Avoid Using Fiberglass Insulation In Basements
Basement insulation installed incorrectly is one of the most common Contractor errors I see on a regular. Often times the results are disastrous with severe mold and mildew problems, not to mention the loss of heating bill savings that mounts up over time.
For years contractors have been treating basements much like regular living space. It’s not uncommon to see fiberglass basement insulation in direct contact with foundation walls. Typically here in the Northeast I see several methods including:
- Plastic vapor barrier against concrete wall, fiberglass insulation inside stud wall, then drywall.
- Fiberglass insulation inside a “bag” hanging from the rim joist down along the foundation wall.
- Stud wall filled with fiberglass insulation an inch or two away from the concrete wall.
This may seem like an obvious problem but the fact that I see contractors still using fiberglass insulation in basements leads me to believe that the industry needs to do a better job educating our builders. In order to understand the issues with basement insulation it’s first important to understand the role of vapor barriers and vapor transmission in basements.
Basement Insulation Vapor Barriers
The trick with basement insulation jobs is in understanding where water vapor is being stored and where it’s moving to. Concrete is like a huge sponge which holds water and water vapor for years and years. As the wall dries the water vapor leaves the concrete and tries to penetrate the insulation and wall. This is where water vapor can get trapped in fiberglass and cause serious mold problems. For a more detailed discussion on vapor barriers check out this article.
Closed Cell Foam – Spray or Board Type
Over the years I’ve come to rely on two approaches for basement insulation projects and remodelling including closed cell spray foam and closed cell XPS foam board. When installed in the correct thicknesses these to methods result in a proper vapor barrier and a superior insulation.
Often times we end up insulating basement walls with a hybrid approach. First we install two inches of rigid foam board insulation (closed cell). Then we build a stud wall which holds the foam board in place but also provides room for wiring and HVAC. Depending on the level of insulation needed the stud cavity may be insulated with fiberglass or mineral wool. To learn more about this method please read this basement insulation article.
Get Educated – Be The Pro!
Let’s face it, we live in a time when the building industry and building science is changing rapidly. In order to stand out in the competition and provide a professional service to your clients you need to stay educated on the latest methods. There are several great publications on this topic including the ones above and ones found at Building Science.
Want More Insulation Tips?
- Insulating door and window headers
- All things about attic insulation (and more attic insulation tips)
- Installing insulation batts
- Crawlspace insulation and renovation project
- And just for fun – read about interesting finds in old walls