Batt insulation consists of rolls or sheets of (inorganic) fibrous mineral wool or fiberglass and is meant to control the transfer of thermal energy through the exterior of a building. Batt insulation is commonly placed between rafters, joists, studs, etc and in addition to it’s insulating qualities also works fairly well as a sound insulator. The most common places batt insulation is utilized is ceilings, roofs, exterior walls, and walls/floors next to unheated spaces. Batt insulation is also sometimes used in interior walls to isolate individual rooms thermal energy.
Batt insulation can come equipped with a facing which acts as a vapor retarder and can be made of kraft paper or foil.
Paper-facing acts as a vapor retarder. FOil-faced insulation is most commonly utilized in areas where it’s left exposed or could be easily exposed to fire or flame spread. Also Foil-faced has high emmissivity (or reflectivity) making it resistant to radiant heat transfer.
Faced batt is not an air/vapor barrier. If a vapor barrier is required within the wall system sheet plastic taped at seams is a minimum design and will provide far superior impermeability.
The typical rule-of-thumb for faced insulation and resisting moisture/condensation is:
–colder climates with interior heating predominant condition (moisture will want to condense on exterior sheathing) –> facing paper towards inside of the house.
-warmer climates with interior cooling predominant (moisture will want to condense on interior drywall) –> facing towards the outside of the house.
Batt insulation can be prone to rotting when exposed to moisture excessively over a long period of time and is somewhat combustible particularly the paper/kraft faced product.
There are common R-Value minimum’s for which Batt (and other types) of insulation should achieve which are also influenced by the temperate zones. The common minmums are:
-R-19 for ceiling (R-26 southern zone, R-30 temperate zone, R-38 northern zone)
-R-11 for exterior wall (R-13 southern zone, R-19 temperate zone, R-19 northern zone)
-R-11 for floor over unheated space (R-1 southern zone, R-19 temperate zone, R-22 northern zone).
Typical Batt insulation thicknesses are the following: 3-1/2″ (R11, R13, or R15), 5-1/2″ (R21), 6-1/4″ (R19), 6-3/4″ (R22), 8″ (R25), 8-1/4″ (R30), 9-1/2″ (R30), 10-1/4″ (R38), 12″ (R38), 14″ (R49).
Batt insulation commonly comes in compressed rolls concealed in plastic.
Roll widths for wood frame construction are typically 15″ or 23″ with lengths of 48″ or 93″.
Roll widths for Metal Frame construction are typically 16″ or 24″ with lengths of 48″ or 93″.
Roll widths for floor/ceiling are typically 15″, 15-1/2″, 23″, 16″, 19-1/4″, 23-1/4″, 23-3/4″, and 24″ with lengths of 48″.
Insulation can be either friction-fit or stapled into place and roll trimming can be done with a standard utility knife.
Batts should be cut +/- 1/2″ long to fit snugly. An efficient way to cut batt is by laying a straight edge against it and scoring it enough to cleanly cut a section off.
FIberglass or mineral wool batt insulation can be a skin and eye irritant so ample personal protection equipment should be utilized during handling and installation. A putty knife can be used in small areas between studs, around windows, doors, etc. If electrical wires, low voltage wires, or small conduit are in the way, split the batt into two and wrap around, leaving no uninsulated space. Cut holes in areas to fit around electrical boxes.
Batt insulation should not be compressed as this can actually reduce the R-Value. Batt insulation can be ‘friction-placed’, stapled to the side of the framing member, or stapled to the face of the framing member via fold out flanged edges.
For floor insulation where the insulation is unfaced and to be exposed, insulation support wires or ‘tiger teeth’ are used every 2′ to support the batts.