This detailed article examines the use of mass timber for vertical additions in the US, addressing topics such as code compliance, construction type, fire-resistance ratings (FRR), structural reinforcement, and constructability.

There is much discussion in the building design and development community about how to build a more sustainable future. Renovations and additions to existing structures have both cost and embodied carbon advantages over demolition and new construction. Designing an addition in wood can add to these benefits.

While ground-up construction is often necessary, vertical additions and adaptive re-use can be an attractive option—especially in urban areas with limited lot availability. Mass timber is a natural solution for these projects due to its enhanced aesthetics, ease of installation on tight urban sites, and relative light weight. Using mass timber can eliminate the need to reinforce the existing structure and/or foundation. This can significantly reduce costs, and potentially allow the existing building to remain open while the addition is under construction. 

When pursuing a vertical addition of any type, using any materials, there are considerations related to design, code compliance, and construction logistics. Will the addition be considered a separate building? Does the existing building have adequate fire-resistance protection relative to the added size and number of stories? Does the existing building have sprinklers and, if not, can they be added? Does the addition add enough weight to require a new lateral analysis, foundation reinforcements, or structural framing upgrades? Does the egress in the existing building account for the added occupant load from the new stories? 

This article examines the use of mass timber for vertical additions in the U.S., addressing topics such as code compliance, construction type, fire-resistance ratings (FRR), structural reinforcement, and constructability. 

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