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Glossary of terms

Sometimes used in outdoor roofing, outdoor structures and external area structures.

We work with architects, designers, builders, landscapers, surveyors, engineers, fabricators, carpenters and joiners as well as many other professions and trades. A lot of the terms below are common to all these professions and trades but sometimes they get interchanged and in some parts of the country different names are given to roof features and components.

We hope this glossary assists our non-construction related customers to understand any terms that they come across which they have not heard before when researching outdoor roofing.

Anchor Bolts: Bolts used to anchor structural members to a concrete base, foundation or other masonry support.Barge Board: Wide decorative board fitted on the end of a gable roof just beneath the edge of the weatherproofing material following the slope of the roof from the eaves to the ridge. Traditionally timber, nowadays can also be uPVC. They may be mounted flush on the end wall or stood off on an overhanging framework with a soffit underneath.

Beam: A structural member subject to bending loads. Usually a horizontal member carrying vertical loads.

Breather Membrane:  Fixed beneath roof tile battens when laying slates or tiles and some other materials. Made from a variety of man-made materials the membrane is breathable (vapour permeable) to allow moist damp air out of a roof construction. (Also known as under roofing.)

Building Control: System of rules on most aspects of building as it affects public safety and health, enforced by Building Control Officers.

Building Services: Plumbing, electrical wiring, ventilation, gas supply and other support systems in a building.

Cantilever:  Projecting beam that is supported and restrained at one end only.

Canopy: An overhead roof or structure over which a covering is attached to provide shade or shelter.

Capillary Action: That action which causes movement of liquid when in contact with two adjacent surfaces such as roof panel side laps.

Clear Span: The distance or clear and unobstructed opening between two supports of a beam; when used with a rigid frame, this is generally less than the nominal building width.

Cold-Formed: Various shapes such as angles, channels, girts and purlins formed by press brakes or rolling mills from strip or sheet at normal room temperature.

Column: A primary structural member used in a vertical position to transfer loads from roof beams, trusses or rafters to the foundation.

Concentrated Load: A load applied to a structural element at one point rather than uniformly across a span, such as a heater unit hung from a rafter.

Coping: Protective capping on the top of a parapet or free standing wall. Sometimes referred to as a skew in Scotland when fixed on a stone built roof verge.

Counter Batten: A batten mounted vertically up the roof along the lines of the rafters – normally used where the roof frame has been boarded to give a space when the underfelt and battens are fixed.

Dead Load: The weight of the materials which form a permanent part of the structure, such as the roof, framing and covering members plus any collateral loads.

Eaves: The eaves are the edge of a roof at its lowest point around the perimeter. The eaves may terminate flush with a structure or they may project and overhang the structure. The term eaves can include the fascia, soffit and guttering.

Fascia Board: External vertical board attached to the ends of the rafter feet to which a gutter may be fixed, traditionally timber, nowadays can also be uPVC.

Felt Roof:  A two or three layers system for flat roofs. Each layer has traditionally been bitumen based. Also known as Built Up Roofing and referred to as BUR.

Firring: A piece of timber cut as a wedge and fixed to the top of a joist. Used to give flat roofs a fall for drainage. Sometimes also called a declivity piece

Flat Roof:  A roof which has negligible slope (less than 10°), usually covered in felt, metal, or other material which is impermeable to water.

Flashings: Strips of weatherproofing material to form a weather seal made of lead, aluminium, zinc or man-made materials that are required at the intersection between the vertical faces of walls or framing and pitched roofs, flat roofs, gutters etc. to prevent moisture ingress.Plain flashing is where the roof meets the vertical surface horizontally. Stepped flashing is where the roof meets the vertical surface at an angle – the steps in the flashing align with the joints of different courses in the brickwork

Footings: Holes dug in the ground which the posts are situated in. The holes are then filled by pouring concrete into them. Typically the holes will be 600 x 600 x 600mm. can also be a pad or mat, usually concrete.

Foundation: The part of a building or structure which transmits loads to the ground.

Frame: Primary structural members, made up of columns and rafters.

