What is Post-Frame Construction?
Figure 1. 3-D drawing o a typical post-rame building with several post oundation options
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ost-rame buildings typically eature large, solid-sawn posts or laminated wood wall columns instead o wood studs, steel raming or concrete masonry. However, studs, steel and masonry elements are sometimes incorporated into post-rame structures to make unique “hybrid” buildings. Wall columns are either embedded into the ground or are attached to pre-cast or cast-in-place reinorced concrete piers, reinorced concrete oundation walls, or reinorced concrete thickened concrete slabs. Post-rame buildings may utilize trusses, solid-sawn lumber raters, or laminated lumber raters to support roo loads. The roo raming may be axed to each post or supported by a header. Horizontallyplaced dimension lumber - roo purlins and wall girts – interconnect the posts
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Figure 2. Post-rame building responses to rated loads with diaphragm action. ( ∆1 is eave deection with diaphragm action; ∆ is eave deection without diaphragm action)
and trusses or raters to orm the basic rame. Exterior sheathing - commonly steel, OSB or plywood - provide lateral load resistance, creating a unique building diaphragm that makes the light wood
rame comparable in strength to light steel and concrete structures. Figure 1 shows a typical post-rame building system; Figure 2 illustrates the response o a Post-rame building system to diaphragm action.
Post-rame building systems were rst developed in the 1930’s as “pole buildings.” They were constructed with pressure treated round wood posts and used primarily or agricultural acilities and small accessory buildings. In the late 1970’s to mid 1980’s, post-rame structures evolved into a nely-tuned engineered building system. Development and documentation o diaphragm design methodologies in the 1980’s to mid 1990’s improved the structural eciency o post-rame building systems and launched the adoption o post-rame into the commercial and residential building sectors. Since then the development o glue laminated and nail laminated posts and the development o alternative post oundation systems have consolidated the adoption o post-rame building systems in the commercial and light industrial sectors.
An embedded pressure preservative treated wood post or reinorced concrete pier post oundation in post-rame buildings oten replaces the continuous concrete oundation o conventional buildings. The in-plane shear strength and stiness o the roong materials transer a signicant portion o the lateral building loads through the roo and ceiling diaphragms to the end walls, thereby reducing the lateral load carried by the posts. Figure 3 shows the dierence in the structural response o a post-rame with and without diaphragm action. Post-rame accommodates a variety o oundation options, including concrete walls, concrete piers, thickened edges o concrete slabs and other products; see pages 8 and 12 or urther details.
Post-rame buildings are durable, longlasting, and adaptable to a wide variety o applications. Post-rame buildings are also exceptionally resistant to wind, snow and seismic loads. The entire structure works as a diaphragm to provide superior lateral load-resistance properties. I a design proessional does not account or the diaphragm action provided by post-rame buildings, he or she may signicantly over-engineer the building. Engineers who do not know how to account or diaphragm action may also mistakenly conclude that a post-rame building will not meet prescribed load criteria. Incorporation o diaphragm design concepts and construction details reduces post sizes and oundation embedment depth requirements or postrame building systems.
(a) Without diaphragm action.
(b) With diaphragm action. Figure 3. Cross section o a post-rame showing the response o post-rame (a) without diaphragm action and (b) with the in-plane l ateral resistive orces provided by the roo diaphragm and ceiling diaphragm.
Figure 4. Post-rame building with stone and log acade.
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Advantages of Post-Frame ue to the application o modern structural engineering principles and testing methods, post-rame technology is recognized as a truly signicant advancement in the centuries-old art o wood-rame construction. Post-rame is now the construction method o choice or any number o commercial, retail, industrial, residential, religious and public building needs.
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Because o the nature o its design and many external açade options, post-rame may be customized to provide the look you want. Post-rame is an eective and versatile choice or building additions and remodeling projects. Entire buildings may be given a new look and/or unction by integrating post-rame with existing structures.
Countless structures, including strip malls, convenience stores, restaurants, multiamily housing and oce complexes, are now erected using post-rame methods. Schools, churches, banks, re stations, airplane hangars, and many other kinds o buildings may also be designed and erected as post-rame structures. Many choose post-rame or homes, residential accessory buildings, garages, workshops and storage buildings.
