replacement windows in new construction

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addition
Posts: 2
Joined: Sat Feb 23, 2008 12:31 am
Location: Seattle

replacement windows in new construction

#1 Post by addition »

Any reason not to install box frame vinyl windows w/o nailing fin in new construction? I would like the windows in the addition I am building to match the exterior look of the windows on the existing house. So having nailing fin windows flush with exterior of the house rather than inset into the window opening is a problem.

With box frame in new construction, what are keys to weather proofing?

Thanks for any assistance.[/u]

tru_blue
Posts: 223
Joined: Fri Jan 13, 2006 2:02 am

Replacement windows in new construction

#2 Post by tru_blue »

I'm not saying you shouldn't "install box frame vinyl windows w/o nailing fin in new construction," but to answer your question here are some reasons why you shouldn't.

I'm assuming the existing windows in the home are vinyl replacement windows in an older wood frame. To have the windows in the addition match perfectly, one would have to build wood frames for the vinyl replacement windows to fit into. It's rare that I've seen people build the wood window frames the way it should be done. The sills should be sloped for water runoff, and the wood frames should be preservative treated (all true wood windows these days need to be preservative treated to meet WDMA standards). I see people using untreated pine and no slope on the bottom - not good. Another issue is installing the wood frame itself. The frame ideally should not rest on the rough sill plate but be shimmed underneath (wish I had a nickel for every time that doesn't happen), caulk should be used, flashing on the top of the wood brickmould should be used, and (ideally) a foam insulation around the wood frame between the rough opening and the wood window frame. The idea is to keep water from infiltrating past the wood frame. Then of course they presumably would properly cap the wood frame with aluminum to make it maintenance free and so that water can't get behind the aluminum to rot the (possibly unsloped or untreated) wood window frame.

A nice alternative to match the appearance of the existing windows is to install a vinyl window with fins, seal the fins to the house with installation tape, insulate around the window as always, and put a cellular PVC brickmould and sill around the perimeter of the window to give it that wood frame look. Looks good, installs easy, hard to screw up, low maintenance.

addition
Posts: 2
Joined: Sat Feb 23, 2008 12:31 am
Location: Seattle

#3 Post by addition »

Thank you for that detailed and very helpful response. I can clearly see how the nailing fin installation is an easier way to go. I do have a follow up question though on the box frame approach. Why the need for a full wood frame around the new vinyl window?

Couldn't I tape flash around the rough opening, wrapping into the opening as well as around the edge of the sheathing then intall a sloped sill in the rough opening on top of the tape. I would then set the new window on top of the sill, trim the outside of the window with metal flashing over the top brick mold.

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