Design & Tools

Building Types

Multi-Family/Mixed-Use

The Marselle – Seattle, WA – PB Architects
Matt Todd Photography
Wood-frame construction offers a number of benefits for multi-residential and mixed-use projects. It allows developers to create high-density, high-quality housing that’s also cost effective, with the added advantages of a shorter construction schedule and lighter carbon footprint.

The detailing of mid-rise wood buildings plays a significant role in the ability to manage investment costs per unit and best use the lot configuration. Implementing a well-considered structural design requires understanding and coordination of several architectural design aspects, such as fire/life safety, acoustics, building envelope and constructability.



Construction Types:

The International Building Code (IBC) allows wood-frame construction in multi-residential occupancies that include multi-family, military, senior, student and affordable housing.

  • Type V construction is the most common type for multi-residential wood buildings. It allows up to four stories of wood with additional levels if mezzanines are included. For residential occupancies, buildings can be up to 135,000 square feet without additional fire separation. Untreated wood is permitted throughout.
  • Type III construction allows five stories of wood with additional levels if mezzanines are included. Multi-residential occupancies can be up to 270,000 square feet without additional fire separation. The use of untreated wood is permitted for roof and floor systems and interior wood-frame walls, and fire-retardant-treated (FRT) wood is required for exterior wood-frame walls.
  • For Type V and Type III buildings, increases beyond the allowable heights and areas can be achieved with horizontal and vertical building separations such as a concrete podium or fire walls. In most U.S. jurisdictions, the above-ground portion of a podium is currently limited to one story; however, the 2015 IBC will allow multiple levels below the horizontal separation as long as the overall height is still below 85 feet and 65 feet for Type III and Type V buildings respectively (assuming the use of NFPA-compliant sprinklers).

Typical Building Systems:

  • Multi-story wood buildings are typically light-frame construction and are either balloon-framed or platform-framed. In additional to traditional framing, advanced framing techniques may be used to increase the thermal performance of the structure.
  • Popular building configurations include podium, wrap-around/donut and walk-up/tuck-under. Each has its own benefits and associated level of density. The specifics of the site will usually dictate which configuration is most appropriate for the project.Mass timber products, including cross laminated timber (CLT), offer potential as a cost-effective option for eight- to ten-story buildings, which may not justify the additional expense of Type I or Type II construction. Although not permitted under the current IBC, examples of taller wood buildings include the 10-story Forté in Australia, made entirely from CLT.

Education

Spanaway Middle School – Spanaway, WA
Ericson McGovern Architects, Bethel School District
The value proposition for wood in schools is that it typically costs less while meeting all code requirements for safety and performance, and that it offers advantages such as speed of construction and a light carbon footprint. Its versatility allows designers to create exceptional learning environments on limited budgets, while meeting energy and other high-performance objectives.

There is also growing research to support the stress-reducing effects of visual wood. The term biophilia describes the instinctive connection and attraction people have to natural materials, and many designers cite the warm and natural attributes of wood as a reason for its use. Evidence also suggests that the use of natural materials can contribute to an individual’s sense of well-being, productivity and health.

Construction Types:

School campuses, including elementary, secondary or higher education, often have multiple buildings with different occupancies such as business (office), assembly (gymnasium) and education (classrooms). The International Building Code (IBC) allows wood construction for all of these occupancies

  • Type V is typically one of the most cost-effective types of construction. The IBC allows use of untreated wood throughout a Type V structure. Under the IBC, one-story Type V educational buildings can be up to 87,875 square feet and two-story buildings may be as large as 138,750 square feet when using an NFPA 13 sprinkler system and full frontage increase. If additional square footage is required, fire walls can be incorporated.
  • Type IV construction, also known as heavy timber, allows use of solid or laminated wood members such as glulam, wood decking and structural sheathing when there are no concealed spaces.
  • Type III construction is permitted to have wood roof and floor systems as well as interior wood-frame walls.
  • In Type III and IV construction, fire-retardant-treated (FRT) wood is required for exterior wall assembly framing.
  • Construction Types I and II may allow the use of heavy timber construction or FRT wood in roof construction and for secondary members. This can be an effective way of reducing cost while improving aesthetics in gymnasiums or multi-purpose structures.

It is not uncommon for states or other jurisdictional entities to add additional restrictions to the IBC requirements. Designers in jurisdictions that limit the use of wood in schools are invited to contact a WoodWorks technical expert for more information.

Typical Building Systems:

  • For school districts pressed for space and finances, light-frame construction offers the combination of cost effectiveness, design flexibility and sustainability that allows projects to come to fruition. Durability is a primary concern for communities and isn’t compromised by the choice of wood framing. (Click the Publications button at the to
    p of this page for case study and CEU examples.)
  • Where creating a unique and inviting space is a priority objective, timber-frame systems may be used to incorporate exposed structure into the aesthetic. Heavy timber and hybrid elements offer an affordable way to achieve large spans and curved profiles.

