Building a 2nd Story onto an Existing Single Story Home

[00Z]

Hello All,

I am involved in a remodel project of an existing single story home built in the 1920's. The project was supposed to be a 1st story addition and has now morphed into a second story addition. The home has a concrete foundation with a wood sub-floor. I have done some preliminary calc's and the foundation is wide enough (assuming 1500 psf soil bearing capacity) to take the load of a second story.

However I am concerned about adding a second story onto a home this old. A few of my concerns are:

Anchorage to the existing foundation and quality of the existing concrete (although I am told the concrete foundation appears to be in good condition).

The existing studs are true 2x3's and I thought there was a code section requiring a minimum of a 2x4 wall to support a 2nd story but I can't seem to find it. I have not check the studs yet but think they should work.

Can I use modern wood design values for the old lumber?

My question is has anyone done a second story addition onto a wood home this old, and if so do you have any general advice on what to look out for?
I am inclined to drop the project. Any opinions, am I being overly cautious?

Thanks in advance to anyone who chooses to reply.

 

[Splitrings]

If you are in the US, this may help:

http://www.huduser.org/portal/publications/destech/residential.html

I have seen it done several times but is was always a non engineered project.

 

[JAE]

Splitrings –
That publication has a lot of info in it and appreciate you posting it. But I’ve always been pretty cynical about these types of government publications – i.e. I think they are a stinking waste of money.

One of the intro paragraphs has this phrase in it:

[blue]”This publication is intended for the use of professional personnel…”[/blue]

So this is a document for licensed engineers. Makes sense.

But then later on there are sentences like this:

[blue]What Is Structural Design?
“The process of structural design is simple in concept but complex in detail. It involves the analysis of a proposed structure to show that its resistance or strength will meet or exceed a reasonable expectation.”[/blue]

Wow – I guess I never would have known that being a structural engineer.

And these:
[blue] “Gravity loads act in the same direction as gravity (i.e., downward or vertically)”

“Loads produce stresses on various systems, members, and connections as load-induced forces are transferred down through the structure to the ground.”

“Dead loads consist of the permanent construction material loads comprising the roof, floor, wall, and foundation systems, including claddings, finishes, and fixed equipment.”

“Steel I beams are often used in residential construction because of their greater spanning capability.”
[/blue]

If the document is for “professionals” why was it written in a format more appropriate to second year college students?

I’m not criticizing your effort to help, please don’t misunderstand me. I’m just venting a bit on our government’s continued efforts at wasting our tax dollars with documents like this that extend out hundreds of pages and took who-knows how many man-hours creating such a document.

 

[JAE]

007 - in response to your question - 2x3's taking roof AND floor load? Not sure I'd do that.

For an addition like that it seems to me that the whole house would have to be reviewed structurally and many things would have to be covered:
1. Second floor connectivity - vs. overturning
2. 2x3 stud capacity under axial and wind
3. Overall lateral capacity (how many braced wall lines are there in the house? Enough?
4. Determining the old wood properties (modern design values don't really apply).
5. How will the upper floor and roof loads REALLY get taken down through the structure? Will various existing floor members get overstressed?
6. What is the current plumbness of the existing framing? Old foundations settle and old wood will creep over time and you might have eccentricity issues.
7. How competent are the exterior basement walls (assuming you have a basement) under higher axial load with lateral earth pressures.

 

[Splitrings]

JAE, I have always thought of this document as an attempt to bridge the gap between non engineered residential homes constructed by self-proclaimed carpenters and a full blown engineered structure. In my part of the US, residential projects are non-regulated structures. This document can be a tool in your “tool box” that can be used if it is ever appropriate.
I agree 100% with you that the likelihood of being able to design a second story on an existing stick build structure and meet an applicable code, is going to difficult at best. There are way too many unknowns for me to feel comfortable slapping my stamp on it. But like I have mentioned, I have seen several older (probably not as old as the 1920’s) single story homes that have had a second floor added. They are still standing. Whether it is because they have never seen a code specified maximum loading event or because of the unaccounted for redundancies in the structure.
Hopefully we haven’t hijacked this thread on OOZ

 

[00Z]

Thanks for the reference Splitrings and thanks for the response JAE.

There is no basement, just a footing with a 16" stem wall. You bring up some valid concerns JAE. I agree that the whole structure would need to be re-analyzed. I'm worried I'll get into it and then realize it just won't work.