rainman
New Member
Posts:37
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| 24 May 2013 09:54 PM |
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Is there a structural engineer on here that can do my basement slab here in TX? I have contacted a few engineers for my slab but think $10K to $18K is a bit on the high side for slab engineering.
Please PM me or you can simply respond to my post.
Thank you to anyone...everyone.
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ICFHybrid
Veteran Member
Posts:3039
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| 24 May 2013 10:10 PM |
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A basement slab? $10K? |
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Lbear
Veteran Member
Posts:2740
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| 24 May 2013 11:55 PM |
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I can get a 2-story 3,500sqft ICF home engineered for $6k and that includes the slab.
$10k - $18k for just a slab is insane.
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insuldeckflorida
Basic Member
Posts:158
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| 25 May 2013 06:30 AM |
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Jerry D. Coombs, P.E.
Coombs Engineering Services
1710 Stonecrest Trail
Wylie, TX 75098
XXX-XXX-XXXX (Phone #'s and email addresses are not allowed in forum posts)
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Alton
Veteran Member
Posts:2164
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| 25 May 2013 08:49 AM |
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Why does the slab have to be engineered? Is there expansive clay at that depth? Is there a high water table? Are you building over uncompacted soil? Do you plan to build on the edge of a turned down slab instead of a footer.
Most homes in my area that have basements do not have any engineering done for the slab. The code requires that either wire mesh or fiber be used in slabs. After the inspection, the wire mesh can and sometimes probably will be removed since it does not do much more than hold down the waterproofing membrane. Wire mesh to help hold any cracks that develop tightly together must be in the upper quarter of the slab. Since it is always on the bottom, then there is no reason other than the code to use it. The code in my area does not require the wire mesh to be in the correct location.
Bottom line: Unless you have a problem site, then rebar in the footers should be sufficient. Does anyone agree with this assessment? I know that engineers have to earn a living also, but they normally concentrate on structural items, not basement floors. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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jonr
Senior Member
Posts:5341
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| 25 May 2013 09:01 AM |
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Wire mesh to help hold any cracks that develop tightly together must be in the upper quarter of the slab. What is the logic behind this? I can see better in the upper quarter, but I would expect it to help prevent lateral movement when placed anywhere. |
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rainman
New Member
Posts:37
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| 25 May 2013 10:09 AM |
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Posted By ICFHybrid on 24 May 2013 10:10 PM
A basement slab? $10K?
When a TX engineer here's the word "BASEMENT" it's like a wave of instant fear immediately takes hold and therefore the price seems to go sky high. I just don't get it. |
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rainman
New Member
Posts:37
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| 25 May 2013 10:11 AM |
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Posted By Lbear on 24 May 2013 11:55 PM
I can get a 2-story 3,500sqft ICF home engineered for $6k and that includes the slab.
$10k - $18k for just a slab is insane.
I FULLY AGREE...it is absolutely INSANE. The sad part is, is that with my soil I do have to have a soil test as well as have my slab engineered. |
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rainman
New Member
Posts:37
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| 25 May 2013 10:23 AM |
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Posted By Alton on 25 May 2013 08:49 AM
Why does the slab have to be engineered? Is there expansive clay at that depth? Is there a high water table? Are you building over uncompacted soil? Do you plan to build on the edge of a turned down slab instead of a footer.
Most homes in my area that have basements do not have any engineering done for the slab. The code requires that either wire mesh or fiber be used in slabs. After the inspection, the wire mesh can and sometimes probably will be removed since it does not do much more than hold down the waterproofing membrane. Wire mesh to help hold any cracks that develop tightly together must be in the upper quarter of the slab. Since it is always on the bottom, then there is no reason other than the code to use it. The code in my area does not require the wire mesh to be in the correct location.
Bottom line: Unless you have a problem site, then rebar in the footers should be sufficient. Does anyone agree with this assessment? I know that engineers have to earn a living also, but they normally concentrate on structural items, not basement floors.
Hey Alton, I do have clay and a ton of limestone so my site is what some would consider a problem site. I will use footers 10" deep and 24" wide although I've been told that 18" wide would be sufficient. The cost difference in the width is minimal and it is worth the additional cost for the additional benefit. I'm sure that a TX engineer will require #8 rebar throughout on the slab which in return will just run up my project cost by thousands. I have a real sneaky suspicion that this would be a contributing factor as to why basements aren't more common in TX. Mike |
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Alton
Veteran Member
Posts:2164
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| 25 May 2013 10:58 AM |
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Rainman,
In some parts of Montgomery, AL expansive clay can and does break slabs built on grade. Since the bad clay in some of the areas is only a few feet deep, until recently about the only precaution that could be taken was to remove the bad clay and then backfill with non-expansive material. The problem with this fix was that basically, even for a slab on grade, the hole dug to remove the clay became a bathtub that held water since only the water-tight clay under the slab was removed. A new fix that seems so far to be working better at a comparable cost is post-tensioning slabs on grade that are supported by reinforced piers under the slab. As you will discover, a closely spaced grid of #8 rebar will get expensive. In my area, the post-tensioning company does the engineering. If post-tensioning is available in your area, it might save you some money.
But before you decide whether to use rebar or post-tensioning, I think you could benefit from knowing how the two systems work. Post-tensioning will still require some rebar but not as much. A rebar system comes into play to keep the slab together by using the tensile strength of the rebar. That is why it makes a difference whether the rebar is 40K or 60K. The bonding of the concrete to rebar is critical for rebar to hold a slab together after the concrete fails. Post-tensioning that I am the most familiar with does not depend upon bonding. In fact, as the concrete gains strength, the cables are stretched various times to increase the compression on the concrete slab. There are a lot more things to learn about the two systems but most of that can be left up to the engineer.
Regardless which system you use to reinforce the slab and walls, there are some things that you need to understand about how to waterproof the walls so the surrounding expansive clay does not cause problems. If you are not already e-mailing me, then feel free to do so.
As I have said many times on this forum, I donate most of my free time to helping homeowners design and build their own homes. This is my way of giving back. To each his own, but that works for me. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Alton
Veteran Member
Posts:2164
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| 25 May 2013 11:33 AM |
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jonr,
I am sure there are plenty of links on the internet that can explain much better than I why the wire mesh should be in the upper quarter of the slab to hold cracks together. I think the logic is somewhat similiar to placing rebar in the right location.
As you probably know, wire mesh, fiber and rebar will not prevent cracks even if properly placed, but can help hold the slab together if cracking occurs. The biggest complaint I have against wire mesh is that residential builders do not see the need to use chairs on 4' centers to keep the mesh where it is supposed to be to be effective. If no chairs, then I do not want wire mesh in any of my projects. If the code requires wire mesh or fiber, I prefer to use fiber for slabs where some exposed fibers on the surface are okay. Since the fibers will be distributed throughout the slab depth, some will be in the upper quarter of the slab where they have a chance to be effective as opposed to wire mesh on the bottom.
Now let me go off on a tangent to make one last point. One of the many things that I like about shotcrete panels is that the wire trusses hold the wire mesh in the correct location. But I have not heard of any panel company endorsing the use of their floor panels for use on grade since the bottom side of the panel cannot be shotcreted. However, with walls, intermediate floors and roofs, both sides of the panel can be shotcreted. In this case, since the shotcrete/gunite is so thin (as thin as 1.35"), the wire mesh is usually in the middle of the shotcrete. Why? Because even wire mesh needs to have a certain amount of converage by concrete to keep it from rusting. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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cmkavala
Veteran Member
Posts:4327
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| 26 May 2013 03:56 PM |
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Post-Tensioned slab we did for a women's shelter because the land was at high risk for sink holes  |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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jonr
Senior Member
Posts:5341
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| 26 May 2013 03:59 PM |
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A nice, thickened edge, monolithic slab. Post tensioning allows less steel and concrete with less chance of cracks. Hopefully it will become more popular in residential slabs. |
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jonr
Senior Member
Posts:5341
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| 26 May 2013 04:03 PM |
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floor panels for use on grade since the bottom side of the panel cannot be shotcreted But in theory it could be set into wet concrete. |
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Alton
Veteran Member
Posts:2164
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| 26 May 2013 05:40 PM |
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jonr,
Your are right in theory. But in practice, the engineers at GCT told me that with rock in the concrete mix, it would be difficult to get the top level. Also there would be a need for chairs to make sure the bottom wire mesh was covered with concrete by at least 3/4". Hey, if I ever try this, then I want the mix to be Agilia with small aggregate that will flow well.
Another way might be to pre-coat the bottom side of the SCIP panels before placing them. A sub slab or chairs would not be needed. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Lbear
Veteran Member
Posts:2740
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| 26 May 2013 09:29 PM |
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Posted By cmkavala on 26 May 2013 03:56 PM
Post-Tensioned slab we did for a women's shelter because the land was at high risk for sink holes
I am a big fan of post-tension. I have it on the current home and it's been great, even with vast ground movement and poor soil, no cracks and no problems. Only downside is that if you need to drill into it later on it because a big hassle and you void the warranty on the slab. |
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robinnc
Advanced Member
Posts:586
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| 26 May 2013 10:12 PM |
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Why is helix not used in slabs? I never hear anyone mention helix for slabs.
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cmkavala
Veteran Member
Posts:4327
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| 27 May 2013 06:20 AM |
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Posted By Lbear on 26 May 2013 09:29 PM
Posted By cmkavala on 26 May 2013 03:56 PM
Post-Tensioned slab we did for a women's shelter because the land was at high risk for sink holes
I am a big fan of post-tension. I have it on the current home and it's been great, even with vast ground movement and poor soil, no cracks and no problems. Only downside is that if you need to drill into it later on it because a big hassle and you void the warranty on the slab.
Lbear, Voiding the warranty would be the least of your worries cutting or drilling of the slab must be avoided, the tensioning on the cables is so great, they have been known to snap thru the concrete slab when cut, it has the potential to cause serious bodily injury or death. |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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smartwall
Veteran Member
Posts:1209
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| 28 May 2013 09:33 AM |
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Helix fiber is the way to go. Had a customer pour a 4" slab instead of a 6" that was spec'd and he got a stonger slab with no cracks and less concrete. The company will do an engineering take-off from your specs with the needed dossage. They did this for a underground basketball court I was involved with in Syracuse NY. This thing had an over engineered rebar schedule that made it difficult to pour, Helix was the answer. |
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rkdzns
New Member
Posts:3
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| 04 Jun 2013 03:48 PM |
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I could probably help you out. The big question is do you have a geotechnical report (or soils report)? If so, that will dictate the type of foundation and slab that is required. If not, I HIGHLY recommend this because if it is designed per the prescriptive code, it will more than likely be overkill and cost substantially more than what the report will cost. The last home I designed in Texas (last summer) the structural engineering was about $1/s.f. That was a post-tensioned mat slab. If it does need to be post-tensioned, you might want to contact a local PT installation company - may times they will design and engineer it for free if they do the install. My contact info is under Architects on this site or my website is www.rkdzns.com. Let me know if can help. |
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