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Roofing in the San Juan Islands is a different game than roofing on the mainland. Salt air, relentless rain, moss, ferry logistics, and stiff west-side wind all conspire against shortcuts. The homeowners who spend the most money over the life of a roof are usually the ones who made an avoidable mistake early. Here are the seven that show up again and again on island homes — and how to sidestep each one. 1. Choosing Materials for the Mainland, Not the Islands The most expensive mistake is spec'ing a roof as if you lived in Anacortes. Cheap fasteners rust in salt air. Thin metal dents and corrodes. Standard coatings chalk and fail years early near saltwater. West-side wind runs roughly 20 percent stronger than mainland averages, so wind ratings that are fine inland come up short here. The fix: near saltwater, specify 24-gauge marine-grade metal with a Kynar 500 / PVDF coating and corrosion-resistant fasteners. Standing-seam metal is the best long-term island roof, routinely lasting 50 years or more. Pay for the climate you actually have. 2. Ignoring Moss Until It Wins Moss is not a cosmetic issue here. On shaded north slopes under the Douglas firs, it thickens, holds water against the roof, lifts shingle edges, and quietly rots the deck beneath. By the time a homeowner notices, the damage is done. The fix: treat moss on a schedule and install zinc or copper ridge strips, which release trace metal ions with every rain and suppress growth for years. As an estimate and not a quote, moss treatment runs $400 to $1,600 — far less than the repair or replacement it prevents. 3. Skipping Ice-and-Water Membrane at the Weak Points Valleys and eaves are where island roofs leak first. With 40 inches of rain a year and heavy November downpours, water finds every unprotected seam. Homeowners trying to shave the estimate often let the contractor skip premium underlayment in these zones. The fix: insist on ice-and-water membrane at valleys and eaves. It is a small line item that prevents the most common and destructive leaks. 4. Hiring the Cheapest Off-Island Bid Ferry logistics are unavoidable. Crews and materials must be staged and barged over, and old roofing has to be hauled off-island for disposal. That reality adds roughly 10 to 25 percent to a comparable mainland job. A bid that ignores this is either inexperienced with island work or planning to cut corners to hit the number. The fix: expect the island premium and treat suspiciously low bids as a warning, not a bargain. Compare the details, not just the bottom line. 5. Treating a Repair Like a Replacement (or Vice Versa) Some homeowners keep patching a roof that is past saving; others tear off a roof that had years left. Both waste money. The table below shows rough island ranges — an estimate, not a quote — to help calibrate expectations: Job Estimated Range When It Makes Sense Repair $450 – $3,500 Isolated leak, young roof, localized damage Moss treatment $400 – $1,600 Active growth, no structural damage yet Asphalt roof $9,000 – $24,000 Cost-conscious replacement, moderate lifespan Standing-seam metal $14,000 – $45,000+ Long-term island durability, 50+ years Full replacement $11,000 – $40,000+ Widespread failure, aged or rotted deck Flat / low-slope $8,000 – $26,000 TPO, PVC, EPDM, or torch-down sections The fix: get an honest assessment of remaining life. Repair a young roof with a localized problem; replace an old roof that keeps failing. 6. Using the Wrong System on Flat Sections Island homes often have flat or low-slope sections — over porches, additions, or modern designs — and homeowners sometimes let a shingle-focused crew improvise there. Sloped-roof materials do not belong on flat roofs. The fix: flat and low-slope areas need a proper membrane — TPO, PVC, EPDM, or torch-down modified bitumen. A light-colored membrane also runs cooler and resists thermal stress. Match the system to the slope. 7. Hiring a Contractor Without Island Experience A mainland crew may build a fine roof and still get island specifics wrong: the fastener spec near saltwater, the wind detailing on the west side, the moss prevention, the disposal logistics. Experience with these islands is not a luxury; it is the difference between a 20-year roof and a 50-year one. The fix: choose a contractor who can speak specifically to salt-air corrosion, west-side wind, moss control, and ferry logistics. Homeowners comparing bids and researching https://sanjuanroofingco.com/ should ask each contractor to explain exactly how they will handle those four island-specific threats. The answers reveal who has actually roofed out here. The Common Thread Notice what ties these mistakes together: every one comes from treating an island roof like a mainland roof. Salt, wind, rain, moss, and ferry logistics are the constants. Respect them in your material choice, your details, your budget, and your choice of contractor, and you avoid the costly errors that catch so many island homeowners. A quick self-audit Are your fasteners and coating rated for salt air? Do you have ice-and-water membrane at valleys and eaves? Are your north slopes protected against moss? Does your bid account for ferry logistics honestly? Does the flat section use a real membrane? Has your contractor roofed on these islands before? If you answered no to any of these, you have found the mistake worth fixing before it costs you. About the Author Corinne Battelle is a coastal home-services writer and former estimator who spent years pricing roofing jobs across the islands and inlets of the Salish Sea. She writes to help homeowners avoid the expensive lessons she watched play out on the job.

