Insulated Crawl Space

Should You Insulate a Crawl Space? How To Decide

In Technical Details by Giovanni ValleLeave a Comment

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Crawl spaces are kind of a pain to insulate. They’re out-of-sight, out-of-mind, and most buildings have them. Nonetheless, before going out and spending time and money on insulating your crawl space, it is important to know whether or not you should do it.

Generally, it’s best to insulate a crawl space if it’s not well-ventilated, has ground moisture, or you need to reduce power bills. By doing that, you increase your home’s thermal efficiency, leading to reduced heating and cooling bills.

If you’re still unsure as to whether or not you should insulate your crawl space, keep reading to find out more about when it’s appropriate to do so. Additionally, I’ll give you some tips on how to insulate it if you decide to do so.

When To Insulate a Crawl Space

When you should insulate your crawl space depends on several factors that vary from home to home. A good rule of thumb is ‘when there’s ground moisture and air.’

The most obvious solution is to get more air flowing through your crawl space, but if the issue isn’t resolved, then insulating it may be the next best course of action.

When There’s Ground Moisture and Air – Insulating a crawl space without proper ventilation can lead to condensation build-up and mold growth. Here are some of the common signs of moisture problems in crawl spaces:

  • Dark spots on wood surfaces. Moisture causes rot in wood and leads to dark spots on all surfaces, including studs, joists, and cross beams. This happens when fungi enter into open cells within the wood.
  • Musty smell. The accumulated moisture produces an unpleasant musty smell.
  • Insect infestations. A heavy build-up of moisture provides the ideal environment for termites, silverfish, and other insects to feed on wood
  • Exterior stains. These are indicative of water entry into the crawl space.

If you notice any one of these signs around your home’s crawl space, it is best to check for moisture right away. If there is no water seepage present, but just an unpleasant smell, bringing in more air through ventilation can solve the problem quickly.

If the Crawl Space Isn’t Ventilated – If there is no air seeping into the crawl space, more air through ventilation can solve the problem fast. If the area is not ventilated, it’s best to insulate your crawl space.

Not only will you be able to regulate the room’s temperature effectively with insulation, but you’ll also save up on energy costs.

When You Need To Reduce Power Bills – Insulating a crawl space may be necessary if you want to reduce energy bills and improve the home’s thermal efficiency.

This is especially true for homes that have dirt floors, poor insulation, and double pane windows. It is also beneficial for older houses with poorly insulated walls and ceilings as well as those built on concrete slabs.

How To Insulate Crawl Space

If you have decided to insulate your crawl space, proper insulation on all four sides of the walls is necessary. The floor, too, should be insulated properly to create an uninterrupted thermal boundary.

To insulate your crawl space, you need the following materials:

  • Fire retardant insulation, like this MEGA FORMAT Polystyrene Foam Board from – relatively inexpensive and comes in five different sizes
  • Roll of felt paper
  • Roll of silver foil tape
  • Vapor barrier membrane

Once you have the tools, follow these steps:

  1. Cover your crawl space walls by laying out the foam sheeting, followed by insulation materials. Be sure that each layer covers the seams where one ends, and another begins.
  2. Cover the floor of your crawl space with sheeting materials. If you are using foam, cut it in sheets to fit properly over the floor surface.
  3. Then cover it with soil or landscaping mulch if you have crawl spaces with dirt floors. To prevent rodent infestations, lay down a piece of sheet metal on top of your crawl space insulation materials.
  4. Finalize your insulation installation by installing a vapor barrier membrane on the crawl space walls. This is necessary to prevent water seepage into the insulation later on.

Note: If your crawl space has concrete walls, you may consider covering it with plywood before laying down insulation materials. Then insulate the wood frame with fiberglass battings followed by the other roofing materials if necessary.

Once you are done installing insulation, cover vents and any opened holes in sheathing materials with aluminum

Tips for Insulating Your Crawl Space Properly

Once you have determined whether insulating a crawl space is what your home needs, use these tips to ensure proper insulation techniques are used:

  • Pay Attention To Your HVAC System.
  • Your crawl space must be connected to your home’s air intake system. If it is not, then you should have one installed without delay.
  • You can make the connection through a dryer vent or any other opening in the house that leads to the crawl space.

Ventilate Your Crawl Space – To prevent mold spores, dust, and other contaminants from being circulated in your home’s living space, have a crawl space that is well ventilated.

Use a blower door test to check if adequate airflow can enter the crawl space. If not, you must install a ventilation system with a dedicated inlet and outlet in the crawl space area.

Seal off Unused Areas – If any areas of your home have been closed off for a long time, you should check if they have adequate insulation to prevent these spaces from cooling down excessively.

If not, you must add extra insulating materials such as batts, blankets, cellulose, or polystyrene.

Seal the Floor and Walls Properly – Once you have installed proper insulation in your crawl space walls and floor, ensure that you have done a good job of sealing them properly.

Ensure that all cracks and holes are sealed off with caulk so no air can seep in.

Check for Temperature Changes – Once you have insulated your crawl space walls and floor, monitor the ground temperature after a couple of days.

If you find that the air in your crawl space is excessively cool, then it means that your insulation job has failed, and more needs to be added.

Final Thoughts

If you succeed in insulating your crawl space properly and it remains dry, then the chances of an insect infestation will be greatly reduced. However, if water seeps under the house again, then insulating the crawl space may not help lower energy bills or prevent insects.

In such a case, repairing or replacing any damaged foundation areas will be necessary. Also, remember that insulating a crawl space must be done carefully to prevent damage to the insulation materials.


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