Tie-in to Existing Elevated Floor 1

[TRAK.Structural]

What's the standard approach/detailing for supporting a new elevated floor off an existing exterior wall that supports an existing elevated level? It would seem that the existing wall could be opened up to thread new floor joists in between existing floor members, but I think the wall sheathing would have to then be replaced and potentially with additional connectors/straps to justify continuity of the shear transfer down to ground from lateral loads. Another approach could be a ledger type design which would eliminate disturbance of wall sheathing but that just feels less secure than using the standard joist bearing on top of walls approach. Anyone done this before?

 

[TRAK.Structural]

No takers here?

 

[phamENG]

Missed it yesterday.

Both are potentially viable, but what's going on down on the first floor? If there's a beam or header down there, are you going to overstress it by adding this floor load? If it's a solid wall, I'd just do a ledger. But you need to follow the load paths (gravity and lateral) all the way to the foundation. Are you familiar with the IEBC and its rules for structural components during an alteration or addition? (That is assuming the IEBC is adopted in your jurisdiction and applies to houses.)

 

[ANE91]

Are you familiar with the IEBC and its rules for structural components during an alteration or addition? (That is assuming the IEBC is adopted in your jurisdiction and applies to houses.)

We’ve hired people straight from the world of home additions/remodels, and they’ve never heard of the IEBC. Aren’t there explicit exceptions for most residences, as you allude? I’ve read that code cover-to-cover multiple times.

I don’t like ledgers. Contractors often miss the studs, even though the sheathing nails are right there. Besides, there’s probably a quarter-board of sheathing at the floor platform, anyway, and removing it allows you the opportunity to make sure there’s no funny business going on with the top plate. If that lower wall ends up needing more studs, then you’re going to be taking off the sheathing, anyway.

 

[TRAK.Structural]

Missed it yesterday.

Both are potentially viable, but what's going on down on the first floor? If there's a beam or header down there, are you going to overstress it by adding this floor load? If it's a solid wall, I'd just do a ledger. But you need to follow the load paths (gravity and lateral) all the way to the foundation. Are you familiar with the IEBC and its rules for structural components during an alteration or addition? (That is assuming the IEBC is adopted in your jurisdiction and applies to houses.)

Wall is solid below.

Yes, for sure need to check wall framing and foundations for increased load. For lateral I would just plan to make sure the new structure can stand on it's own so there is no increased lateral on the existing.

We’ve hired people straight from the world of home additions/remodels, and they’ve never heard of the IEBC. Aren’t there explicit exceptions for most residences, as you allude? I’ve read that code cover-to-cover multiple times.

I don’t like ledgers. Contractors often miss the studs, even though the sheathing nails are right there. Besides, there’s probably a quarter-board of sheathing at the floor platform, anyway, and removing it allows you the opportunity to make sure there’s no funny business going on with the top plate. If that lower wall ends up needing more studs, then you’re going to be taking off the sheeting, anyway.

I am not huge on ledgers either, even though that's the way all decks are framed in my area. Anchoring through the rim/band to hold up a new floor just isn't as comfy as direct bearing on the top plate.

 

[phamENG]

Aren’t there explicit exceptions for most residences, as you allude?

Depends on the jurisdiction.

Here in Virginia, the IRC isn't the code, the Virginia Residential Code is. The VRC is an edited version of the IRC. Similarly, the IEBC is edited and renamed VEBC, and the IBC is edited and renamed the VCC (Virginia Construction Code). Chapter 1 is completely replaced in the VRC, and includes the following:

2021 VRC 103.1.1 Virginia Existing Building Code - Part II of the Virginia Uniform Statewide Building Code, also known as the “Virginia Existing Building Code,” or the “VEBC” is applicable to construction and rehabilitation activities in existing buildings and structures, as those terms are defined in the VEBC, except where specifically addressed in the VCC.

In other words, unless the VRC specifically identifies requirements for an existing structure, the VEBC applies.

Now, the IRC does have Apendix AJ, Existing Buildings and Structures. In Virginia, this is edited with a heading that says "This appendix is informative and is not part of the code." But many other jurisdictions may use it as enforceable code.

 

[phamENG]

Ledgers are common place. Use heavy duty structural screws rather than nails, and hang the joists from them. Cutting into the sheathing will cause all sorts of headaches.

 

[TRAK.Structural]

Update on this.

Client is very private and isn't agreeable to test cuts or even coming inside the home (at least not right now) so I've got to decide on a path forward with very little info on the existing structure. I was able to see the exterior and the crawl-space of the home in this area. Ground level floor framing is NOT supported on the wall where the addition will be added, but no idea about the existing 2nd level framing direction.

Due to the lack of info I have, I am now considering building a new load bearing wall as part of the addition and placing it essentially right next to the existing exterior wall, maybe an inch or 2 clear space. I would probably extend a short CMU stem wall down to the existing perimeter foundation and add additional concrete as needed for the extra load. This way the new addition can be designed as fully self supporting for gravity and lateral; but there are a couple items I need some thoughts on:

1. I think this concept is probably uncommon for residential, but is it totally crazy given the circumstances?
2. The proposed new load bearing wall may have to be sheathed on the inside face since it will be next to an existing wall. Is it possible for them to sheath it on the exterior on the ground and tilt in to place? Even if the answer to that is yes, I don't know that they would be able to get sheathing fastened on the exterior for the band at the second level floor.
3. If the answer to #2 is that sheathing would need to be on the inside face would there be any issues sheathing the exterior faces of the other 3 sides to this addition?
4. Lastly, there will be access to the second level of the addition from the second level of the existing home, just 1 regular doorway. Any kind of real expansion joint like in a commercial building I think is way far beyond what a residential contractor can do. Any ideas on how to connect the new to the old? Just something for flooring/other finishes to fasten to. This is maybe the most critical item to consider; if the detailing doesn't work out than all the finishes at this pass through would likely crack and distort.