What spray foam insulation options are available for a multi-unit apartment building in Saint John?

For a multi-unit apartment building in Saint John, you have two primary spray foam options — closed-cell and open-cell — and the right choice depends heavily on which part of the building you're insulating, the fire code requirements for multi-unit residential construction, and Saint John's particularly demanding coastal climate.

Commercial multi-unit buildings operate under different rules than single-family homes, and spray foam in these applications requires careful attention to the National Building Code of Canada (NBC) and NB Building Code requirements for fire protection, thermal barriers, and air tightness.

Closed-Cell Spray Foam (2-Pound Density)

Closed-cell is the workhorse product for most exterior envelope applications in a Saint John apartment building. At R-6 to R-7 per inch, it delivers the highest R-value per inch of any spray foam, which matters enormously in a multi-unit building where mechanical rooms, party walls, and service chases eat into usable cavity space. More importantly for Saint John's coastal environment, closed-cell foam acts simultaneously as insulation, air barrier, and vapour barrier — eliminating the need for separate 6-mil poly in many assemblies and dramatically reducing the number of trades and penetrations involved in the building envelope.

Saint John sits on the Bay of Fundy, and the persistent coastal winds here are not a minor consideration — they're a major building science challenge. Wind-driven rain infiltration, elevated relative humidity year-round, and wind washing through poorly sealed assemblies are all amplified in Saint John compared to inland NB communities. Closed-cell foam's impermeability to both air and moisture makes it the right choice for rim joists, foundation walls, below-grade applications, roofline details, and any assembly where moisture control is non-negotiable. Expect to pay $3.50 to $7.00 per square foot installed at 2-3 inches thickness in the NB commercial market, though multi-unit projects of significant scale often attract better pricing due to volume.

Open-Cell Spray Foam (Half-Pound Density)

Open-cell foam at R-3.6 to R-3.8 per inch is less expensive ($1.50 to $3.50 per square foot installed) and offers excellent air sealing with superior sound attenuation — a meaningful advantage in multi-unit residential construction where sound transmission between suites is a tenant satisfaction and building code issue. Open-cell's soft, fibrous structure absorbs sound energy rather than reflecting it, making it a popular choice for party walls, floor-ceiling assemblies between units, and interior partition walls where STC (Sound Transmission Class) ratings matter.

The critical limitation of open-cell foam in NB is vapour permeability. Because open-cell foam allows moisture vapour to pass through it, a separate vapour retarder is mandatory on the warm side of any exterior assembly in Climate Zone 6. In a multi-unit building, this means your spray foam contractor and your vapour barrier installation need to be coordinated carefully — skipping or compromising the vapour retarder on an open-cell exterior wall assembly in Saint John's humid Maritime climate is a recipe for concealed condensation, mould, and structural damage inside the wall cavity.

Fire Code — The Critical Consideration for Multi-Unit Buildings

This is where commercial spray foam diverges sharply from residential. The NBC requires that spray foam insulation in multi-unit residential buildings be protected from interior spaces by a thermal barrier — typically 12.7mm (½-inch) Type X drywall — wherever the foam is exposed to occupied or accessible spaces. Spray polyurethane foam is combustible, and in a multi-unit building, fire spread between suites and to egress corridors is a life-safety issue governed by strict code requirements.

Your spray foam contractor must be familiar with NBC Part 3 requirements for large buildings and the specific fire-rating requirements for the assemblies involved. This is not a project for a contractor whose experience is limited to single-family residential work. Building permits are required, and the insulation assembly will be inspected as part of the overall building permit process. Verify that any contractor you engage carries full commercial liability insurance and WorkSafeNB coverage — chemical handling on a multi-unit commercial project carries significant liability exposure.

Practical Guidance for Your Project

Before any spray foam work begins, a blower door test and thermal imaging assessment of the existing building envelope will identify where air leakage is worst and help prioritize where spray foam delivers the greatest return. In older Saint John apartment buildings — many of which were built in the 1960s and 1970s with minimal insulation and no air barrier — rim joists, attic bypasses, and foundation wall penetrations are almost always the highest-priority targets.

For rebate eligibility, multi-unit residential buildings may qualify under Canada's Green Buildings Fund or NB Power's commercial energy efficiency programs — the eligibility criteria differ from single-family residential programs, so confirm with NB Power and Natural Resources Canada before starting work.

New Brunswick Insulation can connect you with experienced commercial insulation contractors in the Saint John area through the New Brunswick Construction Network. Browse the directory at newbrunswickconstructionnetwork.com/directory?category=insulation or get matched directly for a free estimate on your project.