With proper flashing, a wood deck will last many years; without it, the deck and the ledger it's attached to will quickly rot. Detailed photos in this article show the difference.
By the DIY experts of The Family Handyman Magazine
Rotted deck? Here's the right way to install the new one
After you demolish the old deck
but before you start work on the new
one, you'll need to make sure the
wood on and in the house is still in
good shape. Water leaking around
an old deck ledger can cause
significant damage to the house
framing. The existing house rim and
the lower support walls need to be
solid enough to support the multi-ton
weight of a deck filled with people.
After the old deck is removed,
you'll be able to tell if you can still use
the house rim. If the wall sheathing
behind the rim looks good, you're
okay. But if the sheathing is rotten,
investigate further by removing the
rotted areas, and check the house's
rim joist and wall framing to see if
they're rotten too. Don't be too eager
to rip apart and replace moist or discolored
wood; it may still be intact
below the surface. Jam a screwdriver
into the wood in several places. If the
screwdriver penetrates more than
1/4 in. or so, it's replacement time.
Replacing rotted-out rim joists
and lower wooden support walls can
be a huge job. You may want to have
an experienced carpenter on hand to
help walk you through that gauntlet. To properly attach a deck ledger, follow
- Drop the level of the new ledger
enough to allow at least a 2-in. gap
between the bottom of any doors and
the top of the deck boards. That way,
water and snow melt won't be able to
accumulate and seep under doorsills
to ruin interior floors, and storm
doors will swing past ice, snow and
- Install metal flashing (drip cap)
over the entire length of the top of the
ledger. Custom cut and fit another
strip of flashing over this
drip cap and under doors
to cover and protect
areas under doorsills.
Caulk the gap between
the flashing and the bottom
of door thresholds.
Install Z-flashing behind
the bottom of the ledger and over the
siding below. This keeps water from
wicking along the bottom of the
ledger and getting behind the siding.
Leave a 1/8-in. gap between the end
of the ledger and the ends of siding
and fill it with high-quality exterior
caulk to keep water from leaking
behind the ends of the ledger.
- Anchor deck joists to the ledger
with joist hangers, filling each hole
nails rated for pressure-treated wood.
- Predrill and sink
1/2-in. dia., galvanized or stainless steel lag screws
in every other joist
space, alternating up
and down positions to keep the
ledger from splitting. Select lag screws specifically rated for treated wood, in
lengths that will penetrate the ledger,
exterior sheathing and the 1-1/2 in.
thickness of the house rim joist
(4 in. is usually the right length).
- Use only treated wood
intended for soil contact for all the
structural members of the deck,
including the ledger, joists, beams
A Poorly Built Deck
Poor construction details and materials result in a deck that rots quickly and can damage the structure of the house.
Good construction details
A Deck That'll Last
Good flashing details and the proper materials insure that a new deck will last for decades.