How much does AeroBarrier cost per square foot on a multifamily project?

On the multifamily projects we have modeled in Massachusetts, AeroBarrier typically runs between $1.50 and $3.50 per square foot of conditioned floor area, depending on unit count, access, and starting ACH. The per-unit cost drops fast as the unit count rises because the crew mobilization is fixed. On a 12-unit townhome project, you are usually on the lower half of that range.

What Mass Save incentive tier do I need to hit to unlock the bigger rebates on multifamily new construction?

Mass Save offers a tiered structure for new construction, and the larger rebates sit behind tighter envelope and modeled consumption thresholds that sit meaningfully above code minimum. The exact tier thresholds shift year over year, and the jump between tiers is often where the real money lives. We model every project against the current year's tier table before we make a spec recommendation, because a project that is one ACH off a tier boundary is a very different conversation than one that is comfortably inside it.

Do I need triple-pane windows to hit the Specialized Stretch Code?

No. The Specialized Stretch Code is performance-based and does not mandate a specific window assembly. You can meet it with double-pane windows if the rest of the envelope and the mechanical systems are doing enough work. Triple-pane is one tool for hitting the target, not the only one, and on most Boston-area multifamily projects it is not the cheapest tool.

Why Triple Pane Windows Cost This Project $566K

A 12-unit Boston townhome project came out $566,000 ahead by choosing double-pane windows with AeroBarrier over triple-pane. The win included an extra $90,000 in Mass Save incentives the window-heavy path could not reach.

April 22, 2026

Most teams chasing a high-performance envelope default to triple-pane windows. We modeled a 12-unit townhome project in Boston under the MA Specialized Stretch Code, and the double-pane path came out $566,000 ahead. The win was not just construction cost. It was an incentive tier jump that the window-heavy path could not reach.

The Real Comparison

The project was 12 townhome units in Boston, permitted under the MA Specialized Stretch Code. We ran two compliance paths side by side to see which one actually penciled.

Path one was triple-pane windows at a standard air sealing target. This is the reflex choice when a team hears "high-performance envelope" and wants a single spec change that carries most of the load.

Path two was double-pane windows paired with aggressive air sealing using AeroBarrier. Same target energy performance. Very different cost structure.

The Window Premium

Townhomes carry a lot of glazing per unit. The party walls eliminate side glass, but the front and rear facades still do the full job, and the per-unit window area stays high because the facades are narrow and tall. That makes any window premium compound fast.

The jump from double-pane to triple-pane ran roughly $35 to $55 per square foot of glazing on this project, depending on the line and frame. Across 12 units with full front and rear fenestration, that premium alone was the bulk of the construction cost delta. Nothing about that math is unusual for townhomes, which is exactly why the default choice is expensive on this typology.

The Air Sealing Factor

AeroBarrier is a mechanical sealing process that pressurizes a unit and carries an aerosolized sealant to every leak path in the envelope. It closes gaps the framing and drywall crews cannot reasonably chase by hand, and it does it in hours per unit, not days.

On this project, AeroBarrier came in at a fraction of the cost per square foot of envelope compared to the window upgrade, and it moved the whole-unit ACH number far enough to hit the same modeled energy performance that the triple-pane path produced. Two different roads to the same HERS outcome, at very different price points.

The Incentive Differential

The tighter envelope did something the window path could not. It pushed the project into a higher Mass Save new construction incentive tier, which triggered an additional $90,000 in incentives on top of the construction savings.

This is the piece that teams miss most often. Compliance modeling and incentive modeling are not the same exercise. Two paths can both pass code and produce the same HERS score, and still land on opposite sides of a Mass Save tier threshold because the incentive program weights envelope tightness and modeled consumption differently than code does. If you are only optimizing for code, you are leaving the incentive dollars on the table.

When Triple Pane Still Wins

Double-pane plus AeroBarrier is not the right answer on every project. A few scenarios where we would recommend the opposite.

Projects targeting Passive House certification. PHIUS and PHI window U-value thresholds are tight enough that double-pane cannot reliably get there, even with perfect air sealing. If the project is chasing Passive House, the triple-pane premium is a cost of admission.

Very noisy urban sites. Triple-pane assemblies carry an acoustic benefit that AeroBarrier does not. If the project is next to a rail line, a highway, or a flight path, the window upgrade is doing two jobs, and the math changes.

Low glazing ratios. On a project with a low window-to-wall ratio, the triple-pane premium is small in absolute dollars, and the envelope is already tight by default. The incentive tier math described above may not move.

Cold-climate projects north of climate zone 6. In parts of northern New England and upstate New York, the marginal energy benefit of triple-pane on a per-unit basis starts to pay back the premium faster. Boston is not cold enough to change our answer on this project. A similar townhome in Burlington might be.

The Decision Framework

Before you spec triple-pane windows on a Massachusetts multifamily project, model both paths against both the Specialized Stretch Code and the current Mass Save incentive tiers. The right answer depends on your glazing ratio, your site constraints, your certification target, and how close you already are to the next incentive threshold. A spec decision that looks like a straightforward envelope upgrade is often a six-figure swing, and the swing frequently moves in the direction teams do not expect.