How All-in-One Heat Pump Washer Dryers Took Continuous Insulation Off a 205-Unit Lowell Project

On a 205-unit new construction project in Lowell, MA, one appliance let us take an entire layer off the building. We used all-in-one heat pump washer dryers. They're more efficient, and that efficiency helped us take the continuous exterior insulation off the building. Sometimes the best energy code move is picking what's easiest to install. On this job, the easiest thing to install also did the most work in the energy model.

The 205-Unit Lowell Project

The project was 205 units of new construction in Lowell, MA. Like most multifamily work in Massachusetts, it had an energy code target to hit, and the design had to show it could get there. The usual way to close a gap is to add to the envelope. More insulation, better windows, a tighter building.

We went a different way. Instead of adding a layer to the walls, we looked at what was plugged into the units. Laundry is one of the biggest energy users in an apartment. Change how the laundry works, and the model notices.

So we specified all-in-one heat pump washer dryers. One machine washes and dries in the same drum. It uses a heat pump to dry the clothes instead of burning through electric resistance heat. They're more efficient, and the model gave the project credit for that efficiency.

That credit was enough to take the continuous exterior insulation off the building. Not thin it out. Take it off. One appliance choice removed an entire layer from every exterior wall on a 205-unit job.

It was a two for one. The laundry got simpler, and so did the walls.

The Continuous Insulation Problem

Continuous exterior insulation is a layer of rigid board or mineral wool that wraps the outside of the framing. It sits between the studs and the cladding. Its job is to stop heat from moving through the studs themselves, which the cavity insulation cannot do. It works. The trouble is everything it takes to install it right.

A wall with continuous insulation is thicker. Every window, every door and every penetration now sits in a deeper opening. The cladding has to hang off the framing through that layer, so the attachment gets more complicated. The water barrier, the flashing and the air barrier all have to be detailed around it.

Then come the transitions. Where the wall meets the foundation. Where it meets the roof. Where a balcony, a canopy or a deck ties back into the structure. Each of those spots needs its own detail, and each detail has to be drawn, priced, coordinated and built in the field. A miss at a transition is where water and air get in.

That is where the cost lives. Not only in the board itself, but in the design time, the extra coordination between trades, and the labor of getting every edge right on every elevation. On a multifamily building, those details repeat across hundreds of openings and every corner of the building.

Take the continuous insulation off, and none of its transition details have to be designed or built. The walls get simpler. The drawings get simpler. The crew in the field has fewer chances to get something wrong.

Why the All-in-One Heat Pump Washer Dryer Earned Its Place

A standard electric dryer heats air, pushes it through the clothes and blows it out of the building. All of that heat goes out the vent. A heat pump dryer works differently. It moves heat in a closed loop, pulls the moisture out of the air, and reuses the warmth. It does the same job with far less energy, and the energy model counts that.

On this project, that efficiency did real work. It made up the ground the building gave back when the continuous insulation came off. That is the trade the model allowed: a more efficient appliance in place of a thicker wall.

The install benefits stack on top of the energy credit.

No dryer vent ducting. A heat pump washer dryer does not exhaust to the outside, so there is no duct to route through the unit. That means no vent run to fit between framing, no hole in the exterior wall for every unit, and no vent cap to flash and seal.

No 240V outlet. A standard electric dryer needs a dedicated 240V circuit. The all-in-one units did not, which takes a heavier circuit and a special outlet out of every unit's electrical scope.

Two appliances became one. A washer and a separate dryer need space for two machines. One combined unit fits where one machine goes, which saved space in every unit. On a 205-unit building, that space shows up 205 times.

No continuous insulation. This is the big one. With the efficiency credit from the laundry, the exterior layer came off, and none of its transition details had to be designed or built.

Each of these is a line item that disappears. Fewer trades touch each unit. Fewer penetrations get cut into the building envelope. Fewer details sit on the drawings waiting to be coordinated.

Wins like this are highly underrated. They don't look like efficiency upgrades on a spec sheet. They look like a laundry choice. But the model treats energy the same no matter where it comes from, and a building that is easier to build is a building that gets built faster.

When Continuous Insulation Still Wins

None of this means continuous insulation is a bad product. It means it should earn its place on the numbers, the same as any other measure. There are projects where it is the right call.

The appliance credit is not enough. Every building starts in a different spot. If the gap to the target is bigger than what the laundry swap covers, the envelope may still have to carry part of the load. The model tells you how much is left after the appliance.

The cheaper moves are already used up. If a design already has efficient laundry and the other high-value measures, the next gains may only be in the walls. At that point continuous insulation can be the best option left.

The wall assembly needs it for other reasons. Continuous insulation keeps the framing warmer, which can matter for how an assembly handles moisture and for comfort near exterior walls. Pulling it off should be checked against how the assembly behaves, not just against the energy score.

The owner or program asks for it. Some owners, lenders or programs set envelope targets of their own. If a project is chasing a specific certification or a performance spec beyond code, the envelope may be fixed before the laundry is even chosen.

The building shape works against you. A building with a lot of exterior wall relative to its floor area loses more heat through the walls. On a form like that, the envelope matters more, and the trade the Lowell project made may not close the gap.

Why You Should Model Easy Installs Before the Envelope

Start with what is easiest to build, then ask the model whether it gets you to the target. Most teams start from the other end. They load the envelope first because that is how energy code has always been handled, then they pay for every detail that layer brings with it. Flip the order. Look at the appliances, the systems and the simple swaps first, and only add layers the model says you need.

Price the whole install, not just the product. An all-in-one heat pump washer dryer can cost more than a basic washer and dryer. But on the Lowell project it removed dryer vent ducting, a 240V outlet, a second appliance's worth of space and the continuous exterior insulation with all of its transition details. The product price is one line. The install is the whole building.

Then count the schedule. Some of the biggest developers we've seen don't always have the lowest construction cost, but they build fast and efficiently. That saves them a ton in interest and lets them rent faster too. A wall with fewer layers and fewer details goes up faster. A unit with fewer trades in it finishes sooner. That time is money the energy model never shows.

There is no single right answer here. On a 205-unit job in Lowell, the laundry carried the envelope. On another building, with a different shape, a different target or a different team, the answer could land somewhere else entirely. The only way to know which measures can come off your building, and which ones have to stay, is to model your project and price what each choice really takes to build.