astragal
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as·tra·gal
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n.
A narrow convex molding often having the form of beading.
[Latin astragalus, from Greek astragalos.]
1. A bead, usually half-round, with a fillet on one or both sides. It may be plain, but the term is more correctly used to describe the classical molding consisting of a small convex molding decorated with a string of beads or bead-and-reel shapes.
2. A plain bead molding. Also called roundel, baguette, or chaplet.
3. A member, or combination of members, fixed to one of a pair of doors or casement windows to cover the joint between the meeting stiles and to close the clearance gap; provides a weather seal, minimizes the passage of light and noise, and retards the passage of smoke or flame during a fire. Also see overlapping astragal, split astragal.
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Astragal
An astragal is a moulding profile composed of a half-round surface surrounded by two flat planes (fillets). An astragal is sometimes referred to as a miniature torus. It can be an architectural element used at the top or base of a column, but is also employed as a framing device on furniture and woodwork.
The word "astragal" comes from the Greek and Latin for "vertebra," and the original astragals used in architecture were made in a beaded design, thereby resembling a vertebra.
An astragal is commonly used to seal between a pair of doors. The astragal closes the clearance gap. The vertical member (molding) attaches to a stile on one of a pair of doors (either sliding or swinging) against which the other door strikes, or closes to.
Exterior astragals are kerfed for weatherstripping. Also flush head and foot bolt hardware is commonly mortised into the astragal to hold the inactive door in place, when both doors operate, at the top and bottom. It is related to Moulding.
Also known as “meeting stile seals,” the term can refer to the raised half-round overlap where pairs of doors meet, such as is the case with French doors. An astragal is designed to be applied to one or both doors of a pair at their meeting edges (meeting stiles). The astragal closes the clearance gap for the purpose of either providing a weather seal, ensuring privacy, preventing sound from leaking in or out of a room, minimizing the passage of light between the doors, or retarding the passage of smoke or flame during a fire.
Doors are typically the weakest link in any partition that is designed to block sound. This is often due to poor sealing around the perimeter of the door. Astragals, perimeter gasketing, drop seals and door sweeps can all be used to prevent sound from leaking through cracks around the door perimeter.
References
- "What The Heck Is An Astragal?". The Galoot's Progress. http://homepage.mac.com/galoot_9/astragal.html. Retrieved October 12, 2005.
- "Ultimate Astragal". Endura Products. http://www.enduraproducts.com/product-overview/astragal/index.aspx.
External links
Chisholm, Hugh, ed (1911). "Astragal". Encyclopædia Britannica (11th ed.). Cambridge University Press.
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