Basement Windows

I am replacing the basement windows in my house. The current wooden windows are set directly into the cinderblock opening.
The new windows I bought at Home Despot are vinyl. They say I need a pressurized frame between the window and the cinder block.
Which should I do? Do I need the full 1.5 inch thickness of a 2x4 or 2x6 ?? or can I get away with less?

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You may also need a building permit but that's a question for your city.
I would think that if you have a window that fits the opening well and you can secure it to the wall then expanding foam insulation will make up the gap.

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Pure nonsense. Vinyl windows can be mortared into a brick or block opening just fine. At the top where they are fastened to the sill plate you may have to fabricate some wood filler strips. Its nice if the window is close to the opening size, but if not, simply mortar in slices of soft brick, build up some thickness with Sakcrete if needed and you're good to go, Did some of mine that way 7 or 8 years ago and they are weather tight and solid as can be. Good luck.
Joe

Thanks to both you and pipedown.
The windows are almost too exactly the same size. I will caulk and install and then Sakrete it in.
wrote:
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Pure nonsense. Vinyl windows can be mortared into a brick or block opening just fine. At the top where they are fastened to the sill plate you may have to fabricate some wood filler strips. Its nice if the window is close to the opening size, but if not, simply mortar in slices of soft brick, build up some thickness with Sakcrete if needed and you're good to go, Did some of mine that way 7 or 8 years ago and they are weather tight and solid as can be. Good luck.
Joe

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I've done than many times and they are still in place 35 to 40 years later.