Finishing a basement to be water resistant - reducing the damage from basement flooding

Building a flood-resistant basement: Simple, sustainable solutions for protecting your home

Flooding is becoming more common in cities around the world, and it’s a real concern for homeowners. In the U.S., Hurricane Harvey hit in 2017 producing catastrophic flooding in Texas that caused around $125 billion USD in damage and Hurricane Ida in 2021 produced around $95 billion USD (2023 estimates) in damage across Louisiana and the northeastern U.S. The 2020 floods over in the UK, for example, caused upwards of $670 million USD with peoples homes suffering from the deluge, claimed thousands of homes in regions such as South Yorkshire and the Midlands.

In Canada, the summer flooding in Toronto of 2023 caused about $1 billion USD of damage, and even in a small, relatively insignificant city like Montreal, the 2017 and 2019 spring floods caused an estimated $105 million USD in damage to homes and infrastructure, displacing thousands of people and highlighting the rising costs and increased frequency of extreme weather events.

These figures demonstrate just how devastating floods can be for communities, both in terms of financial loss and the disruption to everyday life. As climate change continues to influence weather patterns, flooding will likely become a recurring challenge.

For homeowners, building or renovating a basement that resists future flooding is now a crucial consideration - especially when sustainable, eco-friendly solutions are available to not only protect your property but also help mitigate environmental impact.

Whether you've experienced flooding first hand or are just planning ahead, this article explores simple, sustainable solutions for building and maintaining a flood-resistant basement that helps protect your home - and the planet.

Recommendations for building a flood-resistant basement and home

Before we get into how to renovate after a flood, or to build to resist flooding, let's talk about how you can make your home or basement more flood-resistant in the first place - unless of course you want to skip straight to the "how to rebuild or finish a basement to resist water and mold" section, which is here. These are some basic steps to consider when planning to build a new home or basement below and especially if a home with a basement is a new idea for you:

• Elevate your foundation: Raising your floor above expected flood levels is the only certain way to keep water out - which is why we have many articles explaining which is better, a basement, crawl space or a slab on grade - the easiest way to avoid floods when building a new home is to choose a slab-on-grade foundation sat on a drainage layer that's above anticipated flood levels (and a bit more for safety). If you also live in a northern location where the average winter ground temperature is between 25-35°F you should in our opinion choose to build on a super-insulated frost protected shallow foundation or FPSF.
• Add flood vents or waterproof barriers to the external foundation or basement walls. If you have to build a basement, specify dimple board over peel and stick membranes that lap down over foundation strips to drainage tiles placed under the slab level to help prevent water from seeping in. 
• Use waterproof materials inside: Choose eco-friendly materials that resist water, like breathable membranes or non-toxic sealants. These materials help prevent water from entering, allow basement walls to dry out and help to stop mold developing without affecting air quality inside your home.
• Install a sump pump: A good sump pump (with optional battery backup) is helpful for keeping water out in an area with high hydrostatic pressure. Choose one with a solar-powered battery backup and high level alarm to make sure it works without relying on electricity. Also, note that we're talking about a "real" sump pump here that pulls water away from the foundation on both sides of a foundation strip - not the type that just sucks out the water that gets into a basement using a surface mounted grid along the perimeter wall. 

A flooded basement is more than just an inconvenience - it's a serious problem that can lead to long-term damage in homes, costly repairs and astronomical insurance costs if not handled properly. But then after the water is gone and the mess is cleaned up, many homeowners are left wondering how to rebuild their basements to not only restore their living space but also protect it from future floods and to reduce the amount of damage that flooding and general humidity and mold can bring to a finished basement or man-cave.

I've often called basements "a swimming pool waiting to happen", including on national CTV in Canada - and as I write this from my basement office, I definitely know what I’m talking about when it comes to flooding and damp, moldy basements.

So, if you're thinking about rebuilding or finishing a basement, and want to minimize future water damage from floods or mold (especially if you're just doing the bare minimum to meet code), this guide will walk you through the steps to create a basement that’s better equipped to resist water damage. That way, you can rest easy knowing your home is better protected for the future.

Assessing the damage post-flood

Safety first: What you need to do after your basement floods

Make sure your basement is safe to enter before attempting to do anything. Floodwater can present all kinds of hazards, from electrical problems, to structural damage and even health issues posed by untreated sewage. If the water level was high or if you’re unsure about the state of your basement after a flood, it’s advisable to cut off your electricity at the main breaker and then call in a professional to check things out.

If the water was clean - from, say, a burst pipe or torrential rain - you might want to tackle some of the cleanup yourself. But if the water is contaminated or if there’s any question about safety, it’s a good idea to bring in the pros. The companies that pop up when you search for “flooded basement cleanup companies near me” have trained professionals that are skilled at treating these kinds of situations quickly and safely. After all the water’s been pumped out, here’s our definitive guide of what to do immediately after a basement flood.

