Engineering of Condo vs Apartment

[Ambemily]

Back when I was an EIT I mainly designed residential structures. Every now and again we'd get a condo or apartment building pass through. From what I remember, the lateral design of an apartment building is dramatically differently than the lateral design of a condo building.

For the apartment building, the lateral wind loads would be determined for the entire building and the building structure would to share those lateral loads between all of the units (it was considered a single building vs multiple buildings when looking at the lateral design).

For the condo building, each individual unit in the condo would be designed for the entire wind load on that unit (full wind force regardless of if it's an interior unit or not). This resulted in higher wind loads, particularly in the longitudinal direction as every unit would be taking the entire longitudinal wind loading (compared to the apartment design where all of the units shared the longitudinal wind load).

From what I was told when I was learning is that this is because apartments are owned by a single owner and condos are owned by multiple owners.

I'm trying to determine where this difference in design shows up in the code, if it does, or get some additional guidance on this topic.

Thanks!

 

[phamENG]

By "apartment" I'm guessing you mean a large multifamily residential building with a common entrance, stairs, etc. And by "condos" I'm guessing you're referring to multifamily residential buildings where everyone has a private entrance at ground level, private stairs, etc.

I've seen apartments that fit both descriptions and condos that fit both descriptions, so it has absolutely nothing to do with the fact that people own individual units. It's about the inter-connectivity of the diaphragms and LFRS. In townhouses (your condos) what you describe could make sense if the fire separation at the party walls forces a break in the diaphragm. I'm not sure I would design the inner units for the full force of the side to side wind load, but at least enough to satisfy stability requirements. Similarly I look at the entire building and then apply it to individual shear walls based on how they interact with the diaphragms.

 

[TheDW]

Our office doesn't do condos, but we do townnhomes with firewalls between to have independent LFRS like you say. The IRC provision is here:

My understanding of the intent is that if one unit burns down, the unit next door that was protected by the firewall still has to have a valid LFRS.

 

[Ron]

In the US, townhomes fall under the residential code. Apartments and Condos fall under the commercial code. From a design and construction standpoint, there is no difference between an apartment and a condo, unless you have statutory requirements otherwise in your state. Mostly, statutory condo requirements have more to do with condo management than design and construction.

 

[NorthCivil]

What is a "condo", "apartment", "villa" etc varies a lot depending on local conventional language.

A "villa" in the US is very different from a "villa" in korea for example

 

[IRstuff]

OP's profile says Oregon, USA

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[phamENG]

Daywalker - good call. The townhouses I've done have had the 2 hour party wall, so they're exempt from being 100% independent. Good reminder, though, so thanks.

 

[Canuck65]

In my jurisdiction there would be no structural differences between a condo and an apartment building for a similar type building. As an example, for a 15 storey apartment or condo building, lateral loads would typically be resisted by a central elevator core and also the stairwell cores (which would be shared by all condo owners). Typically the condominium as a whole would be responsible for all base building structural elements, not the individual owners.

 

[XR250]

I am pretty sure insurance companies lime apts. a lot more than condos.

 

[phamENG]

XR - agreed. I recall a whole section of questions about condo work on my PL application. I worked with one developer who built "apartments"...the plan was to rent them out for a few years, clean them up, and sell them as condos after he'd used up the rental tax breaks. I wasn't the EOR for that one, so I don't have to sweat it too much, but I wonder what the insurance folks would say to that...

 

[Brad805]

The important difference is risk.

 

[JoshPlumSE]

XR - agreed. I recall a whole section of questions about condo work on my PL application. I worked with one developer who built "apartments"...the plan was to rent them out for a few years, clean them up, and sell them as condos after he'd used up the rental tax breaks. I wasn't the EOR for that one, so I don't have to sweat it too much, but I wonder what the insurance folks would say to that...

I've thought about the same thing. That some brilliant developer should build an apartment complex and rent them out for 10 years.... Beyond which it becomes difficult to sue for construction defects.

I've not been involved in condo development before, but I hear rumors that developers will do them with the idea that they will declare bankruptcy in 10 years or so because they know they will get their pants sued off for minor issues (i.e. cracked stucco). But, that this generally only applies to the types of condos that all part of a single building.

Just another reason why real estate is so expensive here in California....

 

[EZBuilding]

There was a thread on the Professional Ethics board - most developers in a commercial setting will set up the project through a LLC. Prior to the project being finished all of the profit has been sucked out of the LLC leaving nothing left for compensation of litigation. Which is why attorneys will typical go after the gc's and designers.

 

[phamENG]

Which is why attorneys will typical go after the gc's and designers.

Yay...