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A majority of smaller windows installed in residential and small to medium commercial construction are referred to generically as ‘unit windows’ which are factory-built in terms of being set into a permanent frame prior to shipment. Smaller windows however, may be field glazed, though this practice is most typical with wood windows, and has become increasingly rare with the emergence of factory built window units. The following are common window components:

-A window ‘sash’ is the fixed or movable frame in which a pane is mounted. The sash shouldn’t be confused with the window frame.

-The ‘head’ is the top most horizontal member of the frame.

-The ‘Jamb’ is the vertical member of the frame on either side of the sashes/panes.

-The ‘sill’ is the horizontal bottom most member of the frame (typically refers to exterior side).

-The ‘stool’ is the horizontal bottom most member of the frame (typically refers to interior side).

-The ‘apron’ is the horizontal trim member placed just below the stool.

-‘Head’ and ‘Side’ casings conceal the frame-to-wall joint to complete the finished look of the window.

There are many different types of windows, each providing a different look and function. Windows can be framed and sashed in a all sorts of materials ranging from wood, steel, aluminum, plastic, etc. Because of this different manufacturers have standard sizes and corresponding rough openings. Locations and sizes of windows must be planned for with shop-drawings and or schedules so the rough openings, lintels, and headers are the correct size. Depending on the architect, the standard window size may govern the rough opening size. The alternative to this is custom window sizes which can be more expensive and time consuming with pre-built windows, but required based on the intended design.

The thermal insulation rating and weather tightness are of the utmost importance in terms of a windows successful function of providing light and ventilation to the exterior while locking out moisture and thermal transfer. When picking a window unit, an architect considers building code requirements for: thermal insulation of wall assembly and window; windows structural resistance to wind loading; egress if a residential sleeping space (typically 5.7 SF of greater); fire-rating requirements; ventilation requirements; ADA requirements (clear maneuvering space, within reach, one hand operable); etc.  

Operable windows typically utilize rubber compression type weatherstripping or brush-type weatherstripping.


The rough opening for a window must be slightly larger than the outside of the frame to assure the window can be leveled, plumbed, and isolated from structural stresses. Rough openings will typically require flashing to keep any penetrating moisture from accessing the wall assembly. This flashing is commonly done with asphalt saturated building felt, adhesive backed bituminous or rubber, or corrosion resistant metal.


ALuminum or plastic framed/cladded premanufactured windows are commonly equipped with continous frame flanges around the perimeter of the window. This flange is also sometimes referred to as ‘self-flashing’ and bears against the exterior of the wall and nailed into place once the window is plumbed/leveled.

Window attachment to masonry is done with mechanical fasteners, powder driven fasteners, mortar joint laid steel clips, or masonry attached wood sub-frames; said attachment methods are recommended by the manufacturer. 

The following is a list and description of the major window types and modes of operation:

Fixed Windows – Typically the most economical and least likely to leak water and air due to fixed nature.


Sliding Window – A single hung window placed on it’s side with tracks in frame that hold sashes in place during operation horizontally.

Single-Hung Windows – One moving sash which slides vertically up and down within the frame tracks. Todays advanced systems (counterweights, pretensioned springs, or friction) counterbalance the operable sashes, which have all but phased out the old ‘cord’ and counterweight’ system. Typically utilize brush-type weatherstripping, which don’t seal quite as tightly as compression weatherstripping.


Double-Hung Windows – Two moving sashes which slide vertically up and down within the frame tracks. Todays spring systems counterbalance the operable sashes, which have all but phased out the old ‘cord’ and counterweight’ system

PROJECTED WINDOWS – Sash/pane assembly rotates inward or outward allowing for ventilation and easier cleaning access. Typically utilizes pliable synthetic rubber weather stripping that compression-seals the sash.

Casement Windows – Operating sashes side-hinged and typically swings outward. 100% ventilating. ashes may close on vertical mullion at center or a floating astragal to close on eachother


Awning Windows – Hinge on the head jamb, are typically wider than they are tall.

Hopper WIndows – Hinge on frame sill, commonly used in commercial construction, particularly in basements near grade, are typically wider than they are tall.


Pivot WIndows –  Sashes rotate 90 degrees or 180 degrees around an axis frame

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