Get a professional basement inspection

After making sure the area is safe and setting up the fans and dehumidifiers to dry everything out as soon as possible, the next step is to evaluate the damage done to your basement. Some damage may not be immediately apparent, although you can identify obvious problems such as wet drywall or damaged flooring. A professional can spot issues like structural damage, concealed mold, or compromised wiring.

This inspection is crucial before starting any rebuilding process, as it helps ensures that your basement will be safe and sound in the future. Also, a surprisingly high number of basements in Canada and the US are already full of mold hidden behind the drywall and poly vapor barrier - better to deal with this comprehensively and do mold abatement before attempting to cover it all up again.

Steps to rebuilding a flood-resistant basement

Waterproofing the basement: Your first line of defense

When it comes to protecting your basement from future floods, waterproofing is essential. Here’s how you can do it:

• Exterior solutions: Start with the outside of your home. Make sure your property is properly graded so water flows away from your foundation. Clean and maintain gutters and downspouts to direct rainwater away from your house. If your basement is particularly prone to flooding, consider installing a perimeter drainage system around your foundation.
• Interior solutions: Inside, a sump pump is your best friend. It helps to keep your basement dry by pumping out water that collects in a sump basin. Consider installing a backup pump or battery system, so it works even during power outages. Sealing the walls and floors with waterproof coatings can also help prevent water from seeping in.

For more detailed tips, check out our guide on how to prevent basement flooding during heavy rain. 

Dealing with water damage and mold prevention

Thorough drying and dehumidification

Before beginning any sort of rebuild, it’s important to make sure that your basement is fully dried out. Use fans, dehumidifiers and ventilation to get out any residual moisture. This step is important to prevent mold because it can grow very quickly in humid areas.

Musty odors are often a big problem after flooding. To assist with this use a dehumidifier to remove moisture along with activated charcoal or baking soda to absorb odors. You can also check out our guide on how to deodorize a flooded basement for more tips.

Eco-friendly mold prevention and cleaning strategies

Mold can become a serious issue after a flood, particularly if your basement was not properly dried. If you rebuild, use mold-resistant materials and make sure the space has good ventilation. You can also install a dehumidifier to keep the room humidity level low, lowering the risk of mold growth.

If you’re tackling a full basement renovation, it’s a good time to review our basement renovation guide for additional tips on how to prevent mold and keep your basement healthy.

Natural cleaning solutions after floods

Once you’ve got the water out, you’ll need to clean up. Instead of using harsh chemicals, try these natural, eco-friendly alternatives:

• Enzyme-based drain cleaners: These cleaners break down organic matter blocking your drains without toxic chemicals. They work a little slower than traditional cleaners, but they’re safe and biodegradable.
• Natural antimicrobial solutions: Flooding often brings bacteria and mold into your home. Instead of using bleach, which can be harmful, try using vinegar, tea tree oil, or thyme oil to kill bacteria and fungi naturally.

Removing and killing mold in an eco-friendly way

Mold is one of the biggest issues after flooding. Here’s how you can deal with it and mitigate mold sustainably:

• Anti-mold paints: There are paints available that prevent mold and mildew from growing on your walls. These paints use non-toxic biocides to keep the area dry and safe. 
• Using vinegar for mold: Vinegar is an effective way to remove mold without the dangerous chemicals in bleach. Just spray it on affected areas, let it sit for about an hour, and then wipe it away.​​

For more on the best repair options, see our guide on basement flooding repair and disinfecting basement after flooding.

Rebuilding after a flood, or finishing a basement to resist floods and humidity

The first step when refinishing a flooded basement is to have clearly identified where the water is getting in! Is this an access that is easy to block to make the basement waterproof? Most actual water gets into basements through a break in the building envelope - a crack in the basement wall, a poorly sealed or half rotten egress window, a pipe or wire penetration to outside or a broken exterior tap feeder pipe that's hidden in the wall - especially after a deep freeze.

Many so-called basement specialists go straight for the complicated and expensive solutions like sump pumps and by mentioning the mysterious sounding "hydrostatic pressure" when in reality a simple and relatively cheap fix is all that is necessary to get your basement waterproof again. Once you are certain you blocked all the water access points - and you probably have to rip out a lot of previous basement finishing attempts first to get to the bottom of the problem - then you can get onto basement finishing and making it all good again.

Choosing the right water resistant materials for finishing a basement

Choosing moisture resistant methods and water resistant materials in areas that are at risk of humidity or flooding, such as a basement is a total no brainer for me. Having watched a neighbor get flooded multiple times, and starting again with materials that don't resist flooding or moisture issues just causes me (and their insurance company) to scratch our heads.

