A high-elevation building may need solar control during the day, insulation through cold weather, and glazing that withstands the site’s wind loads. Insulating glass units also need attention to the difference between the elevation where they are fabricated and where they will be installed.
For projects in Colorado, Utah, New Mexico, Nevada, and Idaho, provide the site elevation before the glazing is fabricated. The local climate, opening dimensions, and façade orientation also help establish what the glass and aluminum systems must accommodate.
Assess Solar Exposure and Temperature Conditions
A west-facing room with extensive glazing may need solar control even where winters are cold. A shaded opening on the same building may have different daylight and heat-gain requirements. Start with orientation, shading, glazing area, and how the space will be used.
Select Low-E Glass for the Building’s Solar Needs
Low-E glass uses coatings to reduce radiative heat transfer and can be selected for different levels of solar gain. Compare three performance measures when developing the specification:
- U-factor: the rate of heat transfer through the product; a lower value indicates better insulation.
- Solar heat gain coefficient (SHGC): the fraction of solar energy admitted through the product; a lower value means less solar heat gain.
- Visible transmittance (VT): the fraction of visible light transmitted; a higher value admits more daylight.
The NFRC explanation of window ratings describes how these values relate to climate and orientation. Compare results on the same basis: glass-only data and whole-window ratings describe different assemblies.
The appropriate SHGC depends on the building’s energy design. Some winter solar gain may be useful in a heating-dominated building, while a highly glazed room may need stronger control of afternoon heat. Altitude alone does not determine that balance.
Account for Temperature Differences Across the Glass
A glass panel can be warm in the sun while its edges remain cooler within the frame. Partial shading, interior blinds, and nearby heating outlets can also affect the temperature distribution across the pane.
These differences can create thermal stress. Glass composition, coating location, edge quality, and framing influence how the panel responds. Thermal-stress evaluation must consider temperature differences across the pane, along with the glass construction and its support.
Identify overhangs and shading patterns early enough for them to be included in the glass selection. The appropriate heat treatment should follow the project’s thermal-stress evaluation and safety requirements.
Plan Insulating Glass Units for Elevation Differences
Insulating glass units contain a sealed cavity between glass panes. A difference between cavity pressure and surrounding atmospheric pressure can make the panes bow. Changes in cavity temperature also affect this response.
This is a separate design consideration from wind pressure acting across the façade. The IGU fabricator needs the expected elevation and temperature conditions, while the structural design must also address the project’s wind loads.
Consider Manufacturing, Shipping, and Installation Elevations
When a sealed IGU moves from a lower manufacturing elevation to a higher installation site, the surrounding atmospheric pressure decreases. The cavity pressure may then push the panes outward, placing stress on the glass and edge seal. The amount of deflection depends on the unit’s dimensions and construction.
The route to the site matters too. A shipment may cross a mountain pass above the destination, exposing the units to a larger elevation difference during transport than they will experience after installation.
Share the installation elevation and known shipping constraints before production. This gives the fabricator an opportunity to assess the proposed glass thicknesses, cavity width, and panel sizes against the anticipated conditions.
Confirm Whether Pressure Compensation Is Needed
The fabricator should determine whether the proposed units need pressure compensation. The decision depends on panel dimensions, glass thickness, cavity width, and the anticipated elevation and temperature conditions.
Capillary tubes are one method used in the industry to permit pressure equalization. Their use requires attention to moisture exposure, coating compatibility, gas fill, and sealing procedures. The manufacturer should define the method and any associated installation instructions for the selected unit.
The thermal data must represent the final construction. An air-filled unit, for example, should not be assigned values calculated for an argon-filled unit. Resolve any required pressure-compensation and sealing procedures before the glass arrives onsite.
Determine Wind Requirements for the Actual Site
Elevation above sea level and opening height above the ground are different design inputs. A low-rise building on elevated terrain still needs a wind evaluation based on its location, geometry, and surroundings. Upper-floor openings add height-related considerations.
Ridges, slopes, and surrounding obstructions can affect wind conditions. The project’s design professional should establish the applicable positive and negative pressures rather than deriving a rating from altitude alone. Glass dimensions, framing spans, deflection limits, and structural connections can then be selected around those requirements.
For example, two openings at the same site elevation may need different framing because one has a larger unsupported span. Similar appearance or glass thickness does not establish equivalent structural performance.
Water resistance requires its own performance information. The relationship between structural loads, drainage, and water testing is discussed in PRL’s article on glass and aluminum systems for high-wind regions.
Match Glass and Framing to the Opening
Fixed glazing, operable windows, and larger façades introduce different support and operating details. Glass thickness, unit weight, and overall glazing depth must fit the selected system. Establish these details alongside the thermal and structural requirements.
Laminated Glass for Safety and Retention Requirements
Laminated glass bonds glass layers with an interlayer that can retain fragments after breakage. It can be specified for applications with particular safety or retention requirements and may form part of a compatible IGU.
The laminate’s thickness and weight affect the complete glass makeup and its support. Its use does not establish wind capacity or resolve an IGU’s elevation-related pressure conditions. Those depend on the specified construction and the opening’s design.
Max Windows for Fixed and Operable Openings
PRL Max Windows are available in fixed, awning, and casement configurations, with thermally broken aluminum profiles designed to accommodate 1-inch IGUs. Select the operating type according to the room’s ventilation needs and intended use.
PRL notes that performance results vary with window type, dimensions, and glass configuration. Review thermal, structural, air-leakage, and water-penetration information for the proposed unit. A result for one operating type should not be assumed to cover another.
The window schedule should identify the glass makeup and operating type together. This gives the project team a clear reference when reviewing drawings, quotations, and fabrication details.
Curtain Wall for Larger Glazed Areas
PRL curtain wall systems provide framing options for larger glazed areas. Mullion spacing and depth, structural supports, and connection details need to be developed alongside the glass layout.
For a glazed lobby, establish the panel divisions and solar-control goals together. A change in glass composition can affect weight and overall unit thickness, with consequences for glazing pockets, support details, and installation.
Movement allowances and perimeter connections also need to be detailed for the proposed façade. The selected glass and framing must function as an assembly under the project’s specified conditions.
Share Project Conditions Before Requesting a Quote
Include the opening schedule and site conditions when requesting a quote. This helps PRL discuss available glass and framing options using the dimensions and performance requirements for the actual project.
For a new project or replacement, provide:
- Project address and installation elevation.
- Opening dimensions and position on the building.
- Orientation, shading, and use of the interior space.
- Required U-factor, SHGC, and daylight objectives.
- Positive and negative design pressures.
- Proposed glass makeup, system type, and operation.
- Known shipping constraints or elevation changes.
- Supporting construction and available installation details.
For replacement work, include the existing frame and glass construction. Retained framing must be assessed for its condition and compatibility with the proposed replacement unit.
Contact PRL Glass & Aluminum with your plans, site elevation, opening dimensions, and performance requirements to discuss suitable Low-E glass, IGU, laminated glass, Max Windows, and curtain wall configurations.
