My current project involves constructing a two stall garage appartment.Since this is being built in the city limits and in the 30year flood plain, code requires that the garage level be resistant to the effects of a possible flood.I wasn’t involved in the planning of this structure so I have to make the best of what I was assigned to do.Heres the deal…..the design team decided (with the code office approval) that it would be cheaper to frame the lower level with treated lumber and sheet the outside with 1/2″ 4×8 rockboard…….NO PLYWOOD WHATSOEVER…..not even on the corners. On the inside of the garage I installed diagonal bracing to help stabilize the structure.The outside will be brick veneer up to the second floor then poplar siding.I now have several concerns1)will the interior diagonal bracing be enough with 10’tall 2×4 walls …I don’t think that the rockboard will provide ‘squat’ as far as strength from lateral movement.2) as all of this treated lumber starts drying out the building wont be anywhere near as tight as it is now thus creating all kinds of problems like cracks in the drywall,flooring and doors being constantly out of adjustment. any thoughts?
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Make sure the apt floor is water tight, come the flood it'll probably sail off down the street. Why the pressure treated lumber? Is this flood going to be a permanent condition? Joe H
They took me to the job site ,showed me a mark in the alley and said anything 9' above this needs to be p.t.framing.My first question was...'Why not blocks'....too expensive.Flood water that high(nearly 1 mile from the river) will pretty much wipe out the town anyway.I think part of it might be the code guys flexing their muscles too ...if you know what I mean.
I was under the impression that building in a flood plain fell under FEMA (Federal Emergency Management Agency) rules and had to be engineered. I know that to be the case in Oregon, but because FEMA is federal, I assumed it applied all over.
There have been a lot of issues around the country in recent years with storms and floods and damage to and loss of structures due to complacent or inadequate building practices and the ultimate cost to the public.
The building codes for floodplain areas have to do with public safety and insurability. I'm kind of reading between the lines of your post, but when I read "apartment" I assume "rental" which further raises the public safety flag.
You raise some good questions but it would help if your location and circumstances were clarified a little more.
FEMA...thats a good point I think they were actually in town several years back reviewing the local codes or practices.Something to do with the gov't flood insurance program I believe.This place is actually being refered to as a carrige house (we aren't using the term appartment )Its going to be the caretakers residence.
I'll jump in here with what little I know off the top of my head and see if it helps or confuses you. What I am familiar with is in relation to coastal flood zones. It sounds like you are talking a river breeching it's banks so the standards might be different. Even in coastal there are minor differences and peculiarities because some places are where you just get wet from the rising water. Others are labled velocity zones because the shape of the bottom can either direct water to surge with a funnel action or break it up to cede quickly. So Here we have some that are FL 10 (flood ten feet above the benchmark) or VE15 or VE 19 or whatever(Velocity of storm surge can drive it to 19 feet above benchmark) I think this ios with hundred year floods.
FEMA enforces the national flood codes ( I forget the name of it) because anyone living in a coastal area can and should purchase flood insurance subsidized by the feds. Now the only way they will allow anyone on this island to purchase flood insurance is if the town adopts and enforces the national standards. The reason for this is that my neighbors house might float away and drive itself right into mine. I may have built according to the standard but I've still got major risk if my neighbor built a floater so they have a vested interest in seeing that every new house built in the flood zone is built right. Let FEMA find out that the local inspectors are letting folks skate on the rules and everybody could either get cancelled or get a rate increase.
Since most of the property here rises above flood zone pretty quickly (rocky coast) the easiest way for this town to write a code and enforce it was to pass a flood ordinance that says briefly, "No-one shall build a darn thing in any flood zone on this island"
That pretty well covers it for us so I don't deal with the specifics too often, except when dealing with grandfathered structures.
The lowest finished floor of living space must be one foot above the high flood mark which sounds like for you is ten feet up from that bench mark they showed you. That pretty much just allows the whitecaps to tickle the bottoms of 2x12 floor framing.
Walls below that must be either a kind that will let wave action pass through like latice work, or be built to a serious set of restrictions defining what it will take to resist being swept away to damage something else. I believe there are also provisions for crumple up break away panels too. Your sheet rock sheathing would qualify there.
The brick or block you mention mystifies me. From what I know, it seems like it would have to be a structural brick wall and not just a veneer. But we see little brick or masonry here except for fireplaces.
The diagonal braces? There a reams of pages in the national code about tie-down hardware, piers, bracing, yada, yada, yada. I couldn't begin to go into all that here.
Are your piers driven pillings or atttached posts? I'm speculating that driven piers are the way to go to avoid bracing worries.
Hope this helps or at least gets you started. I'd be suprised if you couldn't find the FEMA standards online somewheres. Good luck!.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit. The second is to look things in the face and know them for what they are." --Marcus Aurelius
You're pretty much on target. The coastal zones and riparian floodplain building codes do usually share one aspect and that is foundations. You point out that "lowest finished floor of living space" must be above the historical high water mark and that is very key: I'm near the coast out here, but also near some river floodplains where residences have been constructed; structures in both areas built in recent years have been put up on )a. pilings driven to point of refusal or )b. concrete columns set to bedrock or on a spread footing over pilings driven as in "a." Both situations require an engineered support array and the cost of the site testing, engineering and the foundation construction often costs more than the entire structure it supports.
Your island tribal leaders were wise to make construction in the floodplain a taboo.
Piffin...alot of good info...tx. Yes I believe this is a 100 year flood plain case (don't know where I came up with the 30 yr. figure). I'm supposed to install some type of special order hattches to alleviate pressure...let the water flow out I guess....seems like 2- 9x7 garage doors would be plenty.
The Flood Insurance Rate Maps (FIRMs) are what you are probably dealing with, and they are concerned with 100 and 500 year events. One caveat, the flood elevations are based on older historical data. Recent research by Cornell University, which serves as the national repository for rainfall data, indicate that the calculated frequency of these events is too low (otherwise here in New England we've been having One Hundred Year storms every 7 years or so). The "Hundred Years" doesn't really refer to once every years, but rather a 1% chance in a given year, of having a rainfall with that intensity (e.g.: in Massachusetts about 7" in a 24 hour period)--statistically there is a 1/10,000 chance of having two "hundred year" events in two consecutive years...Probably unneeded information. Probably also not your concern, but seems that the biggest issue may be the property's insurability--which can have a marked effect on resale. Basically the Feds want to discourage building within the floodplains; alot of the "wetland protection" enforced starting in the early 1980's was really "flood insurance risk reduction". Despite approval by local building and zoning officials, the owner still faces the liability that a potential buyer and/or financer either dislikes the risk or finds the coverage inadequate. If your concern, would check that the property is insurable, and the rates...
Regards,
Rework
Edited 11/10/2002 10:06:14 AM ET by Rework
Here, Rez, the wetlands thing is a whole'nuther ball of wax..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit. The second is to look things in the face and know them for what they are." --Marcus Aurelius
If those garage doors let water in from one side, you need to let it out on the other side..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit. The second is to look things in the face and know them for what they are." --Marcus Aurelius