When it comes to basement walls that can handle moisture from floods or older leaky humid basement walls, here's the real deal on what's actually sustainable.

How to finish a basement to resist humidity - behind the scenes!

Making your basement healthy and safe after water damage or to prevent a basement flood from being a disaster relies on choosing materials that can occasionally get a soaking without falling apart or going dangerously moldy.

Understanding water resistant material choices

Basements need special waterproof materials that won't break down over time if (or should we say when) they get wet. While plastic isn't always the most environmentally friendly choice, in basements it's often the best option. Good quality waterproofing materials prevent mold, won't need replacing and won't go mushy or moldy, which is better for the environment in the long run.

Waterproofing the right way - tanking a basement

New waterproof wall coatings work better than old-style plastic sheets. Unlike plastic vapor barriers that trap moisture and make walls sweat, these proprietary tanking products and coatings on basement walls can really brighten a basement up and reduce the humidity levels.

Vapor retarder and vapor barrier paint instead of a poly vapor barrier on finished surfaces let walls breathe while keeping moisture out and making for a good finish. This works well with ventilation and dehumidifiers to keep your basement dry, clean and mold free.

Building better walls for water resistant basements

Rigid foam insulation boards (EPS) work great in damp basements. They insulate well and last a long time. You can attach them directly to the wall using low expansion professional foams (we're not huge fans, but these really do work well in this application), then fix wall materials directly to them, or use metal studs or ground-rated pressure-treated wood for framing. Leave a small air gap between your walls and the foundation to help moisture escape or put a continuous layer of foam trapped behind the wall framing.

Safe insulation choices for basements to prevent mold

Mineral wool (also called Rockwool) is the best choice for basement walls when it comes to a batt type insulation. It's often made from recycled or upcycled materials, doesn't grow mold when damp, and mineral wool insulation blocks sound really well. Unlike spray foam, it doesn't contain harmful chemicals, and unlike fiberglass, it keeps working even in damp conditions and in our experience doesn't harbor mold the same as fiberglass batts.

Smart floor solutions for warmer dryer basements

If there's a decent headroom in your basement, you can get specialized dimpled floor panels to create a space under your floor where water can drain away and to add a layer of insulation in an older basement that probably has no insulation at all under the concrete floor.

As I'm sat here writing this during a snowy January day, my feet are tucked into a big fleece foot cozy, as we didn't have the headroom to put insulation down - something I regret! While they're usually made of some plastic, they protect your finished floor that you lay on top from moisture and provide insulation. They last for decades, which makes them a good durable choice.

Checking for radon in basements before finishing

Before finishing your basement, check local radon maps and test your space for this natural radioactive gas. Radon can build up in basements, especially in high-risk areas. Test before and after finishing your basement, and install a radon barrier and radon removal system if needed. See all about radon mitgation techniques here, and you can find radon detectors and mitigation products here

Managing moisture

Instead of using plastic vapor barriers, focus on:

• Proper ventilation, HRVs or ERVs are best
• Using dehumidifiers - for the most energy efficient performers get an Energy Star rated one
• Using materials that let moisture escape or that don't retain it
• Connecting basement air systems with your home's ventilation

How to finish a basement to resist water and humidity - alternatives to basic drywall

When finishing a basement, it’s essential to prioritize moisture control to protect your home from potential damage caused by water and humidity. Traditional drywall isn't the best choice for these conditions, as it absorbs moisture like a sponge, leading to mold growth and it falling apart into a crumbly mess.

For homeowners looking to create a more sustainable living space, there are eco-friendly alternatives to basic drywall that not only offer superior resistance to water and humidity but also promote green building practices.

Whether you're seeking energy-efficient solutions, low-impact materials, or products made from renewable resources, these options provide long-lasting durability while helping reduce your carbon footprint. Let’s explore the best sustainable and moisture-resistant insulation and other materials for finishing your basement, ensuring a dry, safe, and environmentally conscious space.

• Cement board is the heavyweight champ. It's basically made from natural materials, can take a serious beating from moisture, and will probably outlast the house itself. Sure, making cement has a big carbon footprint, but this stuff is practically immortal - which means less waste in the long run.
• Paperless drywall is a solid runner-up. It uses fiberglass instead of paper, which means it's way more resistant to that nasty basement moisture. The manufacturing is cleaner, and it doesn't invite mold to the party. Plus, it's got some decent recycled content going on. 
• Pressure-treated drywall sits in the middle. It works, but those chemical treatments are a bit sketchy from an environmental standpoint. It's like putting a band-aid on moisture problems instead of solving them completely.
• Fiberglass-faced drywall is pretty good, but not revolutionary. It'll do the job, but it's not winning any environmental awards.
• Green board? Honestly, it's mostly marketing. It claims to be moisture-resistant, but in a real basement, it's about as useful as a chocolate teapot. You'll be replacing it way more often, which means more waste and more money out of your pocket.