Most homeowners in the San Juan Islands think of their roof as a shield against the weather above it. That is only half the story. The air trapped underneath the deck matters just as much, and on islands that soak up roughly 40 inches of rain a year, poor ventilation quietly rots more roofs than any single storm. If you have ever seen a green carpet of moss creeping up a north slope or found a soft, spongy patch of plywood during a repair, ventilation was probably part of the cause. This guide explains how airflow through an attic or roof cavity protects the structure, why our damp maritime climate makes it non-negotiable, and what a well-ventilated island roof actually looks like. How a Roof Is Supposed to Breathe A properly designed roof pulls cool, dry outside air in low at the eaves and pushes warm, moist air out high at the ridge. That continuous current does two critical jobs: It carries away water vapor that rises from the living space below, especially from kitchens, bathrooms, and laundry rooms. It keeps the underside of the roof deck close to the outdoor temperature, which prevents condensation and reduces ice buildup. When that current stalls, humidity collects against the cold sheathing and condenses into liquid water. The deck never gets a chance to dry, and wet wood is exactly what fungus and rot organisms need to thrive. Intake and Exhaust Must Be Balanced Ventilation only works when intake and exhaust are roughly equal. A ridge vent with no soffit intake starves for air and can even pull conditioned air out of the house. As a rule of thumb, builders aim for about one square foot of net free vent area for every 300 square feet of attic floor, split evenly between low and high vents. Get the balance wrong and you get dead pockets of stagnant, humid air. Why Island Moisture Is Relentless Conditions here are tougher on a roof cavity than most of the mainland. Rain falls heaviest in November, but the real problem is that it rarely stops long enough for anything to fully dry out. Add dense Douglas fir canopy shading north-facing slopes, cool marine air, and long stretches of overcast, and you get a roof that stays damp for weeks. Two failures follow directly from that persistent moisture. Moss on the Outside Moss loves shade, moisture, and organic debris. Shaded north slopes under evergreens are prime territory. Once a mat of moss establishes, it holds water like a sponge against the shingles, lifts their edges, and works granules loose. A poorly ventilated roof runs cooler and damper on the surface, which only encourages that growth to spread faster. Rot on the Inside While moss attacks from above, condensation attacks from below. Trapped vapor beading on cold plywood soaks into the sheathing, into the rafter tails at the eaves, and into any wood that stays wet. Over a few seasons this shows up as delaminating plywood, dark staining, a musty attic smell, and framing that gives underfoot. What Ventilation Does and Does Not Fix Ventilation is powerful, but it is one part of a system that also includes insulation, air sealing, and moisture barriers. The table below sets expectations. Problem Ventilation Helps? Also Requires Attic condensation on deck Yes, directly Air sealing ceiling penetrations Moss on shaded slopes Partially Trimming trees, zinc/copper strips, cleaning Ice buildup at eaves Yes Insulation depth, ice-and-water membrane Rot in existing wet sheathing Prevents more Replacing damaged wood High summer attic heat Yes Radiant barrier, adequate insulation The key takeaway: airflow prevents future damage, but it will not reverse rot that has already set in or scrub off moss that is already established. Signs Your Roof Is Not Breathing You do not need to climb into the attic to suspect a ventilation problem, though a look up there confirms it. Watch for these clues: Frost or water droplets on the underside of the roof deck in winter. Dark streaks or staining on the sheathing and rafters. A stuffy, humid, or musty smell in the attic. Rusted nail tips poking through the deck (a sign of repeated condensation). Persistent moss that returns quickly after cleaning. Blistered or prematurely curling shingles on a relatively young roof. Any of these are worth a professional look. Homeowners searching for https://sanjuanroofingco.com/ should start by asking whether their intake and exhaust are actually balanced, because adding one without the other often makes things worse. Ventilation Choices That Suit Island Homes Not every vent style performs equally in wind-driven rain. The west sides of the islands see wind roughly 20 percent stronger than nearby Anacortes, which matters when choosing exhaust. Continuous ridge vent with baffles. The gold standard for most homes. Baffled designs resist wind-driven rain far better than plain ridge vents. Continuous soffit vents. The best intake, as long as insulation baffles keep the airway open at the eave. Gable vents. Fine as a supplement, but they can short-circuit ridge-and-soffit airflow if mixed carelessly. Off-ridge or box vents. Useful on complex rooflines where a continuous ridge is not possible. For unvented cathedral ceilings or conditioned attics, the answer is different: a sealed assembly with continuous insulation and no cavity to ventilate. That approach can work beautifully here, but it must be detailed correctly, because a half-vented, half-sealed roof is the worst of both worlds. A Simple Maintenance Rhythm Ventilation hardware is low-maintenance, but it is not no-maintenance in a forested, wet environment. Task Frequency Why It Matters Clear soffit vents of debris and paint overspray Yearly Blocked intake starves the whole system Check ridge vent for storm damage After major wind Wind can lift or crack vent material Confirm insulation baffles are still open at eaves Every few years Settled insulation blocks airflow Remove moss and leaf litter As needed Debris traps moisture on the surface Stay on top of these and the roof cavity keeps drying itself out, season after season. The Bottom Line On the San Juan Islands, a roof lives in a permanent state of damp. Ventilation is the mechanism that lets it dry out between rains instead of slowly cooking in its own humidity. Balanced intake and exhaust, wind-rated vents, and a little seasonal upkeep add years to the deck, keep insulation dry, and make it far harder for moss and rot to gain a foothold. It is one of the least glamorous parts of a roof and one of the most important. About the Author Marcus Halvorsen is a Pacific Northwest building-science writer who spent a decade diagnosing attic moisture problems in coastal and island homes. He focuses on the unglamorous systems, ventilation, flashing, and drainage, that quietly decide how long a roof lasts.

It is the question every island homeowner faces eventually: patch the roof one more time, or bite the bullet and replace it? Get it wrong in either direction and you lose money — pouring cash into a roof that is beyond saving, or tearing off one that had a decade left. This guide gives you a clear framework for deciding, calibrated to the specific realities of roofing in the San Juan Islands. Start With Three Questions Before you look at a single estimate, answer these. They resolve most cases on their own. 1. How old is the roof? Age is the strongest single signal. Asphalt shingles on an island typically last 15 to 25 years, less if moss has been neglected. Standing-seam metal can run 50 years or more. If your asphalt roof is past 20 and giving you trouble, you are usually replacing. If it is 8 years old with one leak, you are almost certainly repairing. 2. How widespread is the damage? A single leak at a flashing detail is a repair. Water showing up in several places, sagging areas, or daylight through the deck point to systemic failure. Localized problems get fixed; widespread ones get replaced. 