Grading: fill-in vs cut-out
Hi. I am ready to make my house pad and I am not sure of any benefit to hauling in several loads of material when I can just cut out of the existing slope and have the same pad and drainage without the added cost of several loads of material.
Attached picture is to help understand my question as I do not know the proper terminology.
I did try to find out about cutting out a pad, but could not find anything. Of course, I do not know the proper terminology, so that may have been why all I could find was pads being built up from material being hauled in.
Thank you for any advice and/or links.
Doubt it matters for this subject, but I am in zone 4a (Nashville area)
-Mike
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Replies
Mike,
The more common approach to your "cut-out" house pad is the "cut and fill approach." Ih this approach, you don't have to bring material in or out. You cut material from the uphill side, and fill the downhill side with the removed material. This is often the most cost-efficient approach, but it requires careful placement and compaction of the downhill material so that it doesn't move after the house is built. There are pros and cons of each method.
The fill-only approach raises the house pad above the local grade level. This is good for water management, as any ground water will remain below the pad, and in flood-prone areas, it can raise the pad above likely local flooding. Even ponding water in the soils around a house can cause long-term moisture damage to walls and other infrastructure, and a raised pad can be a good thing. Also, the fill brought in can be selected (must be selected) for good mechanical properties. The downside, as you already know, is that bringing in fill is expensive.
An all-cut approach as you describe is also a possibility, usually if there is a use for the excavated material elsewhere on the site. If you have deep layers of organic topsoil, removing it is often beneficial, and the topsoil has value in itself. There is obviously potential for cost savings of not bringing in fill. It requires good quality subsoils that are suitable for placing the pad. It also requires more attention to water management, as now the pad is below the natural grade level. If the home is going to be slab-on-grade, you now have the base of the walls below grade level, and you will have to modify the wall design to deal with the moisture, and potentially, with soil loading. If the house is going to have a basement, the all-cut approach is somewhat common, as it allows for a walk-out entrance on the downhill side, and the masonry foundation can still extend above grade level on the uphill side.
Cut & Fill is, of course, somewhere in between the two above approaches. The decision on which method to use is generally based on the style of foundation, the site conditions (slope, water, soil), and other design factors. Any of these approaches can work.
I highly recommend having a water management plan before you make your decision on this. I went with the "cut" approach and pushed the soil downslope to level out the yard a bit. The house sits in the hill and seemed like a better option than having the downslope side be VERY tall otherwise. The problem, as mentioned above, is that I'm now I am into some pretty wet ground in the winter and have had to manage it. Nothing a little drainage plan cannot fix but I may have don't things a little different had I known the amount of water I'd be seeing in the winter months.
Peter that is very helpful and Joe, thank you for sharing your experience also. I am seeing where your point is very critical in my situation. I ran the laser to check height on the pad location and I realize if I do a cut and fill, I will have to further excavate out and away from the house on the front and create a valley to be crossed, or have water up near the house also. I really need to hire an experienced heavy equipment operator for consulting purpose as with all my variables I am seeing:
1. Challenge to determine how many loads I will need without under ordering, or over ordering material. My laser readings varied in both directions (Length and Width).
2. Not sure how high the pad should be.
3. Slope away: is it at final grade when? (I assume yes) If yes, how much top soil should I plan for in my detail to arrive at proper grade/slope?
4. If I don't get expert advice from someone who puts eyes on site, I may spend more money in mistakes than it would be to hire him. Of course, getting someone who knows what they are doing vs someone else is another concern I will need address.
Thanks again for the great input. I really want to get going, but I don't want my impatience the create a bunch of regrets either.
-Mike
The usual way to do this in terms of engineering would be to look at the site "sideways", so imaging laying down on the ground and looking towards the horizon along the ground. That's your 2 dimensional view. Imagine the area you need to fill as a wedge shape. The amount of fill needed to fill this wedge is the width x height x the length of the wedge and then divide that by two for volume. If you measured in feet, your result will be in cubic feet.
Make sure your measurements are for worst case (maximum dimensions), since its cheaper to have a little extra fill material on hand than to come up a little short, stop the project, and order another load. You'll need to allow a percentage over what you think you need to allow for compaction too.
That is your answer for #1 and #3. If you want someone to look at this for you and give you a real engineering plan, that's the territory of the civil engineers. If you want to get some help from someone who probably won't charge as much, but will still have the benefit of experience, see if you can find a good excavation contractor and explain what you're trying to do to them.
Bill
Note that there are some fundamental differences between a slab on grade and a raised crawlspace or basement design with stem walls.
I'd give some preference to being fully above grade, supported by undisturbed soil.
Thanks everyone. Turns out I will not be doing a slab. I got a call from a friend of a friend yesterday. He is a local dozer operator and he discouraged me from building up a pad out of "chirt" (name for local dirt and 1-3% clay and rock soil that predominates here and all the dirt roads in the county are made out of it). This is the only economical material for a pad to be built up with here. Anyways, he said that in the right time of year (summer) it can pack up and get as hard as a rock, but this time of year through the winter it will not compact properly. He encouraged me to go with the footer and crawl space. So, the dust has settled on my decision and I am decided on an unvented/conditioned crawl space. This offers some advantages to me also:
1. I have made three houses and all were footer/foundation wall, so I will have no problem DIYing it.
2. I can get started right away.
3. I won't need to hire a concrete man for the finish work.
4. I won't have to figure out as many new experiences such as plumbing under a slab and I am well versed with plumbing under a house.
5. I will have a great spot for my HVAC duct work.
6. Eliminate concern over slab failure.
He said I can scrape off my top soil and dig the footers, or I can scrape it, then level the house area and make footers. and later on use the dug out soil to make my grade work and use the top soil scraped for seeding grass. I am panning on, the latter leveling the house site and forming my footers with 2x8. This is because I want a conditioned crawl space and at this point am leaning toward a 2" slab over foam. I don't know of other details possible for a durable conditioned crawl space, so I need to research that to see if there are better budget minded options for me as this will be about 8 yards of concrete, gravel, metal mesh, concrete skills, etc...
There are some cons to the crawl space:
1. Need for stairs to get into house.
2. Need to add a finish floor.
3. My plan for the master walk-in closet being a concrete tornado shelter will have to be reevaluated since I am unsure how I would support such a structure a few feet off the ground and level with the wood floor.
4. I would say additional costs, but I don't know what it looks like when the dust settles as I will not need the pro for the footer and stem wall whereas I would need a pro for a slab.
Image of what I envision:
Leave more space than you think from the ground to the first wood. Houses settle over time.
Bryce,
No they really don't unless something has gone wrong.
Mike,
Is there some reas0n you can't excavate deeper so that you don't need stairs to get into the house
Malcolm,
The building inspector mentioned that a crawlspace if embedded deep into soil may need to have a slope and drain that allows it to empty out any water. Since I want a conditioned crawl space, I do not want any such thing. He is very reasonable, so with good waterproofing, I imagine he will be fine if I do lower it.
I would think that with a perimeter footing drain you shouldn’t have any water issues inside your crawlspace, unless you have a water pipe break in the floor or something like that.
Bill
Bill, that sounds good and I agree. I am going to lean forward with the idea of no drain under house and when he comes for footing inspection I will have a drawing ready to show him my foundation details and final grading. I am confident he will approve of my plan. Especially since I am trying to do very good practices on a poor man budget - wherever that lands me.