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MTSUBlueraider86

Post Flood Construction

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I was recently speaking with my HVAC service technician and sales representative about getting some work done on my unit. The subject of the flood came up. The following points may have actually contributed to the flood:

1) Removing of topsoil during land development which subsequently developers sold off to landscaping companies and the like.

2) Re-routing of streams and tributaries.

3) Too much rock removal thus making hills vulnerable to mudslides due to too much water.

4) Too much construction near rivers, ponds, lakes, creeks and other tributaries.

5) Crawl space instead of concrete block basements 8-10 feet high.

Number 5 is what surprises me the most. According to several in the construction industry that I spoke with, the crawl space is really unique to this area. Most areas of the country have a concrete basement or a slab. The crawl space is mainly in the hilly southeast where developers do not want to spend money on excavation for a basement, or they don't want the added expense of pouring a thick concrete slab and then building up. The slab is best for high flat area where there is no risk of flooding. The basement also is best to prevent flooding from getting in the house. The concrete basement also works well in tornado prone areas and acts like a bunker.

My house, along with most in the area, has a crawl space where plumbers and HVAC personnel must crawl on mud, rock and dirt to service my house. It would seem that if the houses near the water table had the original 6-8 feet of top soil plus an above ground concrete basement, there would have been no flooding. It was a bit ironic. The houses built on a concrete slab (and actually at a lower price point) much like a lot of commercial buildings, were untouched by the flood. Granted, they were on higher ground, but untouched just the same.

Do you see new standards coming from this tragedy?

SEC

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First, there's no natural capacity to hold15" of rain in any sort of soil. After the first 3 or 4 inches the soil is saturated and everything that falls afterwards is runoff. Plus, at least here in West Meade, there is a thick layer of yellowish-brown clay that is a decomposition of the limestone, and it's hard for water to perk through. In my yard, bedrock comes to the surface (spent several days this spring wirth a pickax chipping pinnacles down for mower clearance).

Second, crawl spaces are not optimal but they are far superior to slab-on-grade. A crawl space makes sub-floor utilities accessible and allows radon gas to vent. A crawl space contributes nothing to the likelyhood of flood damage, other than a flood should it occur will ruin the insulation beneath the floor as well as any air duct it enters. But if you get 2' of water in your crawl space, then that's better than 2' of water on your slab-on-grade floor and your $2k stereo floating about.

You have to divide the flooding into two categories: flash flooding along tributaries and river flooding. Much of Bellevue was hit by floodwaters from the Harpeth that formed from rainfall over Williamson County the previous day. Almost all of Williamson saw 10" on Saturday, and almost all of Williamson drains into the Harpeth or one of its triburtaries. Bellevue could of has sunny skies all that weekend and it still would have flooded just as bad along the Harpeth.

Richland Creek was an example of flash flooding from serial downpours. Several cars were washed off the road at the Hillwood/Harding Pike intersection. However, Richland for the most part runs through a residential area (Belle Meade), much of it one-acre lots and golf course, giving it optimal percolation. No new construction in its watershed of any significance for several decades, so no reason for anything to have made this flooding worse. It has flooded several times almost as bad, and usually from localized downpours.

The typical means of dealing with man-made runoff is retention ponds/basins. The idea is that you build a pond to retain a quantity of water equivalent to the decrease in percolation from pavement and roofs, so only the pre-development runoff amount exits the site. However, in an event that we dealt with where the ground was saturated (we've all seen the resultant landslides around the area), ALL rainfall becomes runoff and the retention ponds overflow. BTW there were several landslides in the Warner parks on land that have never been developed on or around. It was just alot of rain.

Here's some great maps and info that helps puts our flooding into perspective:

http://www.srh.noaa.gov/ohx/?n=may2010epicfloodevent

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Here's another great rainfall map:

http://www.srh.noaa.gov/ohx/?n=may2010epicfloodevent

Looks like a record SNOWFALL map!

As far as what codes may change, I suppose flood maps will be adjusted but I think codes relation to construction in floodplains won't. Retention basins have been code for years, and it would be up to the city to construct them in older developments that don't have them. And homes with full basements have their main floor no higher than those on crawl spaces; the builder just excavates downward for head clearance, which is no real help in a surface flooding situation. In fact, full basements can be a problem because the water that does percolate into the soil will force its way into the basement via hydrostatic pressure. I lived in a neighborhood once with 70+ year old homes that flooded through the cracked floors even when nobody else got flooded.

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I suppose you are right on most of your points I was not familiar with the specs for Radon prevention. Personally, I would not want a slab house being I don't want to live on grade although the slab is 12 inches thick or more. If the slab ever cracks, you may have water seepage. I am sure some builders try to get away with thinner slabs. I would prefer to live in a concrete and steel building where the parking garage is below the residential floors and flooding is not going to effect living space. Some slab issues are having all HVAC and plumbing in the walls as opposed to under the house and if there is ever a leak, drywall has to come down to fix it.