Almost any type o exterior açade may be installed on a post-rame building. Steel siding, wood siding, stucco, brick, stone, and other products can be accommodated. Engineered wood siding products, architectural oam, thin-set brick, concrete, polyurethane or other composite materials that mimic brick or cultured stone can all be used on post-rame buildings.
Figure 6. Post-rame is ideally suited or retail and other commercial applications.
Figure 7. Post-rame is the most economical and versatile option or commercial and residential garages.
The natural insulating properties o wood materials are superior to those o steel or masonry. Also, because the wooden posts are spaced arther apart than in stud-wall buildings, there are ewer interruptions in wall insulating materials. Since wall posts are typically 6 to 8 inches thick, post-rame buildings eature an exceptionally large wall cavity or ample insulation, thereby reducing heating and cooling costs throughout the year.
Figure 5. Post-rame is an energy-efcient choice or attractive residential dwellings.
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Post-rame design has proven so ecient and versatile that it has expanded rom its agricultural building origins to the commercial and light industrial building sectors. Post-rame design is recognized by building codes and standards or many types o building applications.
Figure 8. Mortarless brick and stone siding products allow design proessionals new opportunities to create much more economical and energy-efcient buildings using post-rame techniques.
Advantages of Post-Frame Construction • EngineeredPost-framebuildingsareIBC codecompliant. • Post-frame buildings are durable and permanentwhenproperlydesigned,constructedandmaintained. • Architecturaldesignsthatblendinwith thelocalcommunityareeasilyachieved. • EngineeredPost-framebuildingsperform wellduringhighwindsorhurricanes. • Engineered Post-frame structures performwellunderseismicloadingconditions. • Sitepreparationiseasyandpost-frame structures are very adaptable to problemsitessuchassteepslopesandood plains. • Post-frameconstructioncaneasilycontinueduringwinterconstruction. • Long-span trusses create large, open oorplanswithouttheneedforinterior load-bearingwalls,allowinggreaterdesignexibility. • Buildingsystemcostsavingsarerealized in: Materials–fewer,largerframingmembersoptimizewallframing,therebyreducingtherequiredframingmaterials Labor–shortconstructiontimereducesconstructioncosts Construction equipment-woodpostframebuildingsareeasyto buildbecause they can be constructed with readilyavailabletoolsandequipment, soit’smorecosteffective Lower interest costs-duetoquicker erection. Energy savings–thenaturalinsulating propertiesofwoodandlarge,uninterruptedwallandroofcavitieshelppostframeattainthehighestR-valuespossiblewithminimalthermalbridging. n
Post-rame buildings transer loads to the ground through the posts, which are typically embedded in the ground or surace-mounted to a precast or castin-place concrete pier, concrete oundation wall, thickened foor slab or grade beam oundation. In addition, a number o protective cover systems have been introduced recently or enhanced protection o wood structural elements in contact with the ground. People today are concerned about sustainability and environmental impact o construction. Post-rame buildings are among the most “green” buildings you can build, not only because o the renewable aspects o wood and the recyclable
nature o steel, but because ecient use o materials and long-term energy eciency are superior compared to many other types o construction.
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Post-rame buildings may be designed to meet the highest standards or quality and aesthetic beauty, and are a very ecient and economical choice or most low-rise building applications. Whatever interior or exterior look you preer, post-rame can meet the challenge. For all kinds o buildings two to three or ewer stories tall, rom small garages to commercial and industrial structures with clear-spans up to 100 eet or more, post-rame is an excellent choice due to its many inherent advantages.
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Post-Frame Building System Structural Components The examples provided herein are not intended to mandate any specic practice. Overview
The primary structural components o the post-rame building system are wood sidewall posts, post or oundation wall ooters, post oundations, roo trusses or raters, roo purlins, wall girts, wall and roo sheathing, connections, and secondary wind bracing (Figures 9 & 10). A description o typical details or each are presented in the ollowing subsections. The examples provided herein are to illustrate concepts, not to mandate specic practices. Wood Sidewall Posts
Sidewall posts are either solid-sawn timber, glued-laminated lumber or nail-laminated lumber. Glue-laminated and naillaminated posts that are embedded into the ground have a pressure preservative treated section spliced to the bottom end (Figure 11 & 12). Posts o all types, when not in ground contact, oten are not preservative treated. Glue- and nail-laminated wall posts are typically abricated with 2x lumber. Typical post cross section sizes are nominal 4x6, 6x6, 6x8 or 8x8.
Figure 9. Illustration o typical post-rame building eatures.
