Get To Know The 5 Layers Under Your Roof Shingles

Get To Know The 5 Layers Under Your Roof Shingles

Your skin is your body’s largest organ and has three layers. That’s great, but it pales in comparison to your Michigan home’s roof. A typical roof has around five layers and is the single largest system on your entire home. 

What Goes Under Roof Shingles?

Your roof’s anatomy may not be as alluring as human anatomy, but it performs a vital function: your roof protects all the rest of your house, most of your possessions, and your family. As a wise homeowner, you benefit from knowing as much about your roof as possible. For example, your roof probably has all these layers tucked beneath your visible shingles:

  1. Insulation
  2. Ventilation
  3. Roof deck
  4. Water shield
  5. Underlayment

Let’s examine each layer, one at a time. 


Inside your Grand Rapids home’s attic is thick, fluffy insulation. This insulation—cellulose, paper-backed fiberglass, or blown-in—keeps attic air separated from the air in your living space. That means your attic’s air should be the same temperature and humidity level as the outside air. That keeps your roof in harmony with the surrounding air, helping to prevent ice dams in winter and premature aging in summer. 

Many homeowners mistakenly believe you can never have too much insulation, but packing your attic full of fluffy stuff is just as harmful as having too little. Your attic must allow for air to circulate from the eaves to the ridge, a job handled by ventilation. 


Along the underside of your home’s lower edge, soffit vents allow air to enter your eaves and rise by convection up through your attic. The air travels upward and exits along the ridge through ridge vents. It could also be expelled through gable vents or pushed out by powered ducts. 

Every Grand Rapids-area home benefits from adequate attic ventilation. Your roof stays healthier and your living space stays more comfortable when air constantly moves through the attic. 

Inadequate ventilation can cause your roof to get so hot, the various layers degrade and fail. Poor ventilation can reduce your insulation’s life span, too, or invite pests to invade and set up housekeeping. 

Roof Deck

What does your shingle roof sit on? It sits on your home’s roof deck, which comprises two main parts:

  1. Rafters—The pitch (angle) of your roof is determined by the slant and length of your rafters; these run in parallel from the lower edge of your roof up to your ridgeline, usually every 16” or 24” inches on center to provide plenty of support for all the other layers of your shingle roof
  2. Sheathing—Sheets of plywood or oriented strand board (OSB) cover the rafters and provide ample support for shingles; roofing technicians expertly install these sheets with very slight gaps around them, to allow for thermal expansion

Together, the rafters and sheathing form a single element, the roof deck, which is remarkably sturdy. A typical shingle roof might use 24 squares of shingles, each weighing between 230 to 250 pounds. That is 5,520 to 6,000 pounds (2.76 to 3 tons) of shingles! 

Roofs are inherently dangerous to walk on, but if your roof deck is at all questionable, you greatly increase your odds of getting hurt. For that reason, plus the huge weight your roof is supporting, is why all professional roofers tell homeowners: stay off the roof! 


Sheathing is not waterproof. 

Not even shingles are waterproof. 

Both materials resist water, but only underlayment is waterproof. So this thin, rolled material—either natural or synthetic felt—is rolled out over the sheathing and stapled down. It covers your entire roof before a single shingle is attached.

Underlayment has a resilience that allows it to close up around nail and staple holes, preventing water from seeping through into your sheathing. This helps reduce the chances of roof leaks and mold growth in your attic. 

Water and Ice Shield

Underlayment is good in preventing small quantities of water from infiltrating your attic and wreaking havoc with humidity. But underlayment benefits from a tougher, thicker, stronger substance in vulnerable locations. 

Water and ice shield is a thick, spongy, self-adhesive rolled material that careful roofers use in two key trouble spots:

  • Your roof’s lower edge, where ice dams can form and cause water to seep up under shingles
  • Your roof’s valleys, where two roof sections meet at downward angles and allow water to channel, debris to build up, and snow to freeze

When you arrange for full roof replacement, be sure to ask about these and all other roof components. Budget for the best quality materials you can afford to ensure a long, healthy life for your Grand Rapids-area home’s roof.

Moore and Sons Roofing in Grand Rapids, Michigan is your best choice in residential roofers. Contact us today for all your roofing needs. Be sure to ask us about our quality guarantees and strong warranties!

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