A roof is one of the most important parts of a commercial or industrial building. It provides protection from the elements for building occupants and content. It can provide additional space for equipment storage and recreation. 

Flat roof insulation is just as important. It enhances the energy efficiency of the building and helps manage expenses. Poor insulation and/or an aging roof can quickly impact your bottom line.  

What does it typically cost to insulate a commercial or industrial flat roof?

Insulation Options

If you are building a new building or removing an existing roof down to the deck, you must comply with current building codes. If you are recovering an existing roof, you are not required to add insulation so you can opt for less insulation than the code requires.

Let’s examine insulating according to the building code first.

Insulating According to Building Code

Currently (in 2023) the building code in the Northeast requires R30 in the roof system. R30 is a measure of how well your insulation is preventing heat transfer. The higher the R value, the better your insulation is working and the lower your energy costs are going to be.

Next year, insulation requirements are being raised to R38. You will have to call your local building department to see if your area is affected.

The most common way to insulate a flat roof is with closed-cell polyisocyanurate foam core boards or “polyiso” for short. The boards are sold in 4×8 foot or 4×4 foot configuration of varying thicknesses (between 1” to 4” most commonly). They also sell tapered panels for building crickets.

To achieve R30 in a roof system you need two layers of polyiso at 2.6 inches per layer, or 5.2 inches overall. To achieve R38 in a roof system you need two layers of polyiso at 3.3 inches per layer, or 6.6 inches overall.

Pricing for polyiso is very volatile, like gasoline, but currently R30 in a flat roof is around $3 per square foot. The price could be higher if your roof lacks parapet walls as the roofer will need to build up the perimeter to accommodate the taller insulation. They will also need larger edge metal.

The price for R38 is approximately $1.25 more than R30. These numbers are approximate and individual job characteristics can change the cost, not to mention changing materials pricing.

Unregulated Insulation  

Note, if your roof has parapet walls, mounting a wood nailer around the perimeter is unnecessary. The price for 1.5 inch polyiso is around $1.25 per square foot, but again, these numbers can fluctuate greatly.

Insulating your commercial flat roof is a wise choice if you want to better manage your energy costs. Knowing the local building codes and what insulation to buy makes it even more cost-effective.