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What’s the Purpose of Sill Caps?


Do I need a sill cap for my door frame?

Have you noticed a draft under your exterior doors? Does your front door seem to invite spiders and insects into your home? Having the right sill system in place will help prevent these common problems, and the key component is the sill cap.

Sill caps might seem like a small part, but installing one is essential to keeping your home dry, comfortable, and insect-free.




The Anatomy of Your Door Sill

Your door sill is located at the bottom of the door frame, and it acts like a gateway between the inside of your home and the outdoors.

Your sill consists of three parts: the sill deck, substrate, and sill cap. 

  • The sill deck is usually made of metal such as aluminum and is there to create a smooth walking surface into your home.

  • The substrate forms the base of the sill, securing it against the jamb and subfloor and providing support for the aluminum deck and any weight placed on it.

  • Sill caps are installed to form a seal between the frame and the bottom of your door. 


Sill caps might seem like a small part of your exterior door components, but don’t underestimate the value they provide. Sill caps work to protect your home from the elements and prevent common issues caused by gaps under your doors:

• Drafts and air leaks allowing your heating or air conditioning to escape your home, resulting in higher energy bills and putting a strain on your HVAC system.

• Water leaks from rain and heavy storms which can push moisture into your home. No one likes a damp floor, and you’re also at risk of developing mold, mildew, and even wood rot.

• Extra space under your doors allows insects to crawl through and enter your home. 






Types of Sill Caps

Sill caps are available in several forms: fixed, adjustable, or self-adjusting.

• Fixed sill caps are set in place during installation and cannot be adjusted. These sills will settle over time and eventually allow drafts in, so they’ll need to be replaced from time to time.

• Adjustable sill caps are manually raised or lowered to the right level in order to create a perfect seal between your sill and the door.

If the sill cap is too high, you’ll notice some “sticking” when you try to open your door, and you might need to put a little shoulder action in when you try to close it. On the other hand, if the sill cap is too low, there won’t be a seal between your door and the sill, which could allow for leaks and other issues we mentioned before. You can adjust your sill caps will a screwdriver, but it may take a little trial and error to find the perfect height.

• Self-adjusting sill caps like the Z-Articulating Cap from BetterDoor take away the guesswork and labor involved because they automatically adjust to create a perfect seal every time you close your door. This maintenance-free solution works to seal your home against insects, drafts, and moisture leaks.





Your sill cap is crucial to protecting your home from drafts, leaks, and bugs. If you aren’t sure what type of sill system you need for your home, we’re here to help! Reach out to a BetterDoor representative to talk through which product may work best in
your home.