Ceiling/Roof Insulation

Oftentimes in commercial facilities, the largest exposed area is the roof. Therefore, it is very important that this area be insulated to the recommended levels. A ceiling or roof with too little insulation could be wasting your energy dollars in both winter and summer.

Insulation levels are referred to by R-value. The R-value of a given insulation is an indication of how well it resists the transfer of heat. The higher the R-value, the better it is at slowing heat loss or gain. Listed below are the three most common ways to achieve the recommended insulation levels:

  1. Install moisture-resistant sprayed-on polystyrene insulation on top of the existing roof.

  2. Install rigid insulation between the roof decking and the upper membrane.

  3. Insulate above a dropped ceiling or in an attic with loose-fill fiberglass or cellulose, or fiberglass batt insulation.

Applicability

Sprayed-on polystyrene or rigid insulation is usually installed as part of a re-roofing project. The installation costs can be considerable and, unless the roof must be replaced anyway, the costs usually are not justified. Both types of insulation should be installed by a qualified roofing contractor. Additional load on the roof deck should also be evaluated, especially on metal deck roofs. As with all roofing work, be sure to get a written warranty from the contractor.

Loose-fill fiberglass and cellulose or fiberglass batt insulation is inexpensive and usually pays for itself in two to eight years, depending on the situation. To further reduce the cost, you may be able to do the installation yourself. Remember, wet insulation loses its insulating value, so any roof leaks should be repaired before installing the insulation. The area above a dropped ceiling should not be insulated if it is used as a return air plenum.

How Much Is Enough?

Buildings in colder climates require higher insulation levels. Recommended R-values for ceilings typically range from 19 to 38. Your local utility representative can help determine what level of insulation you need.

The first step in determining the need for more insulation is to measure the existing insulation. Keep in mind that adding more insulation has diminishing returns. For example, the first R-11 of ceiling insulation pays for itself very quickly, whereas the next R-11 added will have a longer payback.

The table below shows the R-values associated with different types and thicknesses of insulation.

R-Values
19
22
30
38
Loose Fill        
Fiberglass
6.5"
7.5"
10.0"
13.0"
Cellulose
5.5"
6.0"
8.5"
10.5"
Vermiculite
9.0"
10.5"
14.5"
18.0"
Batts/Blankets        
Fiberglass
6.0"
7.0"
9.5"
12.0"
Rock Wool
6.0"
6.5"
9.0"
11.5"
Rigid Board        
Polystyrene (extruded)
4.0"
4.5"
6.0"
7.5"
Urethane
3.0"
3.5"
5.0"
6.0"
Fiberglass
5.0"
5.5"
7.5"
9.5"