Figure 10. A typical post-rame building rame. Figure 11. Laminated columns oten splice treated wood on the bottom end to untreated wood above grade.
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Figure 12. Finger-jointed glue-laminated columns provide one o several good post options. Note treated wood spliced to the bottom end.
Post Footings
Post ootings must provide resistance to gravity and uplit loads. Concrete ooter pads, 18 to 24 inches in diameter and in some cases larger, typically resist gravity loads or embedded wood posts or piers. Footers are either cast-in-place or precast concrete placed at the bottom o the wood post, concrete pier or oundation wall. Foot-
ers under oundation walls are typically 18 to 24 inches wide. The mass o the oundation plus the mass o backll above the portion o the ooter attached to the post provides uplit resistance. Pressure preservative-treated wood cleats or concrete collars are typically attached to the bottom 12 inches o the embedded wood posts to increase uplit resistance (Figure 13). Figure 14. Treated posts may be embedded in the ground.
Post Foundation Options and Protective Barriers
Many post-rame buildings utilize a wood oundation comprised o pressure preservative-treated wood posts or laminated columns embedded directly into the ground (Figure 14). Post-rame buildings are also constructed on alternative post oundations, such as embedded precast or cast-in-place reinorced concrete piers (Figures 15, 16 & 17), concrete oundation walls (Figure 18), or thickened concrete slabs (Figure 19). Continued on page 8 Figure 13. Embedded pressure preservative-treated wood post oundation with concrete ooters and: (a) attached concrete collar and (b) attached pressure preservative-treated wood cleats.
Figure 17. Pre-cast concrete piers with concrete oor. Figure 15. Cast-in-place concrete piers may be used or post-rame buildings.
Figure 16 . Pre-cast concrete piers provide one of several foundation options unique to post-frame.
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Post-frame Building System Structural Components Continued rom page 7
Post-rame buildings may also utilize innovative products that provide alternatives to placing embedded wood posts directly in ground contact. Post-rame oundations may utilize enhanced wood treatment techniques and wood protection products developed specically or post-rame buildings, such as plastic sleeves or boots (Figures 20 & 21).
The most common post oundations are either posts embedded in the ground, concrete pier oundations, oundation walls, or thickened edges o concrete slab. Pressure preservative treatment is required or all wood post oundations in ground contact. Protective barriers have been developed to enhance protection o wood oundation material in contact with the ground.
that have been treated in various ways to meet specic purposes. Because decks and playground equipment are not generally considered crucial building structural elements, treated wood or those applications is not produced to the same specications as or post-rame buildings. Properly treated and installed posts will ensure a post-rame building will last.
Whether you choose the time-tested and proven method o embedding pressure preservative-treated wood directly in the soil or you select a concrete oundation wall or one o the other products developed specically or post-rame oundation use, you can be condent that a post-rame building will provide a permanent building solution that complies with all applicable building codes.
Embedded Posts
The USDA Forest Products Laboratory has conducted long-term tests in the harshest environments ound within the continental U.S. Pressure preservative-treated test stakes in place since 1949 have shown no signs o ailure. (Craword, D.M.; Woodward, B. M.; Hateld, C. A., Comps. Comparison o wood preservatives in stake tests. 2000 Progress Report. Res. Note FPL-RN-02. Madison, WI: U.S. Department o Agriculture, Forest Service, Forest Products Laboratory, P. 121). Modern
Many post-rame buildings use pressure preservative-treated wood embedded directly in the ground to orm a post-rame oundation. Post-rame buildings that use properly treated wood products suitable or post-rame oundations have a long history o success. Many people think all treated wood is the same. They are unaware that many types o wood commodities are available
Figure 18. Typical detail o post-rame secured a top a concrete oundation wall.
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Figure 19. Typical detail o a post-rame building atop a thickened edge concrete oundation.
post-rame buildings typically use the improved ormula CCA type C at retention level 0.60 pc or one o the newer copper based preservative treatments at retention levels or structural in-ground contact applications (UC4B). The American Wood Protection Association (AWPA) is the principle standardswriting body or wood protection in the U.S. Evaluation reports rom one o several evaluation services, such as the ICC Evaluation Service (ICC-ES), may also set alternative criteria or code compliance o proprietary wood preservation systems. Various products have been adopted by AWPA and/or ICC-ES or post-rame building applications. Consult evaluation agencies, such as AWPA and ICC or urther details. Copper Chromated Arsenate (CCA) is acceptable to the EPA or post-rame building construction. CCA-treated solid-sawn posts larger than 5x5” and laminated columns o all sizes are allowed or post-rame buildings in any application, including commercial and residential applications Continued on page 10 Figure 20. Blow-molded plastic barrier system
Figure 21. HDPE plastic barrier wood protection system
Figure 22. Post-rame is an excellent choice or strip malls and other retail buildings.
