Ductwork and Ventilation for a Secondary Suite in Nova Scotia

If you are thinking about turning your basement into an apartment, for a parent, a grown child, or a tenant whose rent helps with the mortgage, HRM has a defined route for doing it legally, as a secondary suite, and a short guide that sets out the requirements.

Most of that guide is about things people expect: fire separation, sound control, smoke alarms, the exit. A few lines in it are about ductwork. Those lines can decide the cost, the layout and the headroom of the whole project, and they are the ones that tend to surface late.

Here is what they say, what they mean for the furnace and ducts you already have, and the order to deal with them.

The rule, in the code's own words

Halifax Regional Municipality's secondary suite guide states it plainly:

"A self-contained Mechanical Ventilation System must be installed in the Secondary Suite. No duct work of any type may be interconnected between the Secondary Suite and the Main Suite."

and, on heating:

"A non-ducted heating system may be shared between the Secondary Suite and the Main Suite so long as there are separate controls for the heating system in each suite."

That is HRM summarising the building code, so it is worth reading the code itself. Nova Scotia adopted the 2020 National Building Code in stages from April 2025, and its housing section, Part 9, says:

• 9.33.1.1.(3): "Air duct distribution systems serving one of the dwelling units in a house with a secondary suite shall not be directly interconnected with other parts of the house."
• 9.32.1.2.(2): a self-contained heating-season ventilation system serving a single dwelling unit must comply with the code's mechanical ventilation subsection, and the explanatory note on that sentence says a separate ventilation system for each unit is necessary for fire safety (quoted below). HRM's guide turns that into a flat requirement: the suite's system must be self-contained.
• 9.33.4.3.(1): where a single heating system serves a house with a secondary suite, individual temperature controls are required in each dwelling unit. The explanatory note confirms this applies to electric, fuel-fired or unitary heaters and hydronic systems, which covers the non-ducted kinds of shared heat HRM describes.

Why the code is this strict about air

It is not about comfort or billing. It is about smoke. The code's explanatory note on ventilation in houses with a secondary suite calls smoke transfer between the two units "a critical safety issue," and says that although a second ventilation system is "expensive—and potentially difficult in an existing building—it is necessary to achieving a minimum acceptable level of fire safety."

Think about what a shared forced-air system does during a fire. The return grilles in one unit draw smoke in, and the blower delivers it through every supply register in the other unit, where people may be asleep. Much of the rest of the suite requirements builds a smoke-tight barrier between the two units, with sealed drywall and solid-core self-closing doors, and interconnects the smoke alarms so both units hear a fire in either one. A shared duct system would be a hole straight through that barrier.

The note also closes off the obvious workaround. Smoke dampers in a shared system are "not considered to be a workable solution because they are very expensive, require regular inspection and maintenance, and must be reset after every activation."

What this means for the furnace you already have

This is the part that catches people. Many houses being converted were built as one dwelling, with one forced-air system serving every floor, basement included. Under the rule above, that system cannot keep serving both units once the basement becomes a suite.

There are three broad ways to resolve it. Which one is right depends on the house, not on a general rule.

1. The suite gets its own ducted system. A separate air handler or furnace with its own supply and return ducts, serving only the suite. The main house keeps its system, and every branch and return that used to reach the basement is disconnected and sealed off. This keeps forced air on both sides, but it is two systems, and the suite's equipment needs a home of its own.

2. The suite gets non-ducted heat, and the main house keeps the ducts. Electric baseboard, hydronic heat, or a ductless heat pump in the suite. The main system is cut back to serve the main house only: suite supply runs capped, suite returns removed, duct closed to the suite. This is often the simpler route in an existing house. It does not remove the ventilation requirement, though. The suite still needs a ventilation system of its own (next section).

3. The whole house moves to a shared non-ducted system. Hot-water radiant heat, for example, can serve both units as long as each unit controls its own temperature. That is a bigger change, and it usually only makes sense when the heating system is being replaced anyway.

Two things apply whichever route you take.

Every opening counts, returns included. A supply register left in the suite delivers smoke from a fire upstairs straight into the suite. A return grille left in the suite pulls the suite's air, and its smoke, into the main house's system. When the basement is separated, every supply and every return opening on the suite side has to go, and the main house needs enough return air of its own afterwards. Older Halifax houses are often short of return air before anyone touches them. It is the first item in our list of common ductwork problems in older homes.

Closed off means sealed, not just covered. A capped branch or an abandoned boot that still leaks air through the ceiling is a gap in the smoke-tight barrier. HRM's guide describes that barrier as achieved by "sealing all joints and penetrations" so vapours cannot pass from one side to the other. Every duct penetration through it has to be dealt with properly, which is exactly the kind of work duct sealing covers.

