Blown Fiberglass Attic Insulation in Oklahoma City

The Problem It Solves

Oklahoma is one of the windiest states, with steady south winds through the summer and hard north winds behind winter fronts. That wind presses on the soffits and drives air into the attic at the eaves, right where the roof slope pinches the insulation down to its thinnest. In many metro attics the loose fill over the outside walls has been scoured back over the years, leaving the top plates and the first foot of ceiling nearly bare. That strip runs over the exterior walls and the corners of every room, which is why ceilings near the walls often feel warm in July and cold in January.

Some attics should not take a heavy new layer. Ceilings in older ranch homes are often thin drywall on wide framing, and some already show nail pops, sagging between joists or cracks along the taped seams. Piling a dense fiber on a ceiling like that asks it to carry more than it was hung for. Other attics carry a history instead: a roof leak that soaked the old fill, or a damp spell under the deck after a storm. Owners in those houses want a fill that does not hold water and will not pack down over the next decade.

Then there is the attic that simply needs more. Plenty of homes built from the 1970s through the 1990s have an even but modest layer, well short of R-49, that nobody has touched since the house was finished. Nothing is wrong with it except the depth. The owner wants a clean top-up that brings the ceiling to the benchmark without disturbing what is there, that adds little weight, and that will still read the same on the depth rulers years from now when the house is sold.

How It Works

Blown fiberglass is spun glass fiber, chopped into tufts and blown loose. It commonly runs about R-2.2 to R-2.9 per inch depending on the product, less per inch than cellulose, so the layer is deeper for the same R-value: often about 18 to 22 inches for R-49. In exchange it is light on the ceiling, settles minimally, does not absorb water and does not feed mold itself. Over an existing even layer it goes on clean, and the depth you see on the ruler the day we leave is close to what you will see years later.

The trade-off is air movement. Loose fiberglass is fluffier than cellulose and more prone to wind-washing, where air entering at the soffits drifts through the fill and strips its R-value at the eaves. So on every blown fiberglass job we treat the eaves as the critical zone: rafter vents in the soffit bays, a wind dam at the top plate so incoming air is steered over the fill instead of through it, and enough height over the plate to get real depth there. In a windy state, that edge detail decides whether the job performs.

What Decides the Specification

Product choice drives the depth. Loose-fill fiberglass products vary in R per inch, so R-49 might need closer to 18 inches with one product and over 20 with another. The coverage chart decides, and both the minimum thickness and the minimum bag count on that chart have to be met, because thickness alone can be faked by blowing light. The existing layer counts too. Old batts or loose fill stay in place, and we credit them conservatively after measuring rather than taking the original label at face value.

The roof decides whether fiberglass fits. A steep roof over a large open attic has room for 20-plus inches, but a low-slope ranch roof can leave too little height at the eaves for a baffle plus a deep layer of fluffy fill. There, cellulose’s higher R per inch may get more insulation over the exterior walls. Ceiling condition pushes the other way: sagging or lightly framed ceilings favor fiberglass because it adds far less weight per square foot, and attics with a past moisture problem favor a fiber that will not hold water.

Around Oklahoma City

Moore has one of the metro’s largest stocks of ranch homes, much of it built from the 1960s through the 1980s, alongside the many homes rebuilt in the years after the 2013 tornado. The older ranches often have long, low attics with ducts across the joists and ceilings that have carried the same drywall for decades, which makes a light, non-settling fill a sensible choice. Out west, Yukon’s newer subdivisions toward Mustang Road and the Kilpatrick Turnpike sit open to prairie wind, and those attics show wind-washing at the eaves more than most, so the wind dam detail earns its keep there.