3 Ways To Prevent Water From Coming in Under a Door

You can prevent water from coming in under a door by replacing the threshold with a waterproof one. Also, you can weatherstrip the door or channel water away from it so it doesn’t flow toward the inside of your home.

Water damage can be quite costly, so it’s best to prevent water from getting into your home through non-standard ways. Keep reading to learn exactly how you can ensure that water doesn’t seep under your doors. I’ll also explore the different reasons why you might find water coming in under your door. 

1. Replace the Threshold

Doors are prone to allowing water to seep in from underneath, especially during a storm or flood. Yet, there are ways to stop that from happening.

To prevent water from flowing in under your door, replace an improperly bedded threshold with a correctly sized one. Remove the old threshold, clean up, drill pilot holes, then secure the new threshold plate with sealant/caulking. Ensure the plate fits correctly and reapply the sealant to finish.

Before you get started, gather your tools and prepare everything. This will help you avoid any mistakes along the way and allow you to do a better job. Here are the tools you’ll need:

• Electric drill (with bits)
• Caulk
• Caulking gun
• Sealant
• Fasteners
• Paper towels
• Cleaning materials

Once you have all your tools ready, you’ll need to clean the area to ensure there is no dust and debris to interfere with installation. 

Mop the area thoroughly to remove any residual grime around the door. Also, check if the door (and surrounding area) is dry because the sealant might not adhere properly to a damp surface. 

Threshold Removal and Prep

Remove the existing threshold by unscrewing its fasteners and detaching the threshold plate. Clean the area thoroughly before drilling pilot holes according to your new threshold plate’s dimensions [preferably 6 inches (15.24 cm) apart]. 

For wooden doors, ensure the wood is neither damp nor rotten. Otherwise, you may need to air it out or even sand it down and repair the rotted wood. Doing this is important as it helps ensure the sealant adheres to the wood properly.

Drilling pilot holes will help your new threshold stay attached more firmly, so don’t skip this step. While 6 inches (15.24 cm) is the recommended distance between pilot holes, you may want to measure your threshold plate against the doorway to ensure the best fit. 

Remember to use appropriate drill bits when making the pilot holes. Here’s a table showing common materials and the correct drill bit to use for drilling through them:

Material	Drill Bit Type
Wood	Standard
Metal	Titanium
Concrete or Stone	Masonry

Threshold Installation

Install the threshold by first applying transparent caulking to waterproof it, and drill fasteners into the pilot holes. Wipe off any excess caulking that oozes out before it cures. If the threshold is too low, add shims under it before installation. Spray on fast-drying spray sealant to finish.

Be sure to choose caulk and sealant that dry transparent and do not leave a yellowish hue when cured. Additionally, choose a fast-drying sealant so that you can apply multiple coats. Both caulk and sealant will help waterproof your threshold, making it harder for water to pass through. 

2. Weatherstrip the Bottom of the Door

Preventing water from entering your home through the doorway doesn’t need to be a complex issue. If you ensure you install the weatherstripping and door sweep correctly, you shouldn’t have any problems.

You can weatherstrip the bottom of the door by installing a door sweep. Cut out an appropriately sized trench, and install a channel to allow you to easily slide the sweep in place. Use silicone weatherstripping since it’s durable and stays water-tight regardless of how long the door stays closed.

I suggest you install weatherstripping all around your door because even small gaps [typically an ⅛ of an inch (0.32 cm)] can let in water and also impact your energy bills. In any case, to weatherstrip the bottom of your door, here’s how you can go about installing a door sweep:

Choose the Correct Door Sweep

Measure your door carefully before you purchase a door sweep to ensure a snug fit. Silicone materials are preferable because no air, light, or water can travel through a properly sealed door if you’re using silicone weatherstripping. 

Other options include metal, plastic, etc. However, studies have shown that silicone is more airtight and does not change shape significantly over time.

Make a Trench

You can make a trench on the bottom of your door if you begin by marking a ⅝” square (15.88mm) to guide your router. Use a ½” bit (12.70mm) on your router to create a trench by taking multiple passes in varying directions until the trench is 1⅛” (5.72mm) deep.

I recommend using a sawhorse to keep the door secure and steady as you carve out the trench.   

Install the Channel

Before installing a channel in the trench at the bottom of your door, apply a coat of primer and paint it to waterproof the wood. Then, cut the aluminum channels of your sweep, leaving a ⅛” (3.18mm) space for the end caps. Insert the channel and screw it in place after ensuring it is centered.

Install the Sweep and Adjust

To install the silicone sweep, slide it into the trench and then insert the glides. You will need to seal the ends using plastic caps provided by the manufacturer and rehang the door. Afterward, close the door and inspect for any infiltrating light or air, then adjust accordingly. 

An airtight seal will prevent water from entering.

3. Channel Water Away From the Door

You can channel water away from the bottom of a door to prevent it from seeping through. Do this by installing a rain diverter above the door and ensuring the floor leading up to the door is slightly slanted away from it. 

