Why the Gap Between Double Doors Matters More Than You Think
When two door leaves meet at the center of an opening, that joint is called the meeting stile. Without a proper seal at the meeting stile, a door pair is essentially an open gap in your building envelope -- exposed to air infiltration, noise, dust, weather, smoke, and in some cases, fire. The component designed to close that gap is called an astragal.
This guide covers how to select and install aluminum astragals correctly for commercial openings: schools, healthcare facilities, retail storefronts, and industrial applications. Whether you are a contractor pulling a hardware schedule, a facility manager replacing a worn seal, or an architect detailing a door schedule, the information here will help you get the specification right the first time.
What Is an Astragal?
An astragal is a vertical seal -- typically an aluminum extrusion fitted with a compressible gasket material such as neoprene -- that is surface-mounted to one or both leaves of a door pair. Its job is to seal the gap between the two doors when they are closed. Astragals also provide a surface for the inactive leaf to latch or bolt against, and in fire-rated assemblies, they play a critical role in containing smoke and heat at the meeting stile.
Do not confuse an astragal with a weatherstrip or perimeter seal. Weatherstripping addresses the gap between the door and the frame. An astragal addresses the gap between the two door leaves themselves.
Choosing the Right Astragal: Key Variables
Mounting Method
- Single-piece, surface-mounted: The most common configuration. An aluminum extrusion with a neoprene or vinyl gasket mounts on the edge or face of one door leaf and overlaps the other. This is acceptable when one leaf is designated as inactive, or when a door coordinator is used to control closing sequence.
- Two-piece (split astragal): One extrusion mounts on each leaf. When the doors close, the pieces engage -- either overlapping or butting together. This approach works on pairs where both leaves are active. Hardware consultants and the DHI recommend a tapered, flexible neoprene insert to allow unrestricted operation without drag or binding.
- Spring-loaded single-piece: Mounts on one leaf but uses a spring mechanism that allows both leaves to swing freely without a coordinator. Useful in high-traffic applications where both leaves need to operate independently.
Seal Material
Neoprene is the most widely used gasket material in commercial aluminum astragals. It compresses reliably, holds up in both interior and exterior conditions, and performs well in temperature variation common to school corridors, hospital wings, and loading dock entries. Neoprene also resists compression set better than foam or felt over time.
On fire-rated assemblies, the seal material matters even more. Wool pile -- sometimes used in standard acoustic astragals -- is generally not acceptable at the meeting stile of a fire door pair because of its combustibility. Verify that any astragal specified for a fire-rated opening uses a material compatible with the door and frame label and the requirements of NFPA 80.
Finish and Material
Aluminum astragals are available in several anodized finishes: dark bronze, gold anodized, black anodized, and mill finish are the most common in commercial work. The finish choice should coordinate with other hardware and frame finishes on the opening. Dark bronze anodized is frequently specified on storefront and vestibule applications, as well as in institutional settings where durability and a professional appearance are both priorities.
For exterior-facing pairs or openings in humid environments -- healthcare corridors, commercial kitchens, or covered loading areas -- aluminum construction resists corrosion in a way that steel hardware cannot match without a protective coating.
Length Selection
Standard commercial astragals are available in 84-inch and 96-inch lengths to cover the two most common commercial door heights: 7-foot and 8-foot openings. Always verify the actual door height before ordering. If the door height is non-standard, field-cutting an aluminum astragal to length is a common and acceptable practice -- cut cleanly, deburr the end, and confirm the seal material extends fully to the cut edge.
Fire Door Pairs: What the Code Requires at the Meeting Stile
NFPA 80 governs the hardware requirements for fire door assemblies, including the meeting stile of labeled door pairs. The standard limits the gap at the meeting stile to between 1/16 inch and 3/16 inch for steel doors. Gaps outside that range require correction before the assembly can pass inspection.
Beyond gap tolerances, NFPA 80 requires that fire door pairs be equipped with either an astragal or an overlapping rabbet at the meeting stile -- unless the door is specifically listed without one. An annual inspection of the fire door assembly must verify that the astragal is intact, properly seated, and that it does not obstruct the latching or exit hardware operation.
If you are specifying or replacing astragals on a fire-rated pair, confirm that the product is compatible with the door's UL label and that any installation preparation -- such as screw holes or fasteners -- does not violate the door manufacturer's label service procedures. Surface-mounted hardware on fire doors is generally limited to fastener holes no larger than one inch in diameter unless the listing specifically allows otherwise.
Common Installation Problems (and How to Avoid Them)
Hardware Conflicts at the Meeting Stile
The meeting stile is busy real estate on a commercial door pair. Flush bolts, coordinator strikes, and latching hardware often occupy the same edge where the astragal needs to mount. Notching the astragal to clear hardware interrupts the continuous seal -- and on a fire door, that interruption can create a code compliance problem.
The solution is to detail the opening hardware set completely before ordering. Confirm the astragal mount location does not conflict with flush bolt barrels, exit device rods, or strike cutouts. Some astragal profiles are designed to accommodate hardware clearances; a two-piece design may offer more flexibility in congested openings.
Incorrect Closing Sequence Without a Coordinator
A single-piece overlapping astragal mounted on the active leaf creates a dependency: the inactive leaf must close first, or the active leaf's astragal will block the inactive leaf from latching. In openings without a door coordinator, this is a frequent callback. Either specify a coordinator as part of the hardware set, use a two-piece astragal that allows either leaf to close first, or use a spring-loaded single-piece designed for active-active pairs.
Binding and Drag in High-Traffic Openings
An astragal that is mounted too aggressively against the opposite leaf creates drag that shortens the life of closers, exit devices, and the seal itself. Neoprene should compress slightly when the doors are fully closed -- not be crushed or distorted. Adjust the mounting position to achieve light, consistent contact across the full length of the seal.
Application Contexts Across Facility Types
- Schools and universities: High-traffic corridor pairs benefit from durable neoprene astragals that hold up against repeated use. Finish matching to frame color is common in renovation projects where existing hardware is being supplemented.
- Healthcare: Fire-rated corridor pairs in hospitals and clinics require code-compliant meeting stile seals. Smoke containment at the meeting stile is a life-safety requirement -- not an optional upgrade. Verify NFPA 80 compliance and annual inspection documentation.
- Retail and commercial storefronts: Dark bronze or black anodized aluminum astragals complement storefront framing systems. Draft control and weathertightness at the meeting stile reduce energy costs and improve occupant comfort.
- Industrial and warehouse: Replacement astragals are a common maintenance item in high-use loading areas. Keeping standard lengths in stock -- 84 inch and 96 inch -- reduces downtime on worn or damaged seals.
What to Order: A Quick Spec Checklist
- Single-piece or two-piece configuration based on active/inactive leaf arrangement
- Door height -- 84 inch or 96 inch standard; note non-standard heights for field cutting
- Finish -- dark bronze, black anodized, gold, or mill to match frame and other hardware
- Seal material -- neoprene for most commercial applications; confirm compatibility for fire-rated pairs
- Hardware conflicts -- flush bolts, coordinator strikes, exit device rods at meeting stile
- Fire rating requirement -- verify label compatibility and NFPA 80 compliance
- Quantity -- astragals for a door pair are typically ordered as individual pieces; confirm whether two pieces are required for your configuration
DoorwaysPlus carries aluminum astragals from Hager and other manufacturers in a range of finishes and configurations for commercial, institutional, and industrial openings. If you are working through a hardware schedule and need help confirming the right product for a specific opening condition, our team is ready to assist.