Office

The Bullitt Center – Seattle, WA – The Miller Hull Group, photo John Stamets
Office buildings vary drastically in scale yet tend to be fairly consistent in their need for large open spaces and flexibility for future modification. Wood systems offer the ability to accommodate open floor plans. The value proposition for wood office buildings lies largely in its cost effectiveness, aesthetics and sustainability. While keeping an eye on budget, designers communicate the company’s values through structure—by leveraging wood’s design flexibility to create unique and inspirational work environments and by using a renewable, sustainable material with a light carbon footprint.

Construction Types:

  • Type III construction may include wood roof and floor systems as well as interior wood-frame walls. Fire-retardant-treated (FRT) wood is required to frame exterior wood-frame walls. For business occupancy, Type III buildings are permitted to have six stories of wood construction, more than any other occupancy group.
  • Type IV construction, also known as heavy timber, may include the use of solid or laminated wood members such as glulam, wood decking and structural sheathing in conjunction with no concealed spaces. FRT wood can be used to frame exterior bearing walls or a curtain wall system hanging from the frame. For business occupancy, Type IV buildings are permitted to have six stories of wood construction, more than any other occupancy group.
  • Type V construction may include untreated wood throughout. Exposed light-frame construction, often Type VB, is becoming increasingly popular as a cost-effective way to create a modern industrial aesthetic for office buildings with a single story and less than 36,000 square feet (with an NFPA 13-compliant sprinkler system) or 2-3 stories with less than 27,000 square feet per story (also sprinklered).

Typical Building Systems:

  • Light-frame construction should not be overlooked for business occupancies. Straight walls and low-vibration floors can be achieved with proper detailing and design while saving time and money for the owner.
  • Heavy-timber framing is growing in popularity for multi-story offices because it offers visual interest while cost-effectively addressing the performance criteria for Class A office structures.

Commercial Low-Rise

New Earth Market – Yuba City, CA – KD Architects, photo Kevin Cotter
Wood-frame construction can be a cost-effective alternative to concrete and steel for low-rise commercial projects, which include shopping malls, big box retail centers, convenience stores, restaurants and more. In addition to speed of construction, wood’s design flexibility allows building owners to create versatile spaces for occupants, while its sustainability and light carbon footprint send a positive message to tenants and customers. Wood also has the advantage of being relatively easy to deconstruct and re-use if the objectives for the site change.

Construction Types:

  • Most low-rise designs are possible with Type V wood construction. The height and area limitations for mercantile (M), assembly (A-2), and business (B) occupancies allow three or more stories when the structure is equipped with an NFPA 13-compliant sprinkler system.
  • Type VA single-story retail structures can be as large as 56,000 square feet, which is larger than most typical grocery stores and sufficient for most neighborhood retail anchor stores.
  • With the proper frontage and sprinkler system, Type V can be unlimited in size, allowing opportunities for superstores.
  • Wood roofs are not an uncommon application in retail centers over 100,000 square feet.

Typical Building Systems:

  • Light-frame wood construction is a cost-effective option for commercial low-rise buildings and offers valuable time savings for developers. Solid sawn wall systems are viable up to 25 feet, while engineered wood wall systems can be up to 40 feet.
  • Panelized wood roof systems offer cost savings because wood decks allow for batt insulation whereas metal decks require rigid insulation. According to the Structural Roof Erectors Association, this alone can save approximately 50 cents per square foot. All-wood roof systems offer 35-foot to 40-foot column spacing while hybrid systems offer 60-foot spacing or more.
  • Prefabricated walls and components can further improve the speed of erection and are becoming increasingly common in repetitive low-rise commercial construction.
  • Post-frame construction can be an economical alternative to prefabricated steel, and is common for smaller commercial buildings.

Industrial

Hybrid panelized roof, Panelized Structures
Cost and speed of construction are reasons a designer may choose wood for warehouses, manufacturing facilities and distribution centers. Wood roof applications offer particular value for this market because of both code opportunities and cost savings (see below). New products such as cross laminated timber (CLT), which offer increased thermal performance as well as resistance to high impact, are also helping to expand the opportunities for wood in industrial applications.

Construction Types:

  • Some designers believe that, for large structures, they need the unlimited area offered by Type I and Type II construction. However, per Section 507 of the 2012 International Building Code (IBC), Type V wood buildings may also have unlimited area for factory and storage occupancies.
  • In Type I or Type II buildings, wood roofs are permitted under Section 603.1 of the 2012 IBC. Unprotected wood roofs are also permitted, per the sub-note of Table 601. The unprotected option helps further reduce the cost of the roof system.
  • All-wood roof systems also have a unique advantage for food handling facilities. Glulam beam framing with solid sawn infill and wood structural panel decking has the benefit of no horizontal surfaces on which dirt may accumulate, which is a requirement of the U.S. Food and Drug Administration.

