The height of the bottom of the window causes the problem. That in combination with the distance to the end of the porch does not allow the use of 45-degree angles.
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The angle of the picture is deceiving - the piece of down pipe seen in the picture is actually at the point where it would meet the red line. This is where the first of the constructed fittings would be placed.
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The red line represents where the next piece of copper pipe would go. It is at the highest angle possible to pass under the window, and yet still make it to the end of the porch in a straight line. From there, the copper pipe would turn down (this is where the second constructed fitting would go) and extend straight down for a few feet, and then a 45-degree angle would be added (facing to the right in the picture). A piece of pipe would then extend approximately 8 feet, and this would put it a few inches past the foundation, and drain into some pachysandra.
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?There is not enough height in the wall after the window vs. the distance to the end of the porch to add a 45-degree angle.