Here are a few more options for finishing your basement while addressing both moisture resistance and sustainability:

• Hempcrete: Made from hemp fibers, lime, and water, hempcrete is a highly sustainable material with excellent moisture-resistant properties. Not only does it naturally regulate humidity, but it also acts as an insulating barrier, reducing energy costs. Hempcrete is carbon-negative, which means it helps offset your home's carbon footprint over time.
• Reclaimed wood: For a more rustic, eco-friendly alternative, reclaimed wood is a great option. When sourced responsibly, it’s a sustainable material that adds warmth and character to your basement. While not inherently moisture-resistant, treating it with non-toxic finishes can offer some protection, and its natural beauty can offset any drawbacks. Plus, using reclaimed wood helps reduce the demand for new lumber, conserving forests. 
• Cork panels: Cork is a renewable material that naturally repels water and resists mold and mildew. It's an excellent option for creating a more natural, breathable space in your basement. Cork is also highly durable, sound-absorbent, and provides insulation, making it a great choice for both comfort and eco-conscious construction. 
• Mineral board: Made from non-toxic, inorganic materials, mineral board offers a highly durable, moisture-resistant finish. It’s an environmentally friendly choice that provides fire resistance, making it an ideal material for basements. Mineral board has a longer lifespan than traditional drywall and requires minimal maintenance, cutting down on long-term waste. 
• Bamboo plywood: Bamboo is one of the fastest-growing plants on the planet, making it an incredibly sustainable choice. When used in basement finishes, bamboo plywood provides a strong, moisture-resistant surface that doesn’t warp or absorb water easily. Additionally, bamboo is lightweight and can be sourced ethically, making it a great green building material.

Bottom line: If you want a basement wall that can take flooding or just general moisture and won't kill the planet, cement board is your best bet if you want that freshly drywalled appearance - otherwise, consider using something like wood panelling.

Elevating electrical systems and utilities

Floodwaters and electricity don’t mix. When rebuilding, take the opportunity to elevate electrical outlets, switches, and your HVAC system above potential flood levels. If possible, move major appliances like your furnace, water heater, and washer/dryer to higher ground - or at least raise them on platforms.

This not only reduces the risk of electrical hazards but also can significantly cut down on repair costs if flooding happens again. Speaking of costs, the price of waterproofing and rebuilding can vary depending on your basement’s size and level of finish. For a more detailed breakdown, check out our discussion on basement flood cleanup cost.

Preparedness for future floods

Insurance considerations

Before you finish the rebuilding process, take a close look at your home insurance policy. What does it cover if your basement floods again? Some policies cover specific types of water damage, while others might not. Flood insurance, which is separate from standard homeowner’s insurance, could be a wise investment depending on where you live.

For more detailed information, review our guide on what will insurance cover after a flood to make sure you’re fully informed.

Emergency preparedness

Finally, now that your basement is rebuilt and more resistant to flooding, it’s time to think about the future. Develop an emergency preparedness plan for potential floods, including a checklist for shutting off utilities and securing valuables. Regularly maintain your waterproofing systems, sump pumps, and drainage systems to ensure they’re ready when you need them most. 

Moisture monitoring with smart technology

To prevent future water damage, consider using moisture sensors in your basement. These sensors can detect rising moisture levels and send alerts to your phone. This allows you to take action before the damage gets worse.

Conclusion: building a flood-resistant basement the smart way

Flooding is becoming more common, and we need to be proactive about protecting our homes. Building a flood-resistant basement is a smart move, and using sustainable materials and methods can help protect your property while also reducing your environmental impact.

Whether you're building a new basement or fixing one that’s been damaged, these green solutions will not only help your home stay safe but also contribute to a healthier planet. With these simple steps, you’ll be better prepared for whatever the weather throws your way.

Author: Robert J. Pierson - Ecohome Network

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Now you know more about smart basement design and construction to prevent flooding, find more pages about best practices for basement construction in the Ecohome Green Building guide and in these pages below: How to rebuild a basement after a flood and avoid future water damage Is it smart to buy a home with a finished basement? Why are basements moldy? How to remove and prevent mold in homes Preventing mold when you insulate and finish a basement  Why dry rot is a serious problem for homeowners Smart sewage backup flood prevention devices and alarms  Find more about green home construction in the Ecohome Green Building Guide pages - also, learn more about the benefits of a free Ecohome Network Membership here.