Typical Building Systems:

  • Panelized wood roof systems offer significant cost savings because wood decks allow for batt insulation whereas metal decks require rigid insulation. According to the Structural Roof Erectors Association, this alone can save approximately 50 cents per square foot. All-wood roof systems offer 35-foot to 40-foot column spacing while hybrid systems offer 60-foot spacing or more.
  • CLT wall systems are energy efficient and offer a way to cost-effectively meet new prescriptive energy code requirements for semi-conditioned industrial buildings. CLT is also durable enough to withstand impact from heavy machinery.
  • Post-frame systems offer an economical alternative to prefabricated steel for storage and out buildings.

Civic/Recreational

Arena Stage at the Mead Center for American Theater – Washington, DC – Bing Thom Architects, photo Nic Lehoux
In addition to cost, sustainability and aesthetics tend to be key drivers for the use of wood in civic and recreational buildings such as police and fire stations, community centers, natatoriums and arenas.

The aesthetic value of exposed wood structure is a selling point for public buildings as designers are challenged with creating beautiful, inspirational spaces while demonstrating responsibility with public funds. The sheer range of exposed wood options offers significant opportunity for artistic expression.

Green building certification is often a requirement for publicly-funded projects, and wood can contribute to points in several categories commonly found in rating systems. Wood’s carbon benefits are also a consideration for many designers, who see the use of wood instead of fossil fuel-intensive materials as a way to reduce the carbon footprint of the built environment. Life cycle assessment and Environmental Product Declarations further support the use of wood as a sustainable choice.

Construction Types:

  • Many civic and recreational buildings are low-rise structures with assembly and business occupancies. For one story structures with NFPA 13-compliant sprinklers, Type VA construction allows 46,000 square feet for assembly occupancy, 72,000 square feet for business and more if ample frontage exists around the building.
  • The 2012 International Building Code (IBC) allows heavy timber roofs in Type I and II buildings, per a subnote of Table 601.
  • Type IV construction is also a possibility. Also known as heavy timber, Type IV allows the use of solid or laminated wood members such as glulam, wood decking and structural sheathing with no concealed spaces. Fire-retardant-treated (FRT) wood can be used to frame exterior walls. That said, if the increased heights and areas allowed by this construction type aren’t being utilized, it often makes sense to classify a heavy timber structure as Type V.

Typical Building Systems:

  • All-wood panelized wood roof systems offer significant cost savings for large recreational facilities while achieving the warm aesthetics of a wood finish. All-wood roof systems offer 35-foot to 40-foot column spacing while hybrid systems offer 60-foot spacing or more.
  • Heavy timber products are often used as a cost-effective way to achieve curved roof elements.
  • Light-frame construction is common for public buildings as a way to minimize cost while achieving durability objectives required in public spaces. Wood construction also tends to allow a more competitive bid process because more local contractors have wood framing expertise.

Institutional/Healthcare

Herrington Recovery Center – Oconomowoc, WI – TWP Architecture, photo Tom Davenport
Occupant environment and sustainability tend to be key drivers for the use of wood in institutional and healthcare settings. Institutional buildings include assisted living, foster care and social rehabilitation facilities, overnight clinics and treatment centers, and mental health facilities.

Building materials have the potential to positively influence the experience of occupants for these types of uses. The term biophilia describes the instinctive connection and attraction people have to natural materials, and many designers cite the warm and natural attributes of wood as a reason for its use. Evidence also suggests that the use of natural materials can contribute to an individual’s sense of well-being, productivity and health.

Green building certification may also be a requirement for publicly-funded projects, and wood can contribute to points in several categories commonly found in rating systems. Wood’s carbon benefits are also a consideration for many designers, who see the use of wood instead of fossil fuel-intensive materials as a way to reduce the carbon footprint of the built environment. Life cycle assessment and Environmental Product Declarations further support the use of wood as a sustainable choice.

Construction Types:

  • Many institutional buildings are low-rise structures, the objectives for which can usually be met with Type VA or Type IIIA construction. These construction types allow 30,000-66,000 square feet for one-story sprinklered institutional applications and up to five stories depending on specific use. Firewalls and frontage increases can further increase the allowable footprint.
  • The 2012 International Building Code (IBC) allows heavy timber roofs in Type I and II buildings, per a subnote of Table 601. Heavy timber roofs offer an opportunity to ‘warm a space’ if the building must be classified as non-combustible construction.
  • Type IV whole building construction is also a possibility. Also known as heavy timber, Type IV allows the use of solid or laminated wood members such as glulam, wood decking and structural sheathing with no concealed spaces. Fire-retardant-treated (FRT) wood can be used to frame exterior walls. That said, if the increased heights and areas allowed by this construction type aren’t being utilized, it often makes sense to classify a heavy timber structure as Type V.

Typical Building Systems:

  • Heavy timber construction can be a cost-effective way of creating warm, healing environments that also meet green building objectives.
  • Trends in mass timber construction are expanding the opportunities for exposed wood structure. In addition to the effects of visual wood, exposing the structure has the potential benefit of reducing environmental impact by minimizing the need for finish materials.
  • Light-frame construction can be an affordable choice for clinic and overnight care applications.