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I am in the process of finishing a long term project to replace all the windows in my house. The final two windows are side by side quarter round windows that sit about a foot above two lower side by side casement windows.

I am looking for advice on how to apply flashing over this type of window when it has a circular arc profile. I am installing these replacement windows as if it was a new construction by using nail fin new construction type windows that insert from the outside and are nailed through the fins, through the plywood sheathing and into the studs and blocking around the rough opening. The old windows had narrow 1.5" x 1.5" framing around the windows that then had the cedar lap siding butted up to that. By removing that old exterior framing trim it is easy to remove the old window and that leaves plenty of space around the rough opening to accommodate the nail fins on the replacement windows.

I am replacing the exterior framing with more modern cedar boards that are 1 1/8" thick and being cut to 3" width. When installing the framing I am carefully trimming the existing cedar lap siding so that it fits perfectly against the now wider trim.

These quarter round windows I am now dealing with were rather poorly installed 38 years ago when the house was built. One has no flashing at all and the other one had about a dozen short sections of metal flashing that were installed with small amounts of overlap. So back now to my question as to what would be a decent method to install flashing for these windows. The pictures below show one of the new windows sitting on a sawhorse with the curved section of its new cedar frame already pre-fitted. The flashing would go above this frame and extend up under the cedar lap siding.

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Michael Karas
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3 Answers3

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I can assume that the nailing flange as seen at the bottom of the window continues around the arch. This makes the window considered "self flashed".

Once the window is installed in the rough opening, the nail flange can be taped with flashing tape.. The tape sealing the flange to the sheathing covering, ( Tyvek or similar.) Once that is done the window is sealed and the exterior covering and trim can be installed. No other metal flashing is needed.

RMDman
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I haven't seen anyone use metal flashing on modern windows for a long time. Purpose-made adhesive rubber tape is the way to go, and you don't need to overthink it.

Start at the bottom with a vertical strip. Add more strips, lapping over the lower ones, so that you maintain good contact with the window flange. Run up both sides, then finish with a horizontal strip at the top.

isherwood
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Your second installer had the right idea but needed the small sections, probably because they only had 10" rollstock to work from. Using 24" rollstock needs fewer joints. In all cases, if you need to face mount fasteners to hold down the metal, it detracts from the effect you are trying to achieve.

Also consider using PVC 1" x 4" board stock and creating the casing arch from that. The pieces would be glued together and finished to ensure UV protection.

isherwood
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DelphicOracle
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