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Firewalls for Wood Construction

What is a firewall?

A firewall is a term that is used in the construction industry to describe a fire-resistive-rated wall or fire-stop system, which is an element in a building that separates adjacent spaces to prevent the spread of fire and smoke within a building or between separate buildings. A firewall is actually one of three different types of walls that can be used to prevent the spread of fire and smoke.

Types of fire-resistive-rated walls:

The three types of fire-resistive-rated walls are firewalls, fire barriers and fire partitions. They are listed in order from the most stringent requirements to the least. A firewall is a fire-resistive-rated wall having protected openings, which restricts the spread of fire and extends continuously from the foundation to or through the roof with sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall. A fire barrier is a fire-resistive-rated wall assembly of materials designed to restrict the spread of fire which continuity is maintained. A fire partition is a vertical assembly of materials designed to restrict the spread of fire in which openings are protected. Each type has varying requirements and the table below displays some of the differences between them.

What are some of the typical uses of each type of fire-resistive wall?

As the requirements for each type of wall vary, so do the uses. Typical uses of each are as follows:

Firewalls – party walls, exterior walls, interior bearing walls
Fire barriers – shaft enclosures, exit passageways, atriums, occupancy separations
Fire partitions – corridor walls, tenant space walls, sleeping units within the same building

How do you determine whether your wood building design needs a firewall?

The 2012 International Building Code (the IBC, or “the Code” in what follows), which is adopted by most building departments in the United States, is the resource we are using in this discussion. (As a side note, it’s possible your city or county has supplemental requirements, and it is best to contact your local building department for this information up front.)

To determine your fire-resistive wall requirements, review these chapters in the 2012 IBC:

Chapter 3, Identify Occupancy Group – typically Section 310 (“Residential Group”) for wood construction
Chapter 5, Select Construction Type – Section 504, Table 503
Chapter 6, Determine Fire-Resistive Rating Requirements – Table 601, typically Type III wood-constructed buildings require a two-hour fire separation for the exterior bearing walls

What are typical fire-resistive wall designs?

Information for one-hour, two-hour designs, etc. can be found in tables 721.1(2) and 721.1(3) of the Code provide information to obtain designs that meet the rating requirements (in hours) for your building, including the walls and floor/roof systems. The GA-600 is another reference that the Code allows if the design is not proprietary.

How do I know whether the structural attachments I specify for the wall and roof assemblies meet the Code requirement?

Once the wall or floor/roof assembly design is selected, the Designer must ensure that the components of the wall do not reduce the fire rating. The Code requires that products which pierce the membrane of the assemblies at a hollow location undergo a fire test to ensure they meet the requirements of the design. ASTM E814 and ASTM E119 are the standards governing the fire tests for materials and components of the fire-resistive wall. There are several criteria that the component in the assembly must meet: a flame-through criterion, a change-in-temperature criterion and a hose-stream test.

Simpson Strong-Tie has created the DHU hanger for use with typical two-hour fire-resistive walls for wood construction.The DHU hanger has passed the ASTM E814 testing and can be used on a fire-resistive wall of 2×4 or 2×6 constructions and up to two 5/8″ layers of gypsum board. The DHU and DHUTF have both an F (Fire) and a T (Temperature) rating.

The DHU/DHUTF hanger has two options, a face-mount version (DHU) and a top-flange version (DHUTF). The hanger doesn’t require any cuts or openings in the drywall, which ensures reliable performance; no special inspection is required. To install the hanger, gypsum board must first be installed in a double or single layer, at least as deep as the hanger. For installation, apply a two-layer strip of Type X drywall along the top of the wall, making the base layer a wider strip (bottom edge is 12″ or more below the face layer, depending on jurisdiction). Then install ¼” x 3½” Simpson Strong-Tie Strong-Drive® SDS screws through the hanger and into top plates of the wall. Since the hanger is more eccentric than typical, the top plates of the wall must be restrained from rotation. The SSP clip can be used for restraint, but the design may not require it if there is a sufficient amount of resistance already in place, such as sheathing, a bearing wall above, or a party wall as determined by the designer. See the photos and installation illustration below for guidance or visit our website for further information.

Simpson Strong-Tie® Strong-Wall® Wood Shearwall – The Latest in Our Prefabricated Shearwall Panel Line Part 2

In last week’s blog post, we introduced the Simpson Strong-Tie® Strong-Wall® Wood Shearwall. Let’s now take a step back and understand how we evaluate a prefabricated shear panel to begin with.

