How Many Layers Should A Flat Roof Have?

Riddles are wonderful when you’re five years old. By adulthood, they get a wee bit annoying. But this is no riddle: how many layers should a flat roof have? This seemingly simple question has two answers. 

Building Codes

How many layers should a flat roof have? If we think of a “layer” as a complete, installed roof system, we have to turn to the the International Building Code (IBC). 

You can put down an industrial or commercial roof, let it weather and wear for 15 or 20 years, and then put a whole new roof on top of it, all in accordance with the IBC

Need Chapter and verse? Here it is, from IBC Chapter 15

1511.3.1 Roof recover.

The installation of a new roof covering over an existing roof covering shall be permitted where any of the following conditions occur:

  1. Where the new roof covering is installed in accordance with the roof covering manufacturer’s approved instructions.
  2. Complete and separate roofing systems, such as standing-seam metal roof panel systems, that are designed to transmit the roof loads directly to the building’s structural system and that do not rely on existing roofs and roof coverings for support, shall not require the removal of existing roof coverings…

The Code also outlines what is not permitted: 

1511.3.1.1 Exceptions.

A roof recover shall not be permitted where any of the following conditions occur:

  1. Where the existing roof or roof covering is water soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.
  2. Where the existing roof covering is slate, clay, cement, or asbestos-cement tile.
  3. Where the existing roof has two or more applications of any type of roof covering.

Your commercial or industrial roof can have only two layers; an older roof beneath a newer recover. If you need a better roof, all of the old layers must be peeled away and a completely new roof installed.

Any attempt to work around or against the building codes is almost always counterproductive, since the aging roofs beneath a new roof will continue to weaken. Your new roof needs a firm foundation. Never install a new roof over two aging roofs.

Your investment in a new roof should be protected by ensuring thorough preparation of the roof structure, removal of old roofing as needed, and proper installation of the new materials. 

Layers, Layers

How many layers should a flat roof have? If we think of one roof covering as a complete roof system, what goes into that system? We can build up an accurate cross-section of a commercial or industrial flat roof by starting at the bottom, with the roof structural members, and working our way to the top:

  • Final covering (ballast, single-ply membrane, roof coating)
  • Roofing material (this can be built-up roofing or BUR, modified bitumen, EPDM, metal panels, and so on)
  • Cover board
  • Insulation
  • Vapor barrier
  • Deck (steel plates, wood, concrete)
  • Structural members (wood framing or steel girders)

Every roofing system and installation presents unique challenges. Your roof may vary slightly from this typical arrangement of layers. For most building owners, the complexity and number of layers of their roofing system is surprising.

Adding to the layers are features like HVAC curbs and cooling units, rubber boots for sanitary stacks, vents, electrical wiring, and add-ons such as commercial signs and communications towers. You also have to consider placement of internal drains, clear access to parapet scuppers, and gutter systems.

A commercial or industrial roof, whether low-slope or truly flat, is a far more elaborate and multilayered system than most people think. And every layer needs inspection, maintenance, and prompt repair. 

Ideal

In an ideal world, you work closely with your local commercial roofer to keep your building’s low-slope roof maintained, clean, and long-lasting. Twice-yearly inspections of all the roof’s layers and parts can stave off the expense of reroofing or new roof installation for many years.

When the time comes for that completely new roof, you know the Code requires removal of any two-layer roofs already in place. You can plan and budget for the new roof because you and your roofer know exactly what your roof’s anatomy is.

You can come close to attaining the ideal commercial or industrial flat roof by enlisting your commercial roofer for all the tricks in his toolbox:

It all starts with your telephone call to your helpful, nearby commercial roofer. Please contact us today at Damschroder Roofing Inc. From our Fremont, Ohio headquarters we provide commercial and industrial roofing that lasts. We pride ourselves on treating you, your building, and your roof with the highest levels of respect and attention. Your roof. Our reputation.

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