Burrow's Post Frame Supply
Glossary of Terms
Post-frame building terminology
This glossary of post-frame building terminology produced with permission from the NFBA and utilizing the ANSI/ASABE approved Post-Frame Building System Nomenclature document. The PDF in its entirety can be downloaded from the NFBA site by clicking Post-Frame Building System Nomenclature.
Post-frame building system terms and definitions
Anchored seam fastener
- A seam fastener that penetrates the underlying structural framing a sufficient amount so as to significantly affect the shear characteristics of the connection.
- A corrosion and decay resistant member that is attached to the top of a concrete floor or wall. A base plate is generally located between posts and may function like a bottom girt. Unlike a girt, primary attachment of a base plate is to the concrete and not the posts.
- A relatively short structural support used to transfer vertical load from one structural member to another. Frequently used to transfer load from a girder to a post or a truss to a post.
- A purlin with an edge that has been cut at an angle, generally to facilitate cladding attachment.
- A girt with its wide faces horizontally oriented thus enabling it to effectively function as a shelf when left exposed.
Bottom chord continuous lateral restraint
- A row of structural framing members that provides lateral support to the bottom chords of adjacent trusses.
Bottom chord diagonal brace
- A diagonal brace that lies in the plane formed by the bottom chords of adjacent trusses (a.k.a.., the ceiling plane). The braces are used to prevent bottom chord continuous lateral restraints from shifting.
- The lowest girt. This could be a regular girt, grade girt, or a splash plank.
- Axially-loaded structural members used to help stabilize other structural components. Additional temporary bracing is generally required during construction
Bracing for individual members
- The buckling resistance of an individual framing member is often increased by attaching a T-, L-, or scab reinforcement to the side of the member.
- The area between adjacent post-frames.
- Vertical distance between the floor level and the ridge line. Also known as ridge height.
- Horizontal distance between the outside face of the girts in one endwall and the outside face of the girts in the opposite endwall.
- A post-frame building system is structurally analogous to the typical low-rise metal building system. Conventional buildings of both types have two-dimensional primary frames that are connected with secondary framing members. Nomenclature for both building systems is similar. The major difference is that the majority of framing members in a post-frame building are wood-based.
- Horizontal distance between the outside face of the girts in one sidewall and the outside face of the girts in the opposite sidewall.
- Vertical distance between the finished floor and the lowest part of a truss, rafter, or girder.
- Horizontal distance from the face of one support to the face of the opposite support.
- Foundation component attached below grade to an embedded post or pier, and that moves with it to resist lateral and vertical loads.
- A brace used to provide lateral support to the compressive edge of a beam or column. More commonly referred to as flange brace when used to support the compressive edge of an I-shaped section.
Compression edge bracing
- A compression edge brace may be used to support the bottom edge of a stacked rafter at locations near interior supports. In this case, the brace would be a diagonal member that connects the bottom edge of the rafter to nearby purlins.
Continuous lateral restraint (CLR)
- An uninterrupted row of structural framing members connecting a series of trusses. The row is perpendicular to truss members and thus provides lateral support to the truss members it connects.
- A framing member that runs at an angle to other framing members, and with other framing members generally forms a structurally-stable triangular assembly.
- A structural assembly comprised of structural sheathing (e.g., plywood, metal cladding) that is fastened to roof, ceiling, floor or floor framing in such a manner that the entire assembly is capable of transferring in-plane shear forces.
Diaphragm chord forces
- Chords developing the largest axial forces are often eave and ridge purlins or members near the eave and ridge purlins.
- Diaphragm structural framing members that run perpendicular to the applied load, and thus are subjected to axial forces when the load works to bend the diaphragm.
- When post-frame building components (e.g., purlins, girts, purlin blocks, mechanical fasteners, etc.) are positioned and connected in such a way to form a diaphragm.
Diaphragm structural framing
- Primary and secondary framing members to which structural sheathing panels are attached to form a diaphragm assembly. Diaphragm structural framing (1) resists bending moments applied to the diaphragm, (2) helps transfer in-plane shear forces across the diaphragm, and (3) prevents out-of-plane buckling of structural sheathing.
