Build it right the first time – why you need flashing when building a deck or patio.

Posted on: October 31, 2014

Many homeowners and contractors have pulled off an aging outdoor deck to discover siding, sheathing and framing that’s rotting away underneath. More often than not, a major contributor is worn or missing flashing. Without flashing, there’s nothing to prevent water from seeping behind the ledger board that connects deck framing to the house. The same can be said for the ledger board and flashing installation for patios as well. Over time, trapped water leads to decay, not only in wood building materials, but even in metal fasteners that hold the deck together. The result is never good, and often expensive and time-consuming to repair.

So what is flashing? It’s a thin layer of waterproof material that keeps water from getting into places it doesn’t belong. (Caulk is fine for filling small gaps around windows and doors, but it shouldn’t be confused with flashing.)

no flashing and rot
KW Landscaping discovered no flashing and rot behind the old steps of this home 











remove rotten wood
Removed all the rotten wood, down to insulation










You can count on one thing; water flows unerringly towards the ground. As water travels, flashing carries it safely over the any crevices, cracks and gaps in the building’s exterior.

If it’s going to work, flashing must be installed so no seams face uphill. It’s usually layered with other building materials. The upper edge of flashing, for instance, is protected by house wrap or tarpaper, not installed over it.

replacing rotted wood
Replaced the wood with pressure treated lumber










installing flashing
Installed aluminum flashing, two layers for better protection










If you wonder whether flashing has been installed the way it’s supposed to be, follow a drop of rain water as it moves down the side of your house. It should be carried from surface to surface all the way down, never encountering an open seam or an upturned lip that blocks its progress.

flashing installed
Started putting things back together










When it comes to the deck, a strip of flashing is brought down the wall of the house and over the top of the ledger (the piece of dimensional lumber attached to the house at the edge of the deck). This all-important water barrier should extend up the wall at least 4 in.

KW Landscaping will always use flashing when completing your deck or patio to ensure a level of quality that you can rely on for years to come. Email KW Landscaping with any questions or to schedule an estimate.

front porch remodel
Finished product. Rot is removed and flashing has been properly installed.