Properly waterproofing your house foundation

Waterproofing one the most important parts of your foundation and one of the most neglected by contractors.

It’s neglected because they either don’t know any better, or they do not want to spend the money to do it right.

Waterproofing is in the building code and it requires an inspection from the local municipality, but that doesn’t mean that it is done the proper way.

First things first, I’ll explain how you go about creating a watertight basement or crawlspace and the products available.

Once the foundation has been erected you need to waterproof the walls.

1.Tar.

Now most contractors these days still use the old method of tarring foundations. Now this works but tar dries out over time and will eventually start to leak in a wet area. Lately the trend is to install dimple board over this because they think this will help. The only thing that this does is protect the tar on the wall. Tar will dry out in less than 20 years, depending on how wet the area is and what type of backfill is used around the house the tar could fail almost immediately. Tar is considered in most circles to be a “damproofing” product, not a “waterproofing” product.

2. Dimple board

Dimple board alone should never be used as a waterproofing. But people are installing this on their foundation because big box stores tell them too.  Dimple board is a plastic sheet with raised bumps on it, it is designed to protect the waterproofing behind it and allow any sediment that works its way behind the dimple board to pass down to the footing and back into the soil below. This product should NEVER be used on its own regardless of what the company tells you. What you will be told is that once you tape the joints the dimple board is waterproof. Now you are relying on a thin tape that is buried 8 ft in the ground to protect your basement.

3. Rolled on waterproofing

Rolled on waterproofing is a superior product too tar and dimple board. But it is labour intensive and it is only as good as the people installing it. Rolled on waterproofing is a waterproof membrane that comes in rolls about 3 ft in size by about 50 ft. It has an adhesive that bonds to the foundation wall that is already applied to it in the factory. All you have to do is peel the protective layer off the back to reveal the adhesive. The membrane should be installed top to bottom, with the membrane covering the footing at the bottom. Since it is only 3 ft wide you need to overlap every piece 3 inches. This gives you a very water tight wall. If you’re applying this to concrete or block walls you may need to use an additional adhesive to get it to stick depending on the weather and temperature.

Some people stop there, but you end up with the same problem as when you install tar, if a rock rolls against the membrane during backfill you could end up with a penetration and that will lead to a leak. So you should install dimple board over top of this membrane, this will give you a protection so that the membrane is never penetrated.

4. Sprayed on membrane

This application is the most superior product that you can find for residential construction. It is a rubberized membrane that is installed over the foundation walls. It is sprayed on usually by a professional waterproofing company. This membrane usually comes with a limited life time warranty. Because it’s made from mostly rubber it’s flexible and extremely durable. Most professionals will then install dimple board over this to protect it from rocks and tree roots. To put this in perceptive it’s like installing a pool liner to the outside of your house. This is the most superior waterproofing product but also comes with highest price tags.

Now that you have the waterproofing on the exterior foundation walls you should install drainage around the outside of the foundation. This is covered in the building code and once you are done requires an inspection from the building inspector. You lay a 4 inch drainage pipe around the foundation. The pipe most be perforated to allow water in and must have a filter cloth around it to keep sediment out. The pipe is installed at the footing level around the whole foundation. If you have an attached garage the pipe most pass through the footing or concrete wall along the house wall between the house and the garage. The pipe will continue around the foundation until it reaches the sump pail, the sump pail is installed in the basement of the house. All water will travel around the foundation to this sump pail, the sump pail most have a sump pump installed in it to remove the water from the pail and deposit outside away from the foundation.

Over top of the pipe you most install 6 inches of clear stone, usually ¾ crushed stone. It most cover the drainage pipe and be slumped against the foundation wall. This will allow all water sitting against the exterior of the foundation wall to migrate to the drainage pipe.

Remember the basic rule when doing all of this; water will flow to the area of least resistance. So if you give the water a place to go it will follow that path.

You most backfill the house with clean fill, usually sand or gravel, do not backfill with clay or large stones. This could cause major problems in the future.

On the inside of the foundation before you pour the concrete basement floor you should install 5 to 6 inches of crushed stone and a couple drainage pipes that run to the sump pail to take any water that makes its way under the foundation. Then install a vapour barrier of plastic on top of the crushed stone. Caulk all joints with acoustical caulking; this will help direct all water to the sump pail. Then you can pour your concrete floor over top of it.

A couple more things to help you with your waterproofing. Controlling the water before it gets to the house or when it arrives at the house will help the waterproofing and the humidity in your basement.

Here are some helpful hints:

-          Install a French drain at the level of your weepers. A French drain can be as simple as crushed stone installed with a filter cloth, or it can be a pipe that is connected to the foundation drain that allows the water to flow naturally away from the foundation without the use of a pump. This only works if you have enough slope away from the house to allow the water to run.

-          Proper grading around the house. If you properly grade around the house so that there is sloping earth away from the house this will allow surface water to naturally drain away from the building.

-          Have your gutters clean and working properly. Also have the gutter exhausts drain away from the house, the farther away the better.

-          Your landscaping can do a lot to help handle the water around the house. Having trees planted to close to the house can cause leaks in the future when the tree roots start to come in contact with the foundation walls and the drainage tile. Also planting a lot of plants and scrubs next to the house will help control water flow and help absorb water before it ever gets into the ground around the house.

-          If living in a high ground water area, where during certain times of the year you have unusually high water runoff then you should install a second sump pump in the sump pail. This will give you insurance if the water overwhelms the first pump or if the pump fails.   

-          When digging the foundation keep an eye on how much water runs into the hole, this will tell you how much water will naturally be around the foundation walls. If there is a lot you should keep the house as high up as you can. If this means only going into the ground a couple of feet then so be it. Remember you can always grade up to the house.

-          Make sure all window wells have a drainage pipe that runs down and connects to the drainage pipe at the footing. Then install 6 to 8 inches of crushed stone in the top of the window well and keep the window well clean of mud and debris. If you do not water can become trapped in the window well like a pool and can even end up leaking through your basement windows.

If you have any questions or comments about waterproofing please feel free to email me at robabbott@villagebuilders.ca.

To see pictures of waterproofing go to villagebuilders.ca and look at current projects you should find pictures of the waterproofing on the latest house project that we are building.

Rob Abbott

Operations Manager
Village Builders Inc.