- A member, typically horizontal, that transfers shear from a floor, roof or ceiling diaphragm to a shear wall.
- Girder located at the eave of a building.
- Vertical distance between the floor level and the eave line.
- Line formed by the intersection of the plane formed by the top edge of the purlins and the plane formed by the outside edge of the sidewall girts.
Eave overhang distance
- Horizontal distance from the eave line to the outside of the subfacia.
- A purlin located at the eave line of a building. An eave purlin to which both wall and roof sheathing are attached is known as an eave strut.
- An eave purlin to which both wall and roof sheathing are attached, or a top girt to which both wall and roof sheathing are attached. Simultaneous attachment of an eave strut to both wall and roof sheathing generally provides the strut with effective continuous lateral support to resist bending about both primary axes.
- A sheathing-to-framing connector that is located along the sides or ends of a structural sheathing panel.
- A purlin in the most outer row of purlins. All fascia purlins are edge purlins but not all edge purlins are fascia purlins.
- A relatively short column embedded in the soil to provide support for an above-grade post, beam, wall, or other structure. Piers include members of any material with assigned structural properties such as solid or laminated wood, steel, or concrete. Embedded piers differ from embedded posts in that they seldom extend above the lowest horizontal framing element in a structure, and when they do, it is often no more than a couple decimeters.
- An exterior wall oriented parallel to individual primary frames.
Endwall diagonal brace
- A framing member used to transfer load from an endwall to the roof plane. Generally used above large endwall openings or where an endwall post is not continuous from grade to the rake (e.g., an endpost is terminated near the bottom chord of an endwall truss).
- Consists of endwall posts and the attached endwall truss or rake rafters.
- Post located in an endwall. 5.1.7 Sidewall post: Post located in a sidewall. 5.1.8 Corner post: Post that is part of both a sidewall and an endwall.
- Endwall frame designed with the load-bearing capability of an interior frame (i.e. primary frame) so it can serve as an interior frame when the building is expanded.
- A girt located entirely on the outside of posts. Also known as an outset girt.
- A purlin that helps form the fascia of a building. Also known as an edge purlin.
- A sheathing-to-framing connector that is not located along the sides or ends of a structural sheathing panel.
- Elevation of the finished floor surface. In the absence of a finished floor, the floor level is taken as the elevation of the bottom edge of the bottom girt. In buildings with stemwall foundations and no finished floor, floor level is taken as the elevation of the unfinished floor.
- Rafter at the rake overhang that is supported out from the endwall by rake purlins.
- Foundation component at the base of a post, pier or wall that provides resistance to vertical downward forces. When a footing is located below grade and properly attached to a post, pier or wall, it aids in the resistance of lateral and vertical uplift forces.
- Vertical distance from the grade line to the bottom of the foundation. Typically the vertical distance from the ground surface to the base of the footing. Also known as foundation embedment depth.
- On-center horizontal spacing of primary frames. Frame spacing may vary within a building. Also known as bay width.
Fully recessed purlin
- Recessed purlin whose top edge aligns with or is below the top edge of the trusses/rafters to which it is connected.
Fully recessed purlin
- Recessed purlin whose top edge aligns with or is below the top edge of the trusses/rafters to which it is connected.
Ganged wood truss
- A truss designed to be installed as an assembly of two or more individual light wood trusses fastened together to act as one.
- A large, generally horizontal, beam. Commonly used in post-frame buildings to support trusses whose bearing points do not coincide with a post. Frequently function as headers over large door and window openings.
- Truss designed to carry heavy loads from other structural members framing into it. Frequently a ganged wood truss.
- A member attached (typically at a right angle) to posts. Girts laterally support posts and transfer loads between any attached wall sheathing and the posts.
- On-center vertical spacing of girts.
Glued-laminated post (or glulam post)
- Post consisting of suitably selected sawn lumber laminations joined with a structural adhesive.
