35 feet above sea level??????

Why not just build the full basement, and bring in fill to put around the house?

Does it actually mean you have to build 35ft. up? I need more information before I can answer. I'm in a flood prone area and the highest I need to go is 3 ft.

What type of flooding are you susceptible to? 35' is high for coastal flooding, and is higher than the Katrina storm surge. But if you are next to a creek that is 25' above sea level, 35' sounds reasonable.

A crawl space is less than 6' (5'?) high. You need to make sure that the flood vents are adequately sized. If you have high velocity water or waves, the walls that enclose the crawl space provide a lot of resistance to the water and can fail, taking the house with them. Open crawl spaces allow the water to flow through without obstruction.

I lived in a house with a 3' crawl space. We never had any problems with it. The crawl space was ventilated so that moisture wouldn't build up and rot out the floors. There was insulation under the floor.

We will be building with a golf lake behind our home and another across the street. The North Cape Fear River is across the street. We are not right on the coast. But about 40 miles inland. Believe me it does flood if there is a lot of rain in the community. We saw it last year at Thanksgiving after a coastal storm. There is a very high water table where we live. No ocean waves, hopefully, though! So no basements are built in the development and any pools have to be built above ground some.

When it rains it may take a few days for the water to crest but the water does rise. If there is a major hurricane that stalls in NC all the water runs down the mountains into the coastal plains before it drains into the ocean.

According to our topological survey, most of our property is 29-31 feet above sea level. And one of the builders told us our first floor had to be at least 35 feet above sea level. My architect is checking the regulations to make sure.

Zoe52 - The required elevation is based on the 100 year flood height for your area, plus 1 ft. Our situation is very similar. We had to build up 4 ft and wanted an enclosed crawlspace as it is better for our humid climate (we're in SC). Since we had to elevate for flood reasons, we still had to have flood vents. We were able to use "SmartVents" which are insulated for a closed crawlspace and balanced so they will open to the pressure of rising water. They are pricey though! The crawlspace walls are insulated with foam and the floor covered with heavy plastic - 8 ml I believe, it's been a while since we installed it. We are using passive venting with a 'through vent' in our pantry which has it's own returns. We did it ourselves as we are our builders :) You can hire a company to do it for you or your builder can do it fairly easily with some directions. Duke University did a very good study on the benefits of enclosed crawlspaces with directions and diagrams on best built practices. I have the bookmark on my work computer, I'll look for it tomorrow if you'd like.

The flood zone designation also means, nothing in the crawlspace that can be damaged by flooding, so all the big HVAC duct work is in the attic (the unit is geothermal and in the spare bedroom closet). I really prefer the vents being in the ceilings anyway so it's good for us. We want to foam the attic ceiling and bring it into the house envelope also - but for now that is not in the budget so we had our installers use R-8 insulation and we double checked the mastic work behind them.

Thanks for the info. What do you mean by passive venting? Do you have a vent in the first floor to air it out if it gets too much moisture there?

Also, I would appreciate seeing the Duke study if you can find it. My architect doesn't have our elevation as high one of the local builders had said we should build it. I really want to make sure that we don't have any problems later if it is not built correctly or high enough. Our architect is rechecking the requirements, though. Our architect is not originally from the area, but the builder is. I would rather have the house be too high than not high enough for obvious reasons!

Still even if our elevation is adequate, I am wondering that if we decided to stay during a big coastal event with lots of rain if our home could be fine but be surrounded by water for days or worse! Definitely something to think about for sure.

Here is the main link. The pdf(s) at the bottom have the study results from a couple of groups and directions. The diagrams are pretty much the same for all of the studies. We are doing the foam insulated walls and poly ground cover.

Here is a link that might be useful: how to close a crawlspace

Also, here is a link for the vents we have to use. They are code required for our zone in order to close the space. Our lumber yard was able to order them for us.

Here is a link that might be useful: SmartVENT