What is the average cost of a three-season sunroom versus a four-season one in Ottawa?

The gap between a three-season and a four-season sunroom is large because they are really two different kinds of building. As broad perspective only, a three-season room might range from roughly $30,000 to $65,000, and a four-season room from roughly $80,000 to $180,000, depending on size, glazing and foundation. Treat these as perspective, not quotes. There is no reliable Ottawa average for either.

A three-season sunroom is essentially an enclosed porch: glass or screen panels, a lighter roof and little insulation, often on a deck platform, piers or a simple slab. It isn't connected to your heating system, so it is comfortable roughly from spring through fall. Many are prefabricated panel systems sold through local dealers. Construction is relatively quick.

A four-season sunroom is a heated addition and must meet the Building Code like any other living space. That means:

• A proper foundation. On clay or poorly defined soils, footings must be at least 1.2 m deep and not less than the depth of frost penetration.
• Energy compliance. An addition must meet a compliance package or the addition table. Verified values for this climate zone include R-60 for an attic ceiling and R-19 plus R-5 continuous insulation for above-grade walls. Large glass areas make compliance harder, so your designer balances glazing with insulation.
• High-performance glazing to limit heat loss and condensation. Glazing is often where much of the cost difference lives.
• A heat source, sized with a heat-loss calculation. Options include extending existing ductwork if there is capacity, a ductless heat pump that also cools, or electric baseboards, which are cheap to install but costly to run.

Permits: a four-season room is an addition and needs a building permit, with fees of $12.75 per $1,000 of construction value (minimum $117). For a three-season room, check with Building Code Services; the City's permit trigger covers additions and structures with a building area over 10 square metres. Either way, your zoning sets setbacks and lot coverage, and if you need relief, an urban minor variance application to the Committee of Adjustment is $3,759 in 2026.

Some people add insulation and a heater to a three-season room to stretch its season. Be cautious: an unheated structure isn't designed for winter heating, and turning it into living space later may require it to meet addition requirements. Ask a designer before you plan on that. You can browse addition contractors in the Ottawa Construction Network directory at justynrookcontracting.com and compare itemized quotes for both options.

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