Silly (Flashing) Question?

I’m building a house in Washington State, exposed to tremendous southerly winds, and I’m (naturally) concerned about creating a barrier against Mother Nature. :twisted:

On a typical window, for instance, I’ve typically only flashed the top of the window trim (many builder friends don’t even do this; instead beveling the top trim at 15 degrees and relying on caulk). In reading information from (I know it’s not related to wood siding), it nonetheless piqued my attention that I should (maybe) additionally flash the bottom trim as well to keep water from (potentially) entering the wall beneath the window. I’ve never seen this done before for wood siding, but maybe it’s a good idea. We’ll be using a combination of cedar shingles and horizontal lap siding.

To properly flash our new home, would you recommend flashing the bottom trim as well or is this overkill? Thanks very much!

Tim Hance
All Islands Home Inspections


The complete window opening should be flashed.

The entire window MUST be flashed. Top, bottom and sides. Metal sheds water mush better and much longer than wood. Caulk only lasts a few years.

Why would you possibly skimp on your own house?

As Larry and Will have both said, all sides should be flashed but there is movement toward calking only the top and sides. Caulking and flashing are different. The trend toward not caulking the bottom is to let any water that might get in to drain out the bottom. I think you’ll find some detailed info about what I am talking about here.

From Larry’s recommendation:,%20Door,%20and%20Wall%20Flashing%20Details/APA%20Window%20Flashing.pdf

Near the end of the article is a section on the rainscreen. If you’re in a windy and somewhat damp area like seacoast with hard driving horizontal rains, I would employ the recommended rainscreen. I live on the coast of Nova Scotia and this has been made a code requirement here, albeit 15-20 years too late. Quite a few homes have had wood siding “premature rot” problems in the 1990’s; the code requirement was enacted in 2004.

Tim, being up in Eastsound, why would you want to use Cedar. The maintenance alone is more work than I would want. It will cost you in the long run for yearly staining or sealing, let alone the labor to do it. There isn’t much old growth cedar around anymore. The young stuff just doesn’t hold up without lots of maintenance. Why not go with the Hardi shingles and lap siding?

Great resources and advise! Thanks very much, everyone. I’m definitely not looking to skimp on my own house- that’s why I’m posing the question- it’s just that I’ve never seen metal flashing at the base of a window before and thought I’d pose the question (it seems like a great idea). And, cedar shingles are “in” as my wife wants the “natural look.” I know it’s high maintenance- they seem to blacken almost overnight- but that’s what she wants. I’m still trying to persuade her towards something more durable, maintenance free, and timeless. We’ll see…

And, as a side, I wanted to express my appreciation to the contributing members of the Message Board. What a wonderful resource you all are and we all can be. For me, it’s a BIG part of my decision to join NACHI over other organizations. For my part, I hope to continue and contribute to what appears to be such a great tradition.

I can envision my peers forming a lynch mob for me even suggesting this but have you looked into this wash n’ wear material EcoStar Senaca Shake it’s a little pricey but may be the best solution for your aesthetic and climatic conditions.

Whatever materials you decide upon spend the time and money to properly FLASH all penetrations and fenestrations.
You, your wife and your home will thank you for years to come.

Or don’t and face the grief the rest of America lives with.

This does not have to be metal flashing. It may be tar paper, Tyvek *Flexwrap, *Grace Ice and Water Shield or similar eave protection material.

There was an excellent supplement/insert with The Journal of Light Construction in the mid-late 90’s that had detailed better systems of flashing a window, for both wood or stucco siding. I have a copy of it but a dead scanner for my computer system (Maybe I’ll stop being so Scottish and invest in a new one this week).

An improvement for the bottom sill area is to have a slightly beveled piece of wood here sloped to drain to the outside. Flash over this; if there is a leak, water will not sit here but drain away. A “seconds” piece of thin clapboard or thin shingles will do the trick.

The water will get in and it needs to be back out over the cladding at the closest place as possible.

Is is not just a stucco problem!

Look at post #5.

Look at post #4


Any talk about rainscreen in your area or in your codes?

Flashing in 3 places on windows with trim.

No matter what the cladding.

With out the flashing at the bottom the water that gets in at the wood joints is behind the cladding.

Absolutely. From what I read in your posts it sounds about the same here. I think Tyvek (the source I referanced in post #4) also talks about rain screens a bit is some articles.

I have more info (more in depth) from other sources somewhere.

R703.8 Flashing.Approved corrosion-resistive flashing shall
be provided in the exterior wall envelope in such a manner as
to prevent entry of water into the wall cavity or penetration of
water to the building structural framing components. The
flashing shall extend to the
** surface of the exterior wall finish
and shall be installed to prevent water from reentering the ex-
terior wall envelope. **Approved corrosion-resistant flashings
shall be installed at all of the following locations:

  1. At top of all exterior window and door openings in such
    a manner as to be leakproof, except that self-flashing
    windows having a continuous lap of not less than11/8
    inches (28 mm) over the sheathing material around the
    perimeter of the opening, including corners, do not re-
    quire additional flashing; jamb flashing may also be
    omitted when specifically approved by the building of-
  2. At the intersection of chimneys or other masonry
    constructionwith frameor stuccowalls,with projecting
    lips on both sides under stucco copings.
  3. Under and at the ends of masonry, wood or metal cop-
    ings and sills.
  4. Continuously above all projecting wood trim.
  5. Where exterior porches, decks or stairs attach to a wall
    or floor assembly of wood-frame construction.
  6. At wall and roof intersections.
  7. At built-in gutters.

Here is a rainscreen for a cedar clapboard installation.

Marcel :slight_smile: :smiley: