Connecting to an Existing Structure 1

[dik]

I know it's just good common sense... but, one of my colleagues has asked me if there is a formal requirement in any of the building codes that requires the certification of that portion of the existing structure.

Does anyone know of a formal requirement? other than just good engineering common sense.

Dik

 

[JAE]

dik - are you asking if an engineer is required to go back into the existing building design and back-check it for code compliance if the project involves an addition?

I think there are code provisions whereby an existing building must be brought up to code if the renovation/addition work is beyond a certain percent of the value of the original building. I don't know where that would be in the IBC or Canadian codes - it might be more included in the local government laws and standards.

Having said that, in the US, when there is an addition to an existing building, it is not required really to "certify" anything but it is incumbent on the EOR to ensure public safety/welfare and if the addition causes structural problems with the existing framing then it is on that EOR to deal with it.

I'm not sure how any engineer can certify an existing structure due to so many unknowns. In fact, my seal on a set of my plans and specs doesn't certify anything other than the fact that I was responsible for the work.

 

[dik]

Thanks JAE... your third paragraph sums up my understanding, and that's what I told him. I was unaware of any formal undertaking.

Dik

 

[dhengr]

Dik:
Obviously, it is incumbent on the EOR for the new addition to verify that any new loads imposed on the existing building and foundation can be taken safety, and within current code, just as his addition must. To that extent he must delve into the design of the existing structure. He should be sure that differential deflection and settlement are not significant issues due to the new loads. At that point I would think he has pretty much fulfilled his duty. Then if the use of the existing building and the regular loadings on it don’t change with the new addition I would think a strong argument could be made for grand-fathering it in (leaving it alone) without other structural changes, as having met the code under which it was originally built and approved for occupancy.

I am aware of some of the provisions JAE mentions about percentage of renovation or value triggering code updates, and agree with him that those are mostly local dictates. Usage changes would be triggers also. In the older editions of the building codes, and in their first few sections, there were some general paragraphs on these issues of additions, alterations and repairs, and code complience.

 

[bmrossetti]

dik,

The International Existing Building Code (IEBC) lays out the provisions that JAE and dhengr mention for when modifications/alterations will require checking the existing structure for compliance with the current IBC, or, in certain circumstances, the codes that were in effect when the structure was originally built.

As you say, it is also good common sense to check the existing structure for the new loads, even if the code did not formally require it.

Brandon

 

[JennyNakamura]

IBC 06, 3403.2, says "Additions or alterations to an existing structure shall not increase the force in any structural element by more than 5 percent..." That includes lateral resisting systems.

3403.1 says "Portions of the structure not altered and not affected by the alteration are not required to comply with the code requirements for a new structure."

Not sure if that's what you're looking for, but those are usually the two things I look at when undertaking additions/alterations.

 

[dik]

Thanks gentlemen, and Jenny... I have a reference, now... I couldn't find anything codified.

Dik

 

[msquared48]

If at all possible and the addition is to the side of the existing, I create a seismic joint so the seismic and wind forces do not affect the existing.

If the addition is to the top of the existing, then all bets are off as the whole structure should be checked if the addition is large enough. The last six words of the previous sentence are the crux of the matter.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[dik]

Thanks, Mike...

Dik

 

[MiketheEngineer]

Depending on how the new addition is attached - you may significantly change the "old" building. IBC says something like a 5% change in loads needs to be re-engineered.

For example - say you take off an end wall or install a very big door - things will change - A LOT. Or say you attach a 3 sided building to an existing one - (no end wall) - this will/may impart a whole new load on the existing building.

Check with the local building officials.