- A corrosion and decay resistant beam located on the soil surface. Also a long, thickened, and more heavily-reinforced portion of a slab-on-grade foundation.
- A bottom girt located at grade. May also function as a splash plank.
Grade line (grade level)
- The line of intersection between the building exterior and the finished ground surface and/or top of the pavement in contact with the building exterior.
- Framing member at the top of a window, door or other framed opening. In general, any framing member that ties together the ends of adjacent framing members and may or may not be load bearing.
Heavy timber truss
- A truss manufactured from wood members whose narrowest dimension is equal to or greater than 5 nominal inches. Wood members include solid-sawn timber, structural composite lumber, and glulams. Members generally connected with steel gusset plates that are bolted in place.
Hybrid primary frame
- Primary frame assembled with both open-web trusses and solid-web members for roof support.
Individual web member bracing versus web member continuous lateral restraint
- T-, L- or scab reinforcement of compressive web members is an alternative to web member continuous lateral restraint, and is generally more economical when truss configuration varies along the length of the building, and/or truss spacing is greater than four feet. The probability of a progressive collapse may also be reduced by using T-, L-, or scab reinforcement since a truss connected to another truss via web member continuous lateral restraint may have its lateral support compromised when the adjacent truss fails.
- A girt located entirely between adjacent posts. Frequently used to support both exterior and interior wall sheathing and horizontally-placed batt insulation.
- A girt located entirely on the inside of posts. Generally used to support interior wall sheathing in buildings with exterior girts.
- Post that frames the side of a door, window, or other framed opening.
- A diagonally-oriented member used to stiffen and strengthen the connection between a post and the attached roof truss/ rafter, or between a post and an attached girder.
- Two non-recessed purlins (i.e., purlins-on-edge, purlins-laid-flat, or notched purlins) that bypass each other where they are connected to the same truss/rafter.
Light wood truss
- A truss manufactured from wood members whose narrowest dimension is less than 5 nominal inches. Wood members include solid-sawn lumber, structural composite lumber, and glulams. Members may be connected with metal connector plates (MCP), bolts, timber connectors, and screwed- or nailed-on plywood gusset plates.
- A short member in an eave overhang that connects the sub-fascia and wall. Generally used to support soffit. Unlike a rafter extension, a lookout is not used to structurally support purlins or eave sub-fascia.
- A member that is attached to a structural framing member such that the cross-section of the two adjoined members forms an el.
Mechanically-laminated post (or mechlam post)
- Post consisting of suitably selected sawn lumber laminations or structural composite lumber (SCL) laminations joined with nails, screws, bolts, and/or other mechanical fasteners.
Metal plate connected wood truss (MPCWT)
- A truss composed of wood members joined with metal connector plates (also know as truss plates). Metal connector plates (MCP) are light-gage, toothed steel plates. The most common type of light wood truss.
Nail-laminated post (or nail-lam post)
- A mechanically laminated post in which only nails have been used to join individual wood layers.
- A girt that is notched to facilitate attachment to a post. Notching places a portion of the girt between adjacent posts, with the remainder located outside or inside the posts.
- A purlin that is notched to fit over roof trusses/rafters.
Open-web primary frame
- Primary frame fabricated with open-web trusses and no solid-web members for roof support.
Parallel chord truss
- Truss with top and bottom chords with equal slopes.
Partially recessed purlin
- Recessed purlin whose top edge is above the top edge of the trusses/rafters to which it is connected.
Pier and beam foundation
- A pier foundation that supports a grade beam.
Pier embedment depth
- Vertical distance from the grade line to the bottom of a pier or embedded post.
- A foundation consisting of an embedded pier and all attached below-grade elements, which may include a footing, uplift resistance system, and collar.
- A round, naturally tapered, unsawn, wood post. Poles are sometimes slabbed to aid in fastening framing members.
Pole-frame building system
- A post-frame building in which all posts are round poles. Commonly referred to as a pole building.
