Residential Foundation Repair Methods

Frequently Asked Questions

1. QUESTION:
   Structural engineering question?
   First the background: I want to build a house using CEBs, Compressed Earth Blocks. (If you want to know more about the CEBs check out thes link: http://www.adobemachine.com)

   They are considerably heavier than conventional building materials. Each block is 10″wide x 14″long x 4″ thick. They will be stacked with the 10″ side facing out and thus will make a 14″ thick wall course. The exterior walls will be two courses thick with a small chase between them to allow for electrical and plumbing. The interior walls will be one course.

   Each of the blocks weighs about 40 pounds. Stacked as stated above that will create a wall that weighs 14,400 pounds per 10′ x 10′ section for each course and thus a 28,800 pound 10′ x 10′ section for the double course.

   My main question is: what is the formula to determine the thickness of the of footings and slab given the width of the walls and the weight?

   Once the floor plan is finalized and the interior walls laid out and the lengths of the exterior walls determined I want to be able to estimate what the foundation work and materials are going to run me.

   I would also like to build this with a flat top roof (a little slope for rain runoff of course,) and I would like the roof to be make of concrete. How do I do that? Do you pour it in forms in place or do you precast it in sections and then crane it into place? How thick can/should it be (I want it to be tornado proof?) What sort of support is required during construction and afterwards. The interior walls will provide some support but the rooms will be large and I am wondering if I will have to have support beams from the floor up or will I need support beams spanning from wall to wall at the ceiling (I-beams?)

   Also should I use foundation support piers (like the foundation repair guys drive down to bedrock when they repair a broken or cracked foundation?) I was wondering if that would help support something as heavy as this house is going to be.

   • ANSWER:
     These are all great questions! I really do enjoy designing the structures for all kinds of buildings, especially custom residential homes. This seems like it will be a great project by the way you describe it.

     First of all I want to suggest that you have a licensed structural engineer to work along side you during your design process. The questions you have posed here have fairly complex answers and you may not have thought of all the implications of your design materials yet.

     I would also like to suggest that you employ a geotechnical engineer to investigate the soil on your property. They will be able to determine just what types of loads can be supported and by what types of foundation. They can also help with suggested procedures for preparing the sub grade soil prior to laying a foundation if it needs any type of enhancement or modification to best serve your home’s needs.

     Lastly, I would suggest having an architect review your final design, they are aware of building codes for your area that you may have missed in your initial layout. They might even offer some good suggestions for details on how to waterproof the exterior of your building.

     Anyway, your initial calculation about wall weight is off by a lot, a 10′ x 10′ section of brick should only weigh 4,200 lbs based on your weights and brick sizes. Plus you didn’t account for the weight of your roof, nor for snow, construction, or wind loads. And it seems you are only concerned about the roof being tornado proof… that kind of a design needs to be a whole system approach (walls, foundation, roof, doors, windows, etc.). FEMA puts out some documents to recommend how to create a safe-room, but they don’t make for very pretty homes. I would instead suggest a single safe room made to FEMA standards or better and let the rest of the house blow away. Tornado force winds are too strong for typical construction methods.

     My guess is you would rather not pay the fees for design professionals to come along side and help… but if the building falls down a concrete roof will be devastating. Besides, your local jurisdiction likely requires that you adhere to a building code like the International Building Code. Rather than learn it on your own, along with all the structural design equations, I suggest building a design team to help your dream become a reality.

     Please contact me directly (check my profile for email link) and I’ll help walk you through some of the basics to help get your basic design off the ground before you go to talk to a local professional.

2. QUESTION:
   Half-Life Question.?
   All of the isotopes of radon have half-lives shorter than four days, yet radon is still found in nature. Explain why all the radon has not yet already decayed.