Rain diverters are a part of your gutter system that is often used in rainwater harvesting but are also useful in preventing water from pooling at your doorway. 

While an extreme slope in the ground near your doorway is not advisable, regulations require  that water should flow away from your door and the foundation of your house. Check with your local homeowners’ association for specifics, or ask a contractor to have a look. 

How Can I Make My Door Waterproof? 

You can waterproof your door by sealing all orifices. This means painting the door, caulking, and applying sealant wherever water can come through. Also, install weatherstripping to the top and sides, as well as a silicone door sweep.

Remember that there is no way to make your wooden door completely waterproof. However, the following strategies will help you achieve this goal to a reasonable degree: 

Install Weatherstripping

Silicone weatherstripping can be installed into the grooves of a door on the sides and top to prevent water from passing through the door. The silicon rubber fills the gap entirely, making it water-tight. Install weatherstripping by applying adhesive and sticking the strips in 4” (≅10cm) sections.

It’s best to apply the adhesive in sections because this allows you to apply maximum pressure on each section and ensure that the adhesive works optimally. Essentially, you want to push out all the air in the space between the weatherstripping and the wood.

You can find weatherstripping in any hardware store. They usually come in neutral colors because you aren’t meant to notice them when they are correctly installed. Luckily, it’s a one-man job that most people can do on their own with little to no help from a professional.

Paint the Door

You can apply several coats of water-resistant paint to your wooden doors to seal any small holes and prevent water from going through the doors. This is especially effective with panel doors, as the gaps between panels might allow water leakage.

Panel doors are made of multiple panels that expand and contract as the weather changes. This ultimately leads to small gaps in the door when the panels contract. Also, if they expand too much, the panel might crack, creating a permanent gap in the wood. Painting or applying varnish is an old method of waterproofing doors by sealing these gaps. 

I suggest painting your door once every five years, but you can paint it more often if needed. Here’s the proper way to paint a door:

1. Remove old fixtures. Detach the door handles, knockers, and any other fixtures on your door. Set them aside for later. This is also a good time to clean and polish them if needed or upgrade to new fixtures if you so desire.
2. Sand old paint. Using high-grit sandpaper (preferably 240), sand down the entire door, making sure to sand all the corners and crevices. You can use an orbital sander to speed things up or sand the door entirely by hand. For corners and edges, a finishing sander is a great tool, but sanding by hand will give you more control.
3. Apply a coat of primer. Use a primer to ensure that the paint will stay for longer. Make sure to wait at least four hours before you move on to the next step. Some manufacturers claim that their primers dry faster, so you may wait for a shorter period, but it’s always better to wait slightly longer to avoid streaking. 
4. Apply a coat of paint. When painting, use a brush with angled bristles and paint by moving along the grain. Ensure you cover all the corners and be as detailed as possible because any exposed areas will not be waterproof.
5. Apply a second coat of paint. After waiting at least four hours for the first coat of paint to dry, you can proceed to apply the second coat. Doing so will help prevent streaking. A third coat is not necessary.
6. Reattach or replace fixtures. Finally, it’s time to reattach the fixtures you had taken out in the first step. You could also replace them with new ones if you want to upgrade the decor. 

Keep in mind that not all paint is waterproof. Also, get UV-resistant paint if the door in question sees a lot of sunlight. Finally, don’t forget to read the manufacturer’s instructions before you begin a painting project. 

Caulk the Door

Waterproofing a door includes caulking the frame and the area around any door windows. The sealant prevents water from seeping through and can also cause the door to rot. Use a transparent antimicrobial caulk for better aesthetics and to prevent discoloration.

Follow the steps below to caulk the door frame:

1. Use a sharp knife to remove the old caulk, but be careful not to scratch the wood or paint. 
2. Clean up any dirt and dust before you begin caulking, and ensure that the temperature is not too cold (anything above 46°F/8°C will do).  
3. Prepare your caulk gun by inserting the tube and cutting the tip using a sharp knife. 
4. Run the caulk gun along the corners between the door frame and the wall, applying even pressure to release a continuous extrusion of caulk.
5. Use a clean rag to wipe away the excess caulk by running your covered finger along the edge. 
6. Caulk all the edges around the frame, and leave it to cure for at least 24 hours. 

For doors with decorative windows, you can follow the same steps mentioned above to caulk around the windows. If the weather turns, you can also cover the window panes with a waterproof plastic sheet, but this isn’t ideal.

Also, consider using paintable caulk to apply a coat of paint after you’re done caulking. This step is merely cosmetic, but I highly recommend it nonetheless. Make sure to reapply caulk twice a year for the best results.

With a little effort, you can avoid serious water damage, which can be very costly and time-consuming. Whether you apply all the steps in this guide or only some of them, you can prevent water from flowing under your front door or even the bathroom door.

For more, check out How to Soundproof A Doorway | 3 Key Things to Fix.