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Old 09-29-2009, 05:49 PM   #1
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New basement in high water table


I am planning a new home in Maine on city sewer and water. I have a flat lot and the area is known for a high water table, though I am not sure exactly how high. Does the technology exist today to dig a full basement and prevent it from flooding during the snow melt and rainy season? If so should I price in a 50% increase in cost or 100%? Or should I forgo a full basement and stick with a crawl space.

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Old 09-29-2009, 06:20 PM   #2
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New basement in high water table


I'm no expert.... but my family has been battling basement water issues for decades

I can't tell you how much we wish we had no basement! Instead, invest in a larger garage to store your stuff and have your heater...

(next spring, we're going to dig around the perimeter of the basement and tar the walls..... and rebuild the window well for the gazillionth time )

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Old 09-29-2009, 07:35 PM   #3
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New basement in high water table


whew, JUST got here in time fortunately, i am an expert w/even successfully treated homes in nj, nassau, & suffolk on my resume,,, take a look at my site & the associated links,,, then if you have questions, feel free to e-mail & ask away,,, conc foundations're better'n block but block will work well IF you properly install the exterior wtr management system,,, most won't spend the $$ 'cause its cover'd up & they can't appreciate the value.

ps - ' tar ' is not the proper material NOR method,,, nor is the 3mil dampproofing coating rqd by the bldg code !


Last edited by stadry; 09-30-2009 at 05:50 AM.
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Old 09-29-2009, 07:39 PM   #4
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New basement in high water table


Yes, the technology exists to have a dry basement even if it is below water table. But you may not be able to afford the technology.

There are two distinct approaches. For the first method, you excavate a perimeter trench with perforated pipe, and connect the pipes to an outlet which carries the water to a lower elevation. If necessary, you use a pump. This technique, if successful, produces a dry basement by removal of groundwater. Such as system typically requires design by an engineer, since you need to compute the amount of water the pipes need to carry, you may need a permit to discharge the water, and you need to have a backup plan if the pipes clog or the pump fails during high water season.

Approach number two is to forget about groundwater control, and waterproof the basement. Successful waterproofing requires use of expensive waterproofing materials such as bentonite clay panels, or commercial waterproofing bitumastic compounds such as manufactured by Grace Chemical. The tar that you see applied to basements is NOT adequate for waterproofing, it is damp resistant at best.

If you do not control the groundwater, you need a relatively heavily reinforced concrete slab and walls, else they will crack under the large pressures generated by groundwater. This again requires engineering design, well beyond the capability of most DIY'ers.

The first step is to determine the actual seasonal high groundwater level, which is not as easy as it seems. The best way is to put in a piezometer, and monitor it for a few years. You can also estimate high groundwater level by checking soil mottling, although this requires some training. Remember, unless you are using groundwater control techiques, the maximum high groundwater level control the pressure on the walls and floor, and determines the required thickness of concrete and the amount of steel reinforcing required.
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Old 09-29-2009, 08:36 PM   #5
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New basement in high water table


Quote:
Originally Posted by itsreallyconc View Post
whew, JUST got here in time fortunately, i am an expert w/even successfully treated homes in nj, nassau, & suffolk on my resume,,, take a look at my site & the associated links,,, then if you have questions, feel free to e-mail & ask away,,, conc foundations're better'n block but block will work well IF you properly install the exterior wtr management system,,, most won't spend the $$ 'cause its cover'd up & they can't appreciate the value.

ps - ' tar ' is not the proper material NOR method,,, nor is the 3mil dampproofing coating rwd by the bldg code !
Wow IRC, I can't believe you just said something nice about block!

To the OP, follow IRC's advice, as crazy as some of it may sound, as he usually hit's it on the head with foundation repairs, at least.

I can tell you from experience in foundation repair, a high water table can be a nver ending battle.
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Old 09-29-2009, 09:44 PM   #6
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New basement in high water table


If you expect a possible high water table, you should put in both exterior and interior drain tile. This will eliminate excessive soil and hydrostatic pressures on the basement.

All the waterproofing on the exterior wall will do little good if there is a high water table since this could cause cracks and movement in the walls. Also you could also get cracks in the basement slab and water intrusion through these and the joint between the wall and the floor slab.

If you are building a new home this cost is not excessive if done then. Many good builders do this on every home, whether they anticipate a high water table or not because of the reasonable cost and elimination of problems is done initially.

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Old 09-30-2009, 06:05 AM   #7
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New basement in high water table


' if it were mine ' & we loved that lot & just HAD to build there i'd be thinking spread footings below the frost line ( if any ) & 5,000psi conc ( wtrproof according to aci ), w/steel reinforced walls,,, know it sounds odd but soil pressures can build enough to crk conc walls,,, blocks have compressive strength but much less lateral or the ability to ' stay straight ' w/o some help - columns, steel, & grout.

hopefully you can avail yourself of ext & int toe drains that ' run to daylight ' ( gravity drains ) otherwise you're looking at sumps & pumps along w/ext riser to service that pump.

ALL the advice here's good but, w/this obstacle, i'd work around it rather'n take it head on,,, as mention'd, wet bsmts ARE a lifetime challenge so why risk when its avoidabl think of your bsmt as a ship's hull & remember ALL ships leak
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Old 09-30-2009, 07:05 AM   #8
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New basement in high water table


here's a current job in atl,,, unreinforc'd block walls - just about all the stuff mentioned that should be done wasn't however it was blt according to ' code ' at that time

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Old 09-30-2009, 10:18 AM   #9
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New basement in high water table


Did that failure have drain tile?

I think I see a footing problem because of the multiple diagonal cracks.

The 8x8x16 unreinforced wall that high is definitely not right. We built 1000's of homes with 13 courses or 12x8x16 unreinforced for years, but the newer model codes do require nominal reinforcement for that height.

In the phot, it is not clear, but I don't think there was any blovking between the joints parallel to the problem wall. I also bought if there were pproper anchor bolts, so the wall did not have a chance if it was trying to be a cantilever.

Was the floor slab properly poured on the footing and abutting the bottom 4" of the wall?

Obvious there was poor backfill behind the wall.

Dick
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Old 09-30-2009, 01:02 PM   #10
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New basement in high water table


yes, drain tile ( 4" ads ),,, dick, when i worked w/turner in the city, we had a saying - ' those guys got paid & they're gone ! ' installed correctly ? no habla engineer-ise, senor ! ! !

ps - he did have a home inspection prior to buying this very fine house !
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Old 09-30-2009, 01:44 PM   #11
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New basement in high water table


IRC, you might as well figure on re-enforcing the adjacent wall as while your there. It appears to be layed on 1/4 bond!

I agree with Dick, that wall seems to be constructed in a "strange" method in alot of ways. By no means representative of the current codes for CMU walls in my state.

PS: Why do you think they finished off the top course of a portion of that wall with brick anyways.
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Old 09-30-2009, 07:12 PM   #12
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New basement in high water table


jo, wtf knows why they did it that way,,, all's i know is what we have now met w/fema today & the job's increas'd + it'll be done right this time,,, other walls'll be reinforced w/grout & steel pins, exterior excavation, & a proper toe drain running to daylight

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