What insulation approach is best for a New Brunswick home being converted from seasonal to year-round use?

Converting a seasonal cottage or camp to year-round use in New Brunswick is one of the most demanding insulation projects you can take on — because you're not just adding comfort, you're fundamentally redesigning a building envelope that was never meant to handle -25°C winters, 5,000+ heating degree days, or the moisture dynamics of a continuously occupied home.

Seasonal buildings in NB were built to be left cold. Walls are often 2x4 framing with no insulation or a single layer of fibreglass batt. Attics may have nothing at all, or a thin layer of R-8 to R-12 that was adequate when the building sat empty from October to May. There's typically no vapour barrier, minimal air sealing, and a foundation or crawl space that was designed to drain and freeze rather than stay warm and dry. Every one of those assumptions has to be reversed.

The Conversion Sequence: What to Tackle First

The single most important principle for this type of project is sequence. You cannot insulate your way out of a moisture problem, and you cannot fix air leakage by adding more insulation. The right order is: fix water problems first, then air seal, then insulate, then install vapour management, then verify with a blower door test.

Start with a moisture and structural assessment. Before any insulation goes in, have someone walk the building and identify active water infiltration — foundation seepage, roof leaks, condensation on windows, rot at sill plates. In NB's wet Maritime climate, a seasonal building that has been left unheated for years may have absorbed significant moisture into its framing. Insulating over wet wood traps that moisture and accelerates rot. If you find soft wood, discolouration, or a musty smell, get a professional assessment before proceeding.

Air sealing is your first trade work. Seasonal buildings are notoriously leaky — they were often built without housewrap, with gaps at every rim joist, around every penetration, and at every window and door frame. A typical seasonal-to-year-round conversion will test at 15-20 ACH50 on a blower door — four to five times leakier than what NB's building code requires for new construction. Caulk every penetration, spray foam every rim joist cavity with 2 inches of closed-cell foam, and seal around all window and door rough openings before a single batt goes in.

Attic and Roof

If the building has a vented attic, this is your most straightforward assembly. Air seal the attic floor thoroughly — every electrical penetration, every plumbing stack, every interior wall top plate — then blow in cellulose or fibreglass to R-50 minimum, R-60 if the joists allow it. Install ventilation baffles at every soffit bay before blowing to maintain airflow from soffit to ridge. This is non-negotiable in NB — without baffles, your first winter will produce ice dams and moisture-laden attic air with nowhere to go.

Cathedral ceilings and flat roofs are significantly more complex. If there's no existing insulation cavity, your best option is typically closed-cell spray foam applied to the underside of the roof deck from inside — filling the rafter cavity completely (an unvented assembly) and providing both insulation and vapour control in one step. For a 2x8 rafter cavity, 7.5 inches of closed-cell foam gives you approximately R-45 to R-52 and eliminates the ventilation gap problem entirely. This is professional-only work.

Walls

Most seasonal NB buildings have 2x4 walls, which limits your options. A 2x4 cavity fully packed with R-14 mineral wool or R-12 fibreglass gets you to roughly R-12 to R-14 effective — well below the R-22 to R-28 that current NB code requires for year-round walls. You have two ways to close that gap.

Dense-pack cellulose blown into the existing wall cavities through small holes (drilled from exterior or interior) is the most cost-effective first step — typically $2,500 to $5,000 for a small seasonal building. It fills voids, provides modest air sealing, and gets you to R-13 to R-14 in the cavity.

Continuous exterior insulation is the upgrade that actually gets you to code performance. Two inches of XPS rigid foam (R-10) over the existing sheathing, under new siding, brings your whole-wall R-value to R-22 to R-24 and eliminates thermal bridging through the studs. Combined with new housewrap and careful window extension jambs, this is the gold standard for wall performance. Budget $15,000 to $25,000 if you're replacing siding at the same time — but if the siding needs replacing anyway, the incremental cost of adding continuous insulation is modest.

Foundation and Crawl Space

This is where seasonal buildings most commonly fail when converted to year-round use. An uninsulated or vented crawl space that was fine when the building sat empty becomes a massive heat sink and moisture problem the moment you start heating it continuously.

Encapsulate the crawl space entirely. Seal all vents, insulate the crawl space walls with closed-cell spray foam or XPS rigid foam (R-20 minimum, accounting for NB's 4-5 foot frost depth), install a 6-mil poly vapour barrier across the entire floor lapped up the walls, and condition the space with a small amount of heat or a dehumidifier. This transforms the crawl space from a liability into a controlled, semi-conditioned space that protects your pipes and your floor.

For full basements, closed-cell spray foam at 2 inches on the walls (R-12 to R-14) followed by 2-inch XPS (R-10) gets you to R-22 to R-24 on the foundation walls — meeting NB code requirements. The spray foam layer handles both insulation and vapour control against the cold concrete; the XPS adds thermal mass and brings the total R-value up.

Vapour Barrier — The Critical Detail

A seasonal building converted to year-round use will now be generating interior moisture continuously — cooking, bathing, breathing, laundry. Without a proper vapour barrier on the warm side of every exterior assembly, that moisture will migrate outward through the walls and condense on cold surfaces inside the wall cavity. In NB's Climate Zone 6, this is not a theoretical risk — it will happen, and it will cause mould and rot within two to three heating seasons.

Every exterior wall and ceiling assembly needs a continuous 6-mil polyethylene vapour barrier on the interior face, sealed at all edges and penetrations with acoustical sealant. If you're doing a full interior renovation, this is straightforward. If you're working with existing finished walls, smart vapour retarders (variable permeance membranes) applied to the interior surface before new drywall are a practical alternative that provides vapour control without requiring full wall demolition.

Mechanical Systems and Ventilation

One detail that surprises many homeowners doing this conversion: a properly air-sealed and insulated building needs mechanical ventilation. Once you tighten up a seasonal building to year-round standards, the natural air leakage that used to provide fresh air is gone. You'll need an HRV (heat recovery ventilator) to bring in fresh air without losing the heat you've paid to generate. This is an HVAC question, but it's inseparable from the insulation work — budget for it as part of the conversion.

Rebates and Costs

A full seasonal-to-year-round conversion for a small NB cottage or camp (800-1,200 sq ft) typically runs $18,000 to $40,000 depending on existing conditions, foundation type, and how much of the work is done at once. The good news is that this project is highly eligible for rebates — the NB Power Total Home Energy Savings Program (up to $5,000) and the Canada Greener Homes Grant (up to $5,000) can be stacked for $8,000 to $10,000 in combined incentives. You must have a pre-retrofit EnerGuide evaluation completed by a certified energy advisor before any work begins — this step cannot be done retroactively.

Get that energy advisor booked first. They'll walk the building, run a blower door test, and give you a prioritized list of improvements with projected energy savings for each. It's the best $400 to $600 you'll spend on the entire project.

New Brunswick Insulation can connect you with experienced local contractors who have done seasonal-to-year-round