Blown cavity Wall insulation

Does your home have low or no levels of insulation in its cavity walls? If so, consider injecting insulation into its cavities. Blown cavity wall insulation is excellent to get an energy efficient home and to lower its energy bills.

See: Types of Cavity Walls Insulation - Basics

Blown cavity Wall insulation

Cavity wall insulation (in existing homes) is typically done by blowing loose-fill insulation materials in them, which demands special equipment.

To blow the insulation through and into the cavities contractors use a fill-tube system. Without it, it's difficult to pack the insulation material throughout the entire length of the cavities without empty spaces (see: Wall Cavity Insulation Problems).

Insulation Materials in Wall cavity

Loose-fill insulation is the commonest type of wall cavity insulation in home retrofits, and also the cheapest option. Just take into account problems like settling and fluffing, and how to avoid them.

Pay also attention to specific problems like those of loose-fill cellulose insulation: moisture problems, fluffing, settling and the need of insect treatments and fire-retardants.

See: Problems with wall cavity insulationIn new construction there are several alternatives to blown cavity wall insulation with common loose-fill materials. One of them is spray foams. This solution may add some structural strength to the walls and allows a particularly high insulation value (R-Value). The disadvantage, in this case, is an higher price. Another alternative is fiber insulation. Batt insulation is another alternative.

Quality installation

Blown cavity wall insulation is a typical professional job, demanding adequate equipment (and often a truck, to inject the loose fill insulation into the wall throughout the fill-tube).

Unless you are a very skilled do-it-yourselfer, hire a professional to do the job. Without a proper insulation that avoids gaps and voids, and fluffing and unplanned settling, you are risking the success of the insulation.

Drilling holes

In some cases it’s possible to access the wall cavities through the home's open bottom, top plates, ceiling access openings or other areas.

But if there isn’t such accesses, it will be necessary to drill holes to blow the insulation.

One and Two-Hole methods in Retrofit wall cavity insulation

One and Two-Hole Methods of Blown Wall Cavity InsulationThere are two main blown cavity wall insulation methods in retrofit insulation: the "two-hole method" and the “one-hole method”. Both involve drilling a series of holes in the exterior (or interior) walls of the building… See picture at right, from EnergySavers.gov.

The one-hole cavity method involves, first of all, choosing the most effective location for drilling the holes, in order to access the cavity.

If a single series of horizontal holes isn't enough to blow insulation into the entire length of the cavities, a second series of holes can be the solution.

The two-hole cavity insulation method involves drilling two series of holes (about 2-3 inches/5-8 cm diameter) as pictured in the figure on right. These series of holes (one near the top of the wall, the other about 25 inches/60 cm from the bottom of the wall) should allow the insulation to be blown into the entire cavity.

In both methods, using a fill-tube system to access the interior of the wall cavity is much better than using a short nozzle. Only a sufficiently long fill-tube can blow the insulation material in the most convenient way, avoiding gaps and voids and allowing adequate density, preventing fluffing and unplanned settling…

Cost

Prices of blown cavity insulation in an existing home varies a lot. Prices between $.50 and $1.50 per square foot are common.

See, for details: Cavity Insulation Costs and Prices

Choosing a contractor

Since blown cavity wall insulation is a typical professional job, requiring adequate equipment, selecting a good contractor is important. Prices are important, but the contractor's know-how and its performance are much more decisive in the long run.

Get written cost estimates from several contractors, and do not forget to set the exact amount of insulation you need and want (its R-value). Prices often differ a lot ($.50 to $1.50 per square foot…), and should include air-sealing holes and other related repairs.

Costs will be lower if the insulation is installed during other wall improvements, namely the re-siding or the painting of the walls.

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