Heating costs tend to climb fast in colder regions, and insulation is one of the most direct ways to control them. The material chosen for walls, attics, and floors determines how well a home holds heat and how efficiently the heating system runs. Four options dominate residential projects: fibreglass batts, spray foam, cellulose, and rigid foam board. Each has a distinct performance profile depending on climate, budget, and where it gets installed. Here is how they compare where winters are genuinely punishing.
1. Fiberglass Batts
Fibreglass is the default choice for most residential construction, and for good reason. It comes pre-cut to fit standard wall cavities and attic bays, which makes installation straightforward for contractors and experienced homeowners alike.
1.1 How It Performs in Cold Climates
The R-value is the standard measure of thermal resistance, and fibreglass batts range from R-11 to R-38 depending on thickness. Cold climate building codes generally call for R-38 or above in attics and R-19 in exterior walls, so thicker batts are typically required in harsher regions.
Those evaluating house insulation in Wellington will find fibreglass a reasonable starting point, particularly in homes with conventional stud framing where cavities are already sized to accept pre-cut panels without significant structural changes.
The persistent limitation is air leakage. Fibreglass fills the cavity but does not seal it. Cold air moving through gaps around the material can undercut performance considerably, even when the stated R-value looks adequate on paper.
1.2 Cost and Fit
Fibreglass is the most budget-friendly option in this category. It works well in retrofit situations where wall cavities are accessible and the scope of work is limited. For projects where cost is the primary constraint, it is a defensible choice, though performance trade-offs exist.
2. Spray Foam Insulation
Spray foam expands on contact, filling cavities, seams, and irregular voids that other materials simply cannot reach. It comes in two formulations: open-cell and closed-cell.
2.1 Thermal and Air Barrier Performance
Closed-cell spray foam delivers R-6 to R-7 per inch, the highest per-inch rating among common residential materials. Open-cell foam is less dense and performs closer to R-3.5 per inch, though it costs considerably less.
In cold climates, closed-cell foam has a clear advantage. It serves as a thermal insulator, vapour barrier, and air barrier in a single application. That combination matters in cold climates because temperature differentials between interior and exterior spaces drive moisture into wall assemblies, and without proper vapour control, that moisture accumulates and causes structural damage over time.
3. Cellulose Insulation
Cellulose is made from recycled paper fibre and treated with fire-retardant compounds. Installers blow it into wall cavities and attic spaces using pressurised equipment, allowing it to conform tightly to irregular framing.
3.1 Cold Climate Suitability
The R-value for cellulose falls between R-3.5 and R-3.8 per inch. Those numbers appear similar to fibreglass on paper, but the dense packing reduces air movement within the cavity itself, which significantly improves real-world performance.
Moisture is the primary concern. Cellulose that gets wet compacts and loses R-value. In cold, damp climates, a proper vapour control layer is not optional; it is essential for maintaining long-term performance.
3.2 Environmental Credentials
Cellulose contains up to 85% recycled content, making it the most environmentally favourable option in this comparison. Pricing typically falls between fibreglass and spray foam, making it a solid mid-range choice for homeowners balancing performance and budget.
4. Rigid Foam Board
Rigid panels are manufactured from polystyrene, polyisocyanurate, or polyurethane. Builders use them on exterior wall sheathings, basement walls, and under concrete slabs where other insulation types are impractical.
4.1 Strengths in Cold Applications
The primary advantage of rigid foam is its ability to eliminate thermal bridging. Heat escapes through wall studs just as readily as through uninsulated cavities; standard batt insulation does nothing to address that. A continuous layer of rigid foam over the entire wall surface completely blocks that pathway.
Polyisocyanurate panels reach R-6.5 per inch, the highest in this product category. Applied externally, they add meaningful thermal resistance without consuming interior square footage.
4.2 Limitations to Consider
Panel joints require careful sealing; gaps between boards become air infiltration points that reduce overall system performance. Rigid foam also rarely satisfies full code requirements on its own. Pairing it with interior batts or blown-in insulation is the standard approach for meeting cold climate energy codes.
Conclusion
Each insulation type has a clear role depending on the project constraints. Fibreglass suits tighter budgets and standard framing. Spray foam excels when air sealing and vapour control are priorities. Cellulose offers dense, sustainable fill with solid real-world performance. Rigid foam addresses thermal bridging that other materials leave unresolved. The strongest return comes from selecting based on location, existing structure, and performance goals rather than defaulting to whichever material is most familiar.