Roofing: Under the Shingles - What's Under the Asphalt, Metal, Wood, Rubber Or Clay Tiles on a Roof?

Imagine, you’re standing on the sidewalk, looking at an average house. You see the siding, the windows, the front door, and way up above, you see the roof. Does the roof have asphalt shingles? Wood shakes perhaps? Maybe it’s made of metal or rubber tiles? What you see is where the focus goes, but it’s what you don’t see that really matters. There’s more to roofing than meets the eye. So let’s talk about what goes on, under the shingles.

The Roof Deck

We learn to crawl before we walk, so when talking about roofing let’s start with square one, the surface area of your roof which is made of wood. Your wood roof deck is comparable to an automobiles metal body.  It is installed on top of the basic house frame to give a surface area on which to install Shingles.  Without a roof deck installed on your house, there would be nowhere to install your Shingles.  And of course without the shingles, your roof deck would rot away due to exposure to the sun, rain, snow and ice and etc...not a comfortable home at all!

On Newer Houses, sheets of plywood or OSB boards are fastened on top of wooden trusses in your attic to form the roof deck.  Plywood or OSB boards are installed in a staggered formation with small spaces between them to allow wood to expand and contract as the wood heats in the summer and cools in the winter.  Older homes often have lengths of 2" x 6" installed instead of plywood or OSB board.  When the time comes for you to replace your Roof System, remember to have your Calgary Roofing Contractor replace any and all damaged wood.

Remember, if your roof deck is rotting or damaged in any way, people walking on your roof could potentially crack or break through the wood, causing further damage to the roof system, such as to the shingles...and to the person who walked on it!  However, most roof decks can withstand a little bit of exposure to water or ice before it needs to be replaced.

Metal: Drip Edge and Rake Edge

Drip edge and Rake edge is the first part of the Roof System to be installed.  It is a long and narrow piece of metal which is installed along each end of your Roof Deck, ie: along the eaves trough and along the gable ends. 

Some area local 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 Drip edge or Rake edge.  Therefore many new homes and/or low budget roof systems do not have drip edge installed in order to allow for more affordable roof prices.  We recommend however that Drip edge and Rake edge be installed on every Roof System, no exceptions.

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 an appropriate drip edge often saves hundreds and sometimes even thousands of dollars when your roof system needs replaced.

If your Roof System does not currently have drip or rake edge installed, do not panic, you'll survive well enough.  Just be aware that when your roof needs to be replaced, the Roofing Contractor you may need to replace some of your wood Roof Deck on an as needed basis.

Metal: Chimneys and Skylights

Arguably the most important part of every complete roof system. The metal installed in the valleys, chimneys and skylights take the brunt of water flow on every roof. Poorly installed, a brand new roof system can make a waterfall out of your living room.

Every chimney and skylight needs what is referred to as “a back pan”, which consists of sheet metal folded at around a 90 degree angle (depending on the slope of your roof) and tucks under the shingles and up under the siding, stucco or counter flashing on the chimney or skylight. Every back pan needs a small 2” section of metal sticking out 1” or more from either side of the chimney or skylight to divert water away from the corners. Water should hit the metal back pan and be directed away on either side where it can continue its run into the eaves trough.

Metal: Valleys

In the same way water runs along the valleys between two mountains, water runs along the valleys on your roof peaks. Valleys generally receive the highest concentration of water flowing through them, therefore installing them correctly is extremely important!

As mentioned in the Leak Barrier section, valleys have leak barriers installed underneath them. Even though some Building Codes do not require such a leak barrier to be installed, we recommend installing one always in every valley.

A word of caution: Many roofing contractors install valleys in a style referred to as 'closed'. A closed valley consists of Shingles woven inside the valley, as opposed to an 'open' valley which has sheet metal running from top to bottom. Both the 'open' and the 'closed' style of installation are acceptable by the most Building Codes and by most manufacturers, however, the 'open' style installation has consistently out performed the 'closed' style...and costs exactly the same price to install.  Ask your Roofing Contractor to use the 'open' style of installation for your roofs valleys, this could save you from having to replace your roof system prematurely and also can avoid headaches in the long run.  Typically, an 'open' valley is installed with a 30 gauge sheet metal, 4' wide, coming in 10' sheets. This metal can be ordered in any color to match the shingles on your roof system.

Leak Barrier

Think of a leak barrier as a "second layer" of protection for your Roof Deck.  A backup plan, if you will, and also a protection against moisture build up.  Leak barriers are nearly always installed on top of the Drip Edge and Rake Edge metal along eaves trough areas, gable areas and valleys because of the risk these areas pose for leaks, ice build up, shingle deterioration and water back flow. 

If you've ever looked at your roof during winter, you'll notice how ice and snow builds up along the length of your eaves troughs and inside the roof valleys.  As with Rake Edge and Drip Edge, some Building codes require Leak Barriers to be installed and some Building Codes do not. In Alberta, the Building Code requires a leak Barrier to be installed on all eaves trough and valley areas of a Roof Systems because of issues related to such snow and ice build up.  As an optional upgrade, some high end roof systems even have leak barriers installed on top of the entire Roof Deck (as opposed to only along the special areas we just mentioned) where normally a standard Roof Deck Protection would normally have been installed.

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

Choosing an appropriate Leak Barrier and installing it properly is an important step in every Roof System.  Speak with 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 it.

Roof Deck Protection

Roof Deck Protection is very similar to a Leak Barrier.  The difference is that Roof Deck Protection is installed on the entire Roof Deck area instead of only on "special areas" as we mention in the Leak Barrier section.

Typically, Roof Deck Protection is a step lower in quality than a Leak Barrier.  As with Leak Barriers however, there are many different types of Roof Deck Protection available to choose from ranging from basic felt/tar paper to advanced plastic woven sheets of rip 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 Roof Deck Protection.  Although using felt paper is a standard and acceptable practice, some issues can arise if the felt paper becomes wet during or after the installation.  Ever notice how paper tends to curl when it dries after it was wet?  In a similar way, felt paper can curl if water or excess moisture touches 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 Armour.  For a relatively small additional cost, you'll be rewarded with a much more reliable Roof Deck Protection.

Ask your local trusted Roofing Contractor about which under-layer would be best for your Roof System any why.

Conclusion

So there it is, life beneath the shingles. See how much goes on behind the scenes? Professional roofing contractors know this stuff inside and out and can help immensely in ensuring a roof system is reliable for many years. Product suppliers such as GAF/Elk and IKO can help answer specific questions about products as well.

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