Sunrooms are one of Ottawa's most popular additions — but the choice between a 3-season and 4-season sunroom is the single most important decision in the project. The cost difference is substantial, the construction process is fundamentally different, and the wrong choice leads to a room you don't use. We worked with [Black Sable Group](https://blacksablegroup.com) to clarify exactly when each makes sense in Ottawa's climate.
A 3-season sunroom is a non-insulated structure with single-pane glass or screens, designed for spring-fall use. A 4-season sunroom is a fully insulated, fully heated extension of your home that meets all the same code requirements as the rest of your house.
Use from late April through early October. Single-pane or storm-window glazing, no insulation in walls or roof, no heating, no permanent connection to the home's HVAC. Cannot be classified as habitable space for resale or occupancy purposes.
Use 365 days a year. Fully insulated walls (R-22+) and roof (R-50+), high-performance double or triple-pane windows, integrated heating and cooling, vapour and air barriers, and full code compliance for habitable space. Counts as living area for assessment and resale.
The cost gap between 3- and 4-season is large and worth understanding before committing.
Includes foundation (typically deck-style on piers), pre-fabricated aluminum frame system with single glazing or screen panels, electrical for lighting and outlets. 200–300 sq ft typical.
Full foundation (frost-protected slab or poured walls), insulated framing, high-performance glazing, full HVAC integration, electrical and finishes per habitable space code. 200–400 sq ft typical.
Heating a sunroom in Ottawa is harder than heating any other room because of the high glass-to-wall ratio.
Extending the existing furnace ducts to a sunroom often produces inadequate heat because the room's heat loss exceeds what the existing system can supply through a small duct branch. Air handlers also don't anticipate the high solar gain that creates extreme summer cooling load.
Dedicated mini-split heat pump (12,000–18,000 BTU) is the standard recommendation for Ottawa 4-season sunrooms. Provides both heating and cooling, runs efficiently in shoulder seasons, and decouples the sunroom from the rest of the home's HVAC system.
Hydronic or electric in-floor heating is highly effective in 4-season sunrooms because it counteracts cold downdraft from glazing. Often combined with a mini-split for the cooling load.
Both sunroom types require permits in Ottawa, but the code requirements differ substantially.
Building permit required. Reviewed under accessory structure rules. No insulation, vapour barrier, or HVAC requirements.
Building permit reviewed under full habitable space requirements. Must meet OBC SB-12 energy efficiency standards (R-22 walls, R-50 ceiling, U-value 1.6 max for windows). Air-tightness, vapour barrier, and ventilation requirements all apply.
Honest assessment of what each adds to your property value.
Adds modest value (typically 30–45% of cost). Buyers often discount because the room can't be used in cold months. Often viewed as 'nice to have' rather than 'expanded living space.'
Adds significant value (typically 65–85% of cost) and is reflected in MPAC assessment as additional living area. Counts as bedroom or family room equivalent in MLS listings.
Sometimes, but rarely cost-effective. The foundation, framing, and glazing systems for 3-season aren't designed for habitable-space code, so most conversions become near-rebuilds. Decide upfront.
4-season is the dominant choice in 2026. The relative cost gap has narrowed, the comfort difference is large, and the resale value premium justifies the investment for most homeowners.
3-season: 4–8 weeks of construction. 4-season: 10–18 weeks of construction including HVAC integration. Add 6–10 weeks for permits in both cases.
Not typically for a standard sunroom. Engineering for the foundation and roof structure is usually sufficient. An architect may be helpful for non-standard footprints or when the addition affects the rest of the house.
Only in a 4-season build. Adding plumbing requires the room to be classified as habitable and properly insulated to prevent freeze damage.