Free-Standing: A structure that is not attached to a building or any other structure.

Gable: Triangular vertical upper part of wall at the end of a pitched roof

Gauge: The measurement between the roof battens for positioning the slates or tiles.

Galvanised: Steel coated with zinc for corrosion resistance.

Galvanic Action: An electrochemical reaction between dissimilar metals (such as steel and aluminium) in the presence of moisture.

Gazebo: Freestanding structures or attached to a wall, roofed, and open on all sides to provide shade and shelter.

Gutter: Installed at the eaves, valley or parapet for the purpose of carrying water from the roof to the drains or downpipes.

Green Roof: A flat roof covered (deliberately) with growing material.

Groundwork: Foundations, drainage, levelling and other building operations involving digging.

Hip: A roof feature in which two pitched roofs meet at a corner; the rafter forming such a junction (the hip rafter) is not usually a load bearing member.

Hip Board: The board along the line of a hip from the fascia to the ridge.

Hip End: A sloping end to a pitched roof.

Hipped Roof: A term used to describe a pitched roof, the ends of which are also sloped.

Imposed Load:  The weight of furniture, people, storage, and any other non-permanent loads.

Jack Rafters: These are short spars that run from a hip to the eaves or from a ridge to a valley.

Joist: A load bearing timber spanning an area supporting a floor or flat roof

Joist Hanger: Proprietary steel component to support the end of a joist so that it does not have to be built into a wall.


Lean-to Roof: A simple form of pitched roof consisting of one slope or pitch of rafters inclined against a wall which gives the roof partial support.

Ledger board: A long piece of timber anchored to the structure wall/frame. It is usually the length of the structure and the same height as the rafters.

Live Load: The non-permanent load to which a structure is subjected to in addition to its own weight. Live load includes loads induced by the use and occupancy of the structure, but does not include snow loads, wind loads, seismic loads or dead loads.

Load bearing: Designed to support a load in addition to its own weight.

Load: Anything that causes an external force to be exerted on a structural member. Examples are dead loads, impact load, roof live load, seismic load, and wind load.

Load Combinations:  The various loads such as wind live etc.

Loggia: A covered exterior gallery or corridor usually supported by a series of columns or arches. Loggias can be located either on the front or side of a building and are used as outdoor sitting rooms.

Louvre: An opening provided with fixed or adjustable blades to allow airflow.

Louvreroof: A fixed or adjustable roof made up of a series of louvres. Adjustable louvreroofs are mostly interlocking to provide weather protection. Beam supported or louvre end supported.

Mansard Roof: A roof that has two pitches on each slope. A purlin normally supports the rafters where the two pitches on the same elevation meet.

Method statement: A document which shows how the construction will be carried out safely. Under most forms of contract the contractor will prepare any necessary method statements and the engineer, surveyor or project manager will usually check them. Method statements are also sometimes required by neighbouring owners where potentially hazardous work is being proposed, or by Planning Authorities to ensure that a proposal is buildable.

Noggin: A short length of timber fixed crossways between rafters;

Outdoor roof (External roof): Designed to cover an open structure to protect the area underneath from rain, snow or sunshine (if shade is needed).

Oriel window: A bay window that projects from the wall and does not have its own foundations.

Parapet: A low wall that projects beyond the eaves at the edge of a roof.

Pergola: Used to describe a number of outdoor structures, from a shaded walkway to a freestanding structure with an open roof. It can also be an extension of a building. It is supported by columns and posts and is most commonly made of wood.

Pitch: The slope or incline of a roof. Usually expressed in degrees (e.g.25°).

Pitched roof: A roof which has a slope that exceeds ten degrees.

Posts: The vertical support structures running from the footing to the support beam(s) to allow the structure to stand up. There are usually at least two posts for a lean to structure attached to a building or four if it is free-standing.

Ponding: The gathering of water at low or irregular areas on a roof.

Purlin: Part of the roof construction. A horizontal beam, providing intermediate support to the rafters or roof covering which carries the roof loads to the primary framing members.

