3-Season vs. 4-Season Sunrooms: Which is Best for Edmonton Homes?

Picture a bright February afternoon in Edmonton, −20°C outside, and a glass room on the back of your house that is too cold to sit in. That is what happens when a sunroom is built for the wrong season.

The 3-season vs. 4-season sunroom decision is really a decision about how many months you want to use the space. A 3-season room covers spring to fall for far less money and paperwork.

A 4-season room adds insulated glass, a heat source, and a frost-protected foundation, so it’s closer to a small addition.

In this guide, you’ll see how each type handles Edmonton’s climate, what the City requires, where the price gap comes from, and how to decide which one fits your home.

What’s the real difference in a 3-season vs. 4-season sunroom?

Insulation and heat. A 3-season room is meant for roughly spring through fall. It isn’t insulated to the same standard as your house and isn’t tied into its heating.

A 4-season room is closer to a home extension. It has Low-E glass, thermally broken frames, and insulation in the floor, walls, and roof.

Foundation, permit route, running cost, and comfort on a cold night all follow from that one split. The table shows how Canadian builders and permit guidance typically describe the two. Specific products vary.

Feature	3-season	4-season
Typical use	Spring to fall, plus mild or sunny winter days with a heater	Year-round
Heat	Not connected to the house’s heating	Designed around a heat source, and usually cooling too
Glass	Often single-pane or tempered glass	Low-E, sometimes argon-filled, in thermally broken frames
Foundation	Can sometimes sit on an existing deck if a structural assessment confirms it can carry the load	Frost-protected: screw piles, piers, or concrete, depending on soil and code
City of Edmonton permit type	Unheated room addition	House expansion (heated sunroom)

How does Edmonton’s climate change the choice?

It creates a long stretch of the year when the two types behave nothing like each other. Edmonton’s average daily high sits just below freezing from about mid-November to early March. January’s daily average is around −10°C.

According to Environment Canada normals, lows drop below −20°C on more than 20 days in a typical year. The National Building Code puts Edmonton at 5,120 heating degree-days in climate Zone 7A.

Nearby Stony Plain sits at 5,300, and Fort Saskatchewan at 5,420, so expect a higher heating load outside the city limits. Edmonton gets about 2,300 hours of bright sunshine a year, and even non-insulated glass collects passive solar warmth on sunny spring and fall days. That is the 3-season room’s sweet spot.

The trouble is the cold stretch in between. Sun alone usually won’t carry an unheated glass room through a −20°C afternoon.

Can you use a 3-season sunroom in an Edmonton winter?

Sometimes, with a heater, and only within limits. The limiting factor is the glass. Single-pane glass loses heat at roughly 5.0 W/m²·K. To qualify as ENERGY STAR certified in Canada, a window must achieve a U-value of 1.22 or lower, or an Energy Rating of 34 or higher, according to Natural Resources Canada. That is about four times less heat loss through the same area of glass.

Here is a back-of-the-envelope illustration, not a measurement of any product. Heat loss in watts equals the U-value times the glass area times the temperature difference. Take 10 m² of glass, 20°C inside and −20°C outside.

Single-pane at 5.0 loses about 2,000 W. Glass at 1.22 loses about 490 W. That ignores the frame, roof, floor, air leaks, and any sun coming in, so real numbers will differ.

It still shows why a plug-in heater suited to a well-glazed room can fall short in a single-pane room during a cold snap. Compare your heater’s wattage label against those figures.

Moisture is the other winter problem. Health Canada suggests 30% to 55% relative humidity, but CMHC guidance notes that above about 35% on the coldest days, some condensation on cold surfaces is likely.

A sunroom’s glass and frames are the coldest surfaces in the building, so moisture tends to collect there. A furnace humidifier plus an open door to the house sends moist air straight onto that glass. Expect some frost on frames in a cold snap, turn the humidifier down, and keep the door closed.

What does a 4-season sunroom demand from you?

More than a 3-season room, in glass, heat, cooling, and foundation. It also still won’t behave exactly like your living room.

What glass does a 4-season sunroom need?

Alberta’s energy provisions set a maximum U-value or a minimum Energy Rating for windows and doors separating a heated space from the outdoors. The ENERGY STAR figures above are a sensible target for a room that is mostly glass.

The same ratings apply when you’re choosing energy-efficient windows for the rest of the house, so it pays to learn how to read them once.

Will it need cooling as well as heat?

Yes. A sealed, insulated glass room stores heat, so it needs a cooling source in July and a heating source in January. Orientation matters here, and so does the glass itself. Passive and reflective window coatings are worth considering to tame the afternoon sun on large panes.

