I recently was working on this old block house and noticed I was going to need new windows.  The house currently has aluminum frame, single pane windows (not very efficient).  The problem with a block house with aluminum windows is that it is very difficult to install regular replacement windows.  This is because the aluminum frame is much thinner than the new vinyl frame of the replacement window.   The window would look out of place in the frame and the integrity of the window would suffer.  I found that I would have to remove the complete aluminum window frame and all, and install wood backing then put in a window with nailing flanges (new construction window).  These are the steps that I followed:

1. Remove the old window…if you are lucky the window was screwed in from the outside into  a wood window jamb.  (you will still have to use a new construction window)

2. Install treated wood jamb on inside window opening on bare block surface.  Each house is different, you will have to measure how much the window will have to be offset from the exterior wall of the house.  Usually a 1×6 will be sufficient, but double check before purchasing your wood.  If you would like more trim on the outside of the house and a little less window you can use a 2×6 wood jamb.  Make sure to measure twice before ordering/purchasing anything.   Cut the wood to size then install it in the opening by first placing a bead of construction adhesive on the side of the board that will be touching the block.  Then install 4 – 5 concrete anchors in each board.

3. Install the window.  Place the window in the newly formed opening, make sure it is level, centered, and square.  First center the window in the hole and make sure you can get nails in all sides of the flange.  Put one nail in the top right hand side of the window flange.  Plumb the right hand side of the window using the level, put a second nail in the bottom right hand side of the window.  Level the bottom of the window using the 2ft level, then put a nail on the left hand bottom of the window flange.  Take a tape measure and measure from the top right hand corner of the window to the bottom left hand corner, write down the measurement within a 16th.  Then do the same from the top left hand corner to the bottom right hand corner…It is very important that you measure from the same place on either side of the window…the measurements should be within a 1/8 inch this is to make sure your window is square.   If all is well then put nails in every other hole on the nailing flange all the way around the window.

4. Seal the window.  This is a pain on a block house because you have very little room for sealing.  You will need to get some window wrap from your local building supply store (looks like a roll of 6″ aluminum tape with tar on one side covered with white wax paper to conserve stick surface).   Measure the gap between the window and the block, not counting the flange. This will probably be about 1.5 to 2.5 inches.  Add 1.5 inches to this measurement (3/4″ x 2).  Cut strips of window wrap this wide and at least as long as the opening height and width.  Peel off the sticky backing on the window wrap, and place centered over the nailing flange (your strip should cover the nailing flange and go up on the window frame and the block approx 3/4″)

5. Trim the outside and inside of the house. (coming soon)

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