3. What condition is the deck in? If the wood decking beneath the roofing is rotted or soft — a real risk after years of moss holding moisture on shaded north slopes — patching the surface solves nothing. Deck rot almost always tips the decision toward replacement. The Decision Table Use this to place your situation. Ranges are an estimate, not a quote, and reflect island pricing including ferry logistics — crew and material staging plus off-island disposal — which add roughly 10 to 25 percent over a comparable mainland job. Situation Repair Replace Estimated Cost One isolated leak, roof under 15 yrs ✔ $450 – $3,500 Moss present, no deck damage yet ✔ (treat) $400 – $1,600 Multiple leaks, roof 20+ yrs ✔ $11,000 – $40,000+ Rotted or sagging deck ✔ $11,000 – $40,000+ Failing flashing, sound roof ✔ $450 – $3,500 Frequent repairs, rising cost ✔ Asphalt $9k–$24k / Metal $14k–$45k+ Flat section, aging membrane ✔ or ✔ $8,000 – $26,000 When Repair Is the Right Call Repair wins when the roof is fundamentally sound and the problem is contained. Classic repair situations on island homes include: A leak traced to worn flashing around a chimney, skylight, or vent. Wind damage on the west side that lifted or tore a small area — island wind runs roughly 20 percent stronger than Anacortes, so localized wind damage is common. A cracked valley or a few displaced shingles. Moss that has taken hold but not yet rotted the deck. In these cases a targeted repair, plus preventive steps like ice-and-water membrane at the fixed valley and zinc or copper ridge strips to slow moss, buys you years at a fraction of replacement cost. When Replacement Is the Right Call Replacement wins when repairs are chasing a losing battle. Signs it is time: The roof is at or past its expected lifespan. You are repairing the same roof year after year, and the costs are climbing. Leaks appear in multiple, unrelated locations. The deck is soft, sagging, or rotted. Granules are washing into the gutters in quantity, or shingles are curling across whole slopes. Think in cost-per-year, not sticker price A $2,500 repair that buys two years costs you $1,250 a year. A $28,000 standing-seam metal roof that lasts 50 years costs $560 a year — and it is the best long-term island roof, resisting salt air, wind, and moss when built right. When you find yourself repeatedly repairing an old roof, the "cheaper" repair is often the more expensive choice over time. Island-Specific Factors That Tip the Balance A few things weigh more heavily here than on the mainland: Salt air. Near saltwater, corrosion attacks cheap fasteners and coatings. If a repair means matching an aging, already-corroding system, replacement with 24-gauge marine-grade metal and PVDF (Kynar 500) coating may make more sense sooner. Ferry logistics. Mobilizing a crew and staging materials on-island carries fixed costs. If you are going to pay to get a crew out for major work anyway, doing the job once and completely often beats repeated trips. Moss and rain. With 40 inches of rain a year and heavy November downpours, a marginal roof degrades fast. Deferring replacement on a failing roof risks deck rot that raises the eventual cost. Homeowners weighing these factors and searching for guidance on https://sanjuanroofingco.com/ should get a professional inspection before deciding — the deck condition in particular is hard to judge from the ground, and it frequently settles the question. A Simple Rule of Thumb If your roof is young and the damage is localized, repair. If your roof is old and the damage is widespread — or the deck is compromised — replace. When you are genuinely on the fence, weigh cost-per-year and the island's harsh conditions, both of which tend to favor doing the job right rather than patching indefinitely. The Bottom Line There is no universal answer, but there is a reliable method: assess age, extent of damage, and deck condition; place yourself on the decision table; then think in cost-per-year rather than sticker shock. Do that honestly, factor in salt, wind, moss, and ferry logistics, and you will spend your roofing dollars where they actually protect your home. About the Author Nathan Prewitt is a Salish Sea building inspector who has evaluated hundreds of roofs on the question of repair versus replacement. He specializes in helping island homeowners read the true condition of an aging roof before they commit to a decision.

