IS MIXED-USE COMMERCIAL OR RESIDENTIAL?

[classicT]

Ty J and Rick 18071, you both make good comments. The prescriptive provisions of the law exists for public safety, yet other technologies can provide alternate means of achieving a similar level of safety. I saw one of those British homebuilding shows on Netflix where a guy built his house on a barge in a river floodway.
My point is, if the OP can understand the underlying safety issues behind the original prescriptive provisions of the law, there may be an alternative performance-based solution that provides for equivalent safety.

Ty J, if impedence of floodwaters was the "most important" issue behind the original prescriptive requirement, then why does the WAC allow commercial construction in a floodway?

Since when are there prescriptive and performance based laws?

This is not building code that we are discussing, it is a State Administrative Code. Totally different aspect than building codes.

 

[ADAguy]

Semantics again, unless your house will "float" it is moot to build in a floodway.
Even then, if it breaks loose and floats downstream, who then pays for the damage it does to bridges?

 

[Yikes]

Since when are there prescriptive and performance based laws?

This is not building code that we are discussing, it is a State Administrative Code. Totally different aspect than building codes.

I agree, but every prescriptive law is originally crafted with a performance-based goal in mind. In context with my other posts, all I'm saying (again) is: find out WHY residential is not allowed, but commercial is allowed; then find out how neighboring municipalities addressed this successfully when they allowed vertical mixed use in a floodway; then see if that concept can transfer to this site prescriptively without affecting the safety performance intended in the WAC.

No one (including ADAguy in post #50) seems to be addressing why or how commercial construction is allowed in the floodway.

 

[ADAguy]

Because they have insurance and/or the financial ability to rebuild, residents (whether owners or renters) often lack the ability to rebuild, wait till too late and have to be rescued (even when told to evacuate - remember Katrina).

 

[Yikes]

Because they have insurance and/or the financial ability to rebuild, residents (whether owners or renters) often lack the ability to rebuild, wait till too late and have to be rescued (even when told to evacuate - remember Katrina).

OK, so we have established that commercial vs. residential in a flood way it does not have to do with impeding the flow of water.
We speculate as per post #52 that the "no residential" has underlying performance goals that address (1) the likelihood of unrecoverable damage to residences, and (2) the ability to evacuate.

So, let's picture a vertical mixed use building has residential units that are (1) on the second floor, well above the floodway so they are undamaged in event of base flood, and (2) have an exit path of travel that stays completely out of the floodway (for example, a "U" shaped building where the stairwells/elevators at both ends of the U are outside of the floodway zone). The commercial ground level is concrete construction, designed not to be undermined in event of flood. (Perhaps it is simply a commercial parking garage. This has addressed all the residential-specific safety issues identified in post #52, has it not?

 

[Paul Sweet]

This is probably a zoning issue, not a building code issue.

The National Flood Insurance Program and FEMA regulations are probably behind zoning code restrictions on construction in the floodway, because any structure in a floodway can restrict the flow of floodwater and cause greater flooding upstream. The buildings in the floodway probably predate this program, which I believe started in the late 1960s.

These regulations might make it impossible to get flood insurance on the building. If I remember correctly, NFIP will not allow flood insurance coverage in localities that don't enforce their regulations through zoning.

FEMA distinguishes between commercial and residential buildings when it comes to floodproofing methods. Residential buildings have to be raised above base floor elevation, while commercial buildings can have water barriers to seal off levels below base flood elevation. I don't know how FEMA would treat a mixed use building.

 

[my250r11]

This is probably a zoning issue, not a building code issue.

The National Flood Insurance Program and FEMA regulations are probably behind zoning code restrictions on construction in the floodway, because any structure in a floodway can restrict the flow of floodwater and cause greater flooding upstream. The buildings in the floodway probably predate this program, which I believe started in the late 1960s.

These regulations might make it impossible to get flood insurance on the building. If I remember correctly, NFIP will not allow flood insurance coverage in localities that don't enforce their regulations through zoning.

FEMA distinguishes between commercial and residential buildings when it comes to floodproofing methods. Residential buildings have to be raised above base floor elevation, while commercial buildings can have water barriers to seal off levels below base flood elevation. I don't know how FEMA would treat a mixed use building.

Exactly my point, Paul Said it better.

 

[ADAguy]

OK, so we have established that commercial vs. residential in a flood way it does not have to do with impeding the flow of water.
We speculate as per post #52 that the "no residential" has underlying performance goals that address (1) the likelihood of unrecoverable damage to residences, and (2) the ability to evacuate.

So, let's picture a vertical mixed use building has residential units that are (1) on the second floor, well above the floodway so they are undamaged in event of base flood, and (2) have an exit path of travel that stays completely out of the floodway (for example, a "U" shaped building where the stairwells/elevators at both ends of the U are outside of the floodway zone). The commercial ground level is concrete construction, designed not to be undermined in event of flood. (Perhaps it is simply a commercial parking garage. This has addressed all the residential-specific safety issues identified in post #52, has it not?

No, what of all the flooded vehicles and their environmental contents?
What of the threat to and cost of first responders who attempt to rescue them?

 

[Yikes]

No, what of all the flooded vehicles and their environmental contents?
What of the threat to and cost of first responders who attempt to rescue them?

Vehicles / environmental contents: Again, we go back to the OP's statement that the WAC already allows commercial uses; therefore the parking and environmental contents related to commercial uses has already been considered in the code.
First responders: for residents, in my design scenario that you quoted, they already "have an exit path of travel that stays completely out of the floodway." Therefore it should be no problem for first responders.