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We have a covered porch in our home supported by two columns on each end. We are trying to get sunrooms built on both the ground and first floor where we currently have a porch. The rooms would be 17x10 each. Existing windows currently facing the porch would remain as is. The house was built in 2006.

The porch has the same foundation as the home. So, no need to do make any changes to the foundation. Ground floor framing is relatively easy, and I am comfortable with it. The specific question I have is about first-floor framing. The home has 2x12 supporting floors. So, I'll use the same. How does one attach the rim joist for the first floor to the existing home? Do I need to cut open the stucco wall from three sides and then attach those joists, or can I do it without cutting the stucco? I'd like to avoid it, as one area where I needed to cut stucco was really hard with 1.5" of stucco and then plywood underneath. Would appreciate some guidance in this regard. Here are the floor plans for both rooms.

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  • rent a concrete saw.
    – Jasen
    Dec 12, 2021 at 11:16

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There is some missing information and there is some conflicts with the given information. Rather than ask for clarification on these items, I’ll assume some info and you let me know where I’m wrong. Afterwards, if necessary I can adjust my answer for the corrections.

I see a Ground Floor Plan and a First Floor Plan, and you indicate the addition is for a Second Floor. So, I assume this Second Floor is to be installed on top of the First Floor, making the structure a 3 story building.

I see two Options to install the Second Floor floor joists:

Option 1: This new floor will require the existing roof over the First Floor to be removed. When the roof is removed, the top plates will be exposed and the new floor joists can rest on them.

Option 2: If the top plates are too high for the floor joists, then a rim joist can be fastened to the inside face of the wall. To meet Code, the rim joist will need to support 200 lbs. per linear foot Live Load plus 50 psf Dead Load. A 16d nail has an allowable stress load of 106 lbs. when fastened through a 2x lumber. Therefore it takes a minimum of 3 - 16d nails into studs spaced 12” on center. If the wall studs are 16” on center, then 4 nails are required into each stud.

You asked if the stucco needs to be removed in order to install the rim joist. Yes, the stucco needs to be removed in order to install the rim joist on the house. The rim joist need to be fastened into the studs, so if you cannot locate each stud behind the stucco plywood backer, then it needs to be removed too.

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  • Both Ground floor and first floor are new addition. I incorrectly used second-floor. I should have called it first-floor to begin with. Sorry for the confusion. What I am hearing is that cutting the stucco wall is must to add the floor. Right? Dec 12, 2021 at 14:26
  • Yes, the stucco must be removed. The fasteners that hold the rim joist to the wall studs must penetrate about 2”. If plywood is left on the wall after the stucco is removed, then the nails (or screws) must accommodate that thickness. (A 16d has a diameter of 0.162” don’t go below that.)
    – Lee Sam
    Dec 12, 2021 at 18:26

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