And the heat source for the suite may not be ours to install. A ductless or ducted heat pump is refrigerant work, which is a licensed compulsory trade in Nova Scotia. That goes to our licensed partner. The air side is ours: separating the duct systems, building the suite's own ductwork, sealing the penetrations, and the ventilation. If you are weighing a ductless head for the suite, our guide to ducted vs ductless heat pumps sets out the trade-offs.

The suite needs its own ventilation, and it doesn't have to be an HRV

The code requirement is a self-contained mechanical ventilation system for the suite. It's worth reading that precisely, because some of what you will find online overstates it.

The National Building Code allows heating-season ventilation to be designed in more than one way: to the CSA F326 standard, to the code's own prescriptive method for homes of up to five bedrooms (a principal ventilation fan, a planned supply of outdoor air, supplemental exhaust fans and protection against depressurisation), or to Part 6. The energy-efficiency section doesn't force one either: its heat-recovery article (9.36.3.9.) applies where a system with heat recovery is installed. An HRV is one way to meet the requirement, not the requirement itself.

That said, in a Nova Scotia basement apartment an HRV or ERV is usually the right answer, for three reasons:

• Basement suites are small. Moisture from cooking, showers and drying clothes goes into a small volume of air, and without steady ventilation it has nowhere to go. That is how basement apartments end up with windows running with condensation and a musty smell by February.
• It ventilates without throwing the heat away. An HRV recovers heat from the stale air going out, which matters when someone is paying to heat the suite. Our plain-language guide to HRVs covers how they work.
• HRV or ERV is a real choice in a basement. It depends on the space and how it is used, which our ERV vs HRV guide for Nova Scotia works through.

If the house already has an HRV, it can't simply be extended into the suite. It serves one unit, and that will usually be the main house. The suite gets its own unit with its own ducting, and any HRV ducts that currently reach the basement are disconnected and sealed like the heating ducts. One thing to check: if your HRV is tied into the furnace ducts, it only stops reaching the suite once the furnace ducts do, so the two separations have to be planned together.

Exhaust counts too. HRM's wording is "no duct work of any type." The suite's bathroom fan and kitchen range hood exhaust have to run outdoors on their own, not tie into exhaust ducts serving the main house. If you are planning the suite's kitchen, our guide to range hood venting mistakes is worth reading before the cabinets go in.

Headroom: the 1.85 m rule and the trunk line over your head

This is the requirement that most often turns a ventilation conversation into a ductwork job.

The National Building Code (9.5.3.1.) and HRM's guide set two heights for a secondary suite:

• Ceiling height: at least 1.95 m (6 ft 5 in).
• Clear height under beams and ductwork: at least 1.85 m (6 ft).

And one condition that is easy to miss: the areas that meet those heights must be contiguous with the entry to each room. A low trunk across a bedroom doorway is a problem even if the rest of the room is fine.

In many basements the lowest thing in the ceiling isn't the joists. It is the main supply trunk and the return running beside it. Measure to the underside of the duct as it will be when the suite is finished, not as it is today. The suite's ceiling usually carries resilient channel and drywall to reach the STC 43 sound rating HRM requires, the floor may get a finish, and a duct that is boxed in loses the depth of the box as well.

If a trunk comes in below 1.85 m, there are three ways to deal with it:

• Reroute it along a wall or into a corner, where a bulkhead does not cross a living space or a doorway.
• Reshape it. A deep, narrow trunk can sometimes be rebuilt shallower and wider, sized so it still carries the air it has to. That needs a properly designed, custom-fabricated section rather than a squashed one, because a trunk crushed to fit loses airflow.
• Rethink it. If the suite is getting its own heating anyway (route 2 above), the main house may not need a trunk running through the middle of the basement at all. It may be possible to bring its supply up from a different path.

Rerouting ductwork in an occupied, finished basement is expensive, because the ceiling becomes the cost. In a basement being converted, the ceiling is open, which makes it the cheapest moment this job will ever have. Our guide to adding ductwork to a finished basement covers routing, soffits and bulkheads in more detail.

The order to do it in

Most of the expensive surprises in a suite conversion come from doing the right things in the wrong order. For the air side, this is the order that works:

1. Decide the heating route first (separate ducted, non-ducted suite, or shared non-ducted). Everything else follows from it, including whether the suite needs room for its own equipment.
2. Design the suite's ventilation, including where the HRV or ERV sits, where its intake and exhaust leave the house, and the bathroom and kitchen exhaust.
3. Measure the headroom against 1.85 m and decide what happens to any trunk that fails it.
4. Apply for the permit with that design in hand. HRM requires a building permit for any work to create a secondary suite, and a building official can answer site-specific questions, such as whether a main trunk may pass through the suite enclosure. Ask early, through 311.
5. Do the duct work while the ceiling is open: separate, cap, seal, reroute and install. Then the smoke-tight barrier and the sound-rated ceiling go up over finished, sealed ductwork.
6. Balance both systems afterwards. The main house has just lost part of its duct system and maybe some return air. It needs to be set up for the house it now serves, not the one it used to serve.

