Crawl Space Insulation- The Details

Posted by on Feb 17, 2012 in Crawl Space Insulation | 2 comments

Crawl Space Insulation- The Details

The Details No One Will Tell You and Most Do Not Know!

When it comes to crawl space insulation there is very little useful information written that will guide someone towards the results they seek. Agree? Well then, this article is for you. I will list nearly every way there is to install insulation in a crawl space and what you get for it. I will even discuss the wrong ways so that you will know why it will not work.

Let’s get started…..

Floor Joist Insulation-

I want to discuss what’s wrong with insulating the floor joists (crawl space ceiling) first. Most homes in the U.S. have the floor joists insulated with a fiberglass insulation. This method was thought to be correct since the beginning of time, and still does to a lot of people. The biggest factor that brought homeowners to believing this was the correct way was the building code. The building code left little choice in the matter of insulating a crawl space since the 40’s. The code required R-19 fiberglass insulation installed in the floor joists with the kraft paper facing the conditioned side of the space. The conditioned space is your heated and cooled home, which means 80% of the floor joist insulation is installed wrong. It was most likely installed correctly at the time the home was built, but then replaced due to getting wet and/or falling out of the joist cavity. Installed correctly means to the code at the time it was installed not the way it should be. To clear the air, it really does not matter which way the kraft paper faces on the fiberglass insulation when it comes to performing better in a crawl space. The fiberglass insulation in an open crawl space had its days numbered right from day one.

The number one complaint about crawl spaces in the winter is cold floors. So, crawl space insulation is the number one topic in the colder months. And there are many websites out there that tell you to do what we have always done. One of the big problems with our building industry is there is no requirements to get continued education in order to stay working in this field. This causes a “always do what we have always done” construction blunder. Which then slows, if not entirely halts, implementing new construction technologies that were researched to improve our safety and health. Even the fiberglass insulation companies (in my opinion) won’t set the record straight because they sell so much fiberglass insulation to people installing it wrong. In short, you will search the internet for answers and end up more confused than you were before you started, so be prepared.

Fiberglass, Floor Joists and Poor Performance…..

In order for fiberglass to work properly it needs to be in a clean, dry space and an open crawl space is not that place. Fiberglass insulation works as an insulator because it traps air in the fibers of the insulation and slows the collision of warm and cold air. If the fiberglass insulation gets wet or very damp it will begin to collapse, get heavy and fall from the floor joists rendering it useless to trap air and be an insulator. For this type of insulation to work properly it has to remain “fluffy”, dry and clean.

Picture this, warm air is on one side of the insulation and cold air on the other, they are not allowed to come into direct contact with each other which would cause the cold air to absorb the warm air. As you get closer to the center of the fiberglass insulation it is more of a mixture of both warm and cold, in theory anyway. How well this insulation works depends on how much colder the cold is compared to how warm the warm is. For example, if the temperature outside is 20° F and the home is 70°F a higher R value will be needed to slow the cold air from absorbing the warm conditioned air in the home. If the outside temperature were 40°, the R value requirements would be far less due to the lessened amount of cold air. That is the first part of the equation.

The next part has to do more with the forces of nature than anything else. We all know heat rises and cold falls, and this is a very important part of the solution to cold floors in a home. When the heater, furnace or heat pump comes on to heat the home the heat immediately rises to the ceiling. The rising warm air is replaced on the floor by falling cold air. So, since the heat rises away from the floors and the cold falls toward the floors your feet will always be in the coldest part of the room. Insulation in the floor joists will not change this.

However,  without insulation in the floor joists, your floors will be colder than with insulation. Here’s why; We know cold absorbs heat and lack of heat is cold. The next failure by design is the foundation vents. These allow the cold winter air to penetrate the homes envelope (your crawl space) which in turn absorbs the heat from your home via your floors. The cold temperatures from outside cool the homes structure, water lines (threatening frozen pipes) and subfloor. Like putting these items in a freezer (or outdoors) they will change temperature throughout and radiate the cold from all sides (your home being one of those sides). The structure and subfloor system will then begin to remove the heat from your home, remember cold absorbs heat. When you touch these floors with your bare feet- Oie! As you can see the insulation will slow this problem, but not stop it. Add to it the fact that the heat is rising away from the floors and you have some really cold floors. This of course affects your heating costs.

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