Sealed crawlspaces are a great luxury to have. There are efficiencies to be gained from an energy standpoint. When considering a sealed crawlspace, you have several choices to make based on your particular crawlspace. Remember, not all crawlspaces are alike and what may have worked for your neighbor may not necessarily be in your best interest. Not all crawlspaces necessarily need to be “sealed”.

In many ways, this space is its own environment and changing aspects of this environment may affect other components you didn’t even consider.

The following criteria may help in your decision:

Gas Systems. These usually come in the form of HVAC furnaces or water heaters located in the crawlspace. They may require a fresh air intake so that they can sustain combustion. Before any sealing can take place, these should be checked by a qualified and competent contractor and the appropriate adjustments made.

Drainage / waterproofing must always be considered. In fact, this is NC code. If, during an extreme weather event or a catastrophic systems failure, your crawlspace was to flood…there needs to be a way for the water to get out quickly. Drainage can be handled in a couple of different ways.

The following are examples:

  1. A drain port placed in the vapor barrier at the existing positive / foundation drain for the crawlspace. This is the simplest way to provide drainage although it may not be enough in all cases. Also, you have to make sure the positive / foundation drain actually performs as intended. Many of the drains are only run to the other side of the foundation wall…where they are clogged. Water can then back up into the crawlspace and create all sorts of headaches! These drains must be run to daylight and kept free of debris – if used as your only means of draining water.
  2. An interior perimeter drain (interior waterproofing). An excellent means of controlling water intrusion. This is a drainage system installed around the interior of the crawlspace walls, at the footers. Any water intrusion is caught immediately, given a path of least resistance to an exit point.
  3. The exit point. This can usually be handled by one of two ways. A gravity feed or a sump pump.

A gravity fed system is just what it sounds like. The natural slope of the land is used to channel water away from the homes foundation. The interior drainage system is pitched towards the lowest point of the foundation, where it exits the crawlspace and is extended to daylight away from the home. Not everyone has this as an option.

The sump pump is used when gravity feeds are not an option. The system is installed just like a gravity feed system but, the water is expelled into a sump basin. From the basin, water can be pumped to wherever it needs to go to get away from the home. An excellent choice for flat lots that do not have gravity on their side.

The two most common options when sealing the foundation walls are the use of an insulating foam board or poly / plastic sheeting. Not all crawlspaces need to be sealed and it is usually a matter of preference. Remember, it is NC code that a minimum of three inches be left at the top of the barrier to allow for termite inspections.

The insulating foam board, commonly referred to by the proprietary trade name – Thermax, is great when you are not planning to insulate the floor system. The insulating foam board offers an “R” value to the walls (although not as much as traditional insulation). Insulation (spray foam or traditional fiberglass) is placed at the band of the house only (at the top of the walls). The vapor barrier on the floor is sealed below the insulating foam board. This option is NOT recommended if there is an excessive amount of moisture penetrating the foundation walls or the foundation walls are brick. Brick is known for excessive amounts of moisture passing through into the crawlspace.

Sealing the foundation walls with a poly vapor barrier is also a nice way to protect a space below grade. This is especially true when working with brick foundations. The poly is installed on the walls and sealed at the top, preventing any moisture penetration below the exterior grade from affecting the crawlspace. Traditional insulation is then installed in the floor system between the living space and the crawlspace. This method is cheaper than rigid insulating foam board. It is not recommended to use anything lower than 10 mil poly when sealing a crawlspace.

With both methods, once the crawlspace is sealed a mechanical means must be in place to control the environment.

The mechanical means to control the environment. There are three options that we typically deal with when controlling a crawlspace environment.

The first is dehumidification. A dehumidifier is an excellent means to keep humidity at bay. The unit must be a commercial grade unit rated to handle the amount of square footage. The condensation is either piped out of the crawlspace or to a sump basin. A commercial unit is more expensive but worth every penny. Residential grade units (Lowes or Home Depot versions) are not recommended…at all.

The second is supplied air. This is inaccurately referred to as “conditioning”. This term is inaccurate in that to be conditioned; the air has to be cycled through the HVAC system. This is not allowed through NC code. Crawlspace air cannot enter the HVAC system, no matter how clean it is. So…we refer to this method as “supplied air”. This is where the current HVAC system is utilized by creating a vent port where heated and cooled air is pumped into the crawlspace. This is not our favorite method and we have seen in several cases where this was not an adequate means of environmental control. Fungal growth city…

The third option is fans. We would not recommend this option. There, we said it.

Sealing all penetrations. ALL penetrations through the foundation wall or the subfloor must be sealed with expanding foam. Sub-floor penetrations must be sealed with FIRE foam, which is different than “regular” foam and is NC code.

Of course, there are permit considerations as well. Check with your local permit office for details.

These are just some of the criteria to consider when sealing a crawlspace. Be careful who you contract with and always make sure that these items are addressed before starting a sealing project. The person standing in front of you selling a sealed crawlspace may have worked for a crawlspace company for a month and decided to start his own business. References are a must!

As stated previously, you may not even need to seal your crawlspace to make it a nice place.

Contact us for more options on how to change your crawlspace from “gotta deal with” to “dealt with”!