Can we build on "loam"?
2 study sources mentions "loam"
One says yes we can build on loam (because it is a mix of sand, silt and clay although my understanding clay is not good to build on) and the other says we can not because loam is considered organic.
When researching google, loan can be built on.
Can someone from NCARB clarify please from NCARB point of view and for the purpose of the ARE exams, can we or can't we build on loam?
Thank you
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Hi Yvette,
I don't think you can build on loam. It's topsoil. Anything with clay is going to be unstable. Anything organic is going to decompose, so its volume will diminish.
Silt also isn't a good foundation material, though when it's mixed with sand or gravel is might be ok.
Hope this helps!
Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses
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Yes, loam can support a building. It is a combination of sand, silt and clay.
Gravel, clay, shale, sand are okay; rock (bedrock, limestone, sandstone) is great for supporting foundations of heavy buildings. But rock is VERY expensive to remove for basements and is overkill and not required to support most buildings.
Organic soil and peat (dark brown or black and easily compressible) are not competent soils. Loam is not prohibitively organic.
Soils with very high clay content can be difficult to build on, but we build on soils with moderate quantities of clay (like loam) all the time. Yes, it swells when wet, but our foundations (generally) are made to account for that as best they can and as long as the foundation rises and lowers consistently, without differential settlement in just one corner of the building, we're usually okay.
If Amber Book is one of the study materials that told you you can't build on loam, let me know where you think you saw that error and I'll be sure to fix that. --Michael Ermann, Amber Book creator
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Thank you both for your responses but that is exactly where my confusion comes from. Owning the concept is that we can not build on organic soil. But some consider loam organic and some don't. This is a white and black answer where NCARB need to step in to clarify. In real life we will follow what the soil report recommends but we are here to pass the exam and get licensed. So contradictions between 2 very reliable and popular study sources like these create confusion and doubts. Actually Amber Book, Mr. Ermann, is the one answering "yes" to this question v.s. Black Spectacles, which is NCARB approved, answer is that we can not build on loam.
Thank you
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I waited a while for NCARB to step in and clarify, but enough time has gone by and since they haven’t, I will… the NCARB approved test prep provider program was phased out this year. When it was in effect, NCARB officials never checked material for accuracy…rather material was “reviewed by an NCARB committee of volunteer architects, who evaluated whether the materials adequately addressed the content areas and objectives outlined in the ARE 5.0 Guidelines.”
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Hi Yvette,
NCARB does not use Black Spectacles or any other third-party test prep to author items for the ARE. Instead, a panel of volunteer licensed architects from around the country, typically 5-10, write, review, and approve items for use on the ARE. This panel typically utilizes the reference books listed on pages 111-116 of the ARE Guidelines when authoring items and developing rationales for the correct response(s). I would reference these books in regard to building on organic soil and loam.
One additional note, you most likely won't get a question on the ARE that simply asks if a building can be constructed on loam or organic soil. The ARE does not contain items that assess whether a candidate can remember factual information about building construction. Instead, you'll be presented with various pieces of information like a soil report, boring logs, geotechnical report, client program, project budget, foundation information, or site plan and be required to make a judgment call based on the provided criteria. There are many variables that will need to be considered when answering a question on the suitability of site soil, so we recommend becoming familiar with common soil types, the challenges/opportunities/impact associated with each, as well as how to evaluate different types of soil and geotechnical reports.
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Hi Yvette - I think that you're referring to a note in our Soil Analysis Virtual Workshop. I just want to clarify that we don't say that you can't build on loam (because you can!), we're simply talking about the relative suitability of soils for construction in that workshop. That doesn't mean the less suitable soils are unbuildable upon, just that they require other measures to be taken (which typically increase cost) in order to build on them. If you think there's another area in our study materials that indicate that you can't build on loam, please get in touch with me and I'll take a look at it!
Thanks nrespecki for your note about how this, and other topics, may come up on the exam. We actually write our questions using the same process that NCARB does - a team of architects writes and reviews each item, using the primary NCARB resources listed on pages 111-116 as guidelines. We avoid recall questions and it's comforting to hear that the ARE doesn't feature those types of questions either.
Chris Hopstock RA
Black Spectacles
ARE Community -
At Amber Book we have a different approach. Rather than utilize a panel of architects for technical topics like this, we tap a network of experts to create our content: soils experts, civil engineers, structural engineers, building envelope scientists, lighting engineers, acousticians, wood scientists, code officials, construction lawyers, mechanical engineers, plumbers, electricians, elevator repair technicians, masons, concrete folks, framing & finish carpenters, gutter installers, urban planners, real estate professionals, roofers, steel erectors, cost estimators ….and of course a team of architects.
As discussed above, NCARB exclusively uses volunteer architects to create test items, and we generalists are not as likely to be correct on technical content as the experts. But it seems so unlikely that if NCARB’s architects unknowingly get it wrong on a technical question, that a panel of generalist architects assembled by a test prep provider would get it wrong in the EXACT same way! And if the NCARB architect volunteers get it right (which they usually, but not always, do), we think we’ve taken steps to get it right too. -
Yvette,
As far as the ARE goes, if you see 'loam' as a choice for bearing a foundation, it's not going to be an acceptable choice. "Loam" is sold around here as topsoil, and as the definition below from dictionary.com indicates, it's a humus topsoil. Humus material, clay, organics and peat cannot bear a foundation.
