Moisture Control | Roof
Decks | Rigid Insulation | Roof
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Rigid Board Insulation
Rigid board roof insulation provides
both the insulation for a building as well as the substrate to which the
roof system membrane reinforcing sheets are attached. Rigid insulation
must be compatible with, and provide adequate support for the roof system
membrane in addition to the other associated roof assembly components.
The rigid insulation shall also accommodate limited roof traffic for such
tasks as roof system installations, inspections, and maintenance.
Acceptable Rigid Board Insulation shall
have the following Characteristics
1. Ability to withstand hot asphalt application temperatures when specified.
2. Ability to withstand ambient asphalt mineral spirits when specified.
3. Compatibility with the roof deck and the roof system membrane.
4. High compressive strength, rigidity, density, and impact resistance.
5. Combustibility classifications that comply with local building codes.
6. Materials that resist deterioration, and inhibit degradation of adjacent
7. Moisture resistance and dimensional stability under varying temperature
and humidity conditions.
8. A low K-value and the highest possible R-value with the thinnest dimensions.
9. A K-value that remains constant and doesnt drift higher with
age, causing R-value to drop.
10. A surface that accommodates secure attachment to the substrate.
11. Peel strength that provides sufficient adhesion for the roof system
to comply with wind uplift requirements.
12. Consistency of manufactured dimensions including square and true edges.
Types of Rigid Insulation Allowed for Fields Roof Systems
1. Cellular glass 5. Perlite
2. Composite board 6. Polyisocyanurate foam
3. Fiberglass 7. Wood fiberboard
4. Mineral fiber
Criteria to be Specified for Rigid Insulation
The designer shall first calculate the required R-value for the building,
1. Type of insulation 4. R-value per inch of thickness
2. Thickness of insulation 5. Density of insulation
3. C-value of insulation 6. K-value
Plastic foam insulations, such as polyisocyanurate shall have a cover
board installed over them so as to minimize potential moisture entrapment,
off-gassing, blistering, and so as to serve as a suitable substrate to
which to adhere the membrane reinforcing sheets. Acceptable rigid cover
boards for plastic foam insulations include wood fiberboard, perlite,
and fiberglass insulation.