In regard to basement houses as opposed to houses with crawl space, I have seen basement houses above grade. There are a couple in my neighborhood where the homeowner spent $20,000 extra to have a fully finished concrete basement above grade. I have also seen concrete basements partially below grade but they were constructed correctly with water protection and french drains surrounding the property to keep the basements dry to the point some people actually have living space in the basement.

The fact of having crawl space though presents problems as well. The space is usually wet and damp which can lead to mold, mildew ,and the HVAC system not running at best capacity and efficiency. A dehumidifier could be installed, but what would the point be? MY HVAC guy said a dehumidifier in a crawl space was not needed unless there was a water problem. Even after the flood, mine was fine. Those lucky enough with full concrete basements in this flood however don't have to worry about a muddy swamp because of ground water which is almost impossible to prevent.

However with all of that being said, I wonder why in this area of the country crawl space is allowable but in some part s of the country, basements whether above, partial, or below grade are standard practice. I have seen below grade basements that were created as fallout shelters in the 1950's and 1960's. The have no concrete or masonry block at all. They are simply a hole in the ground and if they get wet by water running under the house foundation, they do become a muddy swamp that may require pumping to get the water out.

I'll take high rise living any day if I could afford it and sell the crawl space house in the flooded suburbs! I would love to live in Velocity, (although not on the grade level), ICON, Terrazzo, Viridian, Encore, Rhythm, Adelicia, 1101 18th etc...high and dry as they say!

SEC

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SEC, I think that in other parts of the country where basements are more prevalent, those houses at one time had (or still have) large furnaces and coal bins or oil tanks to feed them in the basement. Most mid-Tennessee homes you'd see in post-1980 developments have split heat pump cooling / natural gas heating systems with the heat pump and water heater in the living area. In my neighborhood (well, now the old neighborhood since I just moved to Franklin) the ranch homes were built without air conditioning and with ceiling resistance heat from about 1950 to the early 1960's, so there was no heating or cooling equipment to acommodate - and these homes weren't considered cheap. So with bedrock only a few feet down and no mechanical equipment (not even any ducts) I do see why the crawl space became standard. Add to that the shift to single-story (ranch) homes, which had no need for a stairwell whose space would have to come out of the useable floor space in order to add a basement. Multi-story homes just ran their stairs down to the basement, which had no effect on the usable space in the above floors.

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Also, anyone with damp crawl spaces should get that checked - it's not normal (unless in cheaply built home) and will lead to mold. Check for incipid water leaks, natural springs, damage downspout boots, and also make sure the grade around the house isn't either flat or sloping towards the foundations. And make sure foundation vents are open. This has been a public service message from Shuzilla.

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They could at least pour gravel in the crawl space on top of the plastic sheeting to help keep down moisture and make it a bit more tolerable so when one does go underneath the house and actually crawl under to do any plumbing or HVAC repairs, it is a bit easier. I am lucky, part of my crawl space is about 12 feet at the highest point and 3 feet at the lowest point as our house backs up to a hill. They could have easliy excavated appropriately and built a full concrete basement, but they were lazy and had to cookie cutter too many more houses. My water from the flood went through my sump pump rather quickly.

The frustrating thing about my neighborhood and Nashville in gereral is the fact we have so much rock, which is great for skyscraper foundations, but horrible when it comes to ground moisture. There are so many crevices in limestone that pretty much every home in Davidson County is going to get some kind of underwater problem at some point and cheap developers like the one that built my house, Fox Ridge, could at least gravel crawl spaces and do appropriate drainage construction. When we first moved in, we had many drainage issues that they had to repeatedly come back and fix and as the house grows older, 14 years now, and we still find things where Fox Ridge and their subcontractor cut corners to save money.

The problem with suburban construction is that it is really assembly line construction. Not much thought goes into the work. That is one reaosn why I always wanted to live in a high rise in the city. At least when you are dealing with a concrete and steel building and a concrete basement or parking garage there is a feeling of well being knowing that you are living in a solid structure.

Even Velocity which is stick frame, or lumber , on floors two through five has a solid concrete base and the first floor on grade is a very thick slab of steel reinforced concrete. You don't get that type of stability in a suburban home. The Enclave off Hillsboro Road is four story stick frame on concerete grade, but its high on a hill and a very sturdy building. I just wish for environmental reasons and sustainability reasons, we got away from lumber and focused on steel, concrete, lightweight concrete and other resources that are more strudy, strong and don't envolve deforestation, and a need for crawl space.

SEC

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