Part 1: Prepare a Rough Opening for a Nail Fin Window Over Exterior Rigid-Foam Insulation

Flash the sheathing around the buck to the window opening with tape or liquid flashing before installing the exterior foam insulation.
To learn how to install nail-fin windows in 5 common wall types, check out this playlist: www.finehomebuilding.com/2019...
When installing a nail-fin window in a house with exterior rigid-foam insulation, the job is more complicated than with other claddings, but the extra steps are easy once you understand the process. As builder Jake Bruton points out in this video, if you aren’t using the rigid exterior foam as the water-resistive barrier (WRB) then the windows should go in before the foam, allowing the opening to be properly flashed behind where the foam will cover. The most common method, shown in this video, is to pad out the rough opening using framing lumber, often called bucks, that are cut to match the thickness of the exterior foam-in this case 2 in. Then the bucks are flashed as part of the rough opening, with a continuous seal extending from the sill and jack studs across and around the bucks, and tied into the WRB on the wall, which in this case is Zip System sheathing. For this installation, Jake demonstrates using liquid flashing, which is well-suited for weatherproofing a bucked opening. Just like paint on a canvas, the goal here is to cover the exposed wood completely with liquid flashing as well as a little bit of the wall sheathing to create a continuous barrier against the weather. Jake establishes layout lines around the outside of the window frame to ensure that he has sufficient coverage. Adding these lines as a guideline to make sure you properly protect your wall is a great idea, but don’t fret about adding a little too much liquid flashing-there’s no harm in coloring outside the lines. It’s important to recognize that liquid flashing, because of its nature, will act differently depending on the temperature and the humidity. Jake explains how to go about handling these quandaries as well as other problems you may run into when using liquid flashing.
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[@mullally08]

You would need a truckload of flashing caulk to cover every window like this

[@ArthurDentZaphodBeeb]

My experience in hot-dry westher (say 85 and above), I found the liquid flash skins over long before you can finish detailing any sizable window. It's a 2-person job for larger windows. I found pinholes develop in some batches of liquid flash, so needed to go back and touch up. Great reminder to wipe down existing tape with acetone - literally the last place you want a bond failure

[@JohnLee-ed8yi]

Just need this great echnique to replace my windows. Thank you.

[@boboconnor1403]

I'm going to have to try this system when I reside my house.

[@cameronoverfield8764]

That would take 6 years to do a whole house!

[@Hedgehodge-]

how many windows can you get out of one tube of liquid flash doing entire windows like this?

[@coasttal123]

I would only use the liquid flash where taping would not be easier to do. In this case, covering the face of 2x material seems to be a great waste, and time consuming.

[@johnbutter7305]

How do you do this with a peel and stick WRB? I don’t lie the zip system because they use OSB as the substrate vs plywood. Will the liquid flashing adhere to the WRB?

[@Hedgehodge-]

is there any reason why i wouldnt want to use pressure treated for all my bucks? Thank you! Mainly curious for termites

[@ramzy1013]

I've replaced dozens of windows and not one had water penetration. Are the newer homes that much more susceptible to water mitigation than the old ones? Do contractors do that to all windows when building homes?

[@joniboulware1436]

Air tightness is a goal here too.

[@josephkremski8061]

Flex Seal spray. 5 minutes, DONE.

[@bobbray9666]

Should you use 2-7/16" thick bucks for Zip-R12? Huber says OK to nail through using 4" nails but is this safe for large windows?

[@saticharlie]

the external frame is wood, what's the point? It's a thermal bridge, the cold will transfer from the inside to the outside, now there is product, solid foam made to insulate and nail your window frame...

[@RRENH]

Thermal Buck!

[@HarmonsHarbor]

Maybe rip down a sheet of 2 inch Zip-R and screw the window through to the framing?

[@thegoodkid]

This seems like a pain is the arse...

[@jakejohnson7714]

over doing it man f this thank you!

[@joniboulware1436]

So slow.