Ventilation Retrofit in Occupied Buildings: A Simpler Path

The hard part of retrofitting an occupied building isn't the people, and it isn't the building. Managing each separately is difficult enough on its own. The real difficulty is that the two work against each other — the more a retrofit demands of the building, the harder it becomes to keep people living in it.

Keeping people in place is a desired outcome — it's what you're trying to achieve. But that same commitment is a constraint on the building work, limiting what you can do to the structure and how. Getting the building you want — the performance, the envelope, the ventilation — is a desired outcome. But the work required to get there is a constraint on the people — it drives the disruption they have to absorb.

Each side's goal is the other side's obstacle. Neither is something a project gets to choose. That tension is what an occupied retrofit has to solve, and it's worth taking apart, because the two things pulling against each other are both fixed.

This isn't a problem the industry has left unexamined. CMHC's National Housing Strategy funded a national guide to help owners and builders navigate the complexities. Its goal is to address the disruption itself: how far the work reaches into a finished, occupied building — how much it tears into the structure, and through that, how much it forces onto the people living inside. When designing ventilation for an occupied retrofit, whether the system works was never the question. The question is whether you can install a solution without upending the building, and everyone in it.

But the guide does more than describe the problem. In setting out how to reduce the disruption, it describes the kind of system that keeps the work light and out of the way. No system does that more completely than LUNOS." — decentralized, brought into each suite. 

Every apartment in the building is someone's home. That doesn't change because a retrofit is underway, and it sets the terms for everything that follows. Residents remain in place for the duration, so suite entries have to be scheduled and notified rather than simply carried out. Exit routes have to stay intact while work is underway. Elevators are shared with the people who live in the building, so every load of material competes with daily life for the same vertical access. Work areas sit inside occupied homes, which means dust, noise, and disruption land directly on residents rather than on an empty job site.

And beneath all of it is the constraint that governs the rest: in this housing — social and affordable housing, seniors' residences, student and institutional buildings — tenants cannot simply be asked to leave. The work has to happen around them. This much is familiar to anyone who manages these buildings; it's the daily reality of the job.

The residents are only half of what can't be moved. The building is the other half. A retrofit inherits a structure that is already finished — its floor plates, ceiling heights, the routes through it, and the space it does and doesn't have for equipment were all decided decades ago, for a building that was never expected to carry modern ventilation. You inherit it as it stands. You can work within the framework of the existing building, or you can force it to change to accommodate something new. Forcing it to change — carving out room the building doesn't have, opening up what's already closed — is, on its own, among the slowest and costliest things a retrofit can take on.

Now put the two fixed things back together, and the tension in that opening line becomes concrete. The more a retrofit has to alter the building, the more work it drives into occupied suites — more entries, more trades, more time, more disruption to absorb around people who are still living there. Past a point, the alterations get large enough that working around residents stops being possible at all, and the choice narrows to two options: schedule ever more tightly around people through work that keeps demanding more access, or move them out while it happens. And moving them out is the line this housing can't cross. That's the complexity. It isn't the people, and it isn't the building. It's that heavy intervention and continuous occupancy pull against each other, and the heavier the intervention, the harder the pull.

The guide's recommendations are offered as illustration, not instruction — a set of ways to keep the disruption low, not a checklist to comply with. Read together, they point in one direction: reduce what the work demands of the building and reduce what it demands of the people.

One set of recommendations is about managing the people — a structured engagement effort, a single trusted point of contact, clear and repeated communication, room for residents during the work. No ventilation system does any of this; it's human work, and it stays the owner's. But it isn't fixed in size. The more a retrofit asks a resident to endure, the more of it there is — the harder the conversations, the more trust to rebuild. So the lighter a given piece of the work sits on the tenant, the less of that effort it consumes, leaving it for the parts of the retrofit that genuinely demand it.

The other set is about how the work is built. Favour components prefabricated off site. Keep entries into occupied suites few and short. Keep the intervention small enough that the structure doesn't have to be opened up to accept it. The guide ties this directly to cost: reducing the complexity and disruption of the work is what makes an occupied retrofit affordable in the first place.

Taken together, that second set describes a very particular kind of system — one that keeps the intervention light and the entries few. The two ways of ventilating an occupied building meet that description very differently.

Faced with an occupied building that needs ventilation, the conventional answer is a ducted system — central air-handling equipment feeding a network of ducts that carries air through the building to each space. It was the conventional answer for good reason: it's what the code was written around and what the industry was trained to build. In new construction, where the building goes up around the ducts, it's a reasonable way to work. In an occupied retrofit, a ducted system fights the building and the residents at the same time.