   • ANSWER:
     radon is formed from the decay of other materials see th attached link: * The risk of environmental radon levels is not higher now than in the past, when residential exposures were not considered to be a significant health hazard. It has now been raised from a nominal natural background contributor to human exposures to the prime contributor based on a new way of calculating dose, and not on increased exposures in the home due to tighter more energy efficient houses, or new information on radiation dose and/or biologic risk.
     * The great majority of the radiation dose is not from radon itself, but from the short-lived alpha particle-emitting radon daughters, most notably Po-218 (radioactive T1/2=3 minutes), and Po-214 (radioactive T1/2=0.164 milliseconds), along with beta particles from Bi-214 (T1/2=19.7 minutes). [T1/2 is physical half-life].
     * Measurement of radon in homes is simple and relatively inexpensive and may be accomplished by various means. Cannisters remain the method of choice for use by the average homeowner.
     * There is no way to avoid radiation exposures completely, much of which comes from the natural environment as well as from radioactivity in our own bodies.
     * Radon gas can penetrate houses from many sources in many fashions. It is not possible to radon-proof a home, but it is possible to reduce its level. The most important contributor to indoor radon is the soil from which radon can be drawn through large and small subsurface gaps in the house foundation. Houses that are in direct contact with the ground will have higher radon levels than houses with an air space under the dwelling. Radon levels in the upper floors of a multi-story building are lower than on the ground floor. If one lives in a high radon area, it is prudent to determine the level in the home and to take appropriate action if the level is found to be high, i.e. greater than 4-8 pCi/liter (NCRP recommended level is 8 pCi/liter, the EPA recommended level is 4 pCi/liter). [pCi is the activity of the substance and is equal to 10-12 Ci or 2.2 radioacitve emission per minute].
     * The shape of the dose response curves for miners exposed to alpha-emitting particles in the work-place is consistent with current biologic knowledge. It is linear in the low dose range and saturates in the high dose range. No detectable increase in lung cancer frequency is seen in the lowest exposed US miners, i.e. those with exposures <120 wlm, the relevant dose interval for most homes. in most cases, however, it is not possible to exclude a positive correlation due to wide uncertainty ranges on both the dose (x) and effect (y) axes. [wlm is a unit of expsoure to radon, working level month and is defined below]
     * Evidence for a health effect from radon exposure is based upon data gathered from epidemiologic studies of miners, and animal studies. Extensive radiobiologic data predict a linear dose response curve in the low dose region due to poor biological repair mechanisms for the high density of ionizing events that alpha particles create. If this is the mechanism that underlies lung cancer induction, there is reason to believe that there will be some degree of increased lung cancer risk even from low level environmental radon exposures. However, no compelling evidence for increased lung cancer risk has yet been demonstrated from "acceptable" levels (<4-8 pci/liter). increased lung cancer risk is primarily in cigarette smokers, and abatement of that risk can best be accomplished by changes in smoking status.
     * Mitigation of radon in the home can be accomplished by a variety of means. The level to which remediation should be directed is under dispute, to the extent that some groups even suggest the level should be maintained at less than or equal to 0.2 pCi/liter (the average outdoor level). The societal cost of testing and mitigation at the EPA recommended level (4 pCi/liter) is 44.5 billion dollars (1991 dollars), and rises to 101.2 billion dollars if the action level is set at 2 pCi/liter. At the NCRP action level, 8 pCi/liter, the cost is estimated at approx. 15 billion dollars.

     Radon, Rn-222 (T 1/2= 3.82 days), is a daughter product of radium, Ra-226, which in turn is derived from the longer-lived antecedent, U-238. Thoron, Rn-220 (T 1/2 = 56 seconds) is a daughter of thorium, Th-232, which is present in larger amount in the earth's crust than radon. Because of thoron's short half-life, it is essentially all gone before it leaves the ground, and is of no significant radiobiologic consequence. These radionuclide series are present in slowly decreasing amounts in the environment (geologic time scale), due to radioactive decay of their parents, which has been known and understood since the end of the last century.

     Widely varying radon levels exist in different regions related to geological circumstances. New concern regarding radon exposures is traceable to the discovery that there are more houses with high radon levels than previously realized and to the use of a new method of expressing and summing doses from partial body exposures, such as the lung dose from radon daughters (7-16). This method of expressing dose was promulgated by the ICRP and the NCRP based on defined weighting factors which make it possible to sum partial body doses and thereby estimate a total body dose which would have a quantifiable risk. This quantity is defined as the Effective Dose (ED) (16). Thus, the previously estimated partial body environmental radon dose to the tracheobronchial epithelium (TBE) (2500 mrem/year.) was not included in whole body dose calculations because that exposure was limited to a small fraction of the body.

     The new method of calculation multiplies the 2500 mrem/year. dose to the TBE by a weighting factor (WF) which allows the dose to the TBE to be included in the ED from environmental radiation exposure Different WFs have been proposed, including 0.12 (EPA), 0.08 ( NCRP) and (NAS-NRC BEIR V), and 0.06 (ICRP). These WFs raise the radon contribution to the whole body from 0 mrem to 300, 200, and 150 mrem respectively. NCRP quotes an uncertainty of +/- 50% in these numbers. Based on these estimates, radon in equilibrium with its daughters delivers 2 times more dose than previously accepted as the total dose received from all sources of natural background exposure (approx. 100 mrem/year on the average in the United States). Thus, it is not surprising that adoption of the effective dose notion by many radiation protection groups (including the NCRP and the EPA in the United States), has led to increased concern regarding the potential health effects of radon. It should be noted that lung cancer risk coefficients from radon are not increased. There are no new cases of lung cancer that led to the increased dose estimate. In fact, the new estimates of radiation dose, imply a lower risk coefficient. That is, when the same number of lung cancer cases that occur are attributed to the higher doses (ED), the risk per unit exposure is decreased. The effective dose concept is discussed at greater length in NCRP Reports #93 (17) and #100 (18) , and ICRP #60 (7).
     TABLE 1

3. QUESTION:
   Basement cement pad not poured correctly?
   I have a working radon system which is supposed to pull air from under the basement floor. When standing in my basement, I can the air being pulled down where the basement floor meets the cinder block walls. My question is this: Is there supposed to be a gap between my floor and walls where air can be pulled from my basement? Was my concrete floor poured correctly?

   A bit more information: There is a small track that runs around the perimeter of the floor. The track runs to the sump pump pit. My assumption is that this is to channel water to the sump pump if required. As I look in the track, I see places where there does not seem to be enough concrete to finish the track. I see stones instead of finished concrete. My assumption is that when the pad was poured the concrete mix was not worked into the track and hence there is not a good bond between the floor and the walls.

   I poured some water in the track, and sure enough, the water did not run towards the sump, it ran down between the walls and the floor. This is the same path that the air is taking.

   Do I have a defective floor or is this a normal thing? Is the floor designed to let air and water in and out of my basement? Please let me know. Thanks!

   • ANSWER:
     Shrinkage is normal: The basement floor concrete is placed/poured last and even though it was poured directly against the wall (or perhaps some joint material), concrete shrinks as it cures and dries. It is quite normal for about a 1/16″ wide shrinkage joint to develop between the edge of concrete and foundation wall. The joint may even be a bit wider if excess water was used in the concrete mix, a common occurrence in residential work.

     Why Repair? Your situation would normally not present a problem (unless water or insects were coming in through the joint) but since you have a radon mitigation system installed, it is important for you to seal the joint at the intersection of floor and wall. You want the mitigation system primarily drawing radon impregnated air from beneath all of the slab, and that will not happen if it is also drawing air from your basement, as the exhaust fan is designed to remove a certain amount of air.

     The Fix: There are numerous methods and products available to seal the joint. I’d wire brush the entire length (to improve bond) and then use “Polyurethane Caulking For Repairing Cracks in Concrete”. You’ll probably want the tubes that are used in a standard caulking gun – you can also get the self-leveling type but be careful as it tends to flow to where you don’t want it. Polyurethane will bond much better than silicone and will expand and contract as the concrete does. Follow the directions on the tube. I give you much credit for recognizing that radon is dangerous over time and your system was not working quite properly.

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