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Paul LaGrange

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Paul: When it comes to raised foundations, fiberglass just won't do

So you’ve confirmed that water is not pooling underneath your home and installed your 6 mil polyethylene ground cover below your raised house to reduce moisture.  You have a decision to make - what method are you going to use to insulate the underside of your floor? 

“Don’t you just cram some of that ‘pink stuff’ in between the floor joists,” You ask?

Well, that is not such a great idea. In fact, it’s not even a good idea.  There are several reasons why installing that “pink stuff” (or yellow or white) – fiberglass insulation is a risky product as a subfloor insulator, especially in a hot humid climate.  Let me share a few of those reasons with you before you proceed with the insulation process.

1.     In order for the fiberglass insulation to be somewhat effective, it needs to be installed directly in contact with the bottom of the subfloor and between the floor joists with no air space between the insulation, subfloor and floor joists. More specifically, no gaps, voids, or compression can exist between the insulation and wood framing/floor. This rarely occurs because the insulation is usually thinner than the floor joists and tends to sag onto whatever is holding the bottom of the insulation to the subfloor (i.e. netting, chicken wire, vinyl siding, etc.)  Installing the fiberglass insulation properly is also challenging because of the other obstacles within the floor assembly such as drain pipes, electrical wires, HVAC ductwork, etc.. The insulation R value (thermal performance – separating the indoor from the outdoor conditions) will not function very well if any of the installation flaws exist.

2.     The sagging between the wood flooring and the top of the insulation causes another performance problem, which is that the air spaces caused by sagging now give way to the passage of air and moisture though out the floor joist cavities. When air flows through fiberglass insulation, it significantly reduces the r-value (resistance to heat flow), rendering the insulation fairly useless.

3.     If “tiger teeth” are used to hold the insulation in place, each piece of insulation is compressed in the center. Also, improper installation can cause compression in uneven spaces, and around pipes, piers, and wires. Compression drastically reduces the r-value of insulation.

4.     Small animals also want a nice warm place to stay in the winter. The space between your fiberglass insulation and your subfloor makes a cozy living room for any creature small enough to crawl in between your floor joists.

5.     Wind and animals can cause irreparable damage to fiberglass insulation in a subfloor.  In many cases, after several years have passed, much of it has fallen out or been blown out in a storm.

6.     Finally, and most importantly, fiberglass insulation is NOT an air barrier, so even if it does happen to insulate the subfloor from heat and cold, it is still incapable of blocking the outside humid air from traveling through the insulation and into the home through the subfloor. Over time the moist air travels thru the insulation and air from the crawlspace meets the cool flooring because the a/c is operating. Presto! We have moisture.  Once this occurs the fiberglass insulation becomes moist and its performance is greatly affected.  This is where homeowners see problems with mold, buckling wood floors, (possibly termites) and high humidity in their homes, not to mention, higher utility bills caused by air infiltration.   

Using fiberglass insulation in a crawlspace is not only energy inefficient, it greatly affects the moisture levels inside your home. It could also be a very costly mistake to correct.

I know that many homeowners tend to make decisions upon what they have seen others do in the past. For years, fiberglass has been a staple for insulating subfloors, but do yourself a favor and consider using different insulating products more suited for insulating the underside of the floor assembly in our hot humid climate.  In order for the insulation to be effective, protect our homes from moisture, and keep the outdoor conditions outside it needs to have the following performance characteristics: Air barrier, Thermal barrier, and Vapor retarder.  All of these control layers must be installed on the underside of the floor assembly and must be continuous and uninterrupted. 

For more info on how to save energy and improve comfort levels in your home or office, visit LaGrange Consulting’s website at www.lagrangeconsulting.com  or call us at 985-845-2148.

08/09/2014 1:59AM
Paul: When it comes to raised foundations, fiberglass just won't do
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