Results of research on how best to insulate raised floor homes in hot, humid climates is now available on the LSU AgCenter’s website.

The research by the U. S. Department of Agriculture’s Forest Products Laboratory and the LSU AgCenter involved a 12-month monitoring program that looked at how different types of subfloor insulation methods react to Louisiana moisture conditions.

The study was conducted on 12 houses in New Orleans and Baton Rouge and was supported by the Forest Products Laboratory, APA–The Engineered Wood Association and the Southern Pine Council, according to LSU AgCenter housing specialist Claudette Reichel.

“We were looking at ways to insulate raised floors without causing moisture problems, especially in flood zones,” Reichel said.

The research was conducted in eight Musician’s Village Habitat for Humanity homes in New Orleans and four owner-occupied homes in Baton Rouge.

Since hurricanes Katrina and Rita, there has been an increase in the use of raised floors in Louisiana houses because of the potential for flooding as well as new building codes for energy efficiency that require insulation under floors, Reichel said.

“Before this study there had been a lack of research-based information dealing with moisture problems under insulated raised floors,” she said.

Reichel said the four types of insulation systems used in the project included low-density open cell spray foam, high-density closed cell spray foam, low-density spray foam with a spray vapor- retardant paint coating and foil-faced rigid foam that is taped and sealed. Each was compared with conventional fiberglass insulation.

“Most of the research around the country and the trend in raised-floor construction is to construct an unvented crawl space that is insulated and conditioned with indoor air, something like a mini basement,” she said. “One of the major problems with raised floors in Louisiana is the water table is so high and so many of the raised houses are in flood zones, that the sealed crawl space system being recommended in other areas is risky here.”

Local building codes require that raised floor foundations in flood-hazard areas allow floodwaters to move through the space underneath buildings. Homes in flood zones need alternatives to a sealed, conditioned crawl space.

The houses in New Orleans and Baton Rouge were outfitted with devices to monitor temperatures and moisture levels in the wood subfloor.

“The key to preventing growth of mold and decay fungi is proper moisture management. It also is essential for preventing corrosion of nails and screws that hold the structure together and avoiding expansion-contraction damage such as cupping or buckling of wood flooring,” Reichel said.

Increases in moisture content causes wood to expand, and the wood shrinks when it dries. The wood industry guideline for protecting wood and wood products from damage is to keep the moisture content below 16 percent, according to Reichel.

“The rates of wetting and drying of building assemblies, whether they are floors, walls or ceilings, can be affected by thermal insulation,” Reichel said. “The job of thermal insulation is to slow down heat flow – to help keep the inside of the house warm when it’s cold outside and cool when it’s hot outside.”

This research is valuable for the South because high humidity can cause decay in floors, according to LSU AgCenter wood scientist Qinglin Wu, who also worked on the project.

“The benefits from this study will not only benefit Louisiana. The entire region will see benefits,” Wu said.

The publication titled “Insulating Raised Floors in Hot, Humid Climates” can be found online here.

Johnny Morgan