Start with the building. A ducted system's distribution network has to go somewhere, which means finding or forcing the space the fixed structure doesn't have — opening ceilings, cutting shafts, carving out room for equipment the building was never designed to hold. This is the costly, slow alteration of the fixed building in its purest form. Then follow it into the suites, because that alteration doesn't stay out of people's homes. The work arrives as a sequence — demolition, then the mechanical work, then the trades that close everything back up — each stage depending on the last, each requiring its own entry into an occupied home. Materials stage in volume and move through the shared elevators and hallways for weeks. And because the system is balanced and commissioned as a whole, it can't be finished suite by suite; residents live alongside an unfinished system until the entire building is done.

None of this is chosen. A ducted retrofit doesn't decide to disrupt the building and the residents — the disruption is the method. But in an occupied building, it falls on both at once: the structure that has to be torn into, and the people who have to live through it. The heavy alteration of the building drives the maximum amount of disruptive work into occupied suites — which is exactly the pressure that turns scheduling into a question of whether people can stay at all.

A ducted retrofit tears into the building and drives the work into people's homes. LUNOS provides the way — one that leaves the structure intact and minimizes the disruption to residents. Each unit is a self-contained heat-recovery ventilator installed through the exterior wall, supplying and exhausting fresh air directly at the room it serves. There is no central plant, no distribution network, and nothing to route through the building.

The clearest way to see it is by what isn't there. Putting LUNOS into an occupied suite involves no ductwork, no shafts, no ceiling demolition, no mechanical room, and no building-wide commissioning. The fixed structure is asked to change by essentially one small penetration per unit — rather than being opened up to accept a distribution network it was never built to hold. The per-suite work is small and self-contained: hours, not days, and when it's done the suite is whole again, with nothing torn open that has to be rebuilt behind you.

Because the alteration to the building is that small with LUNOS, that pressure never builds — and the in-suite ventilation stops adding to the complexity. The work driven into each occupied home stays brief and contained, so scheduling around residents remains genuinely possible — there's no point at which the intervention grows large enough to put occupancy in question, which means the choice to move people out never has to be raised. And because each unit stands on its own, the building can be done one suite at a time, each finished and working before the next begins.

It also answers one of the hardest logistics of an occupied retrofit: shared vertical access. Where a ducted retrofit shares the elevators with residents for weeks, hoisting sheet metal and equipment, a suite's entire LUNOS material load — the units, the wall sleeves, the grilles, the controls — fits on a handcart and moves in a single trip. The building's daily life and the retrofit stop competing for the same space. Where a ducted system reshapes the building to fit the equipment, LUNOS fits the building as it stands — which is precisely why it suits stock that was never designed around modern ventilation in the first place.

None of this does the human work of a retrofit, and it isn't meant to. Tenant engagement, the trust-building, the on-site liaison — no ventilation system provides those, and they stay with the owner and the project team no matter what goes in. What changes is where that effort has to go. A brief, contained visit is a short conversation, not a campaign — so the engagement a ducted install would have spent on this part of the job stays in reserve for the parts that genuinely test people's patience. LUNOS doesn't lighten the human work of a retrofit. It just refuses to add to it.

With LUNOS, the payoff runs in both directions at once. For the occupant, it means fresh, filtered air delivered continuously to the suite, without a retrofit that turns their home into a construction site for weeks. For the building, it means a ventilation strategy that can actually be carried out in occupied stock — reducing moisture, relieving the load on aging central systems, and letting the retrofit investment perform as intended. To speak of the health of the building and the health of the occupant as a single outcome is to recognize that they follow from the same decision: to treat ventilation as something a retrofit can deliver, rather than something an occupied building has to be gutted to receive.

This article has stayed on one half of the problem — the disruption, the install, keeping people in place while the work happens. The other half, the air itself and why suite-level delivery outperforms what older buildings rely on, is examined across the retrofit articles elsewhere on this site. The point of this one is narrower and, for an occupied building, decisive: the fresh air can be delivered without the disruption that puts residents' occupancy in question. It has been, in occupied Canadian buildings undergoing active deep-energy retrofits — work we've been directly involved in, and documented in the projects linked below.

If you're weighing how to bring ventilation into an aging, occupied building without displacing the people who live there, that's exactly the conversation our team is here to have. Reach out, and we'll work through what it looks like for your building.

This is one piece of a broader library on decentralized ventilation, retrofit strategy, and how it compares to ducted systems. Related reading is linked below.