I’m the looking at lots in Minnesota, where basements are the norm. The lot I love has mottled soil at 986 feet –the surface — elevation. There are ponds on two sides and there has to be a drainage area across the back of the lot. The area is wetlands and open space. The current plan from the developer is to add a whole lot of soil and make walk outs with the lowest floor elevation at 986 feet. We need to build an accessible home for our 7 year old with brittle bones, the walk out isn’t going to work. Can I try to talk to the engineer about leveling out the site and building a basement down into the mottled soil, or is that asking for the impossible? The second best lot has ground water down about 4 feet, again, is it possible to do a basement in that? Or do I have to give up on either the lots or the basement? Thank you thank you for feedback.
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Replies
STTRAHAN--
Initially the first lot does not sound so great, and the second not much better, if a basement is what you seek. Of concern is that the mottling extends to the "surface elevation". In Massachusetts that would indicate a high potential of trying to build in wetlands or at least a very marginal lot. A bit more information would be useful: lot size, distance to ponds and other wetlands and more about the "drainage area" that has to be built in back" ,topography (i.e.: "flat", 10% slope); Soils/vegetation, septic (on-site? sounds like this could be a problem without building a mounded system). I, and probably certainly others, would gladly assist with a bit more info...
Regards,
Rework, a third generation italian ditch (and "cellah") digger
p.s.: wish your seven year old continuing better health.
Sounds like you are asking for a wet basement.
One option would be a crawl space to get the foundation below frost level with a mud slab andf sump pump in the crawl to keep water from the boiler and other utilities. A little soil and grading would put your single floor home just abover ground then with slopes away from the foundation to help guide water away.
Don't give up on the basement too easily. I put one in on a project I am just completing. It worked out great. I was told it couldn't be done. There isn't but a one in 5,000 houses in this lowcountry area that has a basement.
I have a french drain around my footing leading to a sump pump that has not gone on since the roof went on, and 60 mil 3 ply butyl ruber rolled onto the foundation with a contact cement. There are plenty of new materials for water proofing and damp proofing a basement, but do your homework well, and err on the side of overkill.
I did also use the excavated material to grade the run off away from the basement.
I tried Breakthrough on a whim! This is a great site--thank you for the information. How much grade did you put in at this house? For times when Greg is in a wheelchair, we'd like to keep the amount of slope as minimal as possible, but would also like to keep a potential basement dry. It sounds like French drains are the way to go -along with other, I'm guessing all in all pretty expensive, protective measures. Does the landscape have to be significantly sloped to help, or can a foot drop over 12 feet (wheelchair ramp numbers I've gotten) work? The current elevation is at 989 feet, very flat, and from the soil sample, most likely wet in the spring. We have had an unbelievable amount of rain this year. I think we would raise the lot at least 6 feet over the current elevation to put it 1/2 foot above the new street elevation. It's just that the current plans for the area call for a 9 foot change (hense making the walk out possible), and a dramatic drop in elevation from the front to back of the house-- 908 feet filled, down to the existing 989. I'm thinking if we could do the 6 foot drop over the whole lot (150 feet deep) it would feel like a level lot. On another note, is it OK to build a house where that enormous amount of dirt has been hauled in?? This is in a very built up part of the twin cities, lots are few and far between, but we have had no luck in a year of looking for an existing house to meet our needs.
It's sounding like it is possible to put in a basement in mottled soil , but that maybe it would be cheaper and less risky to use a slab 6 feet over the current surface elevation (making it level with the road and above the water) and add a loft over a garage for storage?? We came through a tornado 4 years ago with 1/2 the roof gone on our current house, I'd like the basement area if possible!
Again, thank you for any feedback! Sorry this got to be a book.... Also, how do you feel about architechts??
Sharon
Sharon:
Landscape slope of "foot drop over 12 feet" adequate for surface runoff; larger issue is groundwater. John has a point about mottling not ruling out a basement. However, the ponds remain a concern as they represent actual (mottling a subjective call) water elevations. The current plans seem to be filling to accomodate for on-site septic systems in the front of lots (is this the case?). If so the items (septic, foundation, landscaping, particularly final slopes) are best considered together. Regarding building on a filled lot, with good material and proper compaction that should not be a concern. Before an architect, this sounds like a situation where a good professional engineer may prove of invaluable assistance. Such services may be required by your local laws as far as design of the on-site septic, if that is going to be your responsibility, and if so you may be able to get quite a bit of "additional" guidance.
To once again confirm what John said, and partially retract my first response, if this is the lot you are going to build on, then I suggest adopting the Disney engineering approach "If you can dream it, we can build it..."
My best to you and yours, especially Greg,
Regards,
Rework
Edited 9/3/2002 11:43:44 PM ET by Rework
Sharon,
Did I read your note correctly? You you have an 81 foot drop (989 feet to 908 feet)from the front of the lot to the back. If this is the case, damp proofing the basement and getting good natural drainage from a french drain around the footing should not be expensive, but filling the lot on that scale could easily break the bank.
The house will be supported by the dirt under the basement footing. This will probably be existing udisturbed dirt. As Rework stated, with proper compaction under the house you should be fine. The rest of the fill is of no cosequence.
You saked how I felt about architechts. Again I agree with Rework. This is more a function for a civil engineer or a geo---- (soil engineer). Architechts are better used for large commercial buildings or extra large homes with high vaulted ceilings, walls of glass, balconies and bridges.
Hi John,
You read right, I typed wrong. The difference in elevation is currently planned to be a mere 9 feet. It's completely flat right now and they need to raise the elevation for a new road 6 feet. I'm going to look for an engineer who can take a look at the lot and tell me if it would work to keep the elevation change at 6 or 7 feet rather than 9, and if there is too much water to think about messing with a basement.
Many thanks for your and everyone else's comments!
Sharon
I'm not a soils guy, so I'm not sure what you mean by "mottled" soil. But I don't know why you couldn't have a decent basement.
When you excavate for the basement, you're going to have plenty of dirt that you've removed. Maybe you could raise the level of the house, and use the excavated soil to slope the ground away from the house. Use footing drains to daylight, foundation waterproofing like Dorken, and filter fabric around plenty of gravel in the backfill.
Don't really see why you couldn't make it work.
I was in the grocery store. I saw a sign that said "pet supplies." So I did. Then I went outside and saw a sign that said "compact cars"...
I live in a land of hardpan clays.............what is mottled soil?
....................Iron Helix
I built my last house on a lot with mottled soil. The grey clay content was discovered at about 1' below the surface. This forced me to build a sand mound septic system. It also caused problems with moisture in my basement as the soil drainage was very poor. The foundation walls were waterproofed, footing drains installed, backfilled with gravel, good perimeter drainage and we still suffered very high moisture levels in the basement. It was enough that I never felt comfortable finishing the basement or putting anything of great value down there...basically wasted space.
The house I'm in now was done on a crawl space and I spent the saved money...and then some...on a detached building with a walk up loft.
Ditch
Ditch,
At least I know what problems mottled soil causes when constructing a house...but Why? I guess I would still have to ask, technically, what are the constituents of mottled soil and why does its composition cause such a water drainage problem?
Still trying to understand..........................Iron Helix
Iron,
Mottled soils are soils which have exposed mineral contents, like iron, or grey mottleing which indicates high clay content. They are exposed because the soil has saturated and dried out slowly over and over again (indicating slow drainage). Soil which does not drain well will show signs of mottleing. Mottleing is a symptom of poor soil drainage, just like rusty metal is a symptom of excess moisture. When soils engineers refer to mottleing they are just saying "this is poor soil".
Ditch
Edited 9/2/2002 9:45:31 PM ET by luvditchburns
Iron Helix--
Ditch basically covered it, and here's a textbook definition:
"Mottling, soil. Irregular spots of different colors that vary in number and size. Mottling generally indicates poor aeration and impeded drainage. Descriptive terms are as follows: abundance—few, common, and many, size—fine, medium, and coarse: and contrast—faint, distinct, and prominent. The size measurements are of the diameter along the greatest dimension. Fine indicates less than 5 millimeters (about 0.2 inch)', medium, from 5 to 15 millimeters (about 0.2 to 0.6 inch); and coarse, more than 15 millimeters (about 0.6 inch)."
Common appearance wise can compare it to thick reddish spider webs(iron) against a tan (clay) backdrop. Have to be careful that in some of the wettest soils (gleyed, grey in color) the mottling dissappears. In states such as Massachusetts, the highest level of mottling is now taken as the mean annual high groundwater line. That is what raised my concern when mottling was described as being found at the surface elevation...
Regards,
Rework
Rework & Ditch,
Okay now I understand...............the locals here do not use the term mottled, but refer to a "blue clay" or "blue goo" which gathers in low pockets in old wetlands, or is found at depth when excavating. Acting as an aquifer, this blu goo holds or traps water at that strata level. This blue clay is always wet, and in large lenses holds water like a sheet of plastic. Don't see much of it here.....thank goodness.
Thanks for the enlightenment....................Iron Helix
Luvditch,Was the cost of the sand mound septic dramatically more expensive than a basic pipe and gravel?Thanks in advance,Roland.
This was on the last house I built about 10 years ago....my memories a little foggy...but a standard system installed at that time ran about 3 grand. That included a couple holding tanks, pipe, pea gravel, backfill and rough grade.
The sand mound system ran me about 9 grand. I had to have a number of tandem trailer loads of "approved" sand delivered. Anytime the word "approved" is used in a project you're gonna get hosed. A clay berm had to be built to hold the sand. The sand was piled about 3' high and graded by hand as a machine was not permitted on the field. This raised my elevation beyond what was acceptable (not enough natural fall from the main sewer line at the house) and I needed to incorporate a dosing tank and pump. Then landscape the whole mess so that it didn't look like an ammo dump. About a year after I sold the house I understand it began to fail.
A costly pain in the a$$.
I'm not a big fan of basements in general. IMHO, they are empty swimming pools waiting for water to fill them up. I prefer rubble trench footings w/crawl spaces. I realize in colder areas, basements are tempting because of how deep you have to go to get below frost line. Cheap space versus a continuing battle to keep it dry. Your choice. I understand there a lot of good basements out there, but there are also a lot of bad ones.