By Nikolaus Remus, AIA, Advocacy Engagement Director at AIA Colorado
Samir Mokashi, principal at Code Unlimited, joined AIA Colorado to share his expertise in using lesser-known code compliance paths. These options are proving especially useful as new structural wood products are gaining popularity ahead of their inclusion in the upcoming building code cycle.
Why is mass timber of interest right now?
The first topic in the presentation was an overview of the current structural wood materials available to architects and engineers. New manufacturing techniques have really opened up options for products in the heavy timber type IV construction category. Cross-laminated timber (CLT) in particular is proving to have better fire resistance properties than other manufactured wood products.
Being able to safely design tall wood buildings has the added benefit of promoting structural materials with smaller carbon footprints than concrete and steel.
Stepping off the prescriptive path and code modifications
CLT wood can be manufactured with fire resistance ratings up to 90 minutes, but there are some important considerations on how to work with building and fire departments that may still have hesitations when seeing modern mass timber structural systems.
Extensive fire resistance testing has been done for new engineered mass timber products prior to the “tall wood building” category being added to building codes as construction types IV-A, IV-B, and IV-C. Codes also include straight-forward calculations on how to size mass timber based on this testing.
Samir reminded the audience that building code officials have the power to grant code modifications when alternate means and methods still meet the intent and purpose of the code requirements. For tall wood building projects, this often means making extra effort to talk to the building official to discuss your approach. It’s important to describe not just the materials themselves, but connections, details, and rated assemblies as well. These are all going to receive extra scrutiny during permit reviews of tall wood buildings.
Performance analysis can be used to supplement calculations
Energy modeling isn’t the only computational analysis tool that can take advantage of BIM models created during the design process. Samir shared examples of advanced life safety models using project-specific calculations and conditions. These models can predict the path of fire spread based on its source. They can show where smoke can and cannot accumulate. They can also predict human egress behavior and actual evacuation times based on exit components and locations. Running these models can answer many of the concerns building department officials (understandably) express when design teams attempt to utilize alternate materials and methods.