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With the recent change to the BC Building code allowing mid-rise (five and six storey)
wood frame residential construction effective April 6th 2009, we present below a
sampling of the issues that will affect the construction costs of mid-rise wood
frame residential buildings.
Design Efficiencies - applicable to a scenario of comparing a similar size four
storey and a mid-rise building.
In the case where a four storey building is compared to a mid-rise building with
the gross square footage remaining the same, increased costs will result from inefficiencies
relating to more façade costs, increased circulation space, and possibly a deeper
(more levels) underground parking structure – among others.
Architectural Impacts
The revised BC Building Code has specific requirements related to mid-rise wood
frame construction that will affect construction costs including requirements for
non-combustible façade materials, addition of fire compartments if the floor area
is bigger than 1,200m2, and increased requirements for façade insulation due to
the application of ASHRAE 90.1. Other impacts might include upgraded windows and
facades due to greater exposure to weather and more surface water run-off. In addition,
façade design considerations will have to be given to building shrinkage.
Structural Impacts
The increase in height will have structural impacts including increased requirements
for shearwall quantities, assembly requirements, and code limitations on shearwall
configurations. There may be the possible introduction or increase in the quantity
of kiln dried lumber, an increase in the quantity of wood due to greater loads tied
to additional building height. Also, additional seismic hold downs will be required.
Fire safety
Mid-rise wood frame buildings are required to be sprinklered to NFPA 13 standards
which requires sprinklers to balconies of a nominal width and to attic spaces. Other
impacts include fire compartment requirements, and access / exit requirements.
Mechanical and electrical costs
Mechanical costs include compliance with ASHRAE 90.1 relating to ventilation requirements,
programmable thermostats, etc. In addition, mid-rise buildings will have larger
risers and there may be cost implications in the consideration of building shrinkage
and movement due to greater building height.
Summary
The BC Building Code change to allow mid-rise wood frame construction gives developers
and owners greater flexibility and choice in the use of materials other than concrete
or steel for the structure, and also more choice in site selection. We believe this
type of construction will be economically less to construct than concrete and steel.
For further information on this form of construction please call Ray Bott or Steve
Elias at 604-683-5591.
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