So What Makes A Roof ?


I contend that this question is best answered based on your perspective.There is a classic case of not being able to see the forest for the trees.In this case it’s not being able to see the roof for its shingles(or whatever roof covering system you may have in place). It’s an outside/in view, but to better understand roof systems and what makes a roof you are going to learn to see it from an inside/out view.Usually the only time people take this approach is when the water that’s supposed to be outside is now inside in the form of a leaky roof. So armed with this new approach I want you to start with everything that you can’t see that is above you ceiling.

Items that make a roof can include and aren’t limited to:

  • vapour barriers

  • insulation

  • structural framing

  • skylight wells

  • ventilation and duct work

  • roof sheathing

Once  moving past these items we then begin to encounter the exterior components most of you may or may not be familiar with such as:

  • roof underlayments

  • roof coverings

  • flashings

  • vents

Roof systems are primarily of two types: Low slope and steep slope. All roofs are of these two types and/or a variation of these two types.These different roof types require proprietary systems to make them effective in keeping  the elements out of a structure. As an example of what makes a typical Built-Up low slope system see this image:You can see from the diagram that from the inside out you have a proprietary deck to support the system. Roof decks are usually wood, metal or concrete. Insulation is often installed onto the deck before the water proofing system is applied. A series of tar paper felt “plies” are layered,offset from one another and covered with water proofing asphalt on each layer. A final “flood” coat of asphalt provides a base in which ballasting and UV protecting gravel will be spread.This image shows not only the sections of the roof but also how the low slope roof drains at the scupper into the downspouts as well as how the roof terminates at the perimeter with metal “drip cap” flashing around the perimeter.


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