Expert: Stephen Major (Owner--Major Design Group) - 4/3/2007

Question
We are in the planning process of building a home that utilizes a pre-cast concrete foundation. One side of the foundation is exposed and I would like to have the foundation manufacturer put an opening an area for a window. The window manufacturer recommends a rough opening that is �� larger than the nominal size of the window in a 2 X frame wall. The window manufacturer does not have any recommendations regarding rough openings in masonry walls. They do offer a window with a 1-7/8� �brickmould� which they suggest that we should add 3-1/8� to the frame width and height when using window with a �brickmould�. I know that a frame needs to be built within the concrete opening to accommodate the window. How should that be built with relation to the concrete opening? Do I need to use a window with a �brickmould�? I want to make sure that I furnish the pre-cast wall manufacturer the right dimensions for the openings.

Thank you,


Answer
Eric,

Unfortunately your fractions did not come through correctly, but I get the gist of your letter.  First of all you need to talk with the precast manufacturer.  They have undoubtedly done this many times and they should have definite recommendations for sizing the opening and the best ways to install the window.   Installation methods will vary depending on the style of window ( brickmold, flange, etc.).

Of the conceivable options and considering how thin the precast panels are, I would make the masonry opening (MO) the same as the window's rough opening (RO).  You can use either a brickmold or a flange style window and adhere it directly to the concrete with construction adhesive.  On the inside, frame a wood opening and attach the window jambs securely to it.  If you use a flange-style window you will need to case the exterior with wood or other trim to hide the flange.  In any event, be sure to fully caulk/flash the perimeter with a commercial polyurethane sealant.

Moisture can be a problem with wood against concrete, so your best bet would be to use an all vinyl or all aluminum window (or clad) with all vinyl or all aluminum brickmold.

Good luck with your project!