Hardie siding brings a wealth of benefits to the home. Installing hardie siding around windows properly, however, is essential, or you might not be able to take full advantage. For most homeowners planning to do it themselves, this means selecting the right type of siding, measuring, cutting, and attaching.

When installed correctly, Hardie siding brings durability, curb appeal, pest control, and more to homes. While there are other options for siding, such as trim, they simply don’t match the benefits. If you’re planning on installing Hardie siding yourself, here’s what you need to know before you get started on your next home improvement task.


What is Hardie Siding?

Hardie Siding, also known as Hardie trim, HardieTrim or Hardie Board, is from the James Hardie company. It is a fiber cement material, which is a combination of sand, cellulose, and cement, which increases durability and helps it stand up against weather. According to the James Hardie company, this allows the siding to last up to 50 years.

Why Is Hardie Siding Important Around Windows?

Hardie Board from the James Hardie company, also known as Hardie siding or Hardie trim, is designed to run right up against the window frame. While there are alternatives that have their own benefits, Hardie siding has most of the aspects homeowners are looking for.

Some of the benefits of Hardie trim for windows include:

  • Durability: The fiber cement siding can withstand extreme weather, resists moisture to reduce rot, and requires little to no maintenance, in addition to being fire-resistant.
  • Pest control: This siding can resist termites, carpenter ants, and woodpeckers.
  • Customizable: There are several styles available, so homeowners can select the perfect style and color for their siding. They can also be matched with existing HardiePlank siding.
  • Increased curb appeal: Thanks to the vast availability of styles and colors, Hardie siding can deliver improved curb appeal, enhance home exteriors, and potentially increase home prices.

When Should You Not Use Hardie Siding?

There are some instances where James Hardie siding may not be the best solution for you and your windows. You might want to opt for another type of siding or trim if:

  • You’re on a tight budget. Hardie board siding is expensive. Vinyl siding is less costly, but will be more costly in the long run due to maintenance requirements. One option is to use Hardie siding in the front of the house to improve curb appeal, and less expensive vinyl siding on the back to save money.
  • You have limited time. This type of siding is heavy and fragile, and it takes a while to install. If you’re on a strict timeframe, you simply might not have time to complete the project.
  • The window frame doesn’t project at least 1″ out from the wall. Hardie siding is made to run directly against the window frame and if there isn’t enough room, it can’t be installed.

Common Types Of Trim Around Windows 

James Hardie Trim is only one commonly used type of window trim in the United States. Even if you’re opting for the Hardie product, it’s important to know your options and select the best one for your home and windows.

HardieTrim Boards

In some areas, HardieTrim boards are the most commonly used product. It is made of the same fiber cement material as the HardiePlank siding. It can be a more costly option, but often requires little maintenance. There are several colors to choose from and three siding textures available: Rustic Grain, Roughsawn, and Smooth.

Engineered Wood Or Smart Trim

This type of siding has a combined rich cedar-grain wood texture and is known for its beautiful finish, increasing curb appeal. However, unlike the HardieTrim, Smart Trim does not have factory-painted colors. Thus, you need to paint it yourself or have your local paint shop do the job. 

Frame Lap Siding

Also known as Direct To Window, this type of siding is the most common option in the United States. It doesn’t require much cutting, but its installation can affect window maintenance in the future.

J-Trim Siding

J-shaped trim is specifically for windows that are half-moon, round, curved, or oval. They are more flexible than other options and can be cut to just about any shape. However, color options may be limited and it may require paint to match your home’s appearance.


8 Steps To Install Hardie Siding Around Windows

Before jumping into your Hardie trim installation project, it’s important to gather the tools you need ahead of time to prevent a lot of back and forth.

What You’ll Need

The exact tools you’ll need depend on your particular project, but you should collect:

  • Fiber Siding block
  • Mounting block 
  • Kick-out flashing 
  • Drill machine set 
  • Air compressor and hose
  • Sawhorse or circular saw
  • Drip cap
  • Stapler
  • Galvanized finish nails or 15 gauge stainless steel
  • Caulk gun
  • Trim nailer
  • Chalk line
  • Speed square
  • Paint 
  • Level
  • Hardie Tabs
  • Proper safety gear (gloves and eye protection)

Steps To Follow

Before getting started, make sure you read through all of the DIY steps to follow them correctly. Accidentally skipping a step can result in improper installation.

