Fiberglass Replacement Windows in Waltham, MA
Built Strong, Made to Last
Want windows that won't rot, won't warp, and still look right on an older home? Fiberglass is a strong answer.
Top Sash installs Marvin fiberglass windows and Andersen composite windows in Waltham and across Greater Boston. Licensed, Lead-Safe certified, and most homes done in 1 to 2 days.
What makes fiberglass different?
Fiberglass frames are made of glass fibers bonded with resin and pulled through a heated die. That process is called pultrusion, and it makes a frame that's very strong and very stable.
Here's why that matters in New England:
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It barely moves. Marvin says its Ultrex fiberglass expands at virtually the same rate as glass. Seals stay tight from a January cold snap to an August heat wave.
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It's strong. Marvin says Ultrex is 8 times stronger than vinyl. Strong frames can be slimmer, so you get more glass and less frame.
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It won't rot or swell. Rain, snow, and humidity don't bother it. No scraping, no painting outside.
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It holds color. Ultrex gets a factory acrylic finish that resists fading and chalking. Dark colors like black and bronze hold up much better than on vinyl.
Fiberglass (Marvin Ultrex)
Pultruded glass fibers and resin. Marvin uses it inside and out on Essential, and on the outside of Elevate.
Composite (Andersen Fibrex)
Reclaimed wood fiber blended with PVC polymer. Not fiberglass, but a strong, low-maintenance frame. Andersen says Fibrex is twice as strong as vinyl. It’s used on the 100 Series and on the outside of the A-Series.
The fiberglass and composite windows we install
Two simple questions decide it: fiberglass or composite, and do you want real wood inside?
Marvin fiberglass windows
- Essential: Ultrex fiberglass inside and out. Marvin’s most affordable line. Double-hung, single-hung, casement, awning, glider, picture, and specialty shapes.
- Elevate: Ultrex fiberglass outside, real wood inside you can stain or paint. Our top pick for older homes. Also comes as a Double Hung Insert that fits inside your existing frame, so your trim and plaster stay put.
Andersen composite windows
- 100 Series: Fibrex composite frame. Low maintenance at a friendly price. Double-hung, single-hung, casement, awning, gliding, and picture windows.
- A-Series: real wood inside, a Fibrex and fiberglass composite outside. Andersen’s architectural line, close to Marvin Elevate in quality.
Already have Andersen windows? We can match them.
Which one fits your house?
- Low maintenance, simple look: Marvin Essential or Andersen 100 Series.
- Real wood inside: Marvin Elevate or Andersen A-Series.
- Historic or high-end homes: step up to clad-wood, Marvin Ultimate or Andersen E-Series.
- Tightest budget: ProVia vinyl, our best value. See our vinyl windows page.
What do fiberglass windows cost?
Fiberglass and composite windows usually cost more than vinyl and less than premium clad-wood. Beyond that, every house is different, so we don’t post one-size-fits-all prices.
What moves the price
- The size of each window and how many you’re doing
- The brand and line: Marvin Essential, Elevate, or Andersen 100 Series and A-Series
- Insert vs. full-frame install
- What we find once the old window is out: rot or worn trim
- Whether you want a wood interior, plus exterior color, grilles, and hardware
- Glass upgrades like triple-pane
- The building permit
That’s why we come out and look before we quote. Then we match the window to your house, your expectations, and your budget.
Making it easier
Fiberglass vs. composite vs. vinyl vs. clad-wood
| Feature | Fiberglass | Composite | Vinyl | Clad-wood |
|---|---|---|---|---|
| Lines we install | Marvin Essential, Elevate | Andersen 100 Series, A-Series | ProVia Endure, EcoLite | Marvin Ultimate, Andersen E-Series |
| Interior | Fiberglass or real wood | Composite or real wood | Vinyl | Real wood |
| Strength and stability | Excellent | Very good | Good | Excellent |
| Dark exterior colors | Great | Good | Limited | Widest range |
| Outside upkeep | None | None | None | None |
| Best for | Older homes, big windows, dark colors | Matching Andersen windows | Best value, most homes | Historic districts, custom work |
Energy efficiency in Climate Zone 5
Fiberglass barely moves in the cold, so the frame stays tight to the glass and the seals stay sealed. That’s a big deal in Waltham’s Climate Zone 5 winters. Want the best you can get? Step up to triple-pane glass with krypton gas.
The federal window tax credit ended December 31, 2025. Use Mass Save in 2026.
U-factor
How fast heat escapes. Lower is better. ENERGY STAR's Northern-zone standard is 0.22 or lower.
Low-E glass
A thin coating that reflects heat back inside.
Argon gas
A clear gas between the panes that slows heat loss.
Triple-pane + krypton
Our step-up glass. A third pane and krypton gas for the coldest rooms and the north side of the house.
“They are beautiful, for starters, and we are living in this lovely, quiet, cool bubble right now.”
