Spray Foam Insulation in Chattanooga, TN

What spray foam does that batts and blown insulation cannot

Fiberglass and cellulose slow the movement of heat through a cavity, but they do nothing to stop air moving through it. In a Chattanooga summer, the air leaking into your attic and crawl space carries water with it: NOAA's long-term records put the city's morning relative humidity near 90 percent in August and September. That air condenses on cool surfaces, wets the insulation and feeds mold. Spray foam expands into every gap it touches and cures into a continuous layer, so the assembly is insulated and air-sealed in the same pass.

There are two families of product. Open-cell foam is soft, expands roughly a hundredfold, and delivers about R-3.5 to R-3.8 per inch. It is the economical choice for filling deep cavities like a roof deck or an interior wall. Closed-cell foam is dense and rigid, delivers about R-6 to R-7 per inch, adds racking strength to the framing it bonds to, and at roughly two inches of thickness qualifies as a Class II vapor retarder. It is the product for crawl spaces, rim joists, basement walls and anywhere moisture is part of the problem.

Which one goes where is the most important decision on the job, and it is the first thing we settle on the assessment visit.

Where spray foam earns its keep in a Chattanooga house

Roof decks and attics. Spraying the underside of the roof deck moves the thermal boundary to the roofline and brings the attic inside the conditioned envelope. That protects ductwork and HVAC equipment that builders here routinely put in the attic, and it ends the cycle of a 130-degree attic radiating heat down into the bedrooms every afternoon from June to September.

Crawl spaces. Most homes in Hamilton County were built over a crawl space, and most of those were vented to the outside on the old theory that outside air would dry them out. In a humid climate it does the opposite. Closed-cell foam on the foundation walls and rim joist, paired with a sealed ground vapor barrier, is the modern approach that the residential energy code specifically allows in place of floor insulation, as long as the crawl space is no longer vented.

Rim joists and band boards. The strip of framing where the floor system meets the foundation is one of the leakiest parts of any house and one of the hardest to seal with anything else. Two inches of closed-cell foam handles it.

Walls under renovation, cantilevers, bonus rooms over garages, and knee walls. Anywhere the framing is open and the space has been chronically hot, cold or damp, foam is usually the right answer.

How the installation goes

After the assessment, you get a written scope naming the product, the surfaces, the target thickness and any prep or removal work. On install day the crew masks off the area, sets up ventilation, and removes old material if that is in the scope. Closed-cell goes on in lifts of about two inches or less, with time between passes so the foam cures without overheating. Open-cell goes on in fuller passes to fill the cavity. Depth is checked with a probe, and any thin spots are hit again before the crew packs up.

Once the foam has cured, exposed foam in an attic or crawl space that can be entered has to be protected. The International Residential Code, which Tennessee adopts in its 2018 edition with state amendments, requires a thermal barrier such as half-inch gypsum where foam is exposed to living space and an ignition barrier or a foam product tested for the application in attics and crawl spaces used only for service access. Your scope will spell out how that is handled for your house.

We follow the manufacturer's guidance on ventilation and re-entry for the specific product used, and we give you that guidance in writing rather than a rule of thumb.

What we will and will not spray

Spray foam is permanent, so we are careful about where it goes. We do not spray over wet framing, active leaks, standing water in a crawl space, or knob-and-tube wiring. We do not spray the underside of a roof deck that shows signs of an active leak, because foam will hide the leak until the sheathing rots. And we do not recommend open-cell foam against a below-grade foundation wall, because it will absorb moisture from the masonry.

If your house has one of those conditions, the honest answer is to fix it first, and we will say so on the assessment rather than write a scope that sets you up for a problem later.