Dry floodproofing metal building 1

[Cap07]

I've been asked to design the dry floodproofing measures for a non-residential pole building with 29 gauge metal siding. The owner does not want to elevate the building above the flood elevation, hence the floodproofing.

As I understand it, dry floodproofing the building would involve:

1) Ensuring that the building is securely anchored to resist floation, collapse, and lateral movement.

2) Installation of some kind of flood barriers on building openings (doors, windows).

3) Reinforcement of walls to resist floodwater pressures as well as impact forces from floating debris.

4) Use of membranes and/or sealants to prevent seepage through walls.

Anyone out there have experience dry floodproofing a building of this type? I've found most of the FEMA documents that pertain to floodproofing, but I was hoping someone might be able relate some actual experiences with this type of job. Specifically, what would work best for sealing the walls?

Thanks,

Cap

 

[Ron]

It is very doubtful you'll achieve waterproofing against direct water flow on a metal panel wall using membranes or other means. They are just not designed nor constructed that way.

Build a kneewall to above the flood elevation, then start your metal panels. You can waterproof the kneewall in a variety of ways.

 

[Cap07]

Hi Ron,

Thanks for your reply... by kneewall do you mean a short concrete stem wall, or a wood framed wall? If the latter, what methods are best for floodproofing?

Thanks again for your help.

 

[Ron]

Yes, a kneewall is a stemwall exposed on both sides (at least my definition of such!). I would build with masonry or cast-in-place concrete, as wood is non-durable when exposed to moisture in such applications. Further, the waterproofing system on concrete or masonry will be exposed and maintainable, whereas a waterproofing system for wood framing would necessitate multiple membrane layers to be effective for the long term. Also, ANY breach of the waterproofing could harm the wood and you wouldn't necessarily know it until it's too late (rot). With concrete or masonry, a leak would only be a short-term nuisance and would not deteriorate the base material.

 

[Cap07]

Hi Ron,

Thanks for your reply, that's makes sense to me.

The client wants to do a pole building (see the attached jpeg). But if I recommend that he goes with a concrete kneewall, could he still do a pole building (just encase the posts up to the top of the stemwall)? I've never seen that done with a pole building... but I've never designed one that's located in a floodplain either.

Thanks again.

 

[msquared48]

I believe also that any below ground grade beams and footings that are below the flood elevation have to be low enough to avoid any possible scouring action, still remaining intact after the flood.

He is still going to have to sandbag his doors and have a sump pump and generator on hand too. Just a fact of life. Might want to consider constructing some upstream debris barriers too.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Good points, Mike.

Cap07...encasing the poles in concrete should only be done if you coat them with an asphalt mastic. If you are depending on the embedment for moment resistance, then you'll have to consider that in your design. Otherwise, provide a pier in the kneewall and use a bolted connection for the poles to the concrete. You'll need knee braces at the top of the pole for lateral stability if you choose this route.

 

[Cap07]

Mike - Thanks for pointing that out to me about the scouring. For the man-door and garage doors I was going to design some kind of flood barrier. I haven't gotten that far yet.

Ron - The client originally wanted to do a pole building, so I was planning on using the poles for moment resistance. Please see the jpeg I attached in my third post. Would it make sense to still embed the posts down 4', with the concrete knee wall beginning at a higher elevation, e.g. 1' below grade (whatever is required for frost and scouring protection)?

Thanks.

 

[msquared48]

If you are going to use a pole structure for lateral resistance, you better reduce the available lateral resistance of the soil during the flood scenario. You probably will not have to put the full wind design force on the structure during this scenario, but I would defer to others or the local BD to see what the requirements would be in this case. I have not had to do that yet.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Mike, another good point. In my area, that would certainly apply.

Cap07..yes, you can embed and then encapsulate the poles with the wall at a higher elevation or just inset the poles inside the wall and create an insolation joint at the floor slab, with provisions of waterproofing the joint for hydrostatic pressure during the flood event. The flashing from the wall panels should extend over the top of the wall if you inset the poles.

 

[Cap07]

Mike - Thanks for pointing that out about the reduced lateral resistance.

Ron - Thanks also for your suggestions and comments.

You guys have been very helpful - thank you for all of your suggestions, etc.!

 

[msquared48]

No worries. Glad to help.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[MiketheEngineer]

That is going to be quite expensive to do - whichever way you go. And pole barns are supposed to be cheap... My preference is to just not build in a flood plain. There will always be "some" damage and somebody will have to pay for it.

Around here, they put flood vents at the floor level. With an impending flood - they move everything out. Some people open all the doors. The vents allow the water to come in - do little if any damge and drain out. Hose it out and move back in.

Of course - this idea offers little resistance to debris damage. But 29 gauge metal is really quite cheap. If you only have to do it once in awhile...

 

[paddingtongreen]

I didn't see how deep the water but depending on the depth, the type of soil and the duration of the flood, you might have a water migration problem, i.e. going under the wall rather than over it.

Michael.
Timing has a lot to do with the outcome of a rain dance.