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How To Install A French Drain To Protect Your Home's Foundation

Sam Smith Foundation Repair Consultant

French drains collect excess water from the surrounding soil

If you’re in search of accurate costs to install a French drain to protect your foundation, you’ve come to the right place.

Here’s what you’ll learn by the end of this article:

  • Where a French drain should be installed
  • Materials needed for the job
  • Step-by-step instructions for installation
  • How to save money on a French drain install

The majority of homeowners will experience leaks in their basements and crawl spaces at some point. There are a few root causes of a leaky basement, but poor drainage in the yard is one of the most widespread.

Many people turn to exterior drainage systems like a French drain to solve their drainage problems.

French drains, also called drain tiles or curtain drains, collect excess water from the surrounding soil and direct it to a catch basin for safe disposal. These systems are effective but expensive, so a DIY installation is preferable to many homeowners.

In this article, we will detail how and where to install a French drain, and we’ll give you step-by-step instructions on how to set your drainage pipes properly.

We’ll also go over how you can save some money throughout the French drain installation.

Choose Where to Place Your French Drain

You will first need to decide where your drainage system will be placed before making your first trip to your local home improvement store.

Many people install these drains around the entire outside of their homes, but there are some things to consider before committing to a perimeter drain.

Your drain’s placement should be optimized for the water issues you’re experiencing. For example, gutters, downspouts, and graded soil may be sufficient drainage on three sides of your home, and your water intrusion may be occurring just on the fourth side.

If that is the case, a French drain on only one side of your house may be plenty to stop the water intrusion.

The best placement for your French drain will depend on your property and existing drainage issues. You may be able to see pooling or puddling of water around your foundation during heavy rain, or you may notice areas where your lawn slopes down toward your foundation.

These are both usually good places to set your French drain.

You will need to plan for the excavation after determining the best place on your property for your drainage system. You may know of underground utility lines or landscaping features that will make placing your drainage system challenging.

It’s best to plan and mark where your French drain pipes will run instead of figuring it out as you dig your trenches.

A French drain is designed to move water to a catch basin or a part of your property that won’t cause damage to your foundation if it gets saturated.

You should route your drain pipes toward this area and plan to slope the pipes downward to maintain an ample flow of water.

Lastly, your pipes should be installed within 2 feet of both the ground surface and your foundation wall for the best results.

What Materials Are Needed?

Your French drain will consist mostly of PVC pipe or corrugated drain piping. Both options need to be perforated to allow water to flow into them. You will need to buy drain pipes and connectors based on the French drain map you’ve created.

You will need something to dig your trenches too. Based on the proximity of your drain to utility lines, patios, or decks, you need to decide either to purchase a shovel or to rent a trencher or backhoe.

I strongly recommend buying enough landscaping fabric to wrap fully around all sections of piping. This filter fabric will serve to reduce clogging.

You will need enough gravel or other porous rock to fill up to the top of the trench.

You also may need soil to backfill over the gravel if you’re placing your drains more than a foot below the surface. Shallow dry wells are visible from your yard but won’t require additional backfill.

We recommend dry-fitting your pipes and connections before moving onto the next step.

Dig Your Trench

You are ready to begin digging the trenches for your pipe.

Do so according to your French drain map, and always make sure to avoid utility lines when digging.

Remember that you will need water to be collected by your drain pipes and then flow toward your catch basin. You should dig your trenches such that the slope will allow for water to drain naturally and freely.

How Deep Should a French Drain Trench Be?

Your French drain works by rerouting dangerous runoff away from your foundation. It follows logically that the system should be placed relatively close to the surface.

We never recommend digging trenches deeper than 2 feet because drains this far down will be less effective for managing surface water.

The best placement is 18” at the deepest points where they are meant to collect water near your concrete walls. You can dig the trenches for the drain pipes leading to your catch basin deeper to get the proper slope.

You should also aim for your trenches to be about a foot wide at the top. You can fit plenty of gravel above your piping for the best chance of collecting runoff with this spacing.

Apply the First Layer of Landscaping Fabric

You should lay down the first layer of landscaping fabric along the entire length of your trenches once you have them dug. This bottom layer of material will help stop plants and weeds from growing up into your pipes, which can cause them to clog.

Lay Your Drain Pipe in the Trenches

Next, you can begin fitting your drainpipe into the bottom of the trenches. This is where your previous careful planning will pay off and make laying your piping straightforward.

You can add inlet grates below gutters to help with roof water drainage if you didn’t include them in the planning phase. You can also install your catch basin during the pipe-laying process.

Make sure you check and recheck the slope of your drain pipes regularly throughout this step to ensure proper drainage during rainfall.

We also recommend covering the top of your piping with landscape fabric for extra protection. Trim off any excess fabric before moving to the next step.

What Is The Best Material to Use for Drain Pipes?

The drain pipe that you purchase from a home improvement store will usually be 4” in diameter regardless of the material. Additionally, all drains will be made of perforated pipe for good drainage.

