Insulating Walls

There is more than one reason to insulate the walls of a structure. The primary reason is to help retain cool in the summer and heat in the winter.

Insulation also helps with soundproofing a room; to reduce or eliminate annoying sound from being transmitted from one room to the next. The insulating factor of any given type of insulation is measured by the R-value; the thicker the insulation material, the higher the R-value. Fiberglass batt insulation for 2X4 walls come in R-11, R-13, and R-15 values.

There are numerous ways to insulate a wall for either purpose – to retain temperature or for soundproofing. The most common types of thermal insulation include fiberglass batt insulation, polystyrene foam insulation board, blow-in cellulose, and spray-on foam. Note: installing fiberglass batt insulation or foam insulation board are the two most DIY-friendly types of insulation for a homeowner to install.

Blow-in cellulose continues to be an alternative for retro-fitting insulation; it is blown into existing wall spaces, usually by an insulation contractor. One drawback is that it settles over time, leaving wall spaces near the ceiling un-insulated.

Spray-on insulation might be a good choice for large buildings, and is applied using a spray-on process. It expands as it is applied to unfinished walls between the framing studs, and sets rigid.

Polystyrene foam insulation board may be the only workable choice for shallow wall cavities that have been furred out with 1X2s or 2X2s, such as in a basement with concrete walls. This material comes in thicknesses of ½-inch to 2-inches, with R-values of 3 to 10. It comes either pre-cut to fit standard stud spacing, or in 4X8-foot sheets that are scored to break at standard widths.

Drawbacks include the fact that most stud spacing varies, so using the pre-cut or pre scored pieces will not always fit properly. This can reduce the R-factor by resulting air leakage. In addition, panels must be glued into place with foam-compatible adhesive, such as PL Premium or PL 300. Other adhesives can dissolve the foam.

However, there are advantages to this type insulation. Which include easy cutting, no fiberglass particles in the air, and it stays in place when glued.

Fiberglass batt insulation is by far the most widely used. Since it is installed between the framing studs, it must be installed before walls are finished off. Handling fiberglass insulation causes small particles to become airborne, getting on you and your clothing. Therefore, a face mask, eye protection, and gloves are a must. Fiberglass particles are hazardous to breathe, and cause irritation when they get under clothing.

In addition to the assorted thicknesses and R-factors, fiberglass batts come either faced or un-faced. Faced fiberglass insulation has a paper lining on one side with just enough extra width than the fiberglass to allow it to be stapled to the framing studs on either side. This ensures a snug fiberglass fit between the studs underneath. The paper face is porous and does not make a vapor barrier. Since framing studs are hidden by the paper, however, hanging drywall is made more difficult.

Un-faced batts are simply pressed firmly into place between each stud.

Fiberglass Batt Installation

Fiberglass batts come in a standard 96-inch length, and fit perfectly into standard 8-foot walls. Taller or shorter walls require that batts be trimmed and pieced together. Cut to fit; sandwich pieces in between two 2X4s and then compress them into place.

Either style batt will require trimming to allow for outlets or other elements in the wall. Be sure to trim in such a manner that the insulation will fit snugly around fixtures. In places where wires or pipes run through the framing, simply split the thickness of the batt so that ½ of the thickness rests on each side of the wire or pipe.

Stuff small pieces of insulation into nooks and crannies; such as around door or window jambs. Be sure not to over-stuff. Doing this could force the door jamb or window out of plumb.

Installing a Vapor Barrier

Installing 4-mil clear plastic over the insulation will create a vapor barrier. This prevents warm moist inside air from penetrating the wall, and forming condensation between the insulation and outside wall. Condensation such as this can promote a mold or mildew problem within the wall. This type plastic is readily available at building supply centers. It comes in various widths, and up to 100-foot lengths.

Once insulation is installed, simply roll out the plastic and staple it to the top plate around the perimeter of the room. A swing stapler, (also called a hammer tacker) works best. Working from the top down, smooth the sheet into place and staple it to the studs. Cut out door and window locations, and then tack around them as well. Finally, cut an X over outlets and other fixtures. This helps to simplify wallboard installation.

Helpful Insulation Tips for Whirlpool Baths
When insulating whirlpools, staple insulation batts to the vertical frame supports inside the base/foundation. Affix the insulation so that the paper side is facing inward. This will help keep fibers out of the motor. Note: do not insulate within 6-inches of the pump, heater, or lights.


(Click here to view the Soundproofing page.)

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