Rigid Insulation Overview

Most flat roofing systems require some kind of rigid insulation under the new roofing system. The biggest reason is that all flat roofing systems require a substrate between the structural decking and the new roof system. The second and more obvious reason is for higher R-values, which building owners are asking for, and building code throughout New England is requiring.

The most common types of flat roofing rigid insulation are below. For more information, click on the name of the insulation.

Polyisocyanurate

Polyisocyanurate Rigid Insulation “ISO”

R-Value per inch	6
Cost	Mid Range, but easily the best value.
Strength	Medium
Typical Use	Any (Roof Recover, Re-roof, etc)
Advantages	High R-Value per inch (6), Less than 1% water absorption rate, lightweight, holds up well over time, strong enough for most roof applications
Disadvantages	Higher price than EPS or Fiberboard
Can you taper it?	Yes

HD Coverboard

HD Coverboard

R-Value per inch	5
Cost	High
Strength	High
Typical Use	Any (Roof Recover, Re-roof, etc)
Advantages	Strong 100psi product that resists punctures and crunching, High R-Value per inch (5), less than 1% water absorption rate, lightweight, holds up well over time
Disadvantages	Expensive
Can you taper it?	Yes (add a layer on top of tapered polyisocyanurate)

Expanded Polystyrene Rigid Insulation “EPS”

R-Value per inch	4
Cost	Inexpensive
Strength	Poor
Typical Use	Roof Recover or Flute Fill on metal roofs
Advantages	Low Cost, Highly Customizable
Disadvantages	Highly flammable, absorbs more water than polyisocyanurate, breaks apart or crushes easily.
Can you taper it?	Yes

Fiberboard

Fiberboard Rigid Insulation

R-Value per inch	4
Cost	Inexpensive
Strength	Poor
Typical Use	Roof Recover
Advantages	Low Cost
Disadvantages	Soaks up water, breaks apart, can shrink, find its way into the building
Can you taper it?	No

Tapered

Tapered Rigid Insulation

Tapered Insulation Summary
R-Value per inch	Varies Based on Product.
Cost	Very High.
Strength	Varies Based on Product.
Typical Use	Eliminating water on a ponded roof.
Advantages	Significantly reduces ponding, typically has greater R-value, follows advantages of product used.
Disadvantages	Significantly higher materials cost, significantly higher labor cost, follows disadvantages of product used.
Products that can be tapered	Polyisocyanurate EPS

"I consider Chaffee Industrial Roofing an exceptional roofing contractor and we will continue to use them for any future roofing projects or repairs."

Cardi’s Furniture, Rhode Island and Massachusetts

"Your employees and equipment were always presentable and professional, which was most appreciated in our office environment."

Amica, Lincoln, RI

"The crew and staff are always professional, courteous, and considerate. And all work performed has come in on budget, and on time."

"Your staff did an exceptional job of mobilizing, installing and demobilizing within a rigid time schedule and with minimal disruption to the building occupants."

Gilbane Properties Inc., Providence, RI