What kind of foundation does it need?

A frost-protected one. Depending on soil, structure and local requirements, that usually means screw piles, concrete piers or a full concrete foundation. Bolting a heavy glass room to an old, unassessed deck is the classic false economy.

Will it feel like the rest of the house?

Not always. A room mostly made of glass, with its own heating and a door to the house, is a separate space. On the coldest nights, it will usually be the coolest room you own. The door between the two matters more than people expect, since a leaky patio door sends that cold straight into the house.

A full addition is a different project. It opens into the house, ties into your heating and is built to the same code as every other room. The price and permit route differ, so decide which one you want before anyone draws it.

What does the City of Edmonton require for a sunroom?

A permit either way. The City of Edmonton lists sunrooms and other three-season rooms among projects that need one.

It sorts rooms by whether they’re heated, not by brochure labels. Sunrooms, mudrooms, three-season rooms and screened-in porches fall under “unheated room addition.” Heated sunrooms (four-season) fall under house expansion.

A few other points from the City:

• Kit or pre-assembled sunrooms may need an engineer’s review, and many may not meet Alberta Safety Codes.

• If you place a pre-assembled structure on an existing deck, the City reviews the deck’s foundation for the new loads.

• Permit fees include a development permit fee, a building permit fee based on construction value and a safety codes fee. Check the City’s current schedule before you budget.

• Separate trade permits may be needed for heating and ventilation, plumbing, gas and electrical work.

If you might add a heater later, tell the permit office up front. Rocky View County, for example, requires a sunroom that is open to the house or heated for a substantial part of the year to meet the Alberta Building Code’s energy-efficiency requirements. Edmonton may treat this differently, so ask.

Alberta’s current building code, the 2023 Alberta Edition of the National Building Code, has been in force since May 1, 2024. Whoever installs your room matters as much as the standard of the work. Professional window installation has a few telltale signs worth knowing before you hire anyone.

How much do 3-season and 4-season sunrooms cost?

More than most people expect, and the gap between the two is wide. Published Canadian cost guides don’t agree on the numbers, and none of them is specific to Edmonton. Most put a basic 12 × 12 ft 3-season room between $15,000 and $30,000, though some start nearer $30,000.

A turnkey 4-season room is usually quoted at $45,000 to $85,000 or more, or roughly $400 to $600 per square foot. Some of those figures cover the enclosure only, with footings, deck reinforcement, and permits extra.

The spread mostly comes down to what’s included, so compare scope before you compare price. A sunroom is built to fit your deck or patio, so sizing drives cost, too, just as it does when you compare custom vs. standard windows.

Use national ranges as a sanity check, not a quote. A supplier can only price your room accurately after measuring your deck or patio.

How do you decide between them?

Start from the coldest day you want to use the room.

A 3-season room fits if:

• You want the deck usable from spring through fall, and the occasional mild winter afternoon with a heater is a bonus.

• The room is for lounging or dining rather than a home office, gym or plant room.

• You’re comfortable with it being unheated in the City’s eyes and in the design.

A 4-season room fits if:

• You’ll use it in January as an office, workout space, or reading room.

• You’ll pay for a proper foundation, a heat source, and summer cooling.

• You might open it to the house, which you should settle before design starts.

What should you look for in a sunroom provider?

Someone who puts the important numbers in writing and knows how the permit process works. Before you sign with anyone, ask for:

• The roof snow load rating and the code edition it was designed to.

• The glass specification, meaning the U-value or Energy Rating, and whether the frames are thermally broken.

• Who assesses your deck or specifies the footings?

• What drawings can they supply for the City’s permit application?

• Who installs the room, and who you call if something leaks.

• The warranty terms are in writing.

Supreme Windows & Doors is a family-run Edmonton manufacturer, open since 1970. It makes three- and four-season enclosures in Alberta and has a showroom where you can see the products and get help with measuring.

Which sunroom fits your Edmonton house?

Choose the coldest day you want to be in the room. If it’s a −20°C January morning, you need a 4-season room. If you’re happy to shut it down in November, a 3-season room will do the job for much less. That is the whole 3-season vs. 4-season sunroom decision. Everything else in this guide, from glass to permits to price, follows from that answer.

Your next step is to look at your deck or patio. Take photos and rough measurements, then present them to a provider who will walk you through both options. Not sure whether a 3-season or 4-season sunroom suits your deck? Call 780-447-1070 or reach out to Supreme and talk it through.

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