the frame meets the wall. At locations designed to move, check how far each joint can open or close over the expected temperature range. The gap at installation must leave room for that movement.
For a sealant joint designed to move, match the joint dimensions to the expected movement and the sealant’s rated capacity. Coordinate nearby trim and attachments with the joint detail so they leave the intended movement path clear. NIST’s building envelope guidance explains why seals at these interfaces must accommodate movement between materials.
What IGUs and Thermal Breaks Contribute
Once the assembly has room for expansion and contraction, review how it limits heat transfer. The glass and frame contribute to that performance and should be evaluated together.
Select Insulating Glass for the Opening
Insulating glass units reduce heat transfer by separating panes with a sealed space. The glass makeup, cavity, and spacer affect the unit’s performance. When comparing thermal data for a window or façade, use values that account for the specified framing as well as the glass.
As the temperature inside an IGU changes, the pressure difference across its panes can change and cause them to bow. The response depends on the unit’s dimensions and construction. Share the proposed glass makeup, panel size, and anticipated exposure with the fabricator so the IGU can be reviewed alongside its support and clearances.
Specify a Thermal Break for the Frame
A thermal break uses a less conductive material between the interior and exterior portions of an aluminum frame. It reduces heat flow through the frame. Movement joints and clearances still need to be detailed separately, because they accommodate changes in dimension as the assembly heats and cools.
What to Check in Windows, Storefront, and Curtain Wall
For operable windows, start with sash alignment and seal contact. For storefront and curtain wall, review where the framing meets entrances, adjacent wall materials, and the building structure.
Max Windows: Alignment and Operation
PRL Max Windows are available in fixed, awning, and casement configurations with thermally broken aluminum framing. For an awning or casement unit, review the frame alignment and the clearances needed for the sash to close and engage its weather seals.
Specify the operating type, dimensions, and glass makeup together. PRL reports that performance results vary with those details, so use the thermal and weather performance data for the proposed window.
Storefront: Framing Runs and Entrances
PRL offers a thermally broken configuration of its 251DT storefront series. For a long storefront run, lay out the frame joints alongside the glass panels, supports, and entrance locations. If an entrance shifts during design, check how the new layout affects adjacent frame joints and supports.
At an entrance, review the connection between the door frame and the adjacent fixed glazing. That detail has to account for the movement specified for the storefront while preserving the door’s operating clearances and seal contact.
Curtain Wall: Supports and Connections
With PRL curtain wall systems, coordinate panel dimensions and mullion lengths with the supports, splices, and connections to the building. Identify which connections carry the required loads and where the design allows the framing to move.
When the specification calls for thermal cycling tests, AAMA 501.5-23 provides a laboratory method for evaluating permanent damage in large exterior fenestration and cladding components. If a mockup is required, confirm which glazing, joints, and attachments it needs to represent.
What to Share Before Requesting a Quote
Mark areas of direct sun and long framing runs on the drawings. Send them with the opening schedule and the following information:
- Project location, façade orientation, and shading.
- Opening dimensions, lengths of framing runs, and system type.
- Proposed glass makeup and required thermal performance.
- Expected component temperatures and movement criteria, if available.
- Supporting construction and proposed joint or attachment details.
Send your drawings and project requirements to PRL Glass & Aluminum to discuss insulating glass, Max Windows, storefront, or curtain wall options for your project.
