Expert: Bruce E. Johnson - 1/6/2009

Question
I need to in stall two 40''H x 6o''L windows into a block wall these will serve as egress windows for subgrade living space. My concern is the length of these windows affecting the structural strength of the wall. The wall is 8'' hollow block and supports one side of a single story wood frame structure. The top of the windows will be at the bottom of the top course of block. Should I use some type of steel reinforced lintel to replace the top course of block? Should I build a temporary supporting structure to remove the load from this portin of the wall prior to removing the cut out sections? Are there other considerations that should be adressed before removing such a large part of this wall?

Answer
Hi Bruce, that's a tricky one.  If your masonry wall was done correctly there should be at least one course at the top of the wall that is filled with concrete and has a bar of steel in it.  This is called the "bond beam".  It is usually two courses but sometimes it is only one.  Depending on whether or not you have a bond beam and how the house above sits on the wall will determine the answer to this question.  
A. If you have a bond beam and the floor joists in the house above  run parallel to the basement wall and the only joist on the wall is the one holding up your wall framing above then you can, if possible, double up the joist under the wall above and basically create a wood beam over the weakened area where the window is going to be installed.

B.If you have a bond beam and the floor joists in the house above actually sit on the masonry wall and butt into a rim joist then you are probably going to need some kind of added support, mainly because your bond beam is only one course.  A two course bond beam would probably work okay in this situation.    A 4"x4" x 1/8" steel angle can be installed underneath the inside corner of the window opening.  

When cutting the opening be sure and not overcut your vertical cuts or your bottom horizontal cut.  However you can over cut your top horizontal cut 6" on each side to allow for the bottom flange of the steel angle to slip into.  This provides support for the angle on each side.  Then you can tap con the side of the angle to the bond beam.

I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com