Preparing site for new house on slab

[dave1949]

Originally Posted by EddieWalker

When you mention that one corner is at existing grade, what is the drainage like for that corner? Since you are working the soild, take the time and effort to get your slopes right and ensure that the water will always run away from your home. Never rely or expect to use french drains or pipes. Slope the soil. Pipes plug up, drains fail. Slopes always get the job done!!!!!!

Eddie

One small quibble Eddie, we need good slopes and french drains up north. If you have a site with lots of ground water, or happen to have a very wet Fall, moisture at the surface down to the frost line freezes up for the winter and pretty much stays put until Spring.

There still needs to be a way for the sub-surface water to move away from the foundation during the winter. We use a lot of 'daylight' drains (a pipe that runs at a 1/4"/ft. slope away from the footer until it runs out of dirt) if there is some slope to work with. They can freeze or get plugged up with leaves at the mouth, but gravity beats a sump pump hands down, especially when your power is out .

Dave.

[MarkV]

Why slab on grade? You get pretty good winters out your way so footings will need to be dug below frost line. A crawl space offers you a better ability to insulate and run utilities.

MarkV

[dave1949]

Originally Posted by MarkV

Why slab on grade? You get pretty good winters out your way so footings will need to be dug below frost line. A crawl space offers you a better ability to insulate and run utilities.

MarkV

Most people around here prefer to have a basement. Slabs on grade and crawl spaces are not nearly as popular. A lot of people here simply won't buy a slab on grade house due to their history of frost heaving and cracking when constructed poorly.

80% of homes in Maine are heated with oil. About 90% of those have a 275 Gal. oil tank and oil burning furnace in their basements. Even in old houses, they had basements with roughly cut granite foundations and walls and a dirt floor. They may have used them as root cellars. Some have a bedrock (ledge in NE) 'feature' sticking up out of the basement floor. Some very old houses had beehive oven/fireplaces with a massive 10' square chimney foundation in the middle of the basement.

My house is a passive solar design. It has 8' tall concrete walls on the north, east and west. These are earth bermed to about 6" below the top of the wall. The south wall is built on a standard frost wall such as a crawl space would use. The frost wall wraps around 12' on the south east and south west corners to prevent frost penetration below those walls. For those 12', the 8' concrete wall is poured on top of the 4' frost wall. All the concrete walls have footers below them. They all have continuous inside and outside perimeter drains made of 4" slotted flexible pipe in a bed of washed stone. Moisture is your enemy because it wicks heat away.

My floor is a concrete slab poured inside the 8' walls and covers the top of the south frost wall. The floor slab stores a lot of heat provided by sunshine through south facing windows. For heat conservation the slab needs to be in the ground as much as possible.

The concept of a passive solar system is that your baseline temperature is the same as the earth around and below the foundation, walls and slab. You are adding heat to a structure that 'wants' to be about 50-55 deg. in winter, compared to a regular frame house exposed to the much colder outside air.

Having my plumbing below a slab does not give me the warm fuzzies. I considered trying to come up with a design where all my fixtures and drains would run in horizontal chases in the concrete with some sort of removable cover, or to centralize all the plumbing around a small service room. I never was able to come up with a layout that accomplished that and also had a decent floor plan. I am still convinced it is possible

The plumber I used , who is a really nice old guy, told me I should quit worrying about it, so I did. He said that would be the last thing he would worry about with PEX tubing. So far, he has been right.

Getting back to the drainage discussion, the stone drainage bed below my slab is well below the finished grade level. Moisture that collects there has to go/be sent somewhere or there will be dampness problems and heat loss.

Sorry for the long winded answer. But, I realize this is quite a bit different than typical TX/Southwest construction and thought it might help to add some detail.

Dave.

[EddieWalker]

Originally Posted by dave1949

One small quibble Eddie, we need good slopes and french drains up north. If you have a site with lots of ground water, or happen to have a very wet Fall, moisture at the surface down to the frost line freezes up for the winter and pretty much stays put until Spring.

There still needs to be a way for the sub-surface water to move away from the foundation during the winter. We use a lot of 'daylight' drains (a pipe that runs at a 1/4"/ft. slope away from the footer until it runs out of dirt) if there is some slope to work with. They can freeze or get plugged up with leaves at the mouth, but gravity beats a sump pump hands down, especially when your power is out .

Dave.

I'm of the opinion that every solution has multiple solutions. There is the best, what works, what's cost effective and then what the client wants. I'm of the opinion that an open, wide, trench is the best way to move water. You can make it so wide and gentle that it's almost invisable during dry conditions, but it will turn into a gently river during heavy rains.

When I have to, I'll go the pipe route, but it's always my second option. One house that had a real water issue required this. There was no way to get the water from the backyard, around the house and to the front yard. where it could get to the street. A local landscape company quoted the client $5,000 to install french drains. I came in at half that using catch basins and schedule 40 PVC pipe. While their method would have been invisable when done, mine solved the problem for allot less money.

On other homes, I've just moved a little dirt around to get the water to turn before getting to the house. The results were instant and the clients were very relieved to not have to spend all that money on french drains.

Of the homes with french drains that I've dealt with, all of them were plugged up and not functioning. Again, I just dig a shallow trench that diverted the water and was able to correct the problem.

I don't have any experience with basements. Dealing with water that's under the ground is foreign to me and none of my opinions have any merrit in those situations.

If the original poster is going to build a house on a slab, then I highly recomend grading a slope away from the slab in all directions. Even if it means cutting into a hill, or removing the most beautiful, 100 year old tree ever. The most important thing for maintaining the life and integrity of the foundation is to keep it dry. Nothing else matters if that isn't accomplished.

Eddie

[dave1949]

Eddie,

Didn't mean to nitpick on you. I think it's about regional differences in tastes, traditions, moisture levels and weather. I tried to explain that in my long-winded post. I don't doubt what you do there is the right thing to be doing for that area.

My concern is that people from all over the country read these posts and might be confused if they aren't familiar with construction techniques or realize they can vary widely by geography.

Dave.

[EddieWalker]

Dave,

I didn't think you were nitpicking me. LOL I just wanted to be sure that I was clear in my previous post on drainage and why I'm a fan of open trenches. It's always best to get a variety of opinions and ideas. The more options available, the better!!!

Eddie

[dave1949]

Originally Posted by EddieWalker

Dave,

I didn't think you were nitpicking me. LOL I just wanted to be sure that I was clear in my previous post on drainage and why I'm a fan of open trenches. It's always best to get a variety of opinions and ideas. The more options available, the better!!!

Eddie

That's good to hear Eddie.

Now I am curious as to why you encounter so many plugged up french drains. How are they constructed in your area?

Dave.

[rharkins]

Originally Posted by MarkV

Why slab on grade? You get pretty good winters out your way so footings will need to be dug below frost line. A crawl space offers you a better ability to insulate and run utilities.

MarkV

We're doing passive solar, and the slab is the primary heat storage medium. I am planning on putting down a perimeter footing to well below the frost line. The slab will be insulated along with the footing walls.

Rick

[dave1949]

Originally Posted by rharkins

We're doing passive solar, and the slab is the primary heat storage medium. I am planning on putting down a perimeter footing to well below the frost line. The slab will be insulated along with the footing walls.

Rick

Have you worked out how you will insulate the above grade portion of the frost wall and/or slab?

Dave.

[rharkins]

Originally Posted by EddieWalker

Find out what type of clay you have. Just calling it black clay means nothing. Some clay materials are excellent for building on, others are absolutley terrible.

I've never seen such a variety of soil within a couple of acre area. The primary soil is a mix of gravel and yellow stuff. We called the yellow stuff 'loess' up in Iowa. It's old prairie dust that blew into Missouri from Kansas (we say Kansas blows; they say Missouri sucks...). You can't put a shovel into it when it's dry, but once the heavy equipment breaks it, it turns into loose powder. When it mixes with the leaf litter from the oak trees, it turns into a very plastic black stuff that's slippery and sticky when wet, and impenetrable when dry. Two to three feet down I found some very nice brown clay that looks just like terra cotta. Where the blade sheared it off, it left a dense, almost shiny surface.

Originally Posted by EddieWalker

When you mention that one corner is at existing grade, what is the drainage like for that corner?

The top surface of the slab will be above grade. My thought was to scrape the organic crap off and use that elevation to start from. I'm a big fan of the proper grade, too. The site gently slopes diagonally to the house, so it will be easy to direct any surface water to either side of the house. I was planning on a daylight drain running along the footing, but only as a last defense.

I just spoke with a large contractor in a nearby town. He has several large excavators and is hungry for work. He's very experienced in working with the soil around the Lake of the Ozarks, and he quoted a very reasonable price.

Thanks to everyone who responded!

Rick