Timber Windows Glossary: Complete UK Terminology Guide
Expert Dictionary of Wooden Window Terms, Specifications & UK Building Standards
Understanding timber window terminology is essential when specifying bespoke wooden windows for your UK property. This comprehensive A-Z glossary covers over 70 technical terms including traditional joinery terminology, modern glazing specifications, security standards, timber types, and UK building regulations. Whether you’re researching sash windows, casement styles, U-values, or PAS 24 certification, our expert guide explains everything in clear, simple language.
Window Types & Styles
Sash Windows
Traditional sliding windows with one or two moveable panels (sashes) that slide vertically. Popular in Georgian and Victorian properties across the UK. Available from woodenwindows-online.co.uk in various timber options.
Casement Windows
Side-hinged windows that open outward or inward. The most common window type in modern UK homes, offering excellent ventilation and easy operation.
Flush Casement Windows
Windows where the sash closes flush within the frame, creating a flat external appearance. Traditional design popular in period and cottage-style properties.
Tilt and Turn Windows
Dual-function windows that tilt inward from the top for ventilation or turn inward from the side for full opening. Common in contemporary designs.
Bay Windows
Projecting window construction extending from the main wall, typically combining three or more window units at different angles.
Fixed Light Windows
Non-opening windows designed purely for light admission. Often combined with opening windows in larger installations.
Top Hung Windows
Windows hinged at the top that open outward from the bottom. Ideal for ventilation while maintaining weather protection.
Timber Types & Materials
Engineered Pine
High-quality laminated softwood combining multiple layers for enhanced stability and strength. Excellent paint finish and cost-effective option.
Meranti
Durable tropical hardwood with natural resistance to decay. Medium to dark reddish-brown colour, ideal for staining or painting.
European Oak
Premium hardwood renowned for strength and durability. Natural golden-brown colour with distinctive grain pattern, highly weather-resistant.
Accoya
Modified sustainable softwood with exceptional durability. Acetylated timber offering 50-year above-ground warranty against rot.
Sapele
African hardwood similar to mahogany. Fine grain with natural reddish-brown colour, excellent for traditional window designs.
Laminated Timber
Engineered wood product made by bonding layers of timber. Provides superior stability and reduced warping compared to solid timber.
FSC Certified Timber
Wood sourced from responsibly managed forests certified by the Forest Stewardship Council, ensuring environmental sustainability.
Finger-Jointed Timber
Construction method joining shorter timber pieces with interlocking ‘fingers’. Creates stable, knot-free lengths ideal for window frames.
Window Components
Frame
The fixed outer structure of the window that attaches to the building opening. Comprises head, sill, and jambs.
Sash
The moveable part of the window holding the glass. Can be sliding (sash windows) or hinged (casement windows).
Glazing Bars
Horizontal and vertical bars dividing window panes. Available as authentic solid bars or decorative astragal bars.
Astragal Bars
Decorative bars applied to glass surface creating the appearance of multiple panes whilst maintaining single glazing unit integrity.
Mullion
Vertical structural element dividing window units. Essential in multi-light windows for structural support.
Transom
Horizontal structural element dividing window units. Often separates opening sections from fixed lights above.
Cill (Sill)
Bottom horizontal member of window frame, sloped outward to shed water. Available in various projections and profiles.
Jamb
Vertical side members of the window frame. Houses hinges in casement windows or guides in sliding sash windows.
Head
Top horizontal member of the window frame. May incorporate ventilation slots or drip grooves for weather protection.
Meeting Rail
Horizontal members where two sashes meet in the middle of double-hung sash windows.
Parting Bead
Thin strip separating upper and lower sashes in traditional sash windows, allowing independent movement.
Staff Bead
Decorative moulding holding sashes in place within the frame. Removable for maintenance access.
Glazing & Glass Options
Double Glazing
Two glass panes separated by hermetically sealed air gap. Standard specification offering U-values around 1.4 W/m²K. Available on all our timber window styles.
Triple Glazing
Three glass panes with two sealed cavities. Premium specification achieving U-values as low as 1.0 W/m²K.
Low-E Glass
Low-emissivity coating reflecting heat back into rooms whilst allowing light transmission. Essential for energy-efficient windows.
Argon Gas Fill
Inert gas replacing air between glass panes. Improves thermal performance by reducing heat transfer.
Warm Edge Spacer
Thermally efficient spacer bars between glass panes. Reduces condensation risk and improves overall U-values.