Yes, soil can contain many things - sand, silt, gravel and organic materials, etc. Gravel is your best choice for bearing a foundation, but a mixture of better materials along with small portions of not as good materials can be acceptable. The ARE, I believe, just wants to make sure you know which materials are not acceptable.
Taking measure like compacting poor soil or importing materials to 'fix' poor soils is very expensive, and not always successful, so that's not a great option. And I doubt that'd be presented on the ARE because it's not standard construction.
While it's good you are questioning things, I don't think the circular answers presented here are helpful.
Chapter 21 in Ballast covers soils. You should try to memorize letter symbols of the Unified Soil Classification System on p 21-5, and which materials cannot support a foundation for the ARE - clays, peat, and organics.
Hope this helps!
Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses
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I think we've gotten away from the topic (building on loam) a bit - but I'll share one last thought on our approach to practice questions at Black Spectacles.
We create questions that match the actual ARE as closely as possible - both in content and in user experience. That's why our whiteboard and calculator function just like the real thing, all of our questions function the same way (including image-based questions), our case studies function like the actual exam, etc. An important part of preparing for the ARE (apart from, obviously, studying) is to practice taking the exam, using something that's as close as possible to the real thing.
Since NCARB's questions are written by a panel of architects, then reviewed by architects and psychometricians - we do the same. In our opinion, the best way to get our questions as close to what you can expect on the ARE is to write them using the same process NCARB does. If NCARB began to have concrete folks, roofers, and gutter installers write their questions we would too, but for now they don't. I personally am glad that's the case - I think architects are perfectly suited to write questions about architecture that test aspiring architect's competence to practice in our profession.
Chris Hopstock RA
Black Spectacles
ARE Community -
The foundation depth in loam soil depends on factors like the load-bearing capacity of the soil and local building codes. Generally, for loam soil, a deeper foundation may be needed for stability. A shallow foundation with proper design and reinforcement can work in loam.
The foundation depth in loam soil depends on factors like load-bearing capacity and local regulations. Generally, a depth of 3 to 7 feet (1 to 2.1 meters) is common. For loam soil, a spread footing foundation or reinforced concrete slabs is often suitable due to its stability and ability to distribute loads.
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Architectural Graphic Standards, 12th Edition states:
"Loam: This organic material, made up of humus and sand, silt, or clay, provides excellent material for agriculture, but should not be used for foundations. Organic materials will settle a great deal over time, and even lightly loaded slabs on grade will settle if bearing on loam." (pg. 274)
I've seen industry publications that cite loam as "ideal" for foundation; and perhaps it is in certain climates or conditions.
In general, for the ARE, I'd stick with the information from the primary sources listed in the ARE guidelines; even if it is illogical in current practice, the test questions will come from these resources.
It would have been nice to see NCARB respond to this question directly with the quote I included above.
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Hi Carrie,
Thanks for your response! This was an old thread, but thanks for updating it!My ARE competitors were very cutthroat and tried to discredit my response and my business. They even sent their affiliates and/or customers to “down vote” my responses (which actually also violates a legal agreement that I have with one of them too). But as you pointed out, my response about loam being unsuitable is 100% correct. 👍 Organic material and clay is not suitable for bearing. And Architectural Graphic Standards is a primary source for the ARE.
Good luck with your exams!
Rebekka KlosStep Up Architecture, NCARB, B. Arch. M. Ed
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Hi Carrie,
Michael asked me to give you a bit more context, I'm not NCARB, but I can dig into the dirt a bit. This is far more than you need to know for the ARE, but it is reasonably interesting, and is a good example for understanding what is and isn't actually important for the ARE - and if you understand it, soils problems on the ARE will be layups for you.
All of this comes down to no-one agreeing what is really meant by the word loam.
Wikipedia actually does a good job of acknowledging the nuance in the article on loam here.
To spell it out - the gist is that there is a way of talking about soils that treats % of organic matter (humus) as a separate item (in addition to % sand, silt, and clay), and there is another way that includes organic matter. So there's a definition of Loam that is just soil that is a fairly even mix of sand, silt, and clay, and there is a different definition that is basically "topsoil" with a decent amount of organic matter.
For typical construction, you care the most about whether there are expansive clays, where the water table and bedrock are, and whether there is a lot of organic matter / humus. If you know those 3 things, and why those 3 things are important (read: expensive challenges), you can get the vast majority of the soils questions on the ARE correct.
As NCARB noted a couple of years ago, the ARE avoids what I'll call "first order" questions especially for this type of thing, in favor of questions that provide some context and ask you to make a professional decision. The ARE favors testing topics that are 1. high-risk, high-consequence, or commonly misunderstood in the profession, and 2. easy to write questions for. The question-writers are architects, usually not teachers, and the Modified Angnoff process the test is written with (last I checked) further filters the written questions that you'll actually see.If you did have a first order question that hinged just on your understanding of the appropriateness of different soil types, it would probably be something like:
"Which of these soil types is most likely to present challenges for foundation design?"
