House Wrap Explained Siding Companies

The Myth: New Siding Keeps Water Out

Every cladding leaks - vinyl through its locks and weep holes, lap boards at ten thousand seam inches, everything at windows. Builders have known this for a century, which is why modern walls are built as *systems*: a cladding that sheds most water, a drainage path for what gets through, and a barrier that keeps the remainder off the wood. Judge a siding job by its hidden system and you will hire differently than someone judging color samples.

Meet the WRB: Your Wall's Actual Raincoat

Felt vs synthetic

Asphalt felt is the century-old original - it works, tears easily, and degrades faster. Synthetic wraps are stronger, lighter, and engineered to a specific trick: they shed liquid water while letting water *vapor* pass, so walls can dry outward instead of sealing moisture in.

Drainable wraps and rainscreen gaps

Premium assemblies add texture or furring to hold a small gap behind the cladding - a true drainage plane where water runs down and out at weep points instead of sitting against the barrier.

Lifespan

Sealed correctly behind siding, quality wrap serves for decades - typically outlasting the cladding in front of it. Installed wrong, it fails the first wet season; it just fails invisibly.

How Water Really Moves Through a Wall

Wind-driven rain arrives sideways and pressurized. Capillary action wicks water uphill through hairline gaps. Gravity takes over the moment water lands on any surface. The WRB manages all three the same way a roof does: shingle-lap order, every layer overlapping the one below so gravity carries water down and out. And because some moisture always remains, walls must be able to dry - which is why vapor-open wraps beat plastic sheeting nailed to sheathing.

Flashing: Where Wraps Live or Die

Wrap failures are almost never in the field of the wall. They are at the holes we cut in it:

• Windows and doors - flashing tape must integrate with the wrap in shingle-lap order: bottom first, sides over bottom, wrap over top flange. Reversed laps *collect* water instead of shedding it
• Kick-out flashing - the small angled piece where a roof edge dies into a wall, throwing gutter-bound water away from the siding. It is the single most commonly omitted piece of flashing in residential construction, and missing kick-outs sit behind an outsized share of rotted wall corners
• Step flashing - woven into shingle courses wherever roof meets wall

If you learn one term before hiring, learn kick-out.

Vapor Barriers vs Water Barriers: Stop Confusing Them

A WRB blocks liquid water from outside while breathing vapor. A vapor barrier - plastic sheeting, foil facing - blocks vapor diffusion, and belongs on the *warm* side of a wall: inside in cold climates, outside-ish in hot-humid ones, often nowhere strict in mixed zones. Doubling plastic on both sides builds a wall that can never dry. Smart membranes that change permeability by humidity now split the difference in mixed climates.

Siding Over Old Siding: the Rules and the Risks

Overlays are allowed by many codes and some manufacturers - on flat, dry, single-layer walls, with longer fasteners that still reach studs through both layers. The risks are what you give up: nobody inspects the sheathing, trapped moisture between layers has no drainage path, and old wavy walls telegraph through new panels. The money an overlay saves is quantified in the cost guide; the physics of what it hides is this page's warning.

What Code Requires - and What Good Crews Add

Modern residential code requires a water-resistive barrier behind exterior cladding - one layer, lapped, over sheathing. Good crews exceed the floor: taped seams, integrated window flashing, kick-outs at every roof-wall die-point, and a drainage gap under premium claddings. Code is the minimum wall that passes inspection, not the wall you want.

Reading Your Own Walls

Loosen an exterior outlet cover or peek behind a corner post's edge: wrap or felt should appear behind the siding. Age is the heuristic - most homes sided after the mid-1980s have something; pre-1970s walls may have felt, board sheathing, or nothing. Finding nothing does not demand panic; it demands that your *next* siding job fixes it.

Why This Hidden Layer Should Pick Your Contractor

You cannot inspect the wrap after day three - so hire someone who documents it. Make wrap-stage photos a contract deliverable, have every bid name its wrap brand, grade, and taped seams, and favor top-rated siding companies that photograph the stage unprompted. The panels are the face. This layer is the job.