02.05.2023 · Words by Myles

Tips and Ideas

Do Composite Doors Expand In Heat?

Do composite doors expand in heat?

Do Composite Doors Expand In Heat?

The simple answer is yes - any door can swell during the warmer months, no matter how well-made.

Composite doors, although challenging, are no different and can expand during prolonged exposure to direct sunshine, meaning you may have problems closing your door easily later.

Why Do Composite Doors Swell In The Heat, And How Do You Prevent It?

Any door will naturally swell or warp in direct sunlight, but why does this happen?

There are several reasons, and it's essential to know why it happens so you can take precautions to prevent the same from happening with your home's composite front door or any other swelling door. 

Reason: oversized doors

A primary cause of swelling is when you have an oversized door. When the sun shines directly onto your door, it will expand, as this is a natural effect of direct or harsh sunlight. If this happens too often or if the heat is excessive, your door will become difficult to open and close as it should.

How to prevent a door from expanding in the heat?

If your door is south-facing, you'll probably contend with even more problems regarding the negative impact of direct sunlight on your door.

In this situation, you must insist that the dealer measures your door correctly and that you fit the right composite door size that allows for the swelling and doesn't hamper its most basic function - to open and close securely.

At UK Composite Doors, we measure our doors precisely to ensure you get the size you need without fuss.

New wooden doors are the worst candidates for swelling out of all exterior doors. Although a new uPVC or composite door could invariably experience similar problems if oversized, the prospective owner of a new wood or timber door should be even more cautious.

Reason: not closing the door properly

Who would have thought that simply not closing your door properly could contribute to warping, swelling or bowing? You can damage your door if you don't close it so that all your door locks are fully engaged, which could also lead to problems with the door hinges.

Preventative measures on expanding doors from high temperatures

When you own a modern composite door, you must pull or "throw" the handle up when you close your front door.

The locking mechanism will then kick into action, and all the door's locks will engage fully, ensuring you close your door correctly in the correct position and preventing the chance of future damage.

If you don't pull the handle up when you close your composite door, the door might only rest on the latch, which holds the middle in place, meaning there is a greater risk of the top and bottom of the door bowing while swelling in the heat.

Taking these little actions can eliminate one of the most common composite door problems and markedly improve the lifespan of your door.

Reason: leaving a door open in direct sunlight

We're all tempted to do this from time to time. Leaving your door open to take advantage of the warm weather is a perfectly normal thing many people do.

We can almost guarantee that none of those people thinks of their doors and how they can be damaged when they open them.

Leaving your door open and directly facing the bright light and direct heat from the sun impacts the most vulnerable parts of your door and can cause swelling - especially the door's thin edges.

Expansion of your composite door edges, if allowed, can severely hamper your door's closing, similar to water damage on hardboard door edges.

Preventative measure

Remember not to leave it open and exposed to elements for prolonged periods on hot summer days to ensure your new door continues functioning correctly with minimal maintenance.


Are composite doors fireproof?

No, a standard composite door is not fireproof. Composite doors can be fireproof if you specifically request a fireproof door, they are known as FD30 rated composite fire doors.

Does a swollen composite door go back to its standard size?

Yes, swollen composite doors will generally go back to their regular sizes. Heat and humidity cause swelling; over time, the composite door adjusts to the new conditions and returns to its original size.

How do you decrease the impact of swelling on a door?

Rubbing soap or wax on a sticking area can help. A lithium-based lubricant or silicone spray can also solve sticky locks.

So now you know doors expand with heat, what next?

Composite, timber, wooden, and even uPVC doors will swell in extreme heat. In the case of composite doors, thanks to the different materials used, you're likely to encounter less of a problem than you will with many other door types, but that doesn't mean it can't or won't happen.

Although composite doors are low maintenance and super easy to clean, ensuring they close properly and seal firmly means they will remain more energy efficient, durable and impenetrable from a security perspective and keep out the cold air in winter.

Visit our UK Composite Doors blog for all you need to know about your composite door.

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