Last reviewed October 31, 2026.
The old siding came off the back wall this morning. By lunch the crew is stapling white sheets over the bare plywood, lapping one row onto the next and slicing an X across each window. By tomorrow the new siding will hide all of it.
Today is the one day you can see whether the layer that actually stops water went on right.
What New York’s 2025 code requires behind siding
The 2025 Residential Code of New York State, in Sections R703.1 and R703.1.1, says exterior walls must form a weather-resistant envelope that keeps water from building up inside the wall. That means a water-resistive barrier behind the cladding and a way to drain water that gets past it.
Section R703.2 says “Not fewer than one layer of water-resistive barrier shall be applied over studs or sheathing of all exterior walls,” continuous to the top of the walls and properly terminated at penetrations.
The siding is not the barrier. The Vinyl Siding Institute’s installation manual (posted in 2022, copyright 2020) says vinyl is a cladding designed to let the material underneath breathe. It has to go over a water-resistive barrier that stops liquid water from getting further into the wall.
Every quote on our siding page should name the barrier product. If a wall only needs a few panels replaced, the siding repair page covers that.
Felt paper or a synthetic wrap
The code does not require a brand. R703.2 lists approved materials: No. 15 felt meeting ASTM D226 Type 1, wraps meeting ASTM E2556 Type 1 or 2, foam plastic sheathing systems installed to the maker’s instructions, systems tested under ASTM E331, and other approved materials. Felt and E2556 wraps go on horizontally, the upper layer lapped over the lower by at least 2 inches, with joints lapped at least 6 inches. The InterNACHI life expectancy chart gives felt paper 15 to 30 years and housewrap 80 years or more.
Long Island Exterior Co., in its April 2026 cost guide, lists a house wrap moisture barrier among the items included in its vinyl price. If one quote includes wrap and another never mentions it, ask before you compare totals.
How DuPont says Tyvek goes on
DuPont’s installation guidelines for its Tyvek barriers (revision 5/18, the version we found) start the wrap at the bottom of the wall so each course sheds onto the one below. Vertical seams overlap 6 to 12 inches and get taped with Tyvek Tape. Upper courses lap the lower ones by at least 6 inches, and taping horizontal seams is described as a recommended best practice.
Fasteners go on the stud lines no closer than 6 inches and no farther than 18 inches apart, but not within 6 inches of window sills and jambs or 9 inches of the head.
Time in the sun matters. The guidelines say DuPont requires HomeWrap to be covered within 4 months (120 days) of installation. DuPont’s HomeWrap page gives the same 120-day UV exposure limit and says that if it is exceeded, another layer can go over the old one or the old layer can be replaced.
Typar’s rules for the same job
Typar’s 2017 installation guide also starts at the bottom, printed side out, with at least 12 inches of overlap when the roll starts at a corner. It requires at least 1 inch of overlap onto the sill plate and recommends 2 to 4.
It calls for plastic-capped nails or staples at 32 inches on center both ways over 7/16 inch OSB or 15/32 inch plywood, upper layers lapped at least 6 inches, and every seam and penetration taped once the house is covered. Before cladding, the guide says to inspect the wrap for tears and patch them with Typar tape or flashing.
Where the wrap meets a window
Section R703.4.1 of the New York code requires flashing at exterior window and door openings. The usual way to comply is to follow the window manufacturer’s instructions, or, where those are silent, the flashing or barrier maker’s instructions. The code also accepts a design professional’s method or another approved method. Where no flashing instructions exist, it calls for a pan flashing at the sill that is sealed or sloped to send water out.
Typar’s guide shows the usual sequence for a new window. The wrap is cut across the top of the opening, then from the top center two-thirds of the way down, then diagonally to the bottom corners, and the flaps are pulled inside the opening and fastened. A 6 inch diagonal cut at each top corner lets a flap fold up out of the way.
The sill pan goes in first, the window is set in sealant that stops short of the bottom so water can drain, then flashing goes up the sides and across the head, with the head piece running 1 inch past the side flashing at each end. Last, the flap drops back over the head flashing and its diagonal cuts get taped, but not along the top of the window flange.
When the windows stay and only the siding is replaced, the Vinyl Siding Institute’s manual gives a retrofit method for a nail fin window installed without flashing: a sill flashing at least 9 inches wide set into sealant, jamb flashing pressed into sealant up each side, and a head flashing that runs about 1 inch past the jamb flashing at each end. For windows being replaced at the same time, see our window replacement page.
What to look at before the siding covers it
If you are home while the walls are open, a few checks take minutes. Upper rows should lap over lower ones, never the reverse. The vertical seams should be taped. Hose bibs, vents and light boxes should have no tears or gaps around them. At each window, the head flashing should sit under the wrap above it.
Then walk the house with your phone and photograph every wall before the siding hides it. On a house coming out of old metal siding, our aluminum siding page covers the tear-off that comes first.