Most homeowners judge a roof by what they can see: the shingles or metal panels on top. But the material that does the quiet, unglamorous work of keeping water out of your house is often the layer you never look at. Underlayment sits between the roof deck and the finish surface, and on a rainy island roof it can be the difference between a dry attic and a slow, hidden leak. In San Juan County, where roughly 40 inches of rain falls every year and November storms drive water sideways, understanding these layers helps you spend your roofing budget where it actually counts. What Underlayment Actually Does Underlayment is the sheet material installed directly over your roof deck (the plywood or OSB sheathing) before shingles or panels go on. Its job is to be a secondary water barrier. Wind-driven rain routinely pushes moisture underneath shingles and up around fasteners. Ice dams, moss buildup on shaded north slopes, and simple aging all create paths for water. When that happens, underlayment is what stops the water from reaching your wood deck and the living space below. Think of it as insurance. Your primary roof surface handles 99 percent of the weather. Underlayment handles the leaks your primary surface will eventually let through. The Three Main Types Roofers generally work with three categories of underlayment, and the right choice depends on slope, budget, and exposure. Asphalt-saturated felt is the traditional "tar paper," sold in 15-pound and 30-pound weights. It is inexpensive and time-tested, but it can wrinkle when it gets wet and tears more easily during installation. Synthetic underlayment is a woven polypropylene or polyethylene sheet. It is lighter, stronger, resists tearing, and holds up far better if it sits exposed for a few days before the roof surface goes on — a real advantage when ferry schedules delay material or crews. Self-adhering ice-and-water membrane is a peel-and-stick rubberized-asphalt sheet that bonds directly to the deck and seals around nails. This is the premium layer, reserved for the most vulnerable areas of the roof. Ice-and-Water Shield: Where It Belongs Despite the name, ice-and-water membrane matters on the islands far less for ice than for the sheer volume of wind-driven rain. This membrane creates a fully sealed, self-healing barrier — when a fastener punctures it, the rubberized asphalt grips the shank and closes around it. You do not need it across the entire roof on most homes. It belongs in the trouble spots: Valleys, where two roof planes meet and channel large volumes of water. Eaves, the lower edge where water collects and where ice dams can form during a cold snap. Around penetrations like chimneys, skylights, and vent pipes. Low-slope transitions, where a steep roof meets a shallower section. On coastal and exposed west-side homes — where wind can run roughly 20 percent stronger than nearby Anacortes — many builders extend membrane coverage further up rakes and eaves for extra protection. Comparing Your Options The table below is a general guide to help you weigh cost against performance. Figures are estimates, not a quote, and real pricing depends on roof size, slope, and access. Underlayment Type Relative Cost Best Use Lifespan Range 15/30-lb felt Lowest Budget re-roofs, steep slopes 12–20 years Synthetic sheet Moderate Full-roof primary layer 25–50 years Ice-and-water membrane Highest Valleys, eaves, penetrations 30–50 years Full-coverage membrane Premium Low-slope, high-exposure roofs 30–50 years A common island approach pairs a quality synthetic across the field of the roof with ice-and-water membrane in every valley, eave, and around every penetration. That combination balances cost and protection well for the local climate. Why This Matters More Near Saltwater Salt air is corrosive, and homes within sight of the water take a harder beating on fasteners and metal flashings. When those components loosen or corrode over decades, water finds the gaps. A properly sealed membrane layer under the flashings buys you time and reduces the odds of a leak reaching your deck before you catch it. Homeowners searching for https://sanjuanroofingco.com/ should first ask any prospective installer exactly which underlayment goes where, because the answer reveals how well the crew understands coastal conditions. Questions Worth Asking Before signing off on a re-roof, confirm these details in writing: Which underlayment covers the main field of the roof? How far up the eaves and valleys does the ice-and-water membrane extend? Are all penetrations getting membrane, not just tape or sealant? What fastener type is being used to hold the underlayment (corrosion-resistant matters near saltwater)? The Bottom Line Underlayment is not where you want to cut corners on a wet, windy island. The finish surface gets the attention, but the hidden layers determine whether your roof merely looks good or actually stays dry through a decade of November storms. A modest upgrade from bargain felt to a quality synthetic, plus targeted ice-and-water membrane in the vulnerable spots, is one of the highest-value decisions you can make during a re-roof. It costs a fraction of the total project and protects everything above and below it. When you review a roofing estimate, do not just compare shingle brands and panel colors. Read the underlayment line items. That is where a knowledgeable coastal roofer separates a roof built to survive island weather from one built to look fine on installation day. About the Author Marcus Reilly is a Pacific Northwest roofing consultant who has spent two decades inspecting and specifying roof assemblies for wet, wind-exposed coastal homes. He writes about building envelopes and moisture control for homeowners who want to understand what happens beneath the surface of their roofs.