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Cutting rough opening in a cinder block wall

QuestionI would like to know how to install a steel door (already purchased and pre-hung) into my basement cinder block wall. There isn't a hole there so we'll need to cut a hole through the concrete block wall. I need to know the best way to do that. We won't have to move any outside dirt; the opening is already at ground level. Please get back to me about this, thank you.

AnswerInstalling the pre-hung door will be breeze compared to cutting the opening for the door. If you had a concrete wall I would suggest that you hire a company that specializes in concrete cutting. Cutting cinder blocks will be a project but it can be handled in a weekend. The question is, where should you begin? First, get a building permit, and second, determine your ceiling height. This is important because you need to know if you have the proper height for a pre-hung. Also check to see if the cinder blocks are below ground level and how many blocks will remain above the door (header area). Most likely you will need to take the blocks all the way up to the underside of the sill plate and only down far enough to be level with the finish floor in the basement.

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Start by putting up a temporary wall under and across the joists where the exterior wall will be opened up. Leave enough space between this wall and the cinder block wall so you have enough room to work. This project will require you to cut the wall on both the exterior and interior sides of the cinder block wall, so it is important to know the rough opening of the wall. To determine this, measure the overall width of the pre-hung doorframe and add 1/2" and another 6". (Your header will be this width measurement minus 3". The 3" is for the two studs that will be nailed to the ends of the header. The other 3" is for trimmers to be nailed to the studs under the header to support it. The 1/2" is the space needed to adjust the pre-hung door using shims.) Take this measurement and mark it on the wall both on the exterior and interior sides. Use a straightedge to draw the cut lines and make sure that the cut lines are level and plumb and the measurements between them are the same. Take care so the cut lines land on the outside of the center support of the cinder blocks.

Hang plastic from ceiling to floor around the work area to help contain the dust. Now, make sure you are wearing safety glasses, hearing protection, and a mask when you begin this next phase of the project. Take a 4- or 5-pound hammer and punch about a 10" (or larger) hole in the wall to the outside in the center of the rough opening. This hole is necessary for fresh air and helps move the dust to the outside while you cut the wall. Then use a circular saw and masonry saw blade to score/cut the cut lines. Once the cut lines have been scored/cut on both sides, you can start breaking out the blocks. Take your time and be careful when breaking out the blocks near the cut line. You may need to use a masonry chisel to break any cinder blocks that are attached in the center of the block.

Once this area is clean, it's time to access the opening for framing. It is possible that your rough opening landed in the center of some cinder blocks. If this is the case, then concrete can be poured from the top into these areas, but you will need to build a form in front of these areas to hold the cement while it cures. The form can be supported by 2x material wedged into place horizontally within the rough opening—i.e., up against the form and the cut cinder block on the opposite side. You may need to form up both sides. Before you start this, do a quick double-check on your rough opening measurements. Before pouring any concrete is a good time to enlarge the opening if necessary.

The frame including the header can be pre-built and placed within the rough opening with the trimmers added last; however, before building the frame, temporarily attach your studs (2x) to the cinder blocks using lead anchors and at least 3 lag screws per stud. This will require a masonry drill bit and wood bit. Once you've done a trial fit, build your frame and reinstall the lag screws. The heads of the lags will stick out so you will need to drill a hole large enough on the backside of the trimmers in order for the trimmer to lie flat up against the studs. Consider using screws instead of nails and pre-drill when attaching the trimmers.

When completed, you will have a wide rough opening that will require jamb extensions unless your pre-hung door is custom-built to fit that width. As you install the pre-hung door, keep in mind that if the door is going to swing to the exterior side, the door's frame needs to be flush to the exterior wall. If the swing is to the interior side, then the door's frame needs to be flush with the interior wall. If your door is custom-built, it is already fabricated for the proper installation. If you are going to build your own jamb extensions, putting the door in either of these positions will prevent you from butting the jamb extension up against the hinges. It will force you to put the jamb extensions on the opposite side of the frame, where it is required. Good luck with the project—you'll have your hands full on this one!

Copyright © 2001 & 2006 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.

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