Markham window & door installer
Window Replacement in Markham
Markham starts at Steeles, ten minutes north of our head office at 4725 Sheppard Ave E in Scarborough. Fortress Windows & Doors has been installing replacement windows, entry doors, patio doors and eavestrough in Markham homes since 1989: Milliken, Unionville, Markham Village, Thornhill, Cornell, Berczy, Wismer, Greensborough, Cachet and Box Grove. Family-owned, Ontario-built windows, and an office you can drive to. Call (416) 291-5795.
Reviewed by Steve McCue and Steve Mercer, owners, Fortress Windows & Doors Inc.
Since 1989
Owner-run, family business
Canadian-made
Built for Ontario winters
Our own install crew
No subcontractors
Lifetime warranty
Covers product and labour
What we do
What Markham homes usually need
Milliken, Thornhill and the 1980s streets
South Markham was built out through the 1980s, and those houses are on their original windows or a cheap first replacement. Fogged sealed units, cranks that spin, sashes that will not lock. We replace full-frame so the new unit is not sitting on a 40-year-old wood buck.
Unionville and Markham Village
Main St Unionville and Main St Markham have the heritage stock, and the 1980s and 90s subdivisions around them have big two-storeys with bay, bow and arched windows. We template shaped openings on site and keep the grille patterns so the front elevation looks the way it was designed.
Cornell, Berczy, Wismer and Greensborough
The 2000s neighbourhoods are hitting the 20-year mark, and builder-grade vinyl fails in batches: whole streets with fogged glass at the same time. Cornell’s narrow lots and rear lanes mean we plan access before the crew shows up.
Entry and patio doors
Insulated steel or fibreglass entry systems, with sidelites and transoms rebuilt as one unit and the frame and threshold replaced. Vinyl sliding, garden or French patio doors for the backyard.
Eavestrough and downspouts
Six-inch seamless aluminum, formed on site. Markham sits on clay and a lot of the newer lots drain to a rear swale; we route downspouts to where the grading actually takes the water.
Why Fortress
Why Markham homeowners call Fortress
We are the closest real installer to most of Markham. The office is ten minutes south on McCowan or Kennedy, the crews drive up from there, and if something needs a second look after the install it is not a production. Fortress has 37 years of installs behind it, and the number on this page rings at the office.
Installing since 1989
Family-owned and still run by the family. Markham has been on the route since the beginning.
Best of HomeStars 12 times, including 2026
Verified reviews from real installs. Read them before you book.
Canadian-made, CSA A440 certified, Energy Star
Built in Ontario, certified to CSA A440, Energy Star rated for Canada.
Financing available
A Markham two-storey can have 25 or more windows. Flexible financing lets you do the whole house at once.
What is included
How a Markham job runs
It starts with a measure at your house, not a quote over the phone. We check every opening, the sills and the wall around them, and give you one written price for the whole job. That price includes:
- Written quote with no hidden extras
- Removal and disposal of old windows and doors
- Low-expansion foam around every frame
- Colour-matched exterior aluminum capping
- Interior trim and caulking
- Same-day clean-up
- Warranty registered in your name
Our process
How the job runs
From first call to final walk-through.
Book a measure
Call (416) 291-5795 or use the quote form. Tell us which openings and roughly when.
In-home measure
We measure every opening, template any shaped ones, check for rot or water damage, and go through frame colour, grilles and glass options with you.
One written price
One number for the whole job. It only changes if you change the scope.
Build and install
Custom-built to your measurements, which takes a few weeks and longer in spring. Most Markham homes are installed in one to two days.
Walk-through and warranty
We walk every unit with you, show you the hardware, and register the warranty.
The difference
What changes after the install
Lower heating and cooling bills
Going from 1980s glass or failed builder vinyl to low-E argon-filled units shows on the Enbridge bill the first winter and on the hydro bill in July.
No more cold pocket by the window
That cold spot by the living room window is the frame leaking, not the glass. Foamed frames fix it.
Quieter rooms
Sealed double or triple glazing takes the edge off the 407, Highway 7, Kennedy and the GO line through Unionville.
Rebates when they are open
Ontario and federal energy rebate programs change. We check what is open when you book and tell you what your job qualifies for.
Drier basement
Eavestrough pitched properly with downspouts extended away from the wall is the cheapest basement waterproofing in Markham.
Resale
Markham buyers expect the windows to be done. New, warrantied units go in the listing; fogged 1990s glass comes up in the negotiation.
Service areas
Other areas we cover
Same crews, same warranty, across the GTA and Simcoe County.
FAQ
Frequently Asked Questions
Do I need a permit to replace windows in Markham?
Not for a like-for-like replacement in the same opening. You need a City of Markham building permit if the opening is being enlarged or a new one cut, which covers most basement egress windows.
How long does window replacement take in Markham?
A typical Markham house with 15 to 25 windows is installed in one to two days once the windows arrive. Lead time from measure to install depends on the season; spring and early fall are the busiest.
Do you replace windows in the winter?
Yes. One opening at a time, so the house is never open for long, and the foam and caulking we use are rated for cold-weather application. Winter is often the fastest time to get on the schedule.
Where is Fortress located?
Our head office is at 4725 Sheppard Ave E, Unit 405, Scarborough, ON M1S 5B2, ten minutes south of Steeles. Call (416) 291-5795. We also have a Barrie office at 15 Pepin Ct for Simcoe County.
Need windows, doors or eavestrough replaced in Markham?
One written price, measured by an owner. Call (416) 291-5795 or book online.