Roofing – Under Shingles – What is under asphalt, metal, wood, rubber or clay shingles on a roof

Imagine, you are standing on the sidewalk, looking at an average house. You see the siding, the windows, the front door and, high above, you see the ceiling. Does the roof have asphalt shingles? Does the wood shake perhaps? Maybe it’s made of metal or rubber tiles? What you see is where the focus is going, but what really matters is what you don’t see. There is more to the ceilings than meets the eye. So let’s talk about what happens under the shingles.

Roof deck

We learn to crawl before we walk, so when we talk about roofs, let’s start with the starting point, the surface area of ​​your roof that is made of wood. Its wooden roof deck is comparable to the metal body of a car. It is installed on top of the basic frame of the house to provide a surface area in which to install the shingles. Without a roof deck installed in your home, there would be nowhere to install your shingles. And of course, without the shingles, the roof deck would rot from exposure to the sun, rain, snow and ice, etc. It is not a comfortable house at all!

In newer homes, plywood sheets or OSB boards are fastened over wooden beams in your attic to form the roof deck. Plywood or OSB boards are installed in a staggered formation with small gaps between them to allow the wood to expand and contract as the wood heats up in the summer and cools down in the winter. Older homes often have 2 “x 6” lengths installed instead of plywood or OSB board. When it comes time to replace your roofing system, remember to have your Calgary roofing contractor replace all damaged lumber.

Remember, if your roof deck rots or is damaged in any way, people walking on your roof could crack or break the wood, causing further damage to the roof system such as shingles … and the person who walked . we do it! However, most roof decks can withstand some exposure to water or ice before they need to be replaced.

Metal: drip edge and slanted edge

The drip edge and slope edge is the first part of the roof system that is installed. It is a long, narrow piece of metal that is installed along each end of the roof deck, that is, along the eaves channel and along the ends of the gable.

Some local area building codes require the installation of Drip Edge and Rake Edge and other building codes do not. Check with your local city building offices to find out. In Alberta, for example, the Building Code does not require the installation of a drip edge or sloped edge. Therefore, many new homes and / or low budget roof systems do not have a drip edge installed to allow for more affordable roof prices. However, we recommend that the drip edge and rake edge be installed on all roof systems, with no exceptions.

The drip and rake edge is available in a variety of different colors and sizes and can be custom built for the needs of your roof system. Installing a proper drip edge often saves hundreds and sometimes even thousands of dollars when your roof system needs to be replaced.

If your roof system doesn’t have a drip or slope edge installed, don’t panic, it will survive well enough. Just keep in mind that when your roof needs to be replaced, the roofing contractor may need to replace part of your wooden roof deck as needed.

Metal: chimneys and skylights

It is arguably the most important part of any complete roof system. Metal installed in valleys, chimneys and skylights carries most of the water flow on each roof. If installed improperly, a new ceiling system can make your living room have a waterfall.

All fireplaces and skylights need what is known as a “back tray”, which consists of a sheet of metal bent at an angle of approximately 90 degrees (depending on the slope of your roof) and is placed under the tiles and under intermittent siding, stucco, or countertop in fireplace or skylight. Each rear pan requires a small 2 “section of metal that protrudes 1” or more from either side of the fireplace or skylight to divert water from the corners. The water should hit the metal rear pan and be directed both ways, where it can continue to run into the eave channel.

Metal: Valleys

In the same way that water runs along the valleys between two mountains, the water runs along the valleys on the peaks of their roofs. Valleys generally receive the highest concentration of water flowing through them, so installing them correctly is extremely important.

As mentioned in the Leak Barrier section, valleys have leak barriers installed underneath. Although some building codes do not require the installation of a leak barrier, we recommend always installing one in each valley.

One word of caution: many roofing contractors install valleys in a so-called “gated” style. A closed valley consists of shingles woven into the valley, as opposed to an ‘open’ valley which has metal sheets running from top to bottom. Both the ‘open’ and ‘closed’ style of installation are acceptable by most building codes and by most manufacturers, however, the ‘open’ style installation has consistently outperformed the ‘closed’ style. .. and it costs exactly the same price to install. Ask your roofing contractor to use the ‘open’ installation style for your roof valleys, this could prevent you from having to replace your roof system prematurely and can also prevent long-term headaches. Typically, an ‘open’ valley is installed with a 4 ‘wide, 30 gauge sheet of metal, which comes in 10’ sheets. This metal can be ordered in any color to match your roof system shingles.

Barrier against leaks

Think of a leak barrier as a “second layer” of protection for your roof deck. A backup plan, so to speak, and also protection against moisture build-up. Leak barriers are almost always installed on top of the drip edge and sloped edge metal along the eaves, gable areas, and valleys due to the risk these areas pose for leaks , ice build-up, shingles deterioration, and backflow of water.

If you’ve ever looked at your roof during the winter, you will notice how ice and snow accumulate along the gutters of the eaves and into the valleys of the roof. As with the sloped edge and drip edge, some building codes require the installation of leak barriers and some building codes do not. In Alberta, the Building Code requires that a leak barrier be installed in all eaves and valleys areas of a roof system due to problems related to snow and ice accumulation. As an optional upgrade, some high-end roof systems even have leak barriers installed on top of the entire roof deck (as opposed to just along the special areas just mentioned) where one would normally have been installed. standard roof deck protection.

Virtually all roofs in Calgary, Alberta have leak barriers installed, and there are many different types of leak barriers available on the market today, each offering a different level of reliability, functionality, and warranty and are produced by many manufacturers. different.

Choosing a suitable leak barrier and installing it correctly is an important step in every roof system. Talk to your roofing contractor to learn more about leak barriers, how to choose the right one, and how to choose a professional roofing contractor to install.

Roof deck protection

Deck protection is very similar to a leak barrier. The difference is that the roof deck protection is installed over the entire roof deck area rather than just the “special areas” as mentioned in the Leak Barrier section.

Deck protection is generally one notch lower in quality than a leak barrier. However, as with leak barriers, there are many different types of deck protection available to choose from, from basic felt / tar paper to advanced woven plastic sheeting of tear and wrinkle proof material. Choosing a reliable roof deck protection is an important part of a quality roof system.

A word of caution; most roofing companies use felt paper as deck protection. Although the use of felt paper is standard and acceptable practice, some problems can arise if the felt paper gets wet during or after installation. Have you ever noticed how paper tends to curl when it dries after being wet? Similarly, felt paper can curl if water or excess moisture hits it. For this reason, and because the cost is quite small, we recommend installing a higher quality roof deck protection, such as a GAF / ELK deck truss. For a relatively small additional cost, you will be rewarded with much more reliable base platform protection.

Ask your local Trusted Roofing Contractor which underlayment would be best for your Roof System and why.


So there it is, life under the tiles. Do you see how much happens behind the scenes? Professional roofing contractors know these things inside and out, and they can go a long way toward ensuring that a roofing system is reliable for many years to come. Product vendors such as GAF / Elk and IKO can also help answer specific questions about the products.

All the best with your roofing project and remember, be proactive, make informed decisions.