The common mistake is the reverse order: frame, insulate and drywall, then find out the trunk is 1.78 m off the floor and a supply register is still in the suite bedroom.

What a walkthrough settles

For a suite conversion, these are the things that have to be seen rather than guessed:

• The existing system: forced air or not, its age, and whether the main house can still be served properly once the basement is cut off.
• Every duct that reaches the basement: supplies, returns, HRV ducts and exhaust, so nothing is missed at the separation.
• The trunk's depth against 1.85 m, measured to the finished floor and ceiling that are coming.
• Where the suite's own equipment and ventilation can go, including the outside wall penetrations for intake and exhaust.
• What the heat source for the suite will be, and whether part of it is our licensed partner's work.

We won't put a price on it before seeing it. The same conversion can be a few capped branches and a small HRV in one house, and a rerouted trunk plus a second system in the house next door. The basement decides, not a per-square-foot figure.

Where we fit in

Ductwork and ventilation are our trade, and a secondary suite is a job where both matter at once, under a code requirement that leaves no room for a shortcut. We separate the duct systems properly, returns included. We seal every penetration so the smoke-tight barrier really is one, build the suite's own ductwork and HRV or ERV, and reroute or rebuild trunks that would fail the headroom rule.

We will also tell you which parts aren't ours. The suite's heat pump, if it has one, goes to our licensed partner, and the fire separation and sound assemblies belong to whoever is building the suite. We'll coordinate with both, so the ductwork is done and sealed before the ceiling closes over it.

If you are planning a secondary suite anywhere in Halifax HRM, get in touch while the basement is still open.

Sources

This page makes no cost claims. Code text is quoted from the primary documents below, which were opened and read in full for the clauses cited. Last verified October 5, 2026. All sources are Canadian.

Canadian sources

• Halifax Regional Municipality: Secondary Suites (Planning & Development guide, file dated 2024.01). Source of the statements that "a self-contained Mechanical Ventilation System must be installed in the Secondary Suite" and "no duct work of any type may be interconnected"; that a non-ducted heating system may be shared with separate controls in each suite; the 1.95 m ceiling and 1.85 m under beams and ductwork (citing NSBC B.9.5.3.1.); the smoke-tight barrier achieved by "sealing all joints and penetrations"; the STC 43 sound rating and its resilient-channel construction; and the requirement for a building permit for any work to construct a secondary suite.
• National Research Council of Canada: National Building Code of Canada 2020, Volume 2, Division B, Part 9 (free PDF through the NRC Publications Archive). Clauses cited: 9.5.3.1.(2)–(4) (ceiling and clear heights in secondary suites, contiguity with entries); 9.32.1.2.(2) and Note A-9.32.1.2.(2) (self-contained systems serving one dwelling unit follow Subsection 9.32.3.; the note says a second ventilation system "is necessary to achieving a minimum acceptable level of fire safety"; smoke control as "a critical safety issue"; smoke dampers "not considered to be a workable solution"); 9.32.3.1. (the ways heating-season ventilation may be provided: CSA F326, the prescriptive subsection, or Part 6); 9.33.1.1.(1) and (3) (radiant heating in houses with a secondary suite; air duct distribution systems "shall not be directly interconnected with other parts of the house"); 9.33.4.3.(1) and its note (separate temperature controls where a single heating system serves both units). Also checked: 9.36.3.9.(1), which applies only where a ventilation system with heat recovery is installed, so the energy section does not itself require an HRV.
• Province of Nova Scotia: news release, 20 September 2024, on adopting the 2020 National Building Code in tiers from 1 April 2025.

What we could not source, and what we left out

• Nova Scotia's provincial amendments. We read the national code text and HRM's guide, which agree on every clause cited here. We did not read the provincial regulation itself (the copy we tried to open was not available at its published address). If a provincial amendment changes any of these clauses for your property, HRM's building official has the final word.
• Whether a main-house trunk may pass through a suite's enclosure. Neither document answers this directly for every construction, so we don't either. It is a permit-stage question.
• Suite funding. Nova Scotia has run a secondary and backyard suite incentive program, but the program page we checked now redirects elsewhere, and we could not confirm whether it is open or what it currently pays. Rather than repeat an amount that may be out of date, we left it out. Check with the province directly.
• Costs. None given, on purpose. See the walkthrough section.