★★★★★ Coolidge Corner, Brookline homeowner
Our fiberglass window installation process
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Free consultation
We walk the house with you, look at each window, and bring Marvin and Andersen samples.
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Measure
Every opening measured and checked for square.
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Order
Custom-built windows, about 5 to 6 weeks.
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Permit
We pull the building permit with the Waltham Building Department or your town.
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Install
Lead-safe setup on any pre-1978 home. Old sashes, weights, and storms come out, and the empty weight pockets get insulated. New windows go in, sealed and trimmed.
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Walkthrough
We check every window, show you the locks and tilt, and register your warranty.
Made for Waltham's older homes
Waltham is full of homes where the look really matters: Victorians and early Colonials on Prospect Hill and around Moody Street, and classic Colonials in the Highlands and near Piety Corner. Many still have their original wood windows.
Fiberglass with a wood interior keeps that look inside and ends the scraping and painting outside. And since most of these homes were built before 1978, lead-safe work matters. Top Sash is a Massachusetts Lead-Safe Renovation Contractor (LR4694) and an EPA Lead-Safe Certified Firm (NAT-F251059-1).
Why Top Sash
- Licensed: Massachusetts CSL CS-119052, HIC #208527
- Lead-Safe: LR4694 and EPA Lead-Safe Certified Firm NAT-F251059-1
- Insured: general liability and workers' comp
- Official ProVia dealer, Andersen Certified Contractor, and experienced Marvin installer
- 10+ years of crew installation experience
- 5.0 stars on Google (formerly VIVA Windows)
Fiberglass window projects
Chestnut Hill, MA: 1929 Colonial
29 single-pane wood windows with ropes, weights, and storm windows. Replaced with Marvin Elevate in 2 days. The homeowners were thrilled to keep the home’s original look, with wood inside and a fiberglass exterior that won’t rot.
Reservoir area, Brookline, MA: 1897 Colonial
A repeat customer replacing a few windows each year. This phase included Marvin Elevate windows with wood interiors, along with ProVia Endure windows in the garage. Done in 2 days.
Fiberglass window FAQs
How much do fiberglass windows cost in Waltham, MA?
There’s no one price, because every house is different. The final number depends on the window size, the line (Marvin Essential or Elevate, Andersen 100 Series or A-Series), whether you want a wood interior, insert or full-frame install, any rot we find once the old window is out, and glass upgrades. That’s why we come to every home and quote it in writing. We also offer 18 months 0% financing.
Is Andersen Fibrex the same as fiberglass?
No. Fibrex is Andersen’s composite of reclaimed wood fiber and PVC polymer. Fiberglass, like Marvin’s Ultrex, is glass fibers and resin. Both are strong and low maintenance, and we install both, so we’ll show you each side by side.
Are fiberglass windows better than vinyl?
Fiberglass is stronger, more stable when the temperature swings, and handles dark colors better. You can also get it with a real wood interior. Vinyl costs less and is a great value for most homes. If budget comes first, vinyl. If you want strength, wood inside, or a dark exterior, fiberglass.
How long do fiberglass windows last?
A long time. The frame won’t rot, and it barely expands or contracts, so the seals stay tight for years longer than on frames that move more. Marvin and Andersen both back their windows with limited warranties that transfer if you sell the house.
What is Ultrex?
Ultrex is Marvin’s own pultruded fiberglass. It’s used inside and out on Marvin Essential and on the outside of Marvin Elevate. Marvin says it’s 8 times stronger than vinyl, and its acrylic finish resists fading and chalking.
Can fiberglass windows be painted?
The outside comes factory-finished and doesn’t need paint. The wood interior on Marvin Elevate and Andersen A-Series can be painted or stained, or ordered pre-finished.
Are fiberglass windows good for old houses?
Very good. With a wood interior, simulated divided lites, and slim frames, Marvin Elevate can match the look of 1900s to 1930s windows. We installed 29 of them in a 1929 Chestnut Hill Colonial.
Are fiberglass windows energy efficient?
Yes. Fiberglass frames insulate well and stay tight to the glass in the cold. With Low-E glass and argon, they can meet ENERGY STAR standards for the Northern zone. For the coldest rooms, step up to triple-pane with krypton.
Do fiberglass windows qualify for Mass Save rebates?
They can. Mass Save offers $75 per window when you replace single-pane windows with ENERGY STAR Most Efficient windows certified for the north region, after a Home Energy Assessment. The federal tax credit for windows ended December 31, 2025.
Do I need a permit for fiberglass window replacement in Waltham?
Yes. Massachusetts treats window replacement as an energy code project. We always recommend pulling one, and most of our jobs are permitted. Top Sash pulls the permit with the Waltham Building Department and handles the inspection.
More replacement windows
Get a fiberglass window estimate
We’ll bring Marvin and Andersen samples, measure every window, and give you a clear price.
Top Sash Windows & Doors · Waltham, MA · Serving Greater Boston and Eastern Massachusetts