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Post-frame Building System Structural Components Continued rom page 9
Figure 23. Post-rame allows high sidewalls and wide clear spans or mixed uses.
AWPA organizes standards according to its Use Category (UC) system. Wood or post-rame skirtboards should be treated to AWPA use classication standard UC4A (exterior, ground or reshwater contact in areas with low risk). Wood treated to UCA4 classication levels require both more and deeper preservative retention in the wood than do the use categories or wood decks, playgrounds and other common applications. Any portions o laminated columns and solid-sawn posts in ground contact should be treated to standard UC4B (exterior, ground or reshwater contact, severe environments, high potential or deterioration), or example, to a minimum retention o 0.60 pc CCA. An even higher level o retention may optionally be used or exceptionally harsh conditions or i additional protection is desired. I a customer requests an extra
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level o wood protection, a builder may order wood treated to UC4C (exterior, ground or reshwater contact, very severe conditions or very critical structural components); or or example to 0.80 pc CCA Kiln Drying Ater Treatment (KDAT). Other specialized oundation products may provide increased consumer condence, but they are not required by the International Building Code. The use o properly preservative treated materials – or example, a minimum o 0.60 CCA or to a minimum treatment classication o UC4B or portions o wood columns or posts embedded in the ground, a minimum treatment classication o UC4A or skirtboards, and a minimum treatment classication o UC3 or other dimension lumber less than 18 inches above ground level – is imperative to code compliance o post-rame structures.
IBC 2006, Section 2304.11.1 and 2 species that wood used above ground in the ollowing locations shall be naturally durable or preservative-treated wood using water-borne preservatives in accordance with AWPA-U1 or above-ground use: • Wood joists or bottom ofwood oor closer than 18 inches and wood girders less than 12 inches above exposed ground. •Wood framing members, including wood sheathing that rest on exterior oundation walls and are less than 8 inches above exposed ground. •Slopesandsillsonaconcreteormasonry slab that is in direct contact with the ground. •Ends of wood girders entering exterior concrete or masonry walls unless provided with a 1⁄ 2 inch airspace on top, sides and end.
•Wood siding on exterior of building closer than 6 inches above the ground. •Wood posts or columns supporting permanent structures and resting on concrete or masonry slab or ooting that is in contact with the ground unless: Post is supported by concrete piers or metal pedestals projected at least 1 inch above the slab and 6 inches above the exposed earth and are separated there by an impervious moisture barrier. Post in enclosed crawl spaces or unexcavated areas located within building periphery and supported by a concrete pier or metal pedestal at least 8 inches above ground and separated there by an impervious moisture barrier. n
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Figure 24. Although any exterior fnish may be used, steel siding and roofng are popular due to economy and maintenance-ree durability.
IBC 2006, Section 2304.11.4 species that all wood elements in contact with the ground shall be naturally durable or preservative-treated wood using water-borne preservatives in accordance with AWPAU1 or soil or resh water use. (IBC 2006, p 434 & 435) A quality builder will know manuacturer recommendations or asteners and connectors to be used with treated wood and electrical barriers that prevent corrosion o metal panels. Stainless steel asteners and panels with a thick galvanizing layer provide the best corrosion resistance.
Figure 25. Post-rame community center in an upscale housing development.
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Post-frame Building System Structural Components Continued rom page 11
Reinforced Concrete Piers, Walls, Slabs
groundline. A steel anchor bracket, or attaching a solid-sawn post or laminated column, is mounted to the top o the pier (gure 27). This oundation is usually actory abricated and shipped to the site
Besides embedding treated wood in the ground in accordance with IBC and AWPA guidelines, post-rame is readily adaptable to concrete slab and masonry oundations. Builders may use brackets or other astening systems to install posts directly onto concrete oundations (Figure 26).
