Basement to walk out basement conversion

DoubleStud · Jun 10, 2025

I have a project where the basement has 10 ft ceiling. The concrete basement wall stops just below the joists. They want to cut an opening to put a sliding door (orange) and smaller window (blue). I will be adding insulation just below the slab outside to deal with lack of frost depth. We will add boulder retaining walls to bring it up to grade. At first I was thinking to remove all of the concrete all the way to the top and put beam and columns. But after thinking about it through, It is probably hard to remove the concrete all the way to the top because the existing J bolts will probably make it hard to remove the concrete.

My questions are these:

1. For small window, how would you justify it if you can just cut out an opening and rely on the "concrete header" to support the load above? The joists and the rafters do not sit on this concrete. How deep of existing concrete header would you feel comfortable to span maybe 6.5 ft of rough opening? Is 3 ft deep (8" thick) existing concrete sufficient? How do you justify it?
2. For the sliding door (orange), I will need about 9.5 ft of rough opening. I am thinking to leave maybe 2.5 ft of concrete and just count it as dead load. The beam I specify will support all of the load plus 2.5 ft of concrete. This will support floor joists and the roof above. How would you detail this? Use W beam with studpack each end (stud closest to concrete will be anchored to the wall next to it)? Just add holes on the top flange and screw it to concrete? Or would you do something else? Or shall I go ahead and do my original plan and completely remove the concrete all the way to the top?

SinStrucEng · Monday at 7:49 PM

For the small window: Where I work wall reinforcement is frequently scarce, poorly placed, or missing altogether. I would not leave such a long opening as-is, I would add a steel angle to assist the concrete "header". I recognize that the "header" doesn't have the floor joists bearing onto it, but it will still serve a minor tributary area, as well as support the wall above. The angle can be installed from the interior, and is usually 8 to 12 inches longer than the opening itself so that 4 to 6 inches of angle can be let into the concrete wall on either side of the opening. The angle is typically then fastened to the header. People may say this is overkill but it's a relatively minor task considering that the opening is being cut anyways, and it's a worthwhile "insurance" for little extra cost.

Ron247 · Monday at 8:38 PM

I am not responding to your header question, but I am curious how much shear wall you are removing while also removing an existing lateral load that may be "balancing out" the lateral force from the other side of the house. The right side of your sketch appears to be an exterior deck and so does the top of your sketch.

The "orange" wall appears to line up with a beam that extends to something I cannot see. Trace your lateral load paths in both directions.

I cannot tell where in the house is walk-out other than where you are showing your new rock retaining wall. If the left side is walk-out now, you may need to check shear wall.

Where I work, I routinely see daylight basement homes where the front looks like a 1-story from the street and the right side (for example) is 2 story in appearance but almost the entire right wall is 2 big garage doors. 95% chance the basement wall elevation on the right side is racked in those cases due to unbalanced basement loading coupled with not enough continuous shear wall. Vice versa occurs when it is the left wall that has the garage doors. In your case, I cannot see how much additional wall you have available.

fp23 · Tuesday at 1:52 AM

1- I would check this header as unreinforced concrete. If it's lightly loaded it might work but 6' is starting to feel a little long for my gut feel. If it doesn't work I would bolt a channel to the face of the concrete that hides inside the furring wall, this way you don't have to overcut the corners for the angle bearing but either option can work. You also need to think about out of plane loads which I guess is just wind or seismic in your since you don't have any soil. I did one of these recently and I needed to bolt a vertical steel angle on either side of the opening to take the out of plane loads.

2- You could thrubolt a channel both sides to the concrete remaining above the opening similar to how you would do a masonry opening, might not work for your exterior architecture though. If you did a wide flange below it seems hard to get a great attachment to the concrete above with edge distances. I would want 1/2" epoxy anchors or Titen HD's. Maybe you could offset the WF to the outside face of the concrete and bolt up through the flange into the center of the wall on one side of the web. It also doesn't seem to difficult just remove all of the concrete above the opening and build a wood framed cripple wall above or below. Similar things to think about as #1 concerning out of plane loads.

XR250 · Tuesday at 12:05 PM

I don't think removing the concrete all the way to the band would be an issue. That would be my preference.
As others have stated, you may have a shear problem. Although, you could probably justify a 3 -sided building model depending on the aspect ratio.

jayrod12 · Tuesday at 4:59 PM

XR250 said:
I don't think removing the concrete all the way to the band would be an issue. That would be my preference.
As others have stated, you may have a shear problem. Although, you could probably justify a 3 -sided building model depending on the aspect ratio.

I agree with this, removing it all the way shouldn't be difficult. Honestly they may just cut the sill plate at the same time and take the anchor bolts and sill plate out with the concrete. Then you could do a wood or steel header attached to the walls on each side of the opening.

I also must stress how important @Ron247's point is about checking the lateral capacity of the building as a whole. You have removed a fair portion of the resisting backfill, so now you have an unbalanced fill scenario and that will require your foundation walls to act more like shearwalls than they may normally of needed to.

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