Pairs of doors are common in schools, offices, warehouses, and church entrances, and the center seam is often where cold air, light, and noise slip through first. When that strip is bent, missing, or the wrong type, the doors may also fail to latch. If your pair already shows a gap, you can schedule an astragal check before temperatures drop.
What Does an Astragal Do on a Pair of Doors?
According to industry definitions, an astragal closes the clearance gap between two leaves to improve privacy, reduce light and air passage, slow sound, smoke, and flame, and add security. In practice, it does several jobs at once.
On exterior pairs, it keeps wind and water out of the center seam. On interior corridor pairs, it can help a fire-rated opening perform as tested. On security doors, it covers the latch area so tools cannot easily reach the bolt through the gap.
Overlapping Astragal vs Split Astragal: Key Differences
Overlapping Astragal
This is a single strip attached to one leaf that laps over the other when both are closed. Because it overlaps, the inactive leaf must close first, which usually means adding a coordinator at the frame head so the doors close in the right order.
Split Astragal
This type uses two pieces, one on each leaf, that meet in the middle. It is also called meeting stile gasketing. Since neither piece blocks the other door, both leaves can swing independently, which matters on egress openings.
Which One Fits Your Doors?
The choice depends on the door listing, the hardware on each leaf, and how people use the opening. A pair with panic hardware on both leaves often needs a split design.
Why Pairs Leak Air Before Winter in Chicago
Seals at the center seam take constant abuse as doors open and close, and cold weather makes worn rubber stiff and brittle. You can get a free estimate on repairs before the first cold snap.
At Chicago Door People, we often find that the astragal itself is fine but the doors have sagged, leaving a wedge-shaped gap at the top. Fixing hinges and alignment first lets the astragal seal evenly again.
Do Fire Rated Double Doors Need an Astragal?
It depends on the door manufacturer’s listing. Older editions of NFPA 80 required an overlapping astragal on some higher-rated pairs, but the 2007 edition removed that prescriptive rule. Today, the listing for the specific door assembly decides whether an astragal is needed and which type.
NFPA 80 also prohibits astragals that block the free use of either leaf on egress pairs. That is why many corridor pairs use split astragals or a coordinator setup. More detail on these openings is on our fire rated double doors page.
Signs Your Astragal Is Worn or Wrong
- Light visible along the center seam when both doors are closed.
- Bent, loose, or missing metal sections or screws.
- Gasket material that is torn, flattened, or hard.
- One leaf that will not latch unless the other closes first.
- An astragal added later to a fire-rated pair without checking the label.
Astragal vs Mullion: Two Ways to Close the Center Gap
A mullion is a vertical post fastened to the frame head and floor, and the doors close against it. An astragal rides on the doors themselves. Mullions are common with rim exit devices, while astragals work with flush bolts, vertical rods, or simple locksets. Both appear among the commercial door parts list we stock.
Astragal Replacement in Chicago IL: What the Work Involves
Replacement starts with checking door alignment, hardware function, and any fire label. The new astragal is then sized, fastened, and tested so both leaves close and latch in the correct order. On fire-rated doors, field changes must follow the listing so the label stays valid.
Our team at Chicago Door People is licensed and insured and brings more than 35 years of door experience. Related frame pieces, from stops to strikes, are explained in our guide to door frame parts explained.
Frequently Asked Questions About Astragals
What is a door astragal made of?
Most are aluminum, steel, stainless steel, or wood, often with rubber or brush inserts. The Steel Door Institute glossary also lists Z-shaped and wrap-around styles.
Can an astragal be added to any pair of doors?
On non-rated doors, usually yes. On fire-rated pairs, check the label first, since NFPA 80 points to the manufacturer’s listing, as explained in this industry Q&A on fire door astragals.
What gap is allowed between fire-rated pairs?
Clearances at the meeting stiles are set by NFPA 80 and the door’s listing. The Intertek overview of NFPA 80 explains how the standard governs installation and maintenance of fire doors.
Does an astragal stop drafts completely?
It helps a lot, but the door bottom and jambs also need good seals for a tight opening.
How quickly can you replace a damaged astragal?
We offer same-day response for urgent problems, such as a pair that will not secure at night.
Close the Gap Between Your Doors Before Winter
The answer to what is a door astragal is simple: it is the strip that seals and secures the center of a pair. Choosing the right type and keeping the doors aligned keeps that seam tight through winter. When you need help, you can contact our door technicians at Chicago Door People.