Cast-in-place (poured-in-place) concrete pier systems are similar to pre-cast concrete piers except they are abricated on-site. Once the anchor brackets are placed and the concrete has set, the wood posts/ columns are attached to the oundtion peir (Figure 28).
There are also products available that oer suitable options to avoid woodto-ground contact. Although IBC and AWPA standards allow approved treated wood oundation materials to be in direct soil contact, some customers may choose one o the ollowing oundation options that have been developed specically or post-rame. Pre-cast reinforced concrete piers, designed specically or post-rame construction, consist o an embedded concrete eolumn which may extend to 18 inches above the
Figure 26. Example o a drill-set post anchor that may be afxed upon a concrete slab or masonry oundation wall.
Concrete foundation wall systems or postrame buildings typically have a 6 or 8 inch wide continuous concrete wall that extends below grade to the ooter. The post-rame is attached directly to the top o the oundation wall with properly designed connection hardware (Figures 18 & 26.)
Figure 27. Pre-cast reinorced concrete post-rame oundation piers.
Figure 28. Cast-in-place concrete pier system 12
Thickened concrete slab post-rame oundation systems are an integral part o the building’s foor slab. The post-rame is attached directly to the thickened, reinorced concrete edge o the foor slab with properly designed hardware (Figures 19 & 26). Protective Cover Systems
Blow-molded plastic barrier systems or enhanced protection o copper-based chemical-treated wood posts or laminated columns provide moisture and insect protection rom (Figure 20) the ooter to above nished foor grade. HDPE plastic barrier wood protection systems or enhanced protection o copperbased chemical-treated wood posts and laminated columns orm a plastic sleeve with an enclosed bottom to cover the embedded portion o posts or columns (Figure 21). Polyethylene post sleeve and ooting orms enclose the embedded portion o solid-sawn or laminated post to provide enhanced protection o copper-based chemical-treated post-rame oundations.
Figure 29. Post-rame retail acility with large interior clear-spans and ample room or show rooms and mechanic’s shop.
Asphalt and polyethylene based barrier wrap protections systems, which use shrinkwrapped polyethylene over posts that have been pre-coated with bitumen. Designers and builders should check or code compliance with the AWPA Standards or an ICC, or equivalent, evaluation report.
Figure 30. Post-rame garden center eaturing retail areas, ofces and work areas.
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Post-frame Building System Structural Components Continued rom page 13
Roof Framing (Trusses and Rafters)
The most common roo raming or postrame building systems consists o preengineered metal-plate connected wood trusses. Trusses are typically spaced 4 to 8 eet on center, and may span more than 100 eet. On wider truss spacings and in locales with higher snow loads, the trusses may be doubled. Truss spacings are oten the same as the sidewall post spacings, but sometimes are less than post spacings. I truss and post spacings are the same, trusses are connected directly to the top o the sidewall posts; when truss spacings are less than post spacings, the trusses are attached to headers which are then attached to the tops o the sidewall posts. For shorter clear spans, 2x solid-sawn or structural composite lumber (SCL) raters are used in place o roo trusses. These roo raters are typically spaced 18 to 30 inches on center. For larger clear spans
Figure 31. Typical truss to nail-lam post connection.
and wider rater spacings, the 2x raters are typically replaced with wider SCL or with glue-laminated lumber raters. Post to Truss and Header to Roof Framing Connections
Post-rame buildings are designed in many dierent ways. Builders, suppliers and design proessionals may exercise considerable creativity to create new designs or various connections. Typical post to truss or rater connections are shown in (Figures 31 & 32) or solid sawn or nail-lam wood columns. Trusses or raters are typically attached to the posts when post and truss/rater spacing are equal. When unequal, the roo raming is attached to solid sawn, SCL, or glue laminated headers (Figures 33 & 34). Figure 32. Typical truss to solid sawn post connection.
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Illustrations courtesy o APA-The Engineered Wood Association
Headers and Header to Post Connections
Header beams may or may not be necessary, depending on post and truss spacing. When truss and wall post spacing is equal, header beams are not necessary because trusses are directly supported by the post. Headers are either one or two wood members attached to the side(s) o the top o the wood columns. Header materials are either solid sawn lumber, glulam lumber or structural composite lumber. Headers may span one or multiple posts depending upon bay length and header material. Typical header to post and truss to header connections are Figure 33. Typical truss to solid sawn header and truss to post connections. shown in Figures 33 & 34.