Rafters: Part of the roof construction. Sloping structural member supporting a roof.  Similar to joists but inclined rising from the eaves to the ridge which form the roof shape. Rafters support the pitched roof covering.

Ridge: The highest point of a pitched roof where the rafters from both sides of the roof meet.

Ridge board: The horizontal board along the line of the ridge – normally along the top of the rafters or trusses. In most roofs the ridge board is not a load bearing member.

Ridge Tile/flashing: A purpose designed tile/flashing that covers the ridge of a pitched roof.

Roof: Structure designed to keep out rain and snow including wind-driven spray from a building or structure.

Roof Kerb: A projection on a roof used to mount and level ancillary units or some types of rooflights on a roof.

Roof Live Load: Those loads induced 1) during maintenance by workers, equipment, and materials and 2) during the life of the structure by movable objects, not including wind load, snow load, seismic load, or dead load.

Roof Overhang: A roof extension beyond the end wall or sidewall of a structure.

Roof Slope: See Pitch above.

Roof Snow Load: The load induced by the weight of snow on the roof of the structure.

Roof Covering: The external material laid or attached to a roof to make it weatherproof, e.g. Aluminium, steel, tiles, slates, polycarbonate etc.

Roof Tile Batten: Long strips of soft wood used to support and to fix roof coverings onto.

Roof Truss: A prefabricated structural timber framework delivered to site to form part of the roof structure.

Roof Void: The space beneath the roof structure and above the joists.

Sarking: Boards nailed to the upper edges of the rafters to which slate and other roofing materials are secured. Predominately used in Scotland.

Sarking Felt: Fixed beneath roof tile battens when laying slates or tiles and some other materials. Traditionally a bituminous membrane but can be a variety of materials and breathable (vapour permeable) to allow moist damp air out of a roof construction. (Also known as under roofing.)

Single Slope: A sloping roof in one plane. The slope is from one sidewall to the opposite sidewall. Can also be referred to as a mono-pitch roof.

Single Span: A building or structural member without intermediate support.

Slate: Pitched roof covering. Quality natural slate is becoming more difficult to source. There are manmade alternatives

Soffit: The visible covering on the underside of the projecting eaves of a roof. It is used to seal the space between the back of the fascia and the structure. Traditionally timber but can also be uPVC.

Span: Width of building inside to inside of wall panels (sidewall to sidewall).

Spars: Part of roof construction. Sometimes referred to as rafters Similar to joists but inclined rising from the eaves to the ridge to support a pitched roof covering.

Specification: A statement of particulars of a given job as to size of buildings, quality and performance of men and materials to be used, and terms of the contract, etc.

Structural steelwork: A frame of steel sections supporting other parts of the structure.

Strut: Intermediate supporting timber for a purlin.

Support Beams: On lean to structures abutting a building, the support beam runs parallel with the supporting structure.

Tiles – Interlocking: Traditionally made from concrete with a profile allowing the tiles to overlap each other side to side, so giving much better protection from the ingress of water. Suitable for pitched roofs.

Tiles – Plain: Traditionally made from clay. Suitable for pitched roofs or vertical tile hanging.

Underfelt: A layer of material between the back of the slate/tiles and the roof frame providing an extra waterproof barrier for any moisture. Traditionally made from bitumen but modern alternatives made from plastic materials.

Translucent Panels: Panels used to admit light.

Uplift: Wind load on a building that causes a load in the upward direction.

Valley: Formed by the intersection of pitched roof surfaces having an external angle less than 180º.

Veranda: (or verandah) A roofed open gallery or porch which frequently extends across the front and sides of a building or structure.

Verge: The edge of a roof which runs from eaves to ridge at the gable.

Wind Bracing: Structural members used in roof and walls to transfer wind loads, seismic loads, etc., to the foundation.

Wind Load: A load caused by the wind blowing from any horizontal direction.

Wall Plate: Part of a pitched roof construction that receives the feet of the rafters also part of a flat roof structure that receives the ends of the flat roof joists.

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