All the basic possible answer choices would be:
A Sand
B Silt
C Clay
D Loam
E Humus (or you might see Peat)
F Gravel
G Rock.
But you'll only see 3-4 of the above possible options if it's a single-correct-answer question.
If Humus or Peat is an available option, I'd always pick it. Organic matter rots and moves. When soil under your foundation moves, your foundation moves. When your foundation moves, that is bad. Buildings are not (usually) boats designed to float on a shifting support layer.
If Rock is an available option, I'd always pick it. If you have bedrock, you probably will have to blast, which is expensive and slow in the best case - you can't just dig out most solid rocks. If Humus and Rock are options, the question is a select-all-that-apply, and you should definitely pick both.
If Humus or rock isn't on the list, and clay is, I'd pick clay over everything else, more or less always. Expansive clays are common throughout much of the US, and are responsible for multiple millions of dollars of building damage annually - one of my personal favorite fun facts is that in California, in the majority of years, expansive clays are responsible for the most dollars of building damage. NCARB likes to test on expansive clays because it's an easy topic to write questions on, is high-consequence , and is commonly misunderstood (if you don't understand and account for expansive clays, you're likely to get sued).
If the options were Sand, Silt, Loam, then and only then would I pick Loam. Again, use your professional judgement on the available context. The questions are written with reference to the references, but as folks have found, the references disagree sometimes. (The AGS quote disagrees with almost every other soils reference I'm aware of in that it is including humus as a necessary and significant component of any soil to be called loam - incidentally, a good example of Michael's crit re: architects not always understanding what is meant by words used by other adjacent professions). From everything I've run across, civil engineering also uses the "even mix, organic matter is separate" definition, not the "organic matter is necessary" definition of loam. Usually, for topics where the references disagree, NCARB tends to either avoid them, or write them in a way that the disagreement isn't core to answering the question correctly - for Loam, everyone agrees that organic matter is the problem, so I'd expect where for loam, "to build or not to build on that" is the question on the ARE, you'd see some additional clues or context that point to whether or not you should expect significant organic matter to be present - soil reports typically name the soil in each layer, and also include a more detailed written description, for example. If there is a clue to organic matter, then that's a problem for building, if there isn't, and there are no other available good answers, then loam is probably ok to build on for that question.
Here's the soil triangle - developed by USDA to name soils based on their particle size, and used more broadly.
My understanding is that the UNIFIED classification scale at the bottom is most common for civil engineering (making buildings), AASHO is for road construction. You don't need to know all that, butdo note that the triangle is in the camp of talking about soils in a way that treats organic matter (humus) as a separate thing - partly because it's really critical when it is present, and partly because most of the time, humus is most prevalent in the couple of inches of topsoil on site. Scrape the topsoil aside and you're down to the subsoil, which typically has negligible organic matter. In much of the US, there used to be a lot more topsoil, but it blew and washed away by the end of the 1930s, so it's not so much of a problem for construction now in most places.
Best,
Ralph, the Amber Book Team -
The amber team comment is overly complicated. And still incorrect...
If the choices are:
A. Sand
B. Silt
C. Clay
D. Loam
E. Humus (or you might see Peat)
F. Gravel
G. RockThen GRAVEL is the best choice. Sand is #2. If the options are mixtures of soil, the best one will contain gravel and sand. And will NOT contain CLAY or HUMUS or PEAT. (See the rectangular soil particle size chart above).
Loam contains clay or organic material. It's considered topsoil here, and contractors buy 6" of it for a site to plant grass and landscaping.
NCARB has listed AGS, which Carried quoted. 👍 That is the correct definition of loam per NCARB. That's all you need to know! AGS and the Unified Soil Classification System are ARE materials. A desperate builder in CA who builds unadvisable things is not an ARE resource. Thankfully!
Good luck with your studies!
Rebekka Klos, NCARB, B. Arch M. Ed.
Step Up Architecture
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All,
A reminder - the question posed in my reply was "Which of these soil types is most likely to present challenges for foundation design?". Gravel does not present challenges to foundation design - it is highly competent. Always read the question as-written!
Happy studying,Ralph, the Amber Book Team
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Reflecting on "Always read the question as written." The term for loam in AGS, does seem to limit the definition to the context of topsoil in a slab on grade condition:
"even lightly loaded slabs on grade will settle if bearing on loam."
This is helpful advice:
"NCARB tends to either avoid them, or write them in a way that the disagreement isn't core to answering the question correctly - for Loam, everyone agrees that organic matter is the problem, so I'd expect where for loam, "to build or not to build on that" is the question on the ARE, you'd see some additional clues or context that point to whether or not you should expect significant organic matter to be present."
I'll be sure to look out for these clues!
Thank you for the variety of detailed responses. All very helpful!
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Hi Carrie,
Bingo. Organic matter generally is much more common near the surface. The Unified Soil Classification System doesn't really list "loam" as one of the options, for the ARE, if loam is really the focus of the question, AGS is probably NCARB's source, so I'd go with what it's saying there. I