Figure 34. Post to Glu-lam or SCL header and header to truss connection.
Purlins
Purlins are 2x4 or 2x6 dimensional lumber members that span between main roo members to provide raming or sheathing material attachment. Their unctions are to: •Resist gravity loads (e.g. sheathing dead load and snow loads). • Resistsecondarywindupliftloads. •Laterally brace rafters or truss top chords. Purlins can be placed fat-wise or on edge across roo raming members, or installed between them. See Figure 35 or typical roo purlin raming. It is important that purlin spacing be specied by the truss designer because purlins unction as an integral part o the truss’ permanent lateral bracing. Connection detailing is also very important or proper purlin installation. Purlins can be placed on a designed ledger or in hangers so the top o the purlin is fush with the top o the truss or rater or easier sheathing installation. Figure 35. Typical Post-rame roo raming showing engineered metal plate connected wood trusses, roo purlins afxed atop trusses on edge and lower chord stieners.
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Post-frame Building System Structural Components Continued rom page 15
When diaphragm action is utilized to carry wind or seismic loads to the end walls (shear walls), the purlins must be spliced or overlapped to provide a continuous load path over the entire building length. Purlins are very easy to install because they are light raming members. This helps speed up the roo raming process. Wall Girts
Girts are typically 2x4 wood members attached horizontally to the outside ace o post-rame columns to support the wall sheathing and to carry wind loads. They also provide lateral support or the columns to resist buckling in the plane perpendicular to the post-rame. Wall girts speed construction due to their horizontal orientation, and eliminate the need or the top and bottom plates o standard stud walls.
Figure 36. Many mistake this post-rame building or a less thermally-efcient brick building.
Sheathing
Post rame sheathing oten consists o 26 to 29 gauge ribbed metal cladding attached directly to the roo purlins and wall girts. Structural wood panel products are also used in some post-rame applications. Plywood or oriented strand board (OSB) may provide support or almost any type o exterior siding product.
Figure 37. A post-rame veterinary acility.
Bracing
Wall girts provide lateral bracing or wall posts and columns and support wall sheathing. Roo purlins provide lateral bracing or roo raters or or upper chords o trusses. Permanent bracing is used to make the truss component an integral part o the roo and building structure. Permanent bracing includes lateral, diagonal, and cross bracing.
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Temporary bracing is used during erection to hold trusses in place until permanent bracing, purlins, sheathing, and ceilings (i used) are installed. Proper erection bracing will assure that trusses are installed properly, and create a sae working environment.
For additional guidance on handling, erecting, and bracing wood trusses, contact the Truss Plate Institute (TPI) at 608/833-5900 or the Wood Truss Council o America (WTCA) at 608/274-4849, or visit www.woodtruss.com. Alternatives
Building designers are responsible or the proper design o permanent bracing. Erection contractors are responsible or the proper installation o temporary and permanent bracing.
Post-rame construction can also be integrated into stud-wall construction, depending on client needs. The construction elements may be manuactured on the job site or in a wall-panel plant.
Fire Performance W
ith compartments and an ecient protection system, such as sprinklers, res can be localized and more easily suppressed. Dimension lumber, metal plate connected trusses, gluedlaminated timbers and other structural wood products have a long history o solid re endurance perormance. The three major source documents or dimension lumber and truss re endurance assemblies are: the Fire Resistance Design Manual published by the Gypsum Association; the Fire Resistance Directory published by the Underwriters Laboratories, Inc. (ULI); and the Uniorm Building Code Table 43-C. The assemblies in these documents range in perormance rom 1 hour to 2 hours, providing fexibility or any project need.
Sprinklers
Post-rame easily adapts sprinkler systems and other orms o re protection. Depending on the importance actor o the building and how it will be used, re suppression systems may be recommended. The primary sprinkler installation standard used or commercial/industrial buildings is Installation o Sprinkler Systems, NFPA 13, which is also adopted by the model building codes. For more detailed inormation on sprinklers and their installation, contact NFPA at 617/770-3000, the National Fire Sprinkler Association at 914/878-4200, or a local sprinkler installation contractor.
Proprietary re endurance assemblies and re retardants also exist. For more inormation on these, contact TPI or WTCA. The National Frame Building Association (NFBA) has constructed and tested a 1-hour rated rewall assembly. Builders oten successully modiy this 1-hour assembly to achieve inspector approval o a 2-hour rewall rating by applying additional sheets o drywall. For more inormation visit www.nba.org.
