Understanding Insulation Concepts: A Radiant Heated Crawlspace

Sometimes deciding the best way to insulate your project can be difficult. You must be somewhat like a detective and really examine your particular project, because each application is different. This post is a real life conversation we had with a customer over the winter and it shows how particular each application can be.

The customer called because they wanted to insulate their crawlspace. They had radiant heat installed under the floor. The tubing that supplies the radiant heat in the crawlspace was below the sub-floor. The customer wanted to install our Staple Tab Between Joist insulation in the floor joist from the crawlspace below. The intention was to first install our foil insulation and then later, at another time, install traditional fiberglass batt insulation over the foil. This is typically the ideal procedure using both FG and Foil insulation for an in-floor radiant heat application.

Now, here's where understanding your particular application is important, if not critical. As we were talking about the project, the customer asked which insulation would work best as a stand alone insulation, foil or fiberglass? Our response was asking if the crawlspace was air sealed or not?

From there, and this shows how every insulation application is different depending on local climate and conditions, we learned the house had a continual moisture problem in the crawlspace during the summer months. This had led to the installation of an intake and outtake fan to constantly remove the moisture buildup.

In the winter, the addition of the radiant heating system kept the crawlspace warm and dry.  However, because there was no insulation, the radiant heating system was not working as efficiently as it could. Much of the radiant heat generated was lost to the crawlspace below.

Our recommendation was to not install the fiberglass insulation and instead concentrate on air sealing the basement's perimeter. Besides, fiberglass does not perform well in moisture prone areas. The effectiveness of the insulation would be severely limited. We decided the best decision for this particular application would be to install the foil insulation as discussed and air seal the basement with caulks and foams, also ensuring the fans are properly sealed off for the winter months.

The customer then has a scenario where in the summer months, when moisture is a concern, fans will operate to keep the crawlspace ventilated. All of the insulation installed is designed and is acceptable for use in moisture prone areas. In the winter, the foil insulation reflects back the radiant heat lost in the floor joists back to the floor. This creates a thermal break from the basement and the living space above. By air sealing the basement the temperature stays warmer than it would in the winter without an air sealed basement. The basement wall themselves become the thermal break.

The deciding factor that changed the way this particular crawlspace should be insulated was the presence of moisture and that fans were installed. If moisture was not an issue, the customer's original intention to install both the FG and foil insulation in the floor joists would have been ideal. But this was not the case and its worth discussing how one extra dynamic completely changed the scope of the project.

We hope this post is helpful and helps show you to closely examine your home, and your local climate when you plan your next insulation project. Remember to think of what you want to achieve in both the heating and cooling season. By paying close attention to the forces at work you can install the correct materials resulting in the most efficient, healthy insulation system for your application.

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