Flash windows with no sheathing?

17 years ago

Cross posted on The Old House

I'm planning to renovate the bump out on my 1916 house to make it a usable breakfast nook. I will be replacing 4 windows, and adding an exterior door to a new deck. The hang-up is that outside siding is 1"x8" redwood shiplap, nailed directly to the studs - no sheathing or tarpaper. It is generally in good shape, except where the crappy windows leaked. My main question is: how should I install and flash the door and windows to avoid leaks? Everything I've read assumes there is sheathing under the siding (so window is installed on sheathing, flashed, then siding and trim put on). My two options seem to be:

1)Install nailing flange directly to siding, caulk the hell out of it, and put trim boards over the flange and caulk all seams.

2) Mount windows directly to studs, header, and sill (after wrapping all those in adhesive flashing), flash over flange, and install siding and trim, including a drip cap that goes under the siding but over the top of the window.

I'm leaning toward #2, because I am suspicious that even a well caulked surface mounting won't keep water out. But does anyone have any thoughts or suggestions to make this more waterproof?

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Comments (10)

alphonse
17 years ago
#2 door for me Monty. Never trust caulk where flashing should be.
brickeyee
17 years ago
"The hang-up is that outside siding is 1"x8" redwood shiplap, nailed directly to the studs - no sheathing or tarpaper. It is generally in good shape, except where the crappy windows leaked."

The leaks are possibly related to the substandard method of omitting sheathing.
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alphonse
17 years ago
But sheathing shouldn't see water if siding/flashing are up to snuff.
brickeyee
17 years ago
"But sheathing shouldn't see water if siding/flashing are up to snuff."

Siding is not water tight.
Wind driven rain pretty routinely penetrates (especially modern aluminum and vinyl siding).

That is why another layer is provided under siding to serve as the drainage plane.
fusion866
17 years ago
Just an idea to see what others think but, what about attaching some aluminum sheet metal to act as sheathing spanning from the window frame to wall studs in a descent size area around the windows and possibly all the way down the wall under the windows, then you can ice/water flash to that.
alphonse
17 years ago
"Siding is not water tight.
Wind driven rain pretty routinely penetrates (especially modern aluminum and vinyl siding). "

"The hang-up is that outside siding is 1"x8" redwood shiplap, nailed directly to the studs - no sheathing or tarpaper. It is generally in good shape, except where the crappy windows leaked. "

Leaking siding doesn't appear to be the OP's problem.
brickeyee
17 years ago
"Leaking siding doesn't appear to be the OP's problem."

Without sheathing and the drainage plane on top of it it is nearly imposable to adequately flash the windows.

You might review the recommendations for flashing windows and try to figure out how it can be done without sheathing and a drainage plane.

Is the problem directly related to leaking siding?
Most likely at the joint between the siding and the window.
alphonse
17 years ago
"You might review the recommendations for flashing windows and try to figure out how it can be done without sheathing and a drainage plane."

Nope, no review. I wouldn't flash anything to drain BEHIND the siding. But I'll concede that using the sheathing as the drainage plane is akin to an insurance policy on a car with no brakes.
brickeyee
17 years ago
"Nope, no review. I wouldn't flash anything to drain BEHIND the siding. "

Then you really need to review window flashing details.

The flashing is on top of the drainage plane, but behind the siding, since very little siding is actually water tight.
brickeyee
17 years ago
Window flashing goes under the drainage plane at the top, and over the drainage plane on the sides and bottom.
That means it is indeed behind the siding.

Unless of course you want to have the flashing beside and below the window in plain view on top of the siding.