Insurance Considerations
Post-rame buildings typically eature steel cladding that is very resistant to re. Wood is fammable, although it is not as combustible as some other building materials. Steel, masonry and other products that are re-resistant may also see structural ailure in building res. Like other types o buildings, post-rame buildings may be erected to provide eective re resistance in accordance with building code requirements.
The cost o insuring a building is another major construction consideration, particularly in commercial buildings. The insurance industry uses the ollowing criteria to evaluate the loss potential o buildings: 1. Occupancy load (type o business) 2. Exposure (possible risk o loss) 3. Construction type (wood, steel, or concrete) 4. Special hazards 5. Protection (sprinklers, re alarms)
Occupancy loads and exposure are the two primary decision actors or insurance companies because they will most infuence the risk o loss. The construction type (e.g. post-rame, steel-rame, etc.) portion o the rate does not typically vary by more than 5% rom the most combustible to the least combustible designation or larger commercial/ industrial buildings, based on research perormed in the Midwest. In addition, buildings o three stories or less are oten underwritten using a global or class rate system which does not even dierentiate by construction type. Increased building protection rom sprinklers, periodic security checks, re alarms connected to the re department, etc., can dramatically lower insurance rates because o the reduced possibility o large re losses. Insurance ratings are oten buildingspecic and are based primarily on the statistical loss experience and loss severity that insurance companies have ound or the building type being constructed in a specic geographic region. In some cases, insurance companies use the global Insurance Services Oce (ISO) loss statistics. In other cases, they use their own loss experience. Both infuence the ultimate insurance rate quoted. All o this means the cost o insuring a post-rame building should be comparable to the cost o insuring a steel-rame building. The key to getting the best insurance rate is to get several bids rom dierent insurance brokers using dierent insurance companies. It is also helpul to add re detection and protection systems to get the lowest possible rates.
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Code Compliance Post-Frame is code accepted and compliant with applicable building regulations. Pertinent standards include: American Wood Council
The American Wood Council’s Design or Code Acceptance document “DCA5 – Post-Frame Buildings” summarizes and documents post-rame code compliance. International Building Code
The International Building Code recognizes and approves post-rame construction in accordance with American Society o Agricultural and Biological Engineers’ engineering practice standards EP 486 and EP 484.2 in Section 2306.1 (Allowable Stress Design) since adoption o the 2003 IBC. The IBC recognizes and approves post-rame construction in accordance with the reerenced standards.
ASAE EP559, Mechanically Laminated Columns
This engineering practice presents the rational basis or determining the structural strength and stiness o mechanically laminated columns used in many modern post-rame buildings. American Wood Protection Association
The American Wood Protection Association’s standards and EPA documents conrm the suitability o using properly treated building posts in ground contact or permanent edices. AWPA documents speciy treatment o posts and various other lumber products installed at or below grade or buildings in the use category system: “User Specication or Treated Wood Products.” AWPA species UC4A or above-ground uses such as post-rame skirtboards and UC4B or “building poles and permanent wood oundations” embedded within the ground. These and EPA documents conrm the suitability o using properly treated building posts in ground contact or permanent edices.
ASAE EP486.1, Shallow Post Foundation Design
This engineering practice created through a consensus process by the American Society o Agricultural and Biological Engineers (ASABE, ormerly ASAE) presents the engineering basis or determining the depth o embedment or sidewall posts in post-rame buildings. It presents a rational basis or the required lateral and uplit capacity or the embedded post and or designing the oundation or a post-rame building. ASAE EP484.2, Diaphragm Design
This presents the rational engineering basis or diaphragm design o post-rame buildings in a ormat suitable or acceptance by architects and engineers, reerenced rom IBC section 2306.1. ASAE EP 558, Load Tests for Metal-Clad Wood-Frame Diaphragms
This engineering practice establishes the test procedures and the data analysis procedures or determining the in-plane shear strength and in-plane shear stiness o metal-clad, wood-ramed structural diaphragms typically used in postrame buildings and other sheathing in accordance with their perormance characteristics. The in-plane shear strength and stiness are required inputs or the engineering practices presented in ASAE EP484.2.
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American Society for Testing Standards (ASTM)
ASTM F1667 - Table 45, Type 1, Style 30 Post-Frame Ring-Shank Nails sets production standards or threaded hardened nails, and is reerenced in the National Design Specication (NDS), published by the AWC. NDS establishes the technical specications or the dimensions, tolerances and materials or the manuacture o asteners. Post-Frame Nails have exceptional withdrawal resistance characteristics. This unique astener has been thoroughly tested and is recognized by these construction industry standards. National Frame Building Association
NFBA has assembled all pertinent engineering inormation rom codes and standards into the PostFrame Building Design Manual, the only current and complete published reerence o its kind on how to properly design and engineer post-rame buildings. www. nba.org
Post-Frame Design-Related Documents From the National Frame Building Association (NFBA) www.nfba.org
Errors • BCSI-B6GableEndFrameBracing • Post-FrameBuildingDesignManual • BCSI-B7Temporary&PermanentBracingforParallelChord • FireTestManual Trusses • 1996DiaphragmTestKit • BCSI-B9Multi-PlyGirders • Post-Frame“BeautifulBuildingsBrochure ” • BCSI-B10Post-frameTrussInstallation &Bracing • FramingTolerancesStandard • BCSI-B11FallProtection&WoodTrusses • MetalPanel&TrimInstallationTolerancesStandard • ANSI/TPINationalDesign Standard for Metal PlateCon• “SpotlightonArchitecture:Post-FrameBuildings”Video nected Wood Truss Construction (TPI 1) • 1-03GuidetoGoodPracticeforHandling,Installing&Bracing o Metal Plate Connected Wood Trusses From the American Society of Agricultural and Biological Engineers (ASABE) - www.asabe.org a) Commentary or Permanent Bracing o Metal Plate Con• EP484.2 Diaphragm Designof Metal-Clad, Wood-Framed nected Wood Trusses Rectangular Buildings b) Inormational Series o Documents Titled “Truss Technol• EP558 Load Test for Metal-Clad, Wood-Framed Diaogy in Building” phragms • EP559 Design Requirements, and Bending Properties for From Universities with Inter-Library Loan programs: Mechanically Laminated Post • Walker,J. N. andF. E. Woeste, Editors. 1992. Post-frame • EP486.1ShallowPostFoundationDesign building design. ASAE MonographNo. 11, ASAE, St.Jo• Paper#01-4012UpliftResistanceofPostFoundations seph, MI. – Provides an in-depth and complete discussion o modern post-rame design or a ull understanding on an From the American Society of Civil Engineers (ASCE) engineering level. www.asce.org
• MinimumDesignLoadsforBuildingsandOtherStructure s, NOTE: Complete inormation on how to properly engineer a ASCE/SEI 7 post-rame building is covered in the Post-Frame Building Design Manual, which may be purchased rom the National Frame Building Association. For more inormation, call 800/557-6957 From the American Wood Council (AWC) – www.awc.org • National Design Specication (NDS) for Wood Construc- or visit www.nba.org. tion The materials and inormation contained in this brochure have been gath• DCA5–Post-FrameBuildings From the American Wood Protection Association (AWPA) www.awpa.com
• AWPA U-1 Use Category System: User Specication For Treated Wood From the International Building Code (IBC) www.iccsafe.org
• Section2306.1(AllowableStressDesign) From Wood Truss Council of America (WTCA) www.woodtruss.com
• BCSI-B1GuideforHandling,InstallingandBracingofMetal Plate Connected Wood Trusses • BCSI-B2TrussInstallation&Temporary Bracing • BCSI-B3WebMemberPermanentBracing/WebReinforcement • BCSI-B4ConstructionLoading • BCSI-B5TrussDamage,JobsiteModications&Installation
ered rom a variety o sources and rom qualied individuals, and are thereore deemed reliable. The material is not guaranteed and is not necessarily a complete statement o all available data. Conclusions are based solely upon our best judgment, analysis o technical actors and individual inormation sources. Because the Association has no control over quality o workmanship or the conditions under which engineered wood products are used, it cannot accept responsibility or product perormance or designs as actually constructed. Because product perormance requirements vary geographically, consult your local architect, engineer, or design proessional to assure compliance with code, construction, and perormance requirements. The National Frame Building Association, its principals and members, accept no liability or any errors or omissions herein, or or any resulting injury or damage caused by their use in the design or engineering o any particular structure.
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Published by the National Frame Building Association 4700 W. Lake Ave. Glenview, Illinois 60025 www.postrameadvantage.com
