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Large Sliding Glass Doors, Multi-Slide and Bifold Door Walls in Ontario: What They Cost, the Header Nobody Priced, Winter Performance, Sill Drainage and Snow
Windows & Doors
The Glass Wall to the Deck: What It Costs, What Is Holding Up the House Above It, and What It Does in February
Twelve or sixteen feet of glass that slides or folds out of the way is the thing people want most in a lake house now, and it is the thing most often priced wrong, because the door is half the cost and the structure around it is the other half. Here is the door, the header, the sill, and the honest winter story, from someone who has put them in on Georgian Bay.
The numbers
$11,00012-ft 3-panel multi-slide, aluminum-clad, installed, starting
$3,000 to $8,000header, posts, footing and permit, typical
U 1.4 to 1.8typical whole-unit U-factor; worse than a good window
1/2 in.the sill still has to sit above the deck
| Door wall | Installed, door only | Notes |
|---|---|---|
| 3-panel vinyl slider, 9 to 12 ft (centre fixed) | $6,500 to $9,000 | The affordable version; two narrow sliders, big fixed middle. Not a true opening wall. |
| Multi-slide, 12 ft, 3 panels stack to one side, aluminum-clad wood or fibreglass | $11,000 to $16,000 | Panels stack behind each other; 8 ft of clear opening from 12. |
| Multi-slide, 16 to 20 ft, 4 to 5 panels | $18,000 to $32,000 | Pocket versions (panels disappear into the wall) cost more and need the wall. |
| Bifold, 12 ft, 4 panels | $12,000 to $18,000 | Whole opening clear; panels fold against the jamb; more hardware, more seals. |
| Lift-and-slide, 12 ft, European | $16,000 to $25,000 | Big heavy panels on a lift mechanism; the best seal of the lot. |
The header nobody priced
A 12-ft opening in an exterior wall that carries a floor or a roof needs a header that a doubled 2×10 cannot be. Depending on what is above it: an LVL or steel beam 12 to 18 in. deep, bearing on posts at each end that go down to the foundation, sometimes to a new footing. In an existing house that means opening the wall, temporary support, the beam in, the posts in, and a permit with an engineer’s drawing, because this is past what the code’s span tables cover. $3,000 to $8,000 for the structure, $400 to $1,500 for the drawing, $150 to $500 for the permit. In a new build, it is in the framing price if the plans show it; make sure they do.
A header that deflects a quarter inch under snow load is a door that binds every February. The engineer sizes for deflection, not just strength. Tell them it is a sliding door above.
What it does in winter
A door wall is a lot of glass in thin frames with long seals, and its whole-unit U-factor is worse than a good window’s: 1.4 to 1.8 is typical, under 1.2 on the best triple-glazed lift-and-slides. On a 12 by 8 ft wall that is a heat loss of roughly three ordinary windows. Sit it on the north side and the room is a cold room. On the south, with an overhang, it is free heat in January. Specify the glass by orientation, triple on anything north or east, low-gain on west, and plan the heating for it; the heat loss for the room will show a bigger number than you expected.
The seals: multi-slides and bifolds have many metres of weatherstrip and the interlocks between panels are where the wind finds a way in. Lift-and-slide systems lift the panel off its seal to move and drop it onto the seal to close, which is why they seal best and cost most.
The sill, the drain and the snow
The sill on a door wall is a long track and it has to do three things: drain the water that gets into it (out, through weeps that are not under snow), stay above the deck outside so melt does not sit against it, and not become a solid bar of ice in February. Recessed or flush sills, the ones that let you roll a chair out onto the deck, are the ones that ice and flood; they are a southern product. Here, a raised sill with a proper pan under it, a drain path, and heat trace in the track if you insist on flush. Snow against the lower glass is fine; snow against the sill drains is not. Keep the deck a step down and shovel it. The threshold page applies, times twelve feet.
Screens
Twelve feet of opening and no screen is twelve feet of mosquitoes. Multi-slides take a sliding screen on an outside track (fine) or a retractable pleated screen that spans the opening (better looking, fragile). Bifolds take only the retractable kind. Ask what the screen is before you fall for the door; at the lake it is the difference between using the door and not.
Where homeowners go wrong
- Budgeting the door and not the beam. The beam, the posts and the permit are a second quote from a different trade.
- A flush sill on Georgian Bay. Beautiful in the brochure; a block of ice in the track by January.
- A bifold on a windy wall. The more panels, the more seals, the more the wind gets through. Multi-slide or lift-and-slide there.
- No screen plan. See above.
- The cheap aluminum one. Thermally broken or not? Ask. An unbroken aluminum frame is a cold bar that sweats and ices inside.
Questions people ask
How much does a 12-foot sliding glass door cost?
$11,000 to $16,000 installed for a multi-slide in aluminum-clad wood or fibreglass, plus $3,000 to $8,000 for the header and posts in an existing wall, plus the permit. $6,500 to $9,000 for a 3-panel vinyl slider if you can live with a fixed centre.
Are bifold doors good for Canadian winters?
Good ones, from makers who sell in Canada, with thermally broken frames and triple glass, are acceptable on a sheltered wall. Multi-slide and lift-and-slide seal better. None of them are as warm as a wall with a window in it.
Do I need a permit for a big patio door?
Yes, if the opening gets bigger or the wall is bearing, which for a 12-ft opening it always effectively is. Engineer’s drawing, permit, inspection.
Price the door, then price the wall
The door calculator has the 12-ft multi-slide as a starting point and the bearing-wall line with the permit. For a new build, the window schedule takeoff puts it on the schedule with the header beside it.
Sources and further reading
- Ontario’s Building Code: the official page, with the current regulation. Egress is 9.9.10, glazing and windows 9.6 and 9.7, energy is Supplementary Standard SB-12.
- ENERGY STAR Canada technical specification for windows, doors and skylights: Natural Resources Canada. The U-factor and Energy Rating thresholds, and the certified product lists.
