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I'm trying to determine if I can make some changes to my house's interior walls without making changes or additions to the underlying beam/pier/foundation structure. I have attached a drawing of the existing beam/pier/wall layout and I have marked the changes I want to make as A-E on the drawing (note that the description of the specifics of A-E is on the lower right of the drawing).

To summarize the house in text (also noted on drawing):

  • Built 1924
  • Single story with steep gable roof
  • 4x4 beams on 4x4 posts to piers
  • Continuous footings under exterior walls (raised foundation)
  • 2x6 floor joists
  • 2x4 exterior and interior walls (stucco exterior)
  • 2x4 ceiling joists (for the most part; deviations mentioned on drawing) with 1x4 "cross" braces in the attic above (I'm sure there's a name for these, but I don't know what they're called)
  • 2x4 rafters
  • Lath and plaster walls and ceilings

Changes I'm looking to make (also noted on drawing):

Item A: open the wall from the current 30" doorway to a 7' opening. This wall is not load bearing (it is parallel to ceiling joists and roof rafters), is not directly on top of a beam and is not connected to the roof except where it meets the adjacent walls. My concern is that this is a shear wall since it's lath and plaster.

Item B: move the wall 2 feet. There is no overlap of ceiling joists atop this wall though I'm guessing it helps ease the span of the kitchen ceiling since the existing 2x4's are not to code across the existing 11-foot span. Will likely have to upgrade these joists to 2x6's or maybe even 2x8's based on what I'm seeing in the span table for ceiling joists if I move the wall.

Item C: load-bearing wall with ceiling joists overlapping on top. Wall is currently roughly atop the beam/piers below. I want to move it 2 feet away from the beam below. Guessing this is not possible without potentially putting a new beam and piers below the new location of the wall, but maybe it's possible to cantilever (if that's even the right word)?

Item D: want to add a new wall here to create a hallway. It would not be directly above a beam, though the intent is not to have this be load bearing

Item E: similar to C with ceiling joists overlapping on top. However, this wall is currently not above a beam/piers. It would actually be moved 2 feet closer to a beam with the change I want to make.

Any feedback on items A-E would be greatly appreciated.

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  • might need to strengthn the floor under the new walls. and/or the roof structure above them. – Jasen Sep 11 at 20:23
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    The only way to do it and be safe is to speak with a structural engineer. – Gunner Sep 11 at 20:29
  • Are you located in a high wind area or seismically active area? Any cracks in exterior stucco or interior plaster that would indicate foundation movement? – Lee Sam Sep 11 at 20:49
  • Why don’t the 4x4 floor beams extend to the exterior walls? Does that mean the 2x6 floor joists span 16’ or so without resting on the 4x4 floor beams? – Lee Sam Sep 11 at 21:04
  • A couple pictures of your attic would help. I don’t understand your terms. – Lee Sam Sep 11 at 21:15
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Wow this is complicated...I love it.

You say, you want to know “if I can make some changes to my house's interior walls without making changes or additions to the underlying beam/pier/foundation structure.” Actually, it’s way more complex than just that...

We design from the top down and build from the bottom up. I’d like to start with your roof and how those loads are transferred down through your house. From your picture, it appears that ALL loads transfer to the exterior walls. That is to say, no roof joists or supports rest on ANY interior walls. That’s good. That allows you to move interior walls without affecting roof loads transferring down the walls to the interior foundation system.

Floor framing is designed for the critical span (load) and then used throughout the first floor. The critical span appears to be in the triple door entry area (I presume it’s the Dining Room) at about 8’. (Most of the spans are 6’ ) 2x6 joists at 16” on center spanning 8’ can support about 72 psf (old size lumber dimensions) depending on the species and grade. This is substantially above what is required by Code. (Code requires 40 psf “live load” plus an estimated 15 psf “dead load”. )

The 4x4 floor beams span about 5’ (4x4 posts are about 5’ on center) and can support about 250 - 400 plf depending on the species and grade. However, the total floor load on the 4x4 beams is about 385 plf. (Half of one 8’ span plus half of one 6’ span resting on the joists supporting 55 psf = 385 plf.) Therefore, the 4x4’s are barely adequate, (unless there is a roof load on them.)

Next is footings. No additional weight (load) is being transferred to the footings by moving the walls, so I don’t anticipate any problems with the footings.

Summary:

So, because the roof load is on the exterior walls only, (you should verify that I’m correct by looking up in the attic and checking the entire attic...your pic is for only about 1/3 of attic), then moving walls DO NOT affect your foundation system.

However, there are some major walls that appear to support some roof loads that appear to rest on the floor joists. So, to answer your question about changing your foundation, we won’t know until we know about your roof.

Area A: I think you are correct, the wall is non- load bearing. Lath and plaster are not shear walls. I wouldn’t worry about removing 3’ or so of wall.

Areas B, C, D, and E: Again, I think you are correct about increasing the size of ceiling joists or providing additional support where the ceiling joists do not lap at the new wall locations. However, when you remove the walls that are perpendicular to the exterior walls, you need to “splice” the exterior double top plate. Currently, the walls are “woven” into the exterior walls. Cutting them off requires you to splice the double top plate with 1) tying the roof joists to the double top plate (I like Simpson H-1 clips) and 2) Installing a strap over the top plate where the walls were woven together (I like Simpson MSTA or LSTI in 48” long lengths.)

  • This is incredible, thank you! Hope ok to continue back and forth. To clarify a couple of things... 1. You wrote "2x6 joists at 16” on center spanning... 72 psf..." However, the 2x6 floor joists are 24" on center, but I'm just guessing that if it was 72psf at 16 the 24 OC is still above the 40 live/15 dead? 2. You nailed it on 1/3 of the attic. I'll attach another picture of the outline of the attic/roof if I can figure out how to attach. 3. the stitching I didn't even know was a thing but of course that makes sense. No double top plates, though – newbie Sep 11 at 23:35
  • No problem...let’s work this out. 1) 2x6 joists at 24” on center spanning 8’ can support about 50 psf. If the Live Load is 40 psf, then that leaves about 10 psf for Dead Load. Assuming carpet weighs 2 psf plus underlayment 1.5 psf plus subfloor 2 psf, plus joists 1 psf plus miscellaneous (ducts, insulation, etc.) 4 psf, then the total Dead Load is about 10.5 psf, which is still within the margin of error. 2) Your drawing showing roof loads is exceptional. Those existing walls are important. I’ll have to think about how moving them changes the transfer of loads. 3) No double top plate??? Hmmm? – Lee Sam Sep 12 at 1:19
  • Areas A, B, and D: It should not be a problem moving or adding these walls, because you are not affecting bearing walls. Area C and E: The roof load has been transferred from directly on a wall to mid-span of your ceiling joists that transfers it to a new wall and then to mid-span of your floor joists is a bit tricky. Obviously adding a roof load to floor joists that barely meet current structural Code, will create a problem. Hmmm... – Lee Sam Sep 12 at 1:37
  • I don't want to say this too much in case it gets irritating (or is against the rules here), but, man, this is very helpful. Thank you. And you understand it perfectly and explaining the math is extremely eye opening. And, right, can't just add weight when what's there barely supports the floor let alone the roof weight. Also, I'm going to go back up there tomorrow and check to make sure I'm right about the lack of double top. Possible it's double, but I'm pretty sure it's not (thought I was told by someone that back in the 20's it was standard to only have a single top). – newbie Sep 12 at 3:04

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