- A structural column. Functions as a major foundation element when it is embedded in the soil. Post-frame building posts include solid-sawn posts, structural composite lumber posts, glulam posts, mechanically-laminated lumber posts, and poles.
- A foundation consisting of an embedded post and all attached below-grade elements, which may include a footing, uplift resistance system, and collar.
Post-frame building system
- A building characterized by primary structural frames of wood posts as columns and trusses or rafters as roof framing. Roof framing is attached to the posts, either directly or indirectly through girders. Posts are embedded in the soil and supported on isolated footings, or are attached to the top of piers, concrete or masonry walls, or slabs-on-grade. Secondary framing members, purlins in the roof and girts in the walls, are attached to the primary framing members to provide lateral support and to transfer sheathing loads, both in-plane and out-of-plane, to the posts and roof framing.
- The length of the non-embedded portion of a post.
Post size and spacing
- Post size and post spacing are dictated by such factors as: size of wall openings, wall heights, spacing of primary roof framing, and type and magnitude of structural loads.
- The two-dimensional interior frame that is formed by the direct attachment of a roof truss/rafter to its respective posts. Also known as a post-frame or a main frame.
Primary framing members
- Primary framing members are the main structural framing members in a building. In a post-frame building they include the posts, roof trusses/ rafters, and any girders that transfer load between roof trusses/rafters and posts.
- A member attached (typically at a right angle) to roof trusses/ rafters. Purlins laterally support trusses/rafters and transfer load between roof sheathing and roof trusses/rafters.
- A member placed between purlins to help transfer load from roof sheathing to roof framing, to reduce purlin roll, and/or to eliminate bird perch points.
- A purlin that rests on top of roof trusses/rafters with its narrow face in contact with the trusses/rafters.
- A purlin that rests on top of roof trusses/rafters with its wide face in contact with the trusses/rafters.
- On-center spacing of purlins.
- One of a series of sloped, structural beams that support a roof.
- A framing member attached to the end of a truss or rafter that extends the effective slope length of the roof by supporting additional purlins and/or subfasica. Rafter extensions are commonly used to help form eave overhangs as well as over shot roofs.
- Line formed by the intersection of the plane formed by the top edge of the purlins and the plane formed by the outside edge of the endwall girts.
Rake overhang distance
- Horizontal distance from the rake line to the outside of the fly rafter.
- A purlin that overhangs the endwall of a building.
- A rafter located in an end wall.
- A purlin located entirely between adjacent trusses/rafters. Single-span components that are typically held in place with special metal hangers. Also known as an inset purlin or dropped purlin.
- Girder located at the ridge of a building.
- Line formed by the intersection of the plane formed by the top edge of the purlins on one side of the roof and the plane formed by the top edge of the purlins on the opposite side of the roof. For a mono-slope roof, the ridge line is the line formed by the intersection of the plane formed by the top edge of the purlins and the plane formed by the outside edge of the girts in the tallest sidewall.
- A purlin adjacent to the building ridge.
- A truss that directly supports a roof.
- A member whose wide face is attached to the wide face of a structural framing member.
Screw-laminated post (or screw-lam post)
- A mechanically laminated post in which only screws have been used to join individual wood layers.
Seam (or stitch) fastener
- An edge fastener that connects two structural sheathing panels thereby adding in-plane shear continuity between the panels.
- Bracing is a primary function of virtually all secondary framing members. For example, a principal function of purlins and girts is to provide lateral bracing to trusses and posts, respectively. Unlike braces used to help stabilize other structural components, purlins and girts are generally located to facilitate sheathing attachment, and their sizes are normally based on the magnitude of the loads applied to the sheathing, and on the spacing of the primary framing members to which they must transfer load.
Secondary framing members
- Structural framing members that are used to transfer load between exterior sheathing and primary framing members, and/or laterally brace primary framing members. The secondary framing members in a post-frame building include girts, purlins, eave struts and any structural wood bracing.
- Short framing members used to help transfer shear force into or out of the structural sheathing of a diaphragm. For roof diaphragms, properly connected purlin blocks function as shear blocks.
