Replies

1. 
   Guest_ | Dec 16, 1998 11:32pm | #1

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   The design of hillside foundations is no problem with good soil. The expense of excavation can be a concern. Hand work is very labor intensive, especially if you have soil to move up hill. Machine excavation will depend on the slope and accessibility of the site as well as the size of the foundation. The larger it is the more practical machine work becomes. I have done fairly extensive hand work on sites that were totally inaccessable to machines. If you do work by hand, a jack hammer will be your best friend. Pneumatic is best. For a large job do not even consider electric. You can go with a conventional foundation which will be level stepped footings which can be designed from tables, or a grade beam foundation that will have to be engineered. The choice will depend a lot on the amount of earth to be removed. You will undoubtably need to penetrate at least a foot or to below the frost line. If the frost line is deep grade beams will probably be a better option.

   If the lot is to be served by a septic system, this could be much more complitated than the foundation. Consult a local contractor or engineer on this first. If you make an offer, make it contingent on a preliminary soils report. You don't want to buy the site and find out that the soil is unstable.

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   Guest_ | Dec 17, 1998 08:53am | #2

   *Several considerations come to mind.1) As Mike said, a soils analysis is always a good idea. I have built on very steep slopes, and the septic tank/leach field can easily cost more than the foundation. Check with your local environmental / building code enforcement folks.2) Get a topographic map for the area, look at the watershed. Also maybe check with your county hydrologist, see if you are going to have unusually large amounts of sub-grade water. Also, there are lots of low-cost things you can do on site to help control surface water infiltration.3) Do not, for any reason, skimp on perimeter drains and foundation waterproofing.4) If ICF is still allowed in your area, it might be worth a look. I just built a hillside home on a steep site such that the front of the building is exposed and the back is fully buried (14' of drop across 50'). ICF walls with overturn footings and #5 grade 60 rebar gave us a wall that would easily resist 40psf equivalent hydraulic pressure, and waterproofed with bituthane quite nicely.5) Give careful thought to your driveway, and to water runoff/erosion control. These can be tough on steep sites, especially in winter (depending on where you live).

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   Garth_Hare | Dec 19, 1998 08:04am | #3

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   Dave: Thanks for your input. I have considered ICF but I question their ease of waterproofing, and how do they do as retaining walls? By overturn footings are you talking a wider footing? Do you have any views on retaining soil for the driveway, ie. boulders or concrete walls.

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   Fred_Matthews | Dec 25, 1998 02:50am | #4

   *It is doubtful that the seller will accept an offer contingent on a soils report. A good soils engineer should be consulted ( at your expense) prior to making a decision on buying the property. A good engineer will have knowledge of the local soils, give you ballpark budget costs for foundations and excavation requirements. Very steep excavations can be accomplished using lagging or sheet piling , but this is extremely specialized and can be expensive. Again-if you're serious about the site-talk to a soils engineer.

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   John_Wells | Dec 25, 1998 11:33am | #5

   *Does it look like it might have had a landslide at some time in the past?Looking at the stuff they built here in S. California and in Washington, and where they put it, I'd really dig into the soils issue with an expert. Know the geology of what you want to buy and what is around you - the hillside that can slide with you on it or slide onto you when some Gomer disturbs the drainage above. We chatted with the city building department on our last house purchase as part of Due Diligence. Worth some time talking to them. They should know where they have had problems with drainage in the past.They confirmed that our side of the valley was on sandstone while the far side was composed of hills composed of old lakebottom sediments - which explained the very extensive erosion of the stream beds eating up some back yards over there.It gets beyond foundation design. Just what are the soils and what is their history? A great foundation is not much help when the whole hill is moving and your house is red tagged.Here they tend to build on old landslides, on bluffs composed of marine sediments, etc.In San Juan Cap. they want to form a geological hazard taxing district so the builder can do his thing and if the slopes fail, they will fix it and up your property tax bill to pay for it. Kind of cute.Seeing large sheets of plastic, lines of sandbags and extensive drainage systems on assorted slopes round here, you know that someone is not Having a Good Day, Week or Year.In Seattle they have the same problem - they let them build on assorted ice age soils, till, clays with perched water tables that lubricate layers for easy sliding. Some apartments and very expensive houses have gone down the bluff to land on their neighbors. In several cases, the bluff above a waterfront home failed. In one case, members of the family were crushed to death in the sudden slide. In SE Washington a whole subdivision is involved in a slow motion land slide and they are yelling for FEMA money.J Wells

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   Garth_H. | Dec 26, 1998 10:10am | #6

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   I am looking into buying a .62 acre lot that is quite sloped and I am trying to find as much info as I can relating to hillside construction. It is an uphill lot with a steep frontage, then slopes genrly back to the line. I love the lot but I am concerned about excavation and foundation costs. Any input would be greatly appreciated. Please include what your backround experience is in this subject matter. Thanks, looking forward to your response.

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   Guest_ | Dec 26, 1998 10:10am | #7

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   My ICF experience is limited to Reward, which was very easy to waterproof. You just roll on the primer and lay up the bituthane sheets. Cleanliness and diligence is the rule here. Worked great. By overturn footings, I mean a wider footing than usual with rebar turned down into it, this helps resist the forces of the soil from overturning the wall. We had footings that were four feet (or more) wide for walls that were 9.5' to 11' high, as we had to anticipate some relatively high equvalent hydraulic pressures.
   I agree with the others who have replied that it would be a good idea to talk with your local building officials ahead of time. They know the peculiar conditions of the area as well as anyone, and are, in my experience, willing to help if you just ask.