Acoustic Glass
Laminated glass with acoustic interlayer. Reduces noise transmission by up to 40dB for urban locations.
Toughened Glass
Heat-treated safety glass five times stronger than standard glass. Required for low-level glazing by building regulations.
Laminated Glass
Two glass layers bonded with plastic interlayer. Provides security, UV protection, and holds together when broken.
Obscure Glass
Textured or frosted glass providing privacy whilst maintaining light transmission. Various patterns and obscurity levels available.
Self-Cleaning Glass
Coating that breaks down organic dirt and uses rainwater to wash away residue. Reduces maintenance requirements.
Hardware & Fittings
Multi-Point Locking
Security system engaging multiple locking points around frame perimeter. Standard for PAS 24 compliance.
Espagnolette
Multi-point locking mechanism operated by single handle. Shoots bolts into keeps around frame when turned.
Friction Stays
Hinges allowing casement windows to stay open at any position. Available in various stack heights and opening angles.
Sash Locks
Traditional fasteners for sliding sash windows. Available in brass, chrome, or period-authentic finishes.
Window Restrictors
Safety devices limiting opening distance. Required for upper floor windows to prevent falls.
Trickle Vents
Small ventilation openings providing background airflow when windows are closed. Often required by building regulations.
Draught Seals
Compression seals around frame preventing air infiltration. Modern EPDM or silicone seals offer excellent longevity.
Sash Cords/Chains
Traditional mechanism for counterbalancing sliding sashes. Cords for authentic restoration, chains for durability.
Finishes & Treatments
Factory Spray Finish
Professional paint application in controlled conditions. Provides smooth, durable finish with 8-10 year maintenance cycles. Contact us for available colour options.
Microporous Paint
Breathable coating allowing moisture vapour transmission whilst repelling liquid water. Prevents timber deterioration.
Wood Stain
Translucent finish enhancing natural grain visibility. Available in various colours whilst maintaining timber texture.
RAL Colours
Standardised European colour matching system. Over 200 colours available for consistent colour specification.
Farrow & Ball
Premium heritage paint colours popular for period properties. Curated palette of sophisticated traditional shades.
Dual Colour
Different colours on internal and external faces. Allows coordination with interior décor and external architecture.
Primer
Base coating protecting timber and ensuring paint adhesion. Quality primers essential for finish longevity.
Wood Preservative
Treatment protecting against rot, fungi, and insects. Applied before finishing for comprehensive protection.
Technical Specifications
U-Value
Measure of heat loss through window (W/m²K). Lower values indicate better thermal performance. Building regulations require 1.6 W/m²K or better.
Air Permeability
Measure of air leakage through closed window. Rated Class 1-4, with Class 4 offering best performance.
Weather Resistance
Combined water tightness and wind resistance ratings. Essential for exposed locations and coastal properties.
Acoustic Rating
Sound reduction measured in decibels (dB). Standard double glazing offers 28-32dB reduction.
Window Energy Rating
Overall energy performance rating from A++ to G. Considers U-value, solar gain, and air leakage.
Thermal Bridge
Area of increased heat transfer, typically at frame edges. Minimised through thermally broken designs.
Condensation Resistance
Frame and glazing design preventing internal condensation. Critical for occupant comfort and fabric protection.
Compliance & Certification
PAS 24
Enhanced security standard for doors and windows. Police-preferred specification including multi-point locking and anti-drill cylinders.
Secured by Design
Police initiative promoting security standards. Products meeting SBD requirements significantly reduce burglary risk.
Building Regulations Part L
Energy efficiency requirements for windows. Specifies maximum U-values and minimum ventilation provisions.
CE Marking
Mandatory conformity marking for construction products. Confirms compliance with harmonised European standards.
FENSA Certificate
Certification for replacement windows confirming Building Regulations compliance. Required for property sales.
Listed Building Consent
Permission required for window changes in listed buildings. Must maintain architectural character.
Conservation Area Approval
Planning requirements for properties in conservation areas. Often requires matching original window designs.
ISO 9001
Quality management standard ensuring consistent manufacturing processes and customer satisfaction.
Need Help Understanding These Terms?
Our timber window experts are happy to explain any terminology and help you specify the perfect windows for your project. With over 10 years of experience supplying bespoke wooden windows across the UK, we’ll guide you through every technical detail to ensure you make the right choice.
Ready to Order Your Timber Windows?
Now that you understand the terminology, let’s discuss your specific requirements. We offer made-to-measure timber windows with nationwide delivery across the UK.
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