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I recently cut two holes in my foundation and installed new windows. I lined my hole with 2x8 PT wood bucks that I attached to the masonry with Tapcon screws. Then I attached my window nailing flange to the wood buck. All seemed to work fine.

Now I would like to replace some of the other windows in the room (basement). The existing windows are a reasonable size, but because they are old steel frame, and the frame is very thin, the effective window area is very close to the same size as the hole in the block wall. If I follow the same strategy as I described above, then by the time I add the wood buck and a modern vinyl window, my effective window area is reduced by about 4.5" on each side! (1.5" for the buck, 3" for the vinyl window frame). The resulting window would be tiny. I am looking for a way to maximize the final size of the window without having to cut away any more block.

Does anyone here have experience attaching the window directly to the masonry opening, and skipping the wood buck? For small windows, I have heard of people essentially floating the window in the rough (cmu) opening with spray foam - no nails or screws! - but I am a little hesitant to pursue this option...

For reference I am in Anchorage AK.

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There are a bunch of factors - hard to go wider because the blocks on each side were poured full, so harder cutting, and if I remove the entire poured column, I need to re-fill the new side column. Also wider brings up potential structural issues in needing a different header system which drops the top of the window closer to grade. If I go deeper, it is easy to cut, but then I have more below grade window that I have to worry about drainage in front of, stuff like that... – tbc Oct 24 '13 at 16:46

Just get replacement windows instead of new construction and use tapcons to fasten the windows through the sides. Caulk outside good to keep out water. Foundation should also be graded away from the window to keep out water.

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you don't think the tapcons will blow out the corners of the masonry (screws/holes may only be 1/2" to 3/4" in from edge of the block wall)? – tbc Oct 22 '13 at 22:09
Are you talking about the nailing flange of a new construction window? I was talking about a window without the flange and would install in the middle of your foundation wall like your old window now is. – Justin K Oct 22 '13 at 22:59
The window vendor I was planning on using does not sell a window without a flange. For retrofit windows, they recommend scoring and snapping off the nailing fin and fastening through the brick mould into the buck (vinyl window with built in brick mould). Supposedly works well to replace windows in a framed wall without needing to remove siding. – tbc Oct 23 '13 at 15:02
You said you were replacing an existing basement window. Almost every basement window i seen is install in the middle of the foundation and on the outside of the foundation the concrete is tapered so water drains away. I added a picture to the above post. (Admins keep editing my posts with wrong information) This makes is hard to install a window flush to the outside with nailing flange. – Justin K Oct 23 '13 at 23:00
If your foundation doesnt have this tapper then use the flange and cover with trim but you will be using concrete anchors to attach trim. Or remove flange like you said and install were old window was and chaulk both sides good. Either way I would still use shims and tapcons through the sides of the window into the foundation to hold the window in place square and level. – Justin K Oct 23 '13 at 23:03

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