If it feels like the floor in your home is sucking the warmth from your body, it probably is. Here’s how and what to do about it…
If a floor in your home is room temperature in the winter, it should feel cold to you. Let’s say room temperature is 70 degrees. You’re 98.6 degrees though your feet may be a little cooler. That’s a difference of almost 30 degrees. That’s not terribly uncomfortable because we’re used to it.
This post is focused on common insulation and air sealing problems that cause a much larger temperature difference; especially those big differences that make you feel like you’re losing heat from your body to the floor… because you probably are.
Heat flows from more to less. It spreads out. If you’re warm and your floors are not, you’re transferring heat from your body to the cold floor through conduction or radiation. If you’re warmer than the floor, it may feel like the floor is sucking the heat from your body. You’ve probably had the same experience when seated next to a large window on a cold day. It’s the same principle .
The rudimentary diagram above shows the flow of heat in the winter from a heated space to an unheated space. Since heat flows from more to less, the heat flows from the heated space through the floor to the unheated space. We use insulation to slow the flow of heat.
Slowing the flow of heat is critical any time there’s a temperature difference between the inside of your home and the outdoors. Since there’s almost always a difference between your indoor and outdoor temperatures, insulation is very important.
The energy you buy for heating and cooling the inside of your home is lost to the outdoors through heat flow. Slowing the flow of heat as much as possible saves energy… which saves money.
Floors over outdoor spaces or spaces that are vented to the outdoors need particular care when it comes to air sealing and insulation. Common locations include floors over vented (unconditioned) basements or crawlspaces. Floors over garages and cantilevered bays where part of a home sticks out over the foundation or the story below face the same challenges.
The image above shows a common crawl space condition in older homes. As you can see there’s no insulation at all between the floor joists so the underside of the floor over the floor joists is exposed to the temperature in the crawlspace. The crawlspace is vented (open to the outside) – you can see the sunlight shining through the vent.
The entire underside of the floor is exposed to the extreme temperatures of both winter and summer since the crawlspace is vented at multiple locations. The floor assembly is decking (plywood) over the floor joists and whatever floor finish is above the decking so the house loses energy through the entire floor throughout the year.
Before you insulate, you should air seal. Installing insulation often covers the gaps and cracks in the construction of a home. Those gaps and cracks allow air and humidity to leak in and out of the home. That flow of air may cause drafts that contribute to your discomfort so finish your air sealing before you insulate. Insulation slows the flow of heat though many forms of insulation DO NOT provide significant air sealing.
We use insulation to slow or stop heat flow. We use insulated thermoses to control the flow of heat. We put on clothes in the winter for the same reason; to retain the heat in our bodies. We install insulation in our homes to create a thermal boundary – a continuous layer of insulation on all sides of the building (houses are buildings) to control the flow of heat.
For the thermal boundary to work properly, it must be continuous. Yes, there are openings for windows and doors so that we don’t have to live in a cooler though the industry is making progress in the development of windows and doors with better insulation values. Some windows are now available with triple-pane glass to slow the flow of heat.
The thermal boundary in your home may be broken when an installer fails to insulate in a certain location, insulation (especially on the underside of floors) falls out of place or when insulation is removed or disturbed for maintenance. When the thermal boundary is broken, it’s easier for heat to flow through that location. In the winter, this can result in cold spots and drafts.
The insulation in the image above has fallen out of place. This insulation is located in a vented crawl space so there’s a large spot in the floor over this gap in the thermal boundary that feels colder than the rest of the house.
The insulation in the image isn’t well installed so it will all be replaced. Fiberglass batt insulation (shown here) loses it’s ability to resist heat flow (to insulate) when it’s compressed. This insulation isn’t performing as expected because it’s not evenly installed AND it’s not in continuous contact with the floor above so it’s not providing consistent insulation.
Solving the Problem
The way to address the discomfort of a cold floor in the winter time is to solve the problem of air, humidity and heat moving through the floor. Cold floors are often over an unvented crawl space that may have air temperatures slightly above the outdoor temperature.
The image above shows typical air sealing and insulation details included in the energy code for Georgia. The numbers in black circles refer to a key that’s included in the document.
The enclosure of your home (the air and thermal barriers on the bottom, sides and top of your heated and cooled spaces) should be continuous. Any interruptions can cause health, comfort and efficiency problems in your home. Solving the problem of a cold floor in the winter with the appropriate amount of air sealing and insulation also keeps you from gaining heat in the summer.
RTA uses energy modeling software to explore the benefits of different building enclosure designs BEFORE construction. Whether you’re considering new construction or renovating an existing home to improve your health, comfort and efficiency, don’t guess what design solution might be best. RTA and other companies offer HERS ratings and building analysis to address your specific issues. Hiring a HERS rater will give you an independent advocate to help you identify and address potential problems rather than just treating the symptoms.
Encapsulating Your Crawlspace
Crawlspace encapsulation has become more common in recent years so it’s worth mentioning. Encapsulating a crawlspace is the practice of sealing it off from the outside. There are too many considerations to address here though one of the benefits is often a lower installation cost.
Let’s say you live in a home with a footprint of 2,000 square feet. The dimensions of the floor are 40′-0″ by 50″-0″. If you insulate the underside of your floor, you have to insulate around the heating|cooling, electrical and plumbing systems. You’d need 2,000 square feet of insulation.
Insulating the crawlspace walls slows heat flow to/from the outdoors at the foundation walls rather than at the floor. If the crawl space under the home is 3′-0″ tall, you could figure the area of the crawl space wall by adding the exterior dimensions and multiplying that number by the height of the crawl space wall:
180′-0″ of wall X 3′-0″ of height = 540 square feet
Thus, if you insulate the crawl space walls in this example, you’d use significantly less (just one quarter) of the insulation you’d need to insulate the floor. You’d also still have access to the heating|cooling, electrical and plumbing systems rather than covering them with insulation.
We’ll need to compare the floor area against the area of the foundation walls in your crawlspace or basement to see which has a smaller area. There may be some conditions where the floor area is smaller than the wall area – the opposite of the example above. Still, if you have that much space under your home, it’s probably usable space so insulating the walls could be beneficial. Hopefully, you’ve realized there are multiple considerations to take into account so each home needs its own analysis.
Building codes are a minimum standard so don’t be shy about adjusting the amount of insulation in your building enclosure to make the most of your passive systems. Passive systems like insulation can significantly reduce the need for active systems like heating and cooling systems that are expensive to buy, operate and maintain.
The attic is where a home typically has the most heat flow so we insulate attics. We often ignore floors – the place in a home with the second highest heat flow. If you have a floor with no insulation, you could improve your conditions dramatically with relatively little work. If you have poorly installed insulation like the image above, you could also be more comfortable and lower your bills. Putting off the problem of a cold floor means you’ll continue to be uncomfortable and lose energy almost every day. Take care of yourself by taking care of your home.
As always, if you’ve got a comment or question, please share it below. Thanks!