I am considering buying a plot of land on water. The land was low “soft” ground until the owner began backfilling it since 1950. It has been approved by the town as buildable but recommends all utility connections to the homes be “flexible”. He expects the streets to sink approximately seven inches over 20 years. Homes are now being built on this land with pilons on every corner and at every 10 feet approximately 30 feet deep adding approximately $15,000 to the construction cost. I would love to build a home for myself here and get the great view on the water but I am deeply concerned about anything I build on this land may sink and fall apart after 5-20 years. Any suggestions or comments? Should I walk away from this land?
Apple Tim
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Whether you should walk depends on your gut level tolerance for risk. Engineers CAN build anything. The question is whether you can pay for it. your estimate of costs might be low, since you don't have an engineering design or foundation estimate yet, other than a townies guess work. I would be guesstimating more like 40K or so, depending on size of house.
Talk to an engineer first.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit. The second is to look things in the face and know them for what they are." --Marcus Aurelius
Tim, is this lot part of a development that has any membership requirements? Will you be required to join a homeowners association of any sort?
I'm asking because some day in the future someone & their lawyer friend will decide to sue the previous owner who filled the land. You may be involved whether you like it or not if you are a association member.
If the land does sink, and the homes and infrastructure with it, someone will have to pay. You may be assessed for an amount of money that you do not have, and you may have no say in whether or not the repairs are made.
Sounds like a bad idea to me, but it's you money. And a lot of it too. Joe H
My guess is there are only two reasonable ways to go: Build extremely big or not at all. Five stories or forget about it.
By going big, you divide the extra cost of the bad soil over more square feet. By building something that would have to dig deeper than the incompetent stuff anyway, your extra cost for dealing with it is mainly shoring. That would make the extra cost for the soil conditions a smaller percentage of the total project than with an ordinary house.
-- J.S.
Apple Tim,
This backfill - what is it - dirk, rock, what? Probably not good in an earthquake zone. But it is do-able. Think of a boat, maybe a barge to be exact. What you need is a low per square foot loading. Limit it to one story. Use balsa wood for framing. [Don't laugh, this has been done, Think boats and airplanes.] Flexible connections are good. Hope this spurs some creative thinking.
-Peter
Anything you say will be misinterpreted and used against you. Do you understand these rights?
Sounds like all the advice you've gotten so far (locally) has been from the owner of the land and the city. I'd have a soils engineer review the site before you seriously consider building there. That's the only way you're really going to get a qualified opinion.
If peanut butter cookies are made from peanut butter, then what are Girl Scout cookies made from?
Here goes, some thoughts from Australia
"Soft" ground is unconsolidated, if you put a load on it, water between the soil particles will be squeezed out and the land will settle - and any structure on the land sinks as the subsoil layers consolidate. The consolidation usually occurs rapidly at first, then much more slowly. It is the rapid initial settlement that is usually responsible for damage. You can achieve the same result on solid ground (sinking buildings) by sinking a well and pumping water out of the sediments - this is one of the reasons Venice is sinking into its lagoon.
In general terms you have a number of options
1 build somewhere else
2 pile down to a firm layer - in your case this would appear to be 30 feet down.
3 build your structure on a reinforced concrete raft that "floats" on the soft ground - an engineered raft should be cheaper than piles and if placed on top of 7 inches of fill will be at the "right" level in 20 years time. Also you can do much of the foundation work yourself - the hardest part will be tieing the steel.
4 pre load before building - place a heavy load on the lot before building and later replace it with your house. Say your house will apply 200lb/sq ft to the ground. Two years before building you place extra fill on the land so that the area to be occupied by the house is loaded at over 400lb/s ft. This will force most of the settlement that would normally happen over 20 years to occur before you build. When ready to build remove the extra fill and build normally.
If you decide to build, as well as flexible utility connections, I recommend that items like garages, driveway slabs and decks not be attached to the main building. Then if differential settlement occurs, the exteral bits will not overlaod the house itself.
Lastly, if you decide to build make sure you engage a competent foundation engineer. If the land has been backfilled since the 1950s it is likely that the fill contains building rubble and stuff you now have to dump at licienced land fills.
Ian
Edited 11/21/2002 9:10:47 AM ET by ian
>build your structure on a reinforced concrete raft that "floats" on the soft ground
In the fwiw category, thin-shell concrete domes do really good in this type of environ, as well as expansive clays, etc. Their weight is evenly distributed around the footer, and they are monolithic, with no corners/roof-connections/moments subject to uneven settling. The building will move as a whole if it moves at all. A number of them have been engineered and built to float like you describe, with little extra cost.
Looks like a raft fountation will be the way to go for Tim.
Apple Tim,
A soils engineer is definately the proper course of action. I have personally lived the nightmare you may be getting yourself into. In hindsight there were many choices and different paths that could have brought resolution with a quicker timeframe and for less cost.
A good competent soil test will cost around $2000 depending on how many borings are needed. (split spoon method going down 30ft) A good rule is to bore 4 holes for the 4 corners of the house. If you have high hydrostatic pressures (water) then you will have three resolution methods. Spread footings (for decent boring results), and Compacted stone or pilons for terrible conditions. Spread footings and pilons generally cost a set amount and do not waver from that much. Compacted stone is more of a gamble. In my case spread footings were out so it came down to the other two and at first compacted stone was cheaper than pilons. ($20k vs $35k) So of course we went the cheaper route. A nightmare ensued soon afterwards when digging encountered much worse conditions in various places around the footprint. At that point the only course of action was to take measures to handle the worst conditions and follow that rule around the whole perimiter. Basically deeper excavations with upgrade to crushed limestone. (fist diameter) with larger equipment to 'hoe pack' (drive) the stone down down and down. With tons of stone to drive costs up up up. This is all on a 2700sqft 3 story victorian construction.
The soils engineer should explain all the possible scenarios with the risks associated with them. If pilons are your ticket then there is no set rule for spacing and depth. It will all depend on your individual soil test. Never base any of your conditions on other borings done outside your footprint. (neighbors borings) Building around lakes and ponds is like swiss cheeze.
Words of advice. Do not buy the lot until you get the soil tests. Yes you may blow two grand but that is better and easier than legally backing out of a land agreement that is on an as-is basis. The legal course of action will be a futile attempt.
Consider home values in the future if your engineered house is high and dry while those all around you start sinking. If all the others are build with engineered footings this may not happen. But it is something to consider when problems arise around you and you are caught into the trap. If this is a subdivision then considerations must be made for that. In 5 years the developer will not be around to resolve land issues. As for town approval as 'buildable', that just means it meets zoning requirments. (setbacks, flood easments, etc) It in no way sets the property as 'buildable with normal footings'. And never consider that as a legal tool for engineering cost reimbursment. The only way you will be protected from cost overruns is to have a legal and binding document from the developer the he/she will cover extra engineering costs. (will never happen)
Feel free to contact me at [email protected] if you want to learn more.
Benny