Step 1: Prepare Your Project Tools And Materials

After collecting the items you need for the job, you should list the number of trim you need, the window sizes, budget, and finishing paintings. Remember that good planning results in a successful outcome.

Step 2: Check Existing Trim Conditions

You must first remove the old trim using a knife. Make sure that you carefully cut between the trim and wall joint. Mistakes can damage your wall paint and caulk. Once removed, pull out any remaining nails or debris. Safety gear is advised to avoid injury.

Step 3: Accurately Measure Trim Dimensions

Before you cut your panel or trim, take accurate measurements of the window. You can use a pencil to draw signs on your board. Pro tip: always double-check the size and specific measurements. There’s no room for error, especially when you start cutting. Measure twice, cut once.

Step 4: Cut Your Trim

After the measurement has been carefully checked, it’s time for some cutting. Put on your safety gear and use a saw specifically designed for the materials to avoid ripping.

Step 5: Properly Install Your Trim

Inspect your Hardie trim for possible damages before preparing it for installation.

Start by attaching the trim with two-inch 16-gauge finish nails every 16 inches to make the trim lay flat. To prevent liquid build-up on your siding, you also must leave a ¼-inch gap between the window and the plank. 

For your next step, place the top post across the two vertical blocks and ensure that it is extended at the bottom. Lastly, apply the shims to make an even wall and flange. 

Step 6: Secure The Flashing

After the installation, you must check your flashing thoroughly and make sure it aligns with your local building code. This step will protect your house from rainwater or liquid rolling down inside. To have the best result, vertically and horizontally flash the openings. 

Step 7: Caulk and Seal

Next you will want to caulk all of the trim sides that meet the siding. Use a caulk gun and apply it at a 45-degree angle. Remember not to wipe the excess since high-quality caulk sets naturally. If you find yourself using an excess amount of caulking, it could point to errors made during the installation process.

Step 8: Paint

For some homeowners, this step can be skipped, but you might want to add a layer of paint for aesthetic reasons or to reduce repainting needs in the future. Fading is possible, especially in areas that get a lot of sun. You can do the painting before or after the siding installation. 


Common Hardie Siding Installation Mistakes

When installing Hardie trim around windows, there can be errors made by both homeowners and contractors. Some common mistakes include

  • Uneven siding: Uneven siding boards can affect the look of your home. The gaps created by uneven installation can allow water to infiltrate the home and window.
  • Improper nailing: This can result in visible nails and rusting over time. In addition, it could damage the board, causing it to crack and break.
  • Poor painting: Improper painting can cause patches and spots to appear on the siding, and may fade quickly. This affects curb appeal.
  • Excess caulk: Caulk is used to create a seal between Hardie boards, but excess caulk could mean the siding was improperly installed, resulting in poor water protection.

Get Expert Help If Necessary

Installing window trims and flashing might look like an easy DIY task based on the given steps. However, it still requires skill, patience, and time to install correctly. Mistakes can be costly and result in broken materials, poorly installed siding, reduced curb appeal, and potential water infiltration.

Hardie’s fiber cement siding, in particular, is heavy and fragile. It’s easy to chip and crack. While Hardie products come with excellent warranties, incorrect DIY installations of the trim could affect the warranty.

If you’re not confident in your skills to complete this home improvement task, it might be best to leave it to the experts. While it will cost you more in the long run, opting for home renovation professionals can make sure the siding is installed correctly, allowing you to get the full benefits of Hardie trim for your home and your windows.

Article Update Log
5/8/2024
Reviewed for accuracy, cost data, industry best practices, and expert advice by Hilary Cairns.
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Hilary Cairns

Hilary Cairns is a writer with 12 years of professional writing experience. She has covered a diverse set of topics such as custom home building, plumbing, HVAC, energy efficiency, and others. A graduate of SUNY New Paltz with a bachelor's degree in English and a concentration in Creative Writing, she discovered her passion for helping businesses and organizations deliver impactful content that changed lives. Originally from New York, Hilary now calls Florida home (along with 2 cats). When not immersed in her writing work, she enjoys playing video games, reading Stephen King, and researching her (and her friends') genealogy.

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