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At Core Sash Windows, we have created this helpful Glossary of Sash Window Terms. Hopefully it will help you to understand just exactly what our surveyors are saying!

Architrave: The moulded decorative frame around the outside of the sash windows, to hide where the box meets the brickwork.

Argon: An inert, non-toxic Noble Gas. The most common gas used to fill the empty space in a double glazing unit. This gas provides far better heat retention than standard air, and therefore improves the thermal insulating properties of the unit.

Box: The timber frame that houses the moving sashes.

Bull Nose: A short cill, used at the bottom of a sash box, to cover where the architraving ends. This cill is fat and rounded in shape.

Casement Window: An alternate style to a sash window. This window opens on a hinge, either vertically or horizontally, and is more modern in its design than a traditional sash window.

Façade: Any side of a building that is particularly decorative / viewable by the public.

Fanlight: A small window, opening or non-opening, found above a door or larger casement window.

Fixed: Another term to describe a window that does not open. These windows appear aesthetically the same as an opening sash window, but are cheaper as they do not require the full pulley system or lead weights.

Glazing Bar: Originally, glass could only be made in small sheets. Glazing bars served the practical purpose of holding several smaller sheets into a larger frame. Now, this is no longer necessary as larger whole sheets of glass are easily produced. We now use non-functional glazing bars to keep the traditional aesthetic of your windows.

Lead Weight: Bars of lead, attached to the sash via sash cord and pulleys in order to counterbalance the weight of the sash.

Low-E (AKA Low Emissivity) Glass: A special coating is applied to the glass during the manufacturing process. This coating allows the windows to be more heat efficient, as internal heat is reflected back inwards, retaining expensive warmth in the winter. Equally, the Sun’s UV rays are reflected back outwards, retaining a cool and comfortable inside temperature during the sweltering summer heat.

Meeting Rail: The top rail of the bottom sash, and the bottom rail of the top sash. These rails ‘meet’ in the middle of the sash window, and overlap one another, preventing any gap.

Microporous Paint: A paint that is specially designed to allow the timber to ‘breathe’. Moisture is allowed out of the wood, but rain drops and other water sources are not allowed in. This prevents the timber from swelling and increases the service life of the timber.

Parting Bead: A dividing timber section/bead that prevents the sashes from rubbing against one another.

Pulley wheel: A metal wheel surrounded by a faceplate which allows the sash cords to feed through to the lead weights inside the box frame. This all works together to provide a counter-balance to the weight of the sash.

Sash: The moving section of the window that holds the glass. All sash windows have two separate sashes.

Sash Cord: The rope-like material that attaches the lead weights to the sash via the pulley system.

Sash Horn: A decorative extension of the bottom rail of a sash.

Sash Lift: A handle used to grip when opening the bottom sash.

Security Hardware: Hardware that prevents the windows from being opened by unauthorised persons. Typically, this includes a locking fastener which conjoins the two sashes and prevents movement, and barrel locks which physically limit the movement range of the bottom sash.

Side Rail / Stile: Horizontal outer-edge of a sash.

Spiral Balance Springs: A cheaper alternative to lead weights. These counter-balance the weight of a sash using coiled springs in place of weights and pulleys.

Staff Bead: A timber section/bead that attaches to the inside frame of the box. This acts as an outer-lip which holds the sashes in position. 

Subsidence:  The gradual sinking of an area of land, or the structure built on this land. This can cause different parts of the same house to be at different heights, leading to walls sloping at a downwards angle.

Warm Edge Spacer Bar: A synthetic strip placed inside the double glazed unit in order to separate the two panes of glass. This provides a consistent internal gap that can be filled with Argon to increase the thermal retention properties of the unit. Warm edge spacer bars are designed to keep the cold air from outside from meeting the warm air inside and thereby prevents condensation.

uPVC: unPlasticized Polyvinyl Chloride. A plastic used in the manufacture of non-traditional windows and doors. Not a material that is used at Core Sash Windows.


Enjoy being warm and comfortable!

call us: 020 3302 2060 or email: [email protected]

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