Lynden sits in the flat farmland east of Bellingham Bay, close enough to the Strait of Georgia and the open fields around the Nooksack River that wind-driven rain is a normal part of a fall or winter storm here, not an occasional event. Whatcom County gets a long, wet shoulder season that stretches from roughly October through May, and siding on a Lynden home spends more months damp than dry. That single fact drives almost everything on this checklist. Persistent moisture, not any single dramatic storm, is what actually damages siding in this part of Washington: it feeds moss and algae growth on north-facing walls and anything shaded by trees or eaves, it works into seams and fastener holes and starts wood rot before a homeowner ever sees a stain, and it exploits any gap in flashing or caulking that a drier climate might forgive.
Wind adds a second layer to the problem. Storms tracking in off the Strait push rain sideways against exposed walls, particularly on homes near Blaine, Birch Bay, and the open-water side of Bellingham Bay, and that horizontal rain finds its way behind loose panels and undersized trim in a way that straight-down rain never would. Inland toward Sudden Valley and the foothills, homes see more freeze-thaw cycling in January and February, and water that has already soaked into a seam or exposed wood trim can freeze, expand, and crack a panel or joint that looked fine in October.
The Washington State Energy Code also matters here in a way many homeowners do not expect from a siding checklist. Current code requires a water-resistive barrier and, on most re-sided walls, a drainage plane behind the cladding so bulk water and vapor can escape rather than sit against the sheathing. A siding system that traps moisture against the wall does not just risk cosmetic damage; it undermines the wall's ability to meet that drying performance, which is part of why a professional inspection looks past the visible panel to what is happening behind it.
This checklist is written for a homeowner walking their own property, not a contractor's punch list, and it is meant to be done from the ground with binoculars or a phone camera zoom rather than a ladder. Anything that requires getting on a roof or a tall ladder belongs to a professional, and that boundary is called out explicitly further down.
Not every item on this list means a full re-side. Photograph and date-stamp anything you find, then separate your list into two piles: things that are clearly cosmetic, like fading or light moss that comes off with a soft wash, and things that suggest water intrusion, like soft panels, staining that traces back to a joint or penetration, or fasteners with visible corrosion.
For cosmetic issues, a gentle wash with plain water and a soft brush, done from the ground with a garden hose attachment rather than a pressure washer, is usually enough for moss and light algae. Avoid pressure washing siding directly — the high pressure common in rental units can force water behind panels and seams, creating the exact moisture problem you are trying to prevent. If caulk lines are cracked but the material behind them looks sound, re-caulking with an exterior-grade, paintable sealant rated for wet climates is a reasonable homeowner fix, done on a dry day with a clear forecast for at least 24 hours so the sealant can cure properly.
For anything that suggests moisture is already behind the siding, resist the urge to simply caulk over the symptom. Sealing the surface without addressing what let water in, or without giving trapped moisture a way to dry out, often makes underlying rot worse by locking humidity against the wall. That is the point where a closer, hands-on inspection makes more sense than a homeowner fix.
Bring in a licensed contractor if you find soft or spongy siding in more than one spot, staining that keeps returning after cleaning, a musty smell near an exterior wall from inside the house, visible gaps behind trim and corners, or any area where you are not confident what is happening behind the visible panel. A professional inspection can include removing a section of siding to look directly at the water-resistive barrier and sheathing, which is the most reliable way to know how far rot or moisture has traveled.
It is also worth having a professional look at the whole exterior before a repaint, before a landscaping project that changes grading near the foundation, or if the home is older and has never had its siding assessed against current Washington State Energy Code drainage-plane expectations. Alpine Exteriors, licensed in Washington under contractor license ALPINI751OW, works throughout Whatcom County including Lynden, Ferndale, Blaine, Birch Bay, and Sudden Valley, and can walk a property to separate cosmetic wear from structural moisture problems before either gets more expensive to fix. A second opinion costs little compared to re-siding a wall that rotted quietly behind an unnoticed gap.
Given how much of the year Whatcom County spends wet, a walk-around inspection twice a year — once in late spring after the wettest months and once in early fall before storm season — catches most problems while they are still minor. Homes near open water or under heavy tree shade may benefit from a quick look after any unusually severe wind and rain event as well.
Not always. Light moss or algae on a shaded north wall is common in this climate and is often just a surface issue that washes off. It becomes a bigger concern when it returns quickly after cleaning, spreads onto panels that get regular sun, or shows up alongside soft spots or staining, since that combination usually points to water staying against the wall longer than it should.
Most insurers do not require a formal siding inspection the way some states require separate storm-related inspection forms, but documented maintenance and a clean inspection history can support a claim if damage does occur, and they give a buyer's inspector fewer surprises during resale. Unaddressed rot found during a home sale inspection is a common source of last-minute negotiation, so catching it early tends to protect value rather than just avoid repair cost.
Pricing varies by home size, siding material, and whether any exploratory removal of panels is needed, but homeowners in this area can generally expect a straightforward walk-around inspection to run somewhere in the low hundreds of dollars, with more invasive inspections that open up wall sections costing more depending on how much repair work follows. Getting a written scope before work begins is the best way to avoid surprises.
A siding problem in Whatcom County rarely announces itself with a single dramatic failure; it shows up as a little more moss each spring, a caulk line that keeps cracking, or a stain that will not quite wash off. Walking this checklist twice a year is enough to catch most of it early. When something on the list looks like more than a cosmetic fix, or you would simply rather have a second set of eyes before winter storms roll in off the Strait, Alpine Exteriors is available to inspect siding for homeowners throughout Lynden and the rest of Whatcom County and provide a straightforward assessment of what needs attention now versus what can wait.