- A vertical diaphragm. Any endwall, sidewall, intermediate wall or portion thereof that is capable of transferring in-plane shear forces.
- An exterior wall oriented perpendicular to individual primary frames.
- A corrosion and decay resistant member that is attached to the top of a concrete foundation wall, and upon which posts are attached.
Single-span primary frame
- Primary frame without any interior supports. Also known as a clear span primary frame. Multi-span primary frame: Primary frame with one or more interior supports.
- A reinforced concrete slab that rests on the soil surface. Slab areas located directly beneath structural columns or walls are generally thicker and more heavily reinforced. Long, thickened and reinforced portions are generally referred to as grade beams.
- Post comprised of a single piece of sawn lumber.
Solid-web primary frame
- Primary frame assembled without using any open-web trusses.
- A girder composed of two beams that are separated a fixed distance by special spacers and/or the girder supports.
- Any decay and corrosion resistant girt that is in soil contact or located near the soil surface, that remains visible from the building exterior upon building completion, and is 2 to 4 inches in nominal thickness. Frequently, multiple rows of tongue and groove (T&G) splash plank are used along the base of a wall.
- A mechanically laminated post in which individual laminations are fabricated by end-joining shorter wood members. End joints are generally either unreinforced butt joints, mechanically-reinforced butt joints, glued scarf joints, or glued finger joints.
- A narrow, deep rafter made by placing one rafter on top of another and fastening them together. Generally made by fastening dimension lumber together with metal connector plates.
Stem wall foundation
- A foundation consisting of a continuous wall that may be placed on a continuous footing. The base of the foundation is generally located below expected frost penetration depths.
Structural composite lumber post (SCL post)
- Post comprised of a single piece of structural composite lumber. Structural composite lumber (SCL) includes, but is not limited to: parallel strand lumber (PSL), laminated veneer lumber (LVL), and laminated stand lumber (LSL).
Structural ridge cap
- A component that covers the ridge of a building and is capable of transferring shear force between diaphragms located on opposite sides of the ridge.
- Frame coverings that are selected in part for their ability to absorb and transfer structural loads. Common structural sheathings include plywood, oriented strand board, and corrugated steel.
Structural sheathing panel
- An individual piece of structural sheathing.
- A structural member located under the fascia or eave/ fascia trim. In a building with overhangs, the edge purlins and fly rafters generally function as sub-fascia. In a building without overhangs, the eave strut and rake rafters generally function as sub-fascia.
- A framing member used to attach a roof truss/rafter to a girder.
- The highest girt. A top girt to which both roof and wall sheathing are attached is known as an eave strut.
- A member to which a sliding door track is directly attached.
Track board support
- A structural framing member that is used to support a track board.
- A member that is attached to a structural framing member such that the cross-section of the two adjoined members forms a tee.
Truss (Wood Trusses)
- A structural framework, generally two-dimensional (i.e. planar), whose members are almost always assembled to form a series of inter-connected triangles. Perimeter members of the assembly are called truss chords and interior members are called truss webs.
- A wood truss that functions as a girder. Top and bottom chords of a truss girder are generally parallel.
- A mechanically laminated post in which individual laminations do not contain end joints.
- Any element mechanically attached to an embedded post or pier to increase the uplift resistance of the foundation. Common uplift anchors include concrete footings, concrete collars, preservative-treated wood blocks, steel angles, and concrete backfill.
- A pair of diagonal braces that meet at one of their ends, thus forming a “V”. Generally, one brace will be in axial tension while the other brace is loaded in axial compression.
Web member continuous lateral restraint
- A row of structural framing members that provides lateral support to the web members of adjacent trusses.
Web plane diagonal brace
- A diagonal brace that lies in the plane formed by the web members of adjacent trusses. The brace generally runs from the roof plane to the ceiling plane, and is required in truss web planes that contain continuous lateral restraints to keep the CLR from shifting.
- A pair of diagonal braces that cross each other thus forming an “X”. Generally, one brace will be in axial tension while the other brace is loaded in axial compression.