First, we start with the International Building Code (IBC) or applicable state or regional building code. We would be directed to ASCE7 to determine wind and seismic design requirements as applicable. In particular, this would entail determination of the seismic design coefficients, including the response modification factor, R, overstrength factor, Ω_o, and deflection amplification factor, C_d, for the applicable seismic-force-resisting system. Then back to the IBC for the applicable building material: Chapter 23 covers Wood. Here, we would be referred to AWC’s Special Design Provisions for Wind and Seismic (SDPWS) if we’re designing a lateral-force-resisting system to resist wind and seismic forces using traditional site-built methods.Continue Reading

Simpson Strong-Tie® Strong-Wall® Wood Shearwall – The Latest in Our Prefabricated Shearwall Panel Line Part 1

Some contractors and framers have large hands, which can pose a challenge for them when they’re trying to install the holdown nuts used to attach our Strong-Wall® SB (SWSB) Shearwall product to the foundation. Couple that challenge with the fact that anchorage attachment can only be achieved from the edges of the SWSB panel, and variable site-built framing conditions can limit access depending upon the installation sequence. To alleviate anchorage accessibility issues, we’ve required a gap between the existing adjacent framing and SWSB panel equal to the width of a 2x stud to provide access so the holdown nut can be tightened. Even so, try telling a framer an inch and a half is plenty of room in which to install the nut!Continue Reading

Mass Timber Construction – Building for the Future

The future is here and that future is mass timber construction.

It is common knowledge that wood is a renewable and environmentally friendly building material. There are two types of wood-framing methods in North America. The most common method for residential construction is light-frame construction using either balloon-framing or platform-framing methods. Standardized dimensional lumber has become the dominant building material in light-frame construction because of its economy. The other method is heavy-timber construction, which often uses large solid-wood sections for nonresidential construction, such as for storage, mercantile and industrial buildings.

In Europe, there is a trend to create larger “laminated” wood sections using the more traditional standardized dimensional lumber of the 1990s. This trend culminated in what is now classified as cross-laminated timber, or CLT. CLT can be used to create floor panels and roof panels. In North America, this is classified either as cross-laminated timber (CLT) or generically as mass timber.

CLT is essentially multiple layers of wood panels. Each layer of wooden panels is laid crosswise on the one before at approximately a 90° angle and glued using a polyurethane adhesive to increase the stability of the entire panel. Typical thickness of the individual boards can vary from 3/8″ to 2″ thick. Typical board width can vary from 2-3/8” to 9-1/2” wide. CLT panels are fabricated and marketed from 3-ply CLT up to 7-ply CLT. CLT manufacturers normally publish characteristic properties for their panels – such as bending strength, shear strength, modulus of elasticity and panel stiffness – to assist Designers in specifying these products.

A Cross Laminated Timber Handbook has been published by FPInnovations in Canada as an introduction to CLT. This handbook can be downloaded for free here. The American Wood Council has a self-study guide on CLT that can be downloaded here.

As in all wood buildings, connection designs are critical to the success of this new type of building material. Simpson Strong-Tie offices in Europe have been instrumental in developing and supplying connectors and fasteners in the CLT market. Simpson Strong-Tie has developed many connectors specifically for the CLT market in Europe (Figure 3).

Those connectors are used to join the CLT floor panels to CLT wall panels and CLT wall panels to the concrete foundation (Figures 1 and 2).

Specialized ring-shank nails and long metal screws have been developed as well. In mid-2014, Simpson Strong-Tie North America (Pleasanton, California Testing Facility) embarked on an initial test program to assess those connectors and fasteners developed for the CLT market by Simpson Strong-Tie Europe, using North American CLT panels to verify and quantify the performance characteristics according to North American testing protocols (American Society for Testing and Materials and Canadian Construction Materials Centre).

The initial test program used CLT panels fabricated in Western Canada using Canadian Spruce-Pine-Fir (S-P-F) lumber. The connectors and ring-shank nails were imported from the Simpson Strong-Tie European manufacturing facilities. Testing of the connectors also included the Simpson Strong-Tie Strong-Drive® SD screws, which as expected, provided higher load capacity than the ring-shank nails. A summary of the test program and the load rating developed for both the Canadian and the U.S. market can be downloaded here.

Other types of long countersunk screws such as the Strong-Drive® SDWS Timber screw (countersunk) or Strong-Drive SDWH Timber-Hex (hex head) screw (shown) are used either to splice the floor panels together or to drag the diaphragm loads back to the column or post as necessary.

As CLT continues to gain acceptance in North America, other connection details will also become more popular. Simpson Strong-Tie intends to continue developing and improving connection details to support this type of construction.

Building code acceptance is another important requirement and development that is in progress in both Canada and the U.S. In Canada, the 2014 edition of CSA O86 “Engineering Design in Wood” has reserved a section for CLT.

The 2015 edition of the International Building Code (IBC) recognized CLT when it is manufactured to the product standard. CLT walls and floors will be permitted in all types of combustible construction. The 2015 National Design Specification (NDS) for Wood Construction was recently published and approved as an ANSI American National Standard. The 2015 National Design Specification is also referenced in the 2015 IBC.

The future is here. Environmentally friendly mass timber (including CLT) is poised to grow in use, especially with the recognition of CLT in the building codes. North American manufacturing of CLT has been established and can only grow to support the expanding use of this new building material.

References:

www.cwc.ca

www.awc.org

https://fpinnovations.ca

*Images with permission from FPInnovations