How do I maintain proper attic ventilation when adding insulation in NB? | Insulation IQ?

Maintaining proper attic ventilation during an insulation upgrade is not optional — it is one of the most critical steps in the entire project, and skipping it or doing it incorrectly is the single most common cause of premature roof deck failure, mould growth, and ice damming in New Brunswick homes. Here is how to get it right.

The purpose of attic ventilation in a cold-roof assembly — which is what virtually every New Brunswick home with a vented attic uses — is to keep the attic air temperature close to the outdoor air temperature. This does two things: it prevents the snow-melt-and-refreeze cycle that causes ice dams, and it removes any moisture-laden air that enters the attic before it can condense on the cold roof sheathing. The National Building Code of Canada (NBC), adopted in New Brunswick, sets the minimum ventilation requirement at 1:300 of the insulated ceiling area when both high (ridge) and low (soffit) vents are present, or 1:150 if only low or only high vents exist.

For a typical New Brunswick home with 1,200 square feet of attic floor area, that means a minimum of 4 square feet of net free ventilation area under the 1:300 ratio — half at the soffits, half near the ridge. This does not sound like much, but many older homes in Moncton, Fredericton, and Saint John fall well short of this once soffit vents are partially blocked by insulation or painted over during renovations.

The key installation requirement is eave baffles (also called rafter baffles or vent chutes). These are rigid channels — typically made from cardboard, foam, or rigid polystyrene — that are installed against the underside of the roof deck in each rafter bay, from the soffit vent opening up past the top plate of the exterior wall into the open attic space. They create a physical separation between the soffit air inlet and the insulation mass, ensuring that incoming ventilation air from the soffits can flow freely up the underside of the roof deck toward the ridge without being obstructed by insulation.

Baffles must extend at least 25 mm (1 inch) above the top of the insulation to maintain that clear airflow channel. Given that the NB Building Code target for attic insulation is R-50 to R-60 (roughly 356–430 mm of blown cellulose, or 380–460 mm of blown fibreglass), and given that the rafter depth in older homes is often only 89 mm (standard 2x4 framing) or 140 mm (2x6 framing), you will need to ensure your baffle is tall enough to accommodate the full insulation depth while still leaving that 25 mm airspace. In shallow rafter bays, this sometimes means building up the baffle height or using a foam baffle that can be notched to fit.

For blown-in insulation installs — which are the most common upgrade method in NB because they fill irregular framing and cover top plates more uniformly than batts — eave baffles are absolutely mandatory. Without them, the blown-in machine will simply pack insulation right up to the soffit vents, blocking every one of them within the first 600–900 mm from the eave. This is a surprisingly common installation error, even from experienced crews who get careless near the end of the job.

Ridge ventilation must also be confirmed before or during the insulation project. A continuous ridge vent paired with continuous soffit vents is the gold standard for balanced attic ventilation. If your home has only gable-end vents and no ridge vent, consider adding a ridge vent as part of the project — this often requires a roofer and adds $800 to $2,000 to project cost depending on ridge length, but the moisture control benefit is substantial in NB's Climate Zone 6 winters.

For spray foam attic assemblies (closed-cell foam applied to the underside of the roof deck creating an unvented or conditioned attic), ventilation rules change entirely — no ventilation is required and none should be provided. But this is a fundamentally different assembly type, more expensive, and less common in NB residential retrofits. If a contractor proposes converting your attic to an unvented assembly, ensure they have properly calculated the required foam thickness to keep the sheathing above the dew point — typically R-28 minimum in Climate Zone 6 when combined with additional interior insulation.

Practical checklist before any insulation is added: confirm all soffit vents are open and unobstructed, confirm ridge or high vents exist and are functional, install rafter baffles in every bay before blown-in work begins, and have the contractor show you how they plan to handle the eave zone before the machine starts.

New Brunswick Insulation and the professionals listed through the New Brunswick Construction Network understand these Climate Zone 6 ventilation requirements — ask any prospective contractor to walk you through their baffle installation process before signing a contract.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• moose luxury painting
• 3Tone Construction Ltd
• Brunswick insulation & roofing
• Gionetterenovations
• Thirty Four Renovations