How to reduce window noise with plexiglass inserts

Increase your window’s STC and minimize window noise

Working from home? You might be familiar with the blast of a leaf blower from your neighbor’s driveway, or a steady flow of delivery trucks rattling up your street. On alternate days, you might hear tree trimmers, power washers, moving vans, or road construction.

Your windows are closed, but they sound like they’re open. And you wonder how to reduce that window noise without wasting money on something that doesn’t work. Or, if you’re a renter, doing something that’s forbidden by your landlord.

The answer might be D.I.Y. plexiglass window inserts. No, not the ones that you custom order from a well-known company on the internet. Those might cost almost as much as a new window. Instead, you can buy some plexiglass and cut it to fit snugly inside the window frame or around the exterior of the window frame. This layer of plexiglass — with an air space in-between — creates an extra barrier against noise.

The recipe:

- 1/4-inch thick plexiglass (6.35 mm), cut to the dimensions you need
- Foam weatherstripping or felt strip lengthwise along the windowsill. The bottom of the plexiglass will sit on it to reduce vibration from the windowsill. The strip should be about 1/8″ deep. (This is revised and updated from what I showed in the video.)
- Brackets for wall mounting (if you choose an outside mount). You might also need shims.
- Adhesive-backed foam strips (about 1/2 to 1-inch wide, and 1/8-inch deep) if you create a mount against the drywall. These strips will go on the back of your plexiglass (around the sides and the top) and the foam will press against the wall. I used joist tape, but it’s bright green.
- Joiners if you have multiple panels that need to fit together.

For mounting inside your window frame:

Measure the inside of your window in all four corners, and reduce the measurements by about 1/4 inch on each side. No window is perfectly squared, and it’s better to have the plexiglass slightly shorter than to be too large for the opening on all sides. You’ll pad the plexiglass edges with foam or silicone to make it fit in place securely.

For mounting outside your window frame:

Measure the dimensions of your window frame and add an additional 1 inch to 1.5 inches onto those measurements at the top and on each side of the window frame. The bottom edge of your Plexiglass sheet will sit on the windowsill, and the sides and the top will extend past the window opening. They’ll be held firmly in place by the brackets.

Joining together two pieces of plexiglass (for large windows assembled in multiple pieces)

If you have a large window and you need to assemble your plexiglass insert in multiple panels, you should hold the pieces together with a “joiner,” like this one sold at TAP Plastics. The joiner should have a track on both sides, which will hold two pieces together like a seam. Any gap in your finished window will let some noise in.

The cost

To get a cost estimate, visit the TAP Plastics site and enter the dimensions into their Extruded Acrylic Plastics estimator. For example, a 38-inch by 48-inch piece cost $134.00.

The results

Though not completely soundproof, your new plexiglass window inserts should help to reduce incoming window noise up to 10 decibels. They’re most effective at airborne noise, light traffic noise, and directional noise. Louder, more-vibrational, low-frequency noise such as truck engines and road construction might get slightly muted by window inserts, but not enough to truly quiet your home. Decibel reduction will be less significant in those cases. That’s because this type of noise also comes through your walls, building frame, doors, and other rooms of your home.

See it in action

This Soundproofist video details the process of ordering and installing the window inserts, with before-and-after examples.

In part two, you’ll see how to join multiple panels of plexiglass together to make a large window insert:

Plexiglass/acrylic resources

Country	City or state	Name of store	Description	URL
Australia	Multiple cities. Shipping available.	Plastic Direct	Australian owned and operated. Offers polycarbonate, acrylic, and more, cut to size. Delivery available.	See acrylic sheets
Australia	Salisbury, Adelaide, Australia	Acrylics Online	Free shipping over $150 (excluding full sheets), offers unique patterns and colors.	See all acrylics
Brazil	All	Mercado Livre	Chapa De Acrílico 6mm X 1000 X 2000 Mm Transparente Frete grátis	See the product
Canada	Toronto	Plastic World	We in Plastic World will cut material to size for you often while you wait. For straight cuts under 10 pcs, cutting is free. Note: For more than 10pcs, or for angled cuts charges will apply. Visit the store	Visit the store
Canada	Scarborough, Ontario (confirm that they will ship to you.)	Canada Plastics & Belting	Plexiglass and polycarbonate sheets in different thicknesses, up to 8 feet long. Can cut to size	View their products
France	Online	Plaque Plastique	An online store that offers shipping. You would want to order acrylic or polycarbonate that is at least 6mm thick.	Go to store
India	All - they ship	Acrylic Sheets India	Offers acrylic sheets in different thicknesses, length, and width. You can estimate the cost online. You should order a thickness of at least 6.35mm. They also take orders over WhatsApp.	Review your options
India	Mumbai	IndiaMart	This is a list of B2B suppliers of plastic products that you can contact individually.	See the list of suppliers
India	Jogeshwari, Mumbai, Maharashtra	Acry Plus	They are a wholesaler. Ask them if they sell to individuals. +91-22-26781085	See the products
Ireland	Meath	365 Plastics	Part of Access Plastics (UK), cuts to order acrylic and polycarbonate. (+353) 1 801 0022	Go to store
Kenya	Nairobi - 3 locations!	Gypsum Ceiling Supplies	We are located in on Ring Road Parklands opposite 9 West Building, Westlands, Nairobi and on Eastern Bypass, Next to Rubis Petrol Station, Ruai, Nairobi. Our prices are the same in all our branches. We offer products delivery countrywide either free, subsidized or at a cost based on distance and quantity.	See available sizes
Mexico	Tijuana & other locations	Plastic	"En Acrílicos Plastitec buscamos satisfacer a nuestros clientes ofreciendo asesoría y el mejor servicio de venta y entrega. Somos una empresa multimarcas que agrega valor a proyectos de diversos tamaños e industrias mediante la selección del material más adecuado al proyecto y presupuesto."	See website
New Zealand	Christchurch	Award Plastics	"Award Plastics & Displays is a manufacturer and distributor of plastics (Perspex, Plexiglas acrylic), displays and related products, sales of full sheets in various thicknesses and colours, panels cut to size or shape."	Choose your materials
United States	Colorado and nationwide (303-781-1171)	Plasticare	ABS, Acrylic, Polycarbonate cut to size. Calculate the price online. Shipping available.	Visit the online store
United States	Many cities/states	Professional Plastics	Has an office in Fullerton, CA and ships all over the US. The website also lists offices in Singapore and Taiwan. "Professional Plastics supplies plastic sheets, rods, tubing, films and fabricated parts to all major metro areas in the USA."	Go to online store
United States	San Francisco Bay Area, Portland, Seattle	TAP Plastics	CUSTOM PLASTICS, CUT-TO-SIZE POLYCARBONATE, ACRYLIC & MORE. Offers shipping.	Go to store
United States	Miami, New York, New Jersey	Acme Plastics	Acrylic, polycarbonate, PVC. Offers shipping.	Go to store
United States	New York City	Canal Plastics	Offers plastics and fabrication services with a specialty in hard to find acrylic colors and small-scale projects for both industry and individuals.	Go to store