Expanded Polystyrene (EPS) Rigid Insulation
EPS Rigid Insulation is a product that is can be used in roof recover jobs, or jobs where a new roof is being installed over an existing roof. It has an R-Value of 4.0 per inch and is installed in thicknesses from ½” up to any size you want. EPS is typically a little bit more expensive than Fiberboard insulation, but less than Polyisocyanurate Insulation.
EPS rigid insulation is very similar to styrofoam used in product packaging or food and beverage coolers. It absorbs less water than fiberboard, but a lot more than polyisocyanurate insulation. EPS insulation is also a fairly weak product that shrinks and breaks apart over time, similar to the way Styrofoam breaks up when it is stepped on or crushed.
The biggest drawback to EPS insulation is that it is very flammable and will spread fire. Over a steel deck, if the steel gets hot enough, the EPS can actually melt and drop down through holes in the deck or end laps in the steel. This is why many times, even if there is only 1 roof in place, a full rip is recommended. For some FM insured buildings, a full tear off of all existing roofs may even be required if EPS exists.
Benefits of EPS Insulation
- Lower cost than polyisocyanurate insulation.
- Highly customizable, can get in any size or thickness.
Drawbacks of EPS Insulation
- Extremely flammable material.
- Absorbs more water than polyisocyanurate insulation.
- Weak product that breaks apart or crushes over time.
- Almost always requires another layer of polyisocyanurate insulation over it.
EPS rigid insulation is not typically recommended as the primary insulation for a building. Where it can be useful is in flute fill applications over a pre-engineered metal building, as means to create a flat surface for polyisocyanurate insulation. Under this kind of application, you get the benefits of EPS’s customization with the benefits of polyisocyanurate’s strength and high r-value per inch.