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Isolate the House from the Earth

Isolation of the crawl space from the earth is the key step to solving dirt crawl space problems.

There are a few criteria to deciding which approach to use. The solution must:

  1. Stop water vapor from flowing up from the soil
  2. Stop water vapor from flowing through or off of the crawl space walls
  3. Allow water to drain from the walls to the sump location
  4. Allow water to drain from the floor to the sump location
  5. Not get ruined when someone crawls on it
  6. Be durable, so it lasts as long as the house does
  7. Be affordable

There are two basic approaches - a concrete floor and plastic a liner.

Concrete Floors

If you pour concrete in your crawl space, you have accomplished two of our criteria – the concrete won't get ruined when someone crawls on it and it will last. However, the concrete doesn't allow water from the walls or floor to drain to the sump location, and it doesn't stop water vapor from the walls or floor. In fact, water vapor goes right through concrete; especially a thin layer of concrete, like might be installed in a crawl space.

These problems are solvable. First, to stop water vapor from the floor, you'll have to lay down a vapor barrier of at least 6 mils thick before pouring the floor. The vapor barrier stops the moisture, and the concrete makes it durable. But then, something has to be done to let water flow beneath the concrete. www.buildingscience.com.

And the walls will need to drain. Crawl space walls are usually made of concrete block and they leak readily. leaking crawl spaceYou can put plastic on the walls, but plastic such as 6 mil plastic is difficult to attach permanently to the walls, and is not durable. One solution is to run the plastic from the floor up the walls and attach a wire mesh to the wall over the plastic. Then a stucco coat of concrete can be applied to the walls, before the floor is poured.

Concrete is heavy, and mixing enough by yourself to cover your entire crawl space floor and walls is out of the question. To pour a floor 3" thick over a 1500 square foot crawl space floor alone is 14.4 cubic yards of concrete. That is 1 1/2 truckloads from a concrete truck. Getting concrete from a truck into your crawl space is a difficult process.

A concrete pump is an option. The concrete truck dumps concrete into a trailer-mounted pump, which pumps it through a hose into the crawl space, where workers can spread it out. Caution is recommended as concrete is caustic and can cause severe burns.

Beware of Portland cement mixed with vermiculite to make a lighter concrete. Concrete is usually made of Portland cement, sand, stone and water. The mixture of vermiculite, which may be best described to a layperson as "natural Styrofoam beads", and Portland cement makes for a weak final product, which you can feel your kneecaps push into when you crawl on it. Some vermiculite, from a mine that has now been closed, has asbestos in it.

When any concrete is pumped into a crawl space, there is a strong urge to add extra water to the mix to make it flow easier. This however, weakens the concrete, and makes it crack as it dries. Further, there is little chance of loose concrete staying up on crawl space walls. While you can make concrete work as a crawl space solution, the cost and challenges of preparing for it, and placing it make it hard to argue that it's the best option.

Plastic Liners

In the past, it has been popular to lay down thin plastic such as 6 mil thin plastic on crawl space floors. In fact, building codes have allowed it as an option to cut venting requirements by 90%. But thin plastic does not meet the above criteria for a solution as it will be ruined when somebody crawls on it and it will not last as long as the house. crawl space linerFurther, 6 mil plastic is difficult to attach to walls and can be easily pulled down.

If you'd like your house to last for over 100 years, then anything you put on it or in it to protect it should last as least as long. Otherwise, you'll have to do the same job again in the future. Thin polyethylene film will not last 100 years. The researchers at Advanced Energy found that while polyethylene film holds down moisture, they encourage thicker, stronger materials due to polyethylene film's poor durability. Other contractors and homeowners report that 6 mil poly must be repaired frequently due to holes and rips that occur after they go in the crawl space.

A product called CleanSpace® is made to perform to all the requirements aforementioned. CleanSpace is a 20 mil thick plastic liner, similar to a pool liner, which can be fitted in a crawl space to completely seal off your home from the earth. It has multiple layers of plastics with different characteristics of flexibility and puncture and tear resistance. Put together with two layers of polyester cord reinforcement, the material is incredibly durable, will last as long as the house, and will stay where you install it.

As an added benefit, CleanSpace has an antimicrobial additive manufactured into the material which prevents mold growth on the liner. This additive is odorless and safe, and is used in many plastic household and automotive products.

To satisfy our criteria for our crawl space walls – stopping water vapor and allowing for drainage to the sump – fasten the liner to the upper part of the walls. Stay 3" down from the top of the walls so that termites cannot get to the framing without their mud tunnels being seen. The liner is attached to the walls with fasteners along the top edge, which are permanently driven into holes drilled into the walls. With the crisscross layers of polyester cord reinforcements within the liner, the liner is securely in place and cannot be pulled off.

Satisfying our requirements that we need to allow drainage from the floor to the sump, and we must stop water vapor from permeating up from the floor is easy with this method. By laying the liner over the floor of the crawl space, water can seep or even flow under it to the sump, especially via any drainage channels you may have created before you installed it.

The liner is sealed around obstructions and at seams by a variety of methods, including special tapes and sealants. The top edge around the walls is sealed with urethane caulk. If the liner is on a sloped dirt floor, the liner can be staked to the floor so it doesn't move or pull downward when you crawl on it.

Another benefit of this method and material is that you can use your crawl space for storage after installation – something homeowners could never consider in a dirt crawl space.

Rigid foam insulation board can be installed on the crawl space walls under or over the liner.

If you do not install a sump pump because your crawl space doesn't have groundwater leaks, it's still important to use a water alarm in the low spot. Why? Because you will eventually have a plumbing leak, which can fill your crawl space up with water before you know it. Basement Systems Inc. manufactures special alarms for this purpose that you simply set on top of the crawl space liner in the low spot of your crawl space.

Crawl Spaces with Existing Concrete Floors

Crawl spaces with concrete floors can be treated in the exact same manner – install a sump at the lowest spot and install a CleanSpace liner. One adaptation that can be made is to lay down dimpled polyethylene drainage matting on the floor before installing the liner. This creates an air space for water to flow to the sump on top of the concrete floor.

The Portland Cement Association - Cement and Concrete Basics