Vertical Additions in Mass Timber: Key questions to answer: While ground-up construction is necessary in many cases, what shouldn’t be overlooked, especially in urban areas where lot availability is low, is adaptive re-use of existing structures and placing vertical additions.

Renovating and adding onto an existing building can present cost and embodied carbon advantages over complete demolition and new construction. But doing so also comes with an immensely complex way of building.

Why? — Mass timber is a precisely prefabricated building material. We’re talking tolerances of 1/8″. And you then try to set it on top of a 150 year old masonry building that isn’t, well, square and plumb.

Mass timber has been chosen for vertical addition projects due to its light weight, enhanced aesthetics and ability to be installed in tight urban lots. In many cases, mass timber as the vertical addition structure was the facilitator that enabled the project to take place with little to no reinforcement of the existing structure and/or foundation.

This has benefits in terms of lowering the cost of the renovation project, while potentially allowing some of the existing building to remain open to operations while the vertical addition is under construction.

When doing a vertical addition of any type, using any materials, there are some unique design, code compliance and construction logistical considerations.

Some of the initial questions to consider:

1/ Will the building be considered all one, or will the addition be considered a separate building (with necessary added fire-separation means)?

2/ Does the existing building have adequate fire-resistance protection when considering the added size and number of stories of the existing building?

3/ Is the existing building sprinklered and if not, can it be retro-fitted to add sprinklers?

4/ Does the vertical addition add enough weight so as to require a new lateral analysis, foundation reinforcements or structural framing upgrades?

5/ Is the egress within the existing building adequate to account for the added occupant load from the new stories?

6/ Does the existing building have adequate accessibility design features?

Author: Ricky McLain, WoodWorks US

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