The two common drain pipe materials are PVC and corrugated high-density polyethylene piping (HDPE). Some corrugated options are sold with drain guards that can help limit clogging by blocking plant growth and soil intrusion.

Neither material is better than the other, so you need to decide which you prefer. Both will work well, so choosing is a matter of preference for sturdiness and workability.

Corrugated pipe is easier to work with and will need fewer connection pieces because it flexes. It’s not ideal for bending around corners because it can only bend so much and still maintain its strength. However, you’ll find that it requires less adjusting than PVC during the installation process.

PVC pipe can withstand more soil pressure than HDPE piping and is less likely to get crushed or cinched. PVC is better suited for deeper drains or if you have children or animals that may play or walk on the ground above your drain.

PVC usually requires more precise trench digging, more connecting pieces to accommodate bends and corners, and more adjusting underneath and around the pipe while laying it down.

PVC is also typically a better option for areas where you may have a patio or other heavy landscaping feature placed in the future. It will withstand more weight from pavers or concrete and have a lower chance of getting crushed.

Cover the Piping with Gravel

You can begin filling your trench nearly to the surface with gravel as long as you’ve triple checked that the slope of your drain is adequate. Gravel, crushed stone, and river rock are common fillers for trenches.

You can choose the one you find most appealing and fill your trench up to ground level if you’re leaving your French drain exposed.

Choose whichever is most readily available and leave about 2” of space between the top of the gravel and the ground level if you plan to cover your French drain with soil.

Backfill Over the Gravel With Soil

Covering your gravel with soil is optional. You can leave your French drain exposed for easy access later if you run into drainage problems or if you like the look of the gravel or rock.

If you do backfill with soil, you can either use the dirt you removed during trenching or fill in the space with topsoil. Bring the trench up to ground level with the dirt and gently tamp.

You should always be careful not to put too much weight over your French drain because pressure from the ground above could collapse the pipe. Never use a yard roller or other heavy leveling device for the tamping.

How To Save Money Installing A French Drain?

If you’ve read through this article and plan on installing your own French drain system, you’re already saving yourself some money on labor costs.

Having a professional installation will undoubtedly be easier but is always more pricey. Putting in a French drain as a DIY project is much cheaper.

French drains are helpful for reducing the potential damage caused by excess runoff or rainwater, but they just end up costing you more if they won’t fix your water problems.

A bunch of different things can cause water to seep into your basement. Runoff and poor surface drainage can cause leaks but may not be the source of your wet basement.

You could save thousands by figuring out the root cause of your water intrusion before jumping into a drainage solution. For example, a French drain won’t solve groundwater problems or be sufficient for solving standing water in your basement.

Skip the French drain and choose a more useful solution if you have a high water table or determine that groundwater is your problem.

Instead, have a waterproofing contractor install a footing drain or an interior drainage system and sump pump. They will cost more but ultimately save you money on the French drain install in the future.

You can also save a significant amount on the total cost of your French drain if you choose where to place it strategically. French drains are commonly installed around the perimeter of foundations. However, your plot may not require such an extensive drainage system.

For example, your home probably doesn’t need drainage on the lowest portion of your plot if it’s set on a slope. Your natural yard drainage or gutter and downpipe location may also be sufficient drainage for some portions of your property.

You can save time and money by installing drain pipes where they’re needed and avoid placing them in areas where your property already has good drainage.

I’ve emphasized the importance of planning a few times already, but it’s worth mentioning how much money proper planning can save you.

You can save on unnecessary piping, connections, gravel, and backfill with planning. The real savings can come from planning around underground utility lines and landscaping features.

Knowing what’s below your ground and how to maneuver around it before you even begin can save you thousands.

Hitting pool equipment, sprinklers, gas lines, or electrical lines can be extremely expensive. Disrupting some utility lines can also lead to fines from your utility companies, costly repairs, personal injury, and even death. Plan carefully and know what to expect before you dig.

I’ve detailed above the pros and cons of both PVC and HDPE piping for use in your French drain.

Using HDPE will be much cheaper than going with PVC. HDPE can save you quite a bit in material cost and is a good option if your drain pipes will be shallow and have a low chance of being stepped on or crushed by machinery or landscaping features. HDPE pipes also need fewer connections, which can add up to savings of hundreds of dollars.

Lastly, we’ve given you two options for backfilling above: reusing the excavated dirt and purchasing topsoil. Topsoil may be a better option if you plan to plant flowers or grass above your drain.

It also looks more appealing than excavated dirt. However, you can save on the cost of the fill if you reuse the soil you remove in the first place.

Ultimately, the best way to get the job done right is to at least consult with one of our professionals so they can highlight any potential issues with your unique situation and prevent you from making costly mistakes.

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Sam Smith Foundation Repair Consultant
SHORT BIO: Hey, I'm Sam Smith. I'm one of our service techs here at Regional Foundation Repair. I'm here to help you learn more about your home's foundation. I've been doing this for a while, so I have a few insider tips and tricks to share!

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