When a new roof is finished, you see shingles. What actually keeps the water out of your house during a wet February week is mostly underneath them. When two bids for the same roof in Bellevue or Puyallup come in far apart, the difference is very often in these hidden layers. Here is the system beneath the shingles, what each layer does in our climate, and how to tell whether a bid is skipping it.
Underlayment: Synthetic Versus Felt
Underlayment is the sheet material laid over the bare deck before shingles go on. For decades that meant asphalt-saturated felt paper. Felt absorbs water, wrinkles, tears in wind, and breaks down over time. Modern synthetic underlayment is a woven polypropylene sheet that is lighter, much stronger, lays flat, and does not absorb water. That last point matters more here than almost anywhere. If a shower comes through between tear-off and shingling, a synthetic deck stays dry and tight. Felt buckles.
We do not recommend felt on a replacement in Western Washington, and we would question any bid that still specifies it.
Ice and Water Shield: Where It Belongs in Our Climate
Ice and water shield is a self-adhering rubberized asphalt membrane. It sticks directly to the deck and seals around every nail driven through it. The name comes from ice dams, rare in the Seattle lowlands but real in North Bend and Snoqualmie. Its bigger job here is handling water that backs up or wicks under sustained rain.
Where it goes:
- Valleys, the full length, because valleys carry the most water and collect the most debris
- Eaves, and in foothill homes extended far enough up the slope to pass the interior wall line
- Around every penetration: chimneys, skylights, plumbing vents, and exhaust fan caps
- Along walls beneath step flashing and headwall flashing
- At low-slope transitions, such as where a porch roof meets the main roof
Building code requires some of this. We consider valleys and penetrations mandatory regardless, because that is where the leak calls come from.
Drip Edge
Drip edge is an L-shaped metal strip installed along the eaves and rakes. It carries water off the edge of the deck into the gutter, rather than letting it curl back under the shingles and run down the fascia. A missing drip edge is one of the most common things we find on older roofs in Everett and Renton, and the soft, rotted fascia behind the gutter is the direct result. At the eaves it goes under the underlayment. At the rakes it goes over it. It is an inexpensive detail with an outsized payoff, and it is also one of the first things a low bid quietly reuses or leaves out.
Starter Strip
The first course of shingles at the eaves and rakes needs a starter beneath it to seal the edge and back up the joints. Purpose-made starter strip carries a sealant bead right at the edge so the first course bonds down tight against wind, which is what keeps the edge shingles on the roof during a November blow. Manufacturers generally require their own starter product for full wind coverage under the warranty.
Ridge Cap and Ventilation
Ridge cap shingles are thicker and pre-formed for the ridge, and they go on over the ridge vent that exhausts warm, moist air out of the attic. Caps cut from standard shingles crack within a few years. The ridge vent itself only works when paired with clear soffit intake below, and a balanced system is a condition of most shingle warranties. A replacement is the right time to correct ventilation, not after.
Why Cheap Bids Skip or Thin These Layers
Every one of these components is invisible the day the crew drives away. Reusing old drip edge, substituting felt for synthetic, running ice and water shield only where an inspector will look, or cutting caps from field shingles each shaves a modest amount off the bid without changing how the roof looks from the driveway. Five or ten years later, the difference shows up as a leak at a valley, a rotted fascia, or a ridge that lets water in.
The protection is simple: ask every bidder to list each component by product name and specify where it goes. Manufacturer system warranties, including the GAF Golden Pledge warranty we offer as a GAF Master Elite contractor, require the manufacturer’s own accessory components installed by a certified installer. As a CertainTeed ShingleMaster and a certified installer with four major shingle manufacturers, we build every roof to those specifications, because the warranty depends on it and so does the roof.
Ask to See the Layers
If you are comparing roof bids, bring them to us and we will explain what each one includes and leaves out. Premier Roofing NW has served the Greater Puget Sound area for more than 30 years with free inspections and free estimates, and our replacements carry a 45 to 50 year manufacturer warranty on 50-year architectural shingles plus our own 15-year workmanship warranty. Discounts are available for seniors, military, and first responders. Call us at (425) 247-0088 and we will show you what a complete roof system looks like before a single shingle goes on.