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Cold Floors Over Your Crawl Space, Basement, or Garage? Read This

Friday, December 11th by Kristina McGovern


Fiberglass batt insulation in a crawl space ceiling

When poorly installed, fiberglass batts aren’t effective at preventing cold floors over unheated crawl spaces, basements, and garages.

Why your floors are cold and the best ways to make them warmer

Is the floor or room over your crawl space or garage colder than the rest of the house? This is a common problem in homes built over a dirt crawl space or with a basement or garage that’s unheated and not insulated.

If you’ve been researching how to make the floors over your crawl space, garage, or basement warmer, then you know there’s lots of information on the best solution. The key takeaway from the research is that to make cold floors and uncomfortable rooms over these areas warmer, you need a continuous air barrier and proper insulation in place to stop cold air. We’ve put together this guide to explain what causes cold floors (and rooms) over the crawl space, basement, and garage, as well as solutions for making them warmer.

First, we’ll discuss the reasons why the floors over unheated spaces get so cold.

Why the floor (or room) over the crawl space, garage, or basement is cold

Houses suck in cold air

In the winter, the warm air inside the house is lighter (less dense) than the cold air outside. As the warm air rises through the house and escapes out through leaky windows, the attic and roof, this draws cold, dense air from outside into the basement, crawl space, garage, and first-floor windows. To add to the problem, most garages, basements, and crawl spaces either don’t have insulation at all or don’t have proper insulation. If nothing is stopping the cold air from reaching your floors and the rooms above, it’s no wonder they are cold.

Problems with fiberglass batts

Insulation works by trapping pockets of air that slow the flow of heat out of the house in the winter (and into the house in the summer). The R-value of the insulation is an indicator of how well the insulation resists this movement; the higher the R-value, the more effective it is at lowering heating and cooling costs and maintaining comfort.

Fiberglass batts are inexpensive and quick to install, which is why they are the most common type of insulation. However, challenges with properly installing fiberglass batts make blown-in insulation or rigid foam a better choice for insulating the ceiling in unconditioned basements, crawl spaces, and garages.

So what are the problems associated with fiberglass batts?

Compressed batts

When fiberglass batts are shoved into the ceiling in the basement, crawl space, or garage, the compressed insulation can’t trap as much air, making it less effective at reducing heat loss.

Loose batts and gaps

Basement, crawl space, and garage ceilings have lots of obstacles, including electrical wires, plumbing, and HVAC ducts. This makes it difficult to fit the fiberglass batts without leaving gaps that air can easily flow through.

Moisture and wet insulation

Moisture can cause fiberglass insulation in the basement, crawl space, or garage to become wet. Once the fiberglass batts get wet, this can lead to mold problems and rot. Wet batts also tend to sag and droop from the ceiling, leaving gaps where air can flow through.

Cold Floors/Rooms Over Crawl Space

Fiberglass insulation on the crawl space floor

Fiberglass batts soak up crawl space moisture like a sponge, causing mold and rot.

What you should know
Adding spray foam or rigid foam board insulation to the underside of the floor can help warm up the floor and rooms above the crawl space. However, this approach makes it difficult to access plumbing and electrical wires when the need arises. Another common mistake that homeowners make when repairing the crawl space is adding plastic (or a vapor barrier) to the underside of the floor joists in an attempt to make their floors warmer in the winter, but doing so can trap moisture that can lead to mold and rot.

The best approach
Sealing or “encapsulating” the crawl space involves more material and the help of a professional, but it’s a much more effective solution than insulating under the floor. Covering the ground with a crawl space vapor barrier reduces moisture and sealing the rim joist and crawl space vents keep out cold air during the winter, which will make the floors above feel warmer. Additionally, crawl space encapsulation and insulation can prevent cold ducts and frozen pipes.

Cold Floors/Rooms Over Basement

What you should know
The area on top of the foundation walls and below the floor joists, called the rim joist, is one of the biggest sources of heat loss and air leakage in a home during the winter. The long-accepted DIY solution has been to add fiberglass insulation to the basement ceiling. However, there are several problems with this approach. Although the floors above might be a little warmer, the basement itself is still cold, which means there’s a risk of freezing pipes in the basement.

The best approach
Spray foam insulation or a combination of spray foam and rigid foam insulation can be used in an unconditioned basement to seal around joints, plumbing, wiring, and other penetrations in the basement ceiling, as well as ducts in the basement. This method can create an effective barrier between the cold basement and the other living spaces, making the floors and rooms above warmer. If the goal is to create a comfortable, conditioned, finished basement living space, adding basement wall insulation is a preferable solution and as an added benefit, the floors and rooms above will be more comfortable. Basement Systems contractors not only make basements drier with waterproofing, but they also make basements comfortable with insulated wall panels, flooring, and replacement windows.

Cold Floors/Rooms Above Garage

What you should know
In most homes, the garage is unconditioned, unheated space. And most floors above garages are insulated with fiberglass batts. Many times, DIYers or even professional installers leave gaps when they place the batts, leading to significant air leakage and heat loss. Worse, there’s a risk of car exhaust, paint, solvents, and other contaminants in the garage migrating into the conditioned space.

The best approach
The floor above the unconditioned garage should be properly sealed and insulated with blown-in cellulose or dense-pack cellulose insulation to prevent cold in the garage from reaching the floors above. This strategy has the added benefit of minimizing the risk of contaminants migrating into the living space. It’s also a good idea to address drafts around the garage door by adding or replacing the bottom door seal and the weather-stripping along the sides and top of the door.

If you’re worried about how your unheated basement or crawl space is impacting your home’s comfort and energy efficiency, check out our 7 Tips to Winterize Your Basement or Crawl Space or contact Basement Systems for a free evaluation and estimate from your local basement or crawl space repair contractor.

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