Structural Implications of Reuse of an Existing Building

Occasionally, property owners may wish to make changes to the use and/or location of an existing building.  This might mean moving a building across the property, across town, or across the country.  It may mean changing the use from residential to commercial or industrial to assembly.  It might be a relatively new building or several decades old.  Regardless of the exact circumstance, there are structural implications within the National Building Code that should be addressed.  These may include:
• Change in geographic location impacting loading on the structure;
• Change in use and/or occupancy impacting loading on the structure;
• Addition of fire protection causing a load reduction to an element or assembly; and/or
• An event trigging a need to address non-code-conforming elements

Changes in Geographic Location

A change in geographic location may be the most tangible structural impact to a building.  If you are moving a building from the prairies of Saskatchewan to a mountainous area of British Columbia, you might see the snow load double or triple.  It may be obvious in this instance that a structural engineer should review the existing structure and determine if the additional structural capacity exists.  If the capacity is not there, it may be necessary to design or retrofit reinforcement required to carry the new loading and transfer the loading down to the foundation.

Snow load is not the only implication however, you must also consider wind load and seismic load.  Generally, a decrease in loading is acceptable.  

Whereas a large geographic move may seem a very obvious trigger for reviewing structural loading, climatic conditions do change over much smaller distances.  Moving only a couple hours down a highway may trigger higher loading even though you’ve moved from one bare field to another.  Moving only a short distance in elevation in a mountainous area may trigger significant changes in climatic conditions. 

As a reminder, climatic data provided in the National Building Code is not intended to be interpolated without thorough consideration of elevation, topography, and other potential constraints. Specifically, interpolation within mountainous regions is advised against. In mountainous areas, data points tend to be applicable to the valleys or bases of such mountains, and not to the slopes or higher passes.  Where climatic data is not provided, it may be obtained by contacting the Meteorological Service of Canada (formerly the Atmospheric Environment Service, referred to in the NBC).

Changes in Use and/or Occupancy

The National Building Code provides minimum specified loads to be applied to floors and/or roofs based on use.  A change in use may trigger a change in loading.  For instance, if a house is to be converted to a commercial use such as a restaurant or office, it may trigger an increase in minimum specified load from 1.9 kPa to 4.8 kPa on the main floor.  Most residential construction is not intended to carry such an increase in loading, so it may be necessary to add additional beam lines and/or reinforce existing beam lines in the basement to accommodate the increase in loading.

Further, Part 9 of the National Building Code allows for reduced snow loads for housing and small buildings.  However, Part 9 does not apply to Assembly, Care, or High-Hazard Industrial occupancies.  Therefore, a change in occupancy of a residential or small building (< 600m2) to an occupancy not covered by Part 9 may cause an increase in climatic loading, even on the same lot and/or in the same community.

Another potential implication may be a change in use that triggers a change in importance category.  For instance, property owner may wish to reuse a low-occupancy farm building as a commercial shop.  This may trigger an increase in importance category from “low” to “normal.”  It is then important that the structure has the capacity required to carry the increased loading correlated to the change in importance category.

Sometimes it is not the prescribed structural loading of the change in use or occupancy, but the mechanical systems associated with the change.  For instance, renovation of an office space to a restaurant may require installation of large mechanical units on the roof of the structure.  In this instance, the roof structure should be reviewed to confirm that additional capacity exists, or reinforcement should be provided as required.

Addition of Fire Protection

Change in use or occupancy may trigger changes in fire protection requirements.  Change in placement of a building on a site so that it is closer to property lines may also trigger changes to fire protection requirements.  This could mean revising assemblies to obtain certain fire ratings.  Whereas the loading of a revised assembly maybe trivial, there may be other implications.  For instance, some fire separation assemblies are load-restricted.  If a load-restricted assembly is intended to be used, then the assembly must have sufficient capacity for the intended loading at its restricted capacity.

Another implication may be applying a fire separation onto a ceiling structure.  If the design deflection of a ceiling structure was not intended to carry a rigid finish such as drywall, then the deflection that occurs during design loads may cause damage to the fire separation, impacting the performance of the fire separation.

Non-Code-Conforming Elements

Depending on the jurisdiction, there are many items that may trigger review of existing non-code-conforming elements.  If a building was to remain in the same location and with the same use, the Authority Having Jurisdiction may never have reason to require remediation of non-code-conforming elements.  Occasionally the argument is made that the building has proven its ability to perform under those exact conditions.  

However, relocation of a building or change in use or occupancy of a building may trigger a review of such elements.  This may include undersized structural elements, even though the revised occupancy may not trigger a change in loading, or may even trigger a reduction in loading.  This is most common in older buildings where the original design may not have been engineered.

In Closing

Always ensure that you’re aware of code implications for reuse of a building in the jurisdiction in which you wish to redevelop.  The threshold for such implications often vary from jurisdiction to jurisdiction.  Some jurisdictions have formal adaptive reuse processes or guides; others review reuse projects on a case-by-case basis.  This process can be frustrating for property owners or developers.  The process may seem unnecessarily administrative, overly time consuming, or cost-prohibitive.  However, at the end of the day, Authorities Having Jurisdiction are not intentionally creating barriers to development, they are upholding minimum standards for public safety.