Indoor Air Quality/crawl space insulation


I am confused and need advice. I need to insulate my crawl space which is the length of my house. Some sites state to insulate under my home floor and place plastic on crawl space floor. Other sites state that insulation is not needed under my home floor. They state to apply plastic to my crawl space floor and apply rigid foam board to my concrete walls to seal out all air. So, another question, I have fiberglass insulation under my home floor that is falling down.  Should I leave it up and reinforce it? Or tear it down? Is it okay to leave it up and apply foam boards also? And Can I staple plastic over the insulation so that it will not continue to fall down?  Some say a double barrier is a no-no, I don't want to rot out my floors. Thanks!

crawl space
crawl space  
Hello Mary,

First off, never place plastic sheeting over the cold side of fiberglass insulation.  You are correct in presuming that this will cause rotting.

For most crawl spaces, I greatly prefer to insulate the foundation (as opposed to the floor).  This method allows your wood floor framing to stay ventilated and dry, and allows you to easily look at it in case of moisture issues.

I have included a drawing of the correct way to do this.

Best of luck and please let me know if you have any additional questions.

Thank you,  Steve Major  

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Stephen Major (Principal--Lakeland Environmental)


I can answer questions on indoor mold, indoor air quality, asbestos, and indoor moisture problems. This includes mold testing and mold remediation. PLEASE indicate your state or region, so I can provide the best possible answer.


I have extensive experience in the investigation, testing, and remediation of indoor fungal (mold) infestations, including the design and oversight of remediation projects, hands-on cleaning and removal, and safe work practices. I developed a successful mold remediator training and certification program, and have trained many mold workers and remediation supervisors in proper techniques. I have a strong knowledge of the ways in which moisture and airlow patterns in buildings can affect fungal growth and air quality.

BS Cornell University. IAQA Certified Mold Remediator. 40-hour HAZWOPER certification. NYS Department of Health Certified Training Director.

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