Roofing 101 the basics
In this article, we will discuss the basic science of roofing, how it works, a brief look at the history of the development of the modern roof systems we have today.
Why do we need a roof?
For most people, the roof is out of sight and out of mind, about the only time anyone other than a roofer thinks about roofing is when theirs’s is leaking. Oh and by the way, if your roof is leaking that means it has failed, do not wait for a failure in any component of your business before taking care of it. (see “why roof maintenance is so essential” ). So why do we need a roof?
- To keep the water outside, outside.
- To keep the heat from the sun outside.
- To keep the cold air inside, inside
- To keep the building comfortable and safe.
- To help keep us healthy. To reduce noise.
- To protect our property.
- To reduce noise.
Try living outside for a week or two, and you will quickly appreciate a good a roof and all that it does for you. I might be a little biased, but I would suggest that of all the building components the roof is the most important perhaps secondary to the foundation. Without a good roof, the rest of the building, the stuff and the people in it are all exposed to various damage and health issues.
The two basic types if roofs
There are two basic types of roof construction, the steep sloped and the low sloped roof. Each one has its specific uses and challenged to cover come.
The first job of the roof system is to keep the water out which means it also needs to drain the water that gets on the roof off and away from the building. (see "Roof drains")
A steep sloped roof system, one with a pitch of 3/12 and more (see "Roof slopes"). These roofs are constructed by overlapping some material or another, starting from the bottom to the top creating a stair-step pattern. The water is pulled from the roof by gravity and if everything works the way it should it moves off the roof pretty fast. The systems designed for steep sloped roofs are known as "water-shedding" which is essential to know because the materials typically used will allow water to get in if the water sits their long enough.
The fancy word for this system, if you want to impress your friends is "Hydrokinetic." Hydro meaning water, and Kinetic meaning in motion or water in action.
The second type of roof system is a low sloped roof, on that is less than 3/12 (see "Roof slopes"). When the roof reaches such a low slope, that there is no slope at all that is called a "dead flat" roof. This system is very different in that it relies on a drainage system and have to be designed to carry the load longer. The systems designed for low sloped roof systems have to be "watertight." The materials used for this type of roof system are designed to keep the water out for much more extended periods.
The fancy word for this system, if you want to impress your friends is "Hydrostatic." Hydro meaning water and static meaning not in motion.
Each system comes with its own design and installation challenges. Knowing that going into the project will help you make good decisions.
Common systems we see around here.
Steep sloped; (each one links to the article about that roof system)
- Wood shake/shingle
- Asphalt Shingle
- Concrete Tile
- Clay Tile
Low sloped; (each one links to the article about that roof system)
- Asphalt built up
- Polyurethane and coating
- Single Ply
There are many more roof systems in the world, we are only touching on the types we see in this area more commonly.
A brief history of roofing
I suppose the first roofs may have been trees and caves? I mean I was not there, but I assumed that early humans looked for someplace to be warm, dry and safe. From there human beings started building tents, then thatch roofs, eventually using wood and other natural materials such as stone and clay, metal and pine tar on paper or cloth later becoming the modern asphalt built-up and granular roofing. Each one was seemingly better at doing the job than the previous one. Of course, the client has a lot to with the types of systems developed in different parts of the world.
Before the 1800s, we see a lot of wood, slate, and clay roof systems in use. The materials are durable and readily available but also heavy and sturdy to work with. (link each roof system mentioned to the article about that roof system)
In the early 1800s roofers starting using metal as a roofing material. Starting with Tinplate and zinc then galvanized in the 1860s and eventually Aluminum and Terneplace in the 1890s. Metal is lighter and more fire resistant than the previously used materials.
In the 1840s, we start seeing the first built-up roof systems (see "Built-up roof systems) using pine tar and paper or cloth, piling them up on each other and adding sand to the surface. Eventually, cole tar replaced pine tar and sand was replaced with fine gravel.
In the 1850s Coal, tar roofs started dominating the market. Coal tar, by the way, is the by-product of making steel and from extracting coal gas for the street lighting of those days. Roofers have always been pretty good at making the best of what was available.
The Great Chicago Fire of 1871 burned down over 17,000 buildings mostly constructed of wood. That tragedy and others like it forced the hand of society and started shaping our code and insurance industry of today.
In1886 and the modern wonder of the automobile, things started to change again in the roofing industry. Remember roofers have always been able to see the things around them and find a way to turn it into a roof.
Using asphalt to waterproof things was nothing new. As far back as Babylon people have been using asphalt to keep the water out or in. But when we started refining it to make gasoline, the roofing industry noticed that the by-products could be used instead of coal tar. Once again roofers saw a thing and found a way to improve on roofing materials with it.
In 1903 a man by the name of Henry Renolds started cutting rolls of built-up materials with crushed rock in the surface, into strips for use on steep roof systems.
By the 1930s to the 1950s coal tar was relegated to the history books and built up was all asphalt. By saturating felts and layering them in four or five layers. Applied directly to the decking and covered with slag or gravel. (see "ballast roof systems)
Jumping ahead to the 1970s, we start seeing glass felts coming into the market and replacing the old organic ones. I am old enough, to remember tearing off some of those first organic felts. Like the fires in Chicago and around the nation impacted and changed the way we did things, the Oil crisis in 1973 changed how we did roofing again.
Before the crisis gasoline was cheap and the by-products were pretty good for use in roofing. But when the price went up, the manufacturers needed to get more, and so the by-products become less pure and harder to work with. So, in comes the fiberglass mat that more water resistant and made up for what was lost in the newer refining processes. Manufacturers also started adding synthetic rubber and other polymers to improve the raw materials and make a better product.
By the 1980s organic felts where gone, all coal tar was gone, and all built up was asphalt. Eventually rolls of materials where being manufactured with crushed roof pressed into the surface area to replace the gravel on the rooftops.
Here come the shingle ply roof systems (see "single ply) such as EPDM (LINK), PVC (LINK) and TPO (LINK) These systems are easier to install and do not reply on asphalt making them more popular in the post-oil crisis world where the cost of asphalt materials jumped so high.
And that is it in a nutshell, there is much more that can be told. The history of roofing is a long and colorful history of innovation and reaction to the times. If a roofer looks at anything long enough, he or she will figure out how to make a roof out of it.
Roof Consultant and Roof Industry Advocate