The purpose of this guide is to provide an introduction to the concept of encapsulated mass timber construction. This guide provides an overview of encapsulation techniques for mass timber construction, and other related fire protection measures, and summarizes some approved encapsulation materials and application methods and identifies additional requirements for safety during construction. This guide is intended to help architects, engineers and designers by reducing uncertainty and allowing for more confidence in design, as well as providing authorities having jurisdiction and inspectors with a reference for simple design review.
Project contact is Yelda Turkan, Oregon State University
Over the past decade, fires have caused significant losses, both financial and through loss of lives, in timber buildings during construction (USFA 2020). Buildings under construction or in development are largely unprotected as they are not yet equipped with active fire protection systems (sprinklers), and for those buildings that are not designed for exposed timber, multiple floors are left exposed at a time as the fire protection trade trails in schedule behind the erection of the mass timber structural elements. With the addition of Type IVA, B, and C in the 2021 International Building Code (IBC), the IBC also adopted stricter requirements for mass timber buildings under construction. Under-construction mass timber buildings require that the mass timber is protected with noncombustible material within four levels of any construction more than six stories above grade. However, limited research has occurred to demonstrate that this construction sequence results in the optimal balance of safety, property loss, and cost.
The goals of this project are to: (a) develop a methodology to couple multiple commonly-used computational tools to evaluate the sequence of installation of passive fire protection in mass timber buildings under construction fire scenarios, (b) develop an analytical framework that can be implemented by industry to evaluate the risk and impact of fire protection construction sequencing on a job site while balancing property loss, cost, and life safety of construction workers due to a construction fire, and (c) identify knowledge gaps in fire dynamics in timber buildings that would increase the accuracy of predicting fire spread in mass timber buildings under construction.
January 26-28, 2009, San Francisco, California, USA
Fire-resistive wood construction is achieved either by having the structural elements be part of fire-rated assemblies or by using elements of sufficient size that the elements themselves have the required fire-resistance ratings. For exposed structural wood elements, the ratings in the United States are calculated using either the T.T. Lie method or the National Design Specifications (NDS) Method. There is no widely accepted methodology in the United States to determine the fire-resistance rating of an individual structural wood element with the protective membrane directly applied to the exposed surfaces of the element. In these tests, we directly applied one or two layers of 16-mm thick fire-rated gypsum board or 13-mm thick southern pine plywood for the protective membrane to the wood element. The wood elements were Douglas-fir laminated veneer lumber (LVL) specimens and Douglas-fir gluedlaminated specimens that had previously been tested without any protective membrane. The methodology for the tension testing in the horizontal furnace was the same used in the earlier tests. The fire exposure was ASTM E 119. For the seven single-layer gypsum board specimens, the improvements ranged from 25 to 40 min. with an average value of 33 min. For the three double-layer specimens, the improvement in times ranged from 64 to 79 min. with an average value of 72 min. We concluded that times of 30 min. for a single layer of 16-mm Type X gypsum board and at least 60 min. for a double layer of 16-mm Type X gypsum board can be added to the fire rating of an unprotected structural wood element to obtain the rating of the protected element.
The vulnerability of any building, regardless of the material used, in a fire situation is higher during the construction phase when compared to the susceptibility of the building after it has been completed and occupied. This is because the risks and hazards found on a construction site differ both in nature and potential impact from those in a completed building; and these risks are occurring at a time when the fire prevention elements that are designed to be part of the completed building are not yet in place. For these reasons, construction site fire safety includes some unique challenges. Developing an understanding of these hazards and their potential risks is the first step towards fire prevention and mitigation during the course of construction (CoC).