Foundation question

Reply

  #1  
Old 09-11-13, 09:18 AM
M
Member
Thread Starter
Join Date: Jun 2005
Location: New Hampshire
Posts: 253
Received 0 Votes on 0 Posts
Foundation question

I'm considering buying a building lot. the lot has an existing poured concrete foundation on it that was poured 10 years ago but has never been built on. it has been backfilled and was inspected and ok'd to pour and ok'd to backfill 10 years ago by the town's building official. they did not pour the slab floor, it is filled with rock up to the footings. I know the contractor that poured the foundation is a very reputable company with an excellent reputation.

I'm concerned that because it has not been built on and no framing to hold it out, that the walls may have become compromised over the 10 years.

question is: other than placing a level on the foundation walls to see if they have been pushed in, is there any way to test it to make sure it is structurally sound?
There are two cracks in the wall, one in a corner and the other in a section that should be very strong (where there is a U shape in the wall. the walls still appear plumb.

second question: I want to raise the foundation 2 feet for a finished basement. can that be done without compromising the structural integrity of the foundation?
 
Sponsored Links
  #2  
Old 09-11-13, 11:34 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 21,859
Received 357 Votes on 327 Posts
Check with your building inspections dept. to see if they will allow use of the footer and foundation walls. Had work continued on the project, even at a very slow pace, the foundation would still be good under the original approval. They may consider the original construction abandoned and require you to start from square one with a new permit and new footer or require you get a Professional Engineer to sign off on the existing construction.
 
  #3  
Old 09-11-13, 01:28 PM
BridgeMan45's Avatar
Member
Join Date: Oct 2011
Location: USA
Posts: 3,196
Received 0 Votes on 0 Posts
There are too many unknowns and variables for anyone on this forum to provide an accurate assessment of the foundation. When you hire that P.E. to examine everything and write his/her report, then you'll have answers to the questions you've asked.
 
  #4  
Old 09-12-13, 06:15 AM
M
Member
Thread Starter
Join Date: Jun 2005
Location: New Hampshire
Posts: 253
Received 0 Votes on 0 Posts
the PE did come out and that is all he did was put a level on the walls to see if they were level. To me that seemed very unscientific. Parts of the wall were slightly pitched in and parts were pitched out of the same wall. the forms must have been slightly bowed or bulged in spots under all the pressure of concrete when it was poured.

When we put a longer level on it, all the walls seemed plumb overall. is there anyway that a 10" wall could 'bend' under the pressure of the backfill, but not crack?
 
  #5  
Old 09-12-13, 09:26 AM
BridgeMan45's Avatar
Member
Join Date: Oct 2011
Location: USA
Posts: 3,196
Received 0 Votes on 0 Posts
The P.E. that came out (and whom I assume you paid for) didn't do a very thorough job. A complete inspection should have involved taking some in-place compressive strength tests (a Schmidt hammer is great for doing so, even though some young engineers consider it "old" technology), or even taking a few core samples to have broken by a lab. And he should also have taken enough pachometer readings on the wall in an effort to determine the size and spacing of embedded rebar. Without knowing what steel the wall has in it, it's not possible to determine if the wall can be retrofitted and made taller to accommodate the basement you mentioned wanting.

If you requested a thorough foundation examination and report, and only received a "bare bones" minimal effort using a carpenter's level by the engineer, you should file a complaint with the state professional engineering disciplinary board. They will conduct an investigation into his performance, and could well issue both a reprimand and possible fine if he was derelict in his professional duty. He would also be required to refund your $$$ in most states.

All bets are off regarding the foregoing, however, if he only did exactly what you told him to, in an effort on your part to save a few bucks.
 
  #6  
Old 09-12-13, 11:32 AM
M
Member
Thread Starter
Join Date: Jun 2005
Location: New Hampshire
Posts: 253
Received 0 Votes on 0 Posts
thanks BridgeMan. I can't speak for what was requested of the PE. he was brought in by the builder to 'evaluate' the soundness of the existing foundation for building is what I thought he was going to do. I agreed with the builder that I would pay for his services. I don't think he is planning to charge anything for that visit. when he left, the builder asked him to let him know what would need to be done to ensure it is sound and raise it 2'. I think he is going to suggest adding buttress walls, which does not make me happy as I'm planning to finish the basement and don't like the idea of being limited by buttress walls.

I'm seriously considering that the best thing might be to tear it out and start over. The difference between the cost of engineering/and raising the wall, along with some remaining uncertainty vs tearing it out and rebuilding may be worth it to sleep better at night. I'm pushing the builder to give me that number, but he is hesitating because he believes the foundation is perfectly sound and would rather we spend that money elsewhere. If we did tear it out and start over, I'd think that we would reduce the purchase price of the land by all or part of that difference. even though we are getting a sweet deal on the land already.
 
  #7  
Old 09-12-13, 11:43 AM
Join Date: Mar 2005
Location: USA
Posts: 6,130
Received 0 Votes on 0 Posts
Bridgeman was correct about the thoroughness of the inspection. The contractor initially hired/scheduled the engineer and report is between him and the contractor that has an interest in getting going. I suspect the engineer was paid (since they do not work for free) and the builder wanted the report. Raising it 2' will increase the loads and usually something extra will be needed to comply with the current codes since the old foundation is not the same as what was originally permitted. - Who knows what winters did the freezing and heaving of areas that were not planned to be exposed for 10 seasons of summer and winter, and that could be the reasons for the cracks that were not thoroughly looked at.

Dick
 
  #8  
Old 09-12-13, 11:48 AM
M
Member
Thread Starter
Join Date: Jun 2005
Location: New Hampshire
Posts: 253
Received 0 Votes on 0 Posts
thanks Dick,
you raise a good point about the areas that froze for 10 seasons, which would include the footing. it will be interesting to see what he says. so far i'm not out of pocket anything, but if the project goes forward, i'm sure i'll get charged back whatever the fee was for that 'walk through' was.

I think the builder's and my interest are somewhat aligned in that if it goes bad, it will be his responsibility....but i have to live there.
 
  #9  
Old 09-12-13, 01:53 PM
M
Member
Thread Starter
Join Date: Jun 2005
Location: New Hampshire
Posts: 253
Received 0 Votes on 0 Posts
could anyone out there give me a ball park number of what it would cost to tear out the existing 10" x 8' wall and footing, and re do it? my guess is that the drainage would need to be redone as well.
the garage should be fine as it was backfilled inside and outside so footing was never exposed. so I guess the new foundation would be pinned to the garage.

the lot is in Hartford Ct. area. the linear footage of the whole foundation is approximately 250'. There is a basement walk out of approximately 40' that doesn't need any walls, but i assume it would have to come out to be a single pour for the footing all the way around.

the new foundation will be 10' tall poured concrete and I'd like to have a shelf for some stone wall facing.
thanks!
 
  #10  
Old 09-12-13, 03:26 PM
BridgeMan45's Avatar
Member
Join Date: Oct 2011
Location: USA
Posts: 3,196
Received 0 Votes on 0 Posts
Only someone local in the business of concrete demolition and earthwork grading can provide you with an accurate figure of what it will cost. If I was to submit a guess, from 3000 miles away, I'd expect you'll be paying more than $25 per linear foot for the 250' of concrete removal, and another chunk for the dirt work.

Call it $10,000, in ball park numbers.
 
  #11  
Old 10-07-13, 09:48 AM
M
Member
Thread Starter
Join Date: Jun 2005
Location: New Hampshire
Posts: 253
Received 0 Votes on 0 Posts
Following up my question. I hired my own structural engineer to inspect the foundation and test the concrete. all the walls are plumb and square. there is one crack in a section of the wall that has lots of jogs in it and should be very strong. and one hairline crack in a corner. the PE said both were normal cracks. and was impressed that it did not have more cracks especially after 10 years exposure.
I've seen the original invoice for the foundation. it called for 3000 psi, 3/4" aggregate unreinforced 10" thick walls.
I hired a separate firm to come out and do 4 Windsor Probe tests on the foundation. results were very good. the tests were all upper 4000 to lower 5000 psi.

My structural engineer said that the most we should raise the foundation is 16" because going 2' more would exceed height of the current building code for a 10" thick unreinforced concrete wall.

the PE also drew up a sketch to add a 4"wide x 8" tall brick shelf to the 16" addition by adding a corbel and re bar. The brick shelf will support 10' tall of stone veneer on one wall. that wall will have lots of windows and jogs in the foundation. I think normally the brick shelf would go all the way down to the footing but that is not possible now. do you think doing it this way will add too much lateral stress to the foundation wall?

If anyone here sees a problem with this (especially the brick shelf), I would LOVE to know before I buy the property!!! thanks!
 
  #12  
Old 10-07-13, 10:29 AM
Join Date: Mar 2005
Location: USA
Posts: 6,130
Received 0 Votes on 0 Posts
I see no problem (even though I cannot see the actual job). The concrete strengths seem to be where they would be expected to be. You also have an ideal opportunity to easily put in a internal drainage system (perforated pvc and gravel) at the level of the bottom of the footings with a sump if you think there may be a water problem.

Corbeling is a well accepted method if done according to the masonry codes. It adds very little lateral load because the loads are well distributed bu following the corbelling requirements in codes.

Pouring the basement slab inside is a very common method and usually it is not connected to the exterior footings or walls in any way (rebar is a no-no) and no "soft" joint. It is a "floating slab that can also provide some lateral resistance for the walls in the case of a extreme loads or unnatural slight movement.

The vertical loads on a residential loads are extremely low and continuity is more important than the strength of the wall. - Especially if you only have 2x4s carrying the vertical loads down and a few sf of stone veneer.

Dick
 
  #13  
Old 10-07-13, 01:04 PM
M
Member
Thread Starter
Join Date: Jun 2005
Location: New Hampshire
Posts: 253
Received 0 Votes on 0 Posts
it will be framed with 2x6 throughout.

http://www.youtube.com/watch?v=TgFp8W4gP3w&feature=youtu.be Here is a link to a short video took of the foundation. as you can see there are many jogs in the perimeter. at 0:13 you can see where the one hairline crack is in the far right corner and at 0:19 you can barely make out the other crack.

According to the PE the walls are attached to the walls of the garage which have been backfilled on both sides and so protected from frost. If the footing that was not frost protected had heaved, it would show signs of cracking where it meets the garage wall. Also the area of the basement walkout has such lower walls, that they would have cracked in that area if it heaved. That all makes sense to me. The area of the corbel will be along the wall from :13 to :20

I'm not sure what you mean about the internal drainage system? the house does have a sump pit installed with drains leading into it. I thought those drains were on the exterior side of the footing though. the house is up on the top of a hill, so i dont expect much of a water problem. could you elaborate on the internal drainage system?
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: