Is spray foam or continuous insulation cheaper for a multifamily wall in Massachusetts?

On a straight material and install comparison, the batt-plus-continuous-insulation assembly is usually the lower line item. On the 57-unit Revere project we modeled, closed-cell spray foam ran about 2 percent higher on cost alone. The line item is not the full cost of the assembly once the build sequence is counted.

Why would a more expensive wall assembly be the better choice?

Because the cheaper line item can carry a longer and more weather-exposed build sequence. Continuous insulation adds a furring layer, an exterior insulation trade, and a shifted window plane, all on the critical path. On this project the simpler spray foam build saved roughly a week of construction problems, which was worth more than the 2 percent it added.

When is continuous insulation still the right call?

When embodied carbon is a constraint, when the thermal target needs a continuous layer to break thermal bridging, when the contractor already has the CI detail standardized, or when the cladding system requires the furring layer anyway. The right answer is specific to the building, the cladding, and the team.

Does dropping continuous insulation hurt energy code compliance?

Not necessarily. On this project the R-30 closed-cell spray foam assembly hit the same thermal target as the batt-plus-CI baseline, so the building still cleared code. Whether a cavity-only assembly can match a continuous insulation assembly depends on the wall and the target, which is why we model both before recommending one.

Why Spray Foam Won on a 57-Unit Revere Project Despite Costing 2% More

On a 57-unit Revere project, spray foam ran 2% over continuous insulation and still won by dropping the CI layer and saving a week of construction schedule.

June 01, 2026

If you are building multifamily in Massachusetts, the default wall assembly on the cost estimate is almost always batt insulation plus a layer of continuous exterior insulation. It is the cheapest way to hit code on paper, and most teams never look past it. On a recent 57-unit project in Revere, we modeled the alternative. Closed-cell spray foam at R-30, no continuous insulation layer, no furring strips, and double pane U-0.25 windows. It came in about 2 percent higher in raw material and install cost. We recommended it anyway.

The Real Comparison

The starting point was the conventional assembly. Batt insulation in the stud cavity plus continuous exterior insulation over the sheathing. On paper it is the lowest first cost path to the thermal target, and the estimator priced it without a second look.

We modeled a second assembly against the same thermal performance. R-30 closed-cell spray foam in the wall, no continuous insulation, no furring strips to carry the cladding off a CI layer, and double pane U-0.25 windows in place of a higher spec.

On raw material and install cost, the spray foam assembly ran about 2 percent over the batt-plus-CI baseline. On a straight line-item comparison the conventional assembly wins, which is exactly why it is the default.

The line-item comparison is not the whole cost of the assembly. The continuous insulation layer carries a build sequence that the spray foam assembly does not. That is where the 2 percent stopped being the deciding number.

The Constructability Math

Continuous exterior insulation is not a single product on the wall. It is a sequence. The sheathing goes on, the air and water barrier goes on, the insulation board goes on, the furring strips go over the board to carry the cladding, and the cladding hangs off the furring. Every window and door has to be bucked out to the new exterior plane. Every penetration has to be detailed through the added thickness.

Each of those steps is a trade on the exterior of the building, working in sequence, exposed to weather. When one step slips, the steps behind it wait. On a 57-unit building that sequence runs the length of the schedule, and the exterior envelope is on the critical path for closing the building in.

The spray foam assembly collapses that sequence. The foam goes in the cavity from the inside. There is no CI board, no furring layer, no shift of the window plane, and no exterior insulation trade waiting on weather. The wall closes faster and with fewer hand-offs.

On this project we put a value on the time that the simpler build returned. It came out to roughly a week of construction problems that the conventional assembly would have created and the spray foam assembly avoided. On a 57-unit building, a week on the critical path is worth far more than the 2 percent the foam added in material and labor.

When Continuous Insulation Still Wins

The recommendation on this project does not flip the rule everywhere. Continuous insulation is the right call on plenty of buildings.

Projects where embodied carbon is a constraint. Closed-cell spray foam carries a high embodied carbon load, and a project tracking embodied carbon may not be able to spend it. The CI assembly with a lower carbon insulation board wins on that metric.

Buildings where the thermal target needs a continuous layer. When the assembly has to break thermal bridging at the studs to hit its number, continuous insulation does something the cavity foam cannot. The CI layer earns its sequence.

Teams that have the CI detail standardized. A contractor who builds the continuous insulation assembly on every project has the sequence down and does not lose the week. For them the constructability gap closes and the lower line-item cost wins.

Cladding systems that need the furring layer anyway. Some rainscreen and panel systems already require the furring and the offset plane. When the build carries that sequence for the cladding regardless, adding the CI board is a small step rather than a new trade.

The Decision Framework

The lesson on this project is not that spray foam beats continuous insulation. It is that the line-item cost of an assembly is not the cost of the assembly. The conventional batt-plus-CI wall looked 2 percent cheaper on the estimate and carried a build sequence that the simpler assembly avoided. Once the schedule risk went into the number, the cheaper line item lost.

The conventional move is to price the assembly and stop. The better move is to price the assembly and the build. A wall that costs 2 percent more in material can be the cheaper wall once the trades, the sequencing, and the weather exposure are in the comparison.

Where a specific building lands depends on the cladding, the contractor, the carbon constraint, and the thermal target. On this 57-unit project the simpler build was worth more than the savings on the board. On the next building the answer can run the other way, and the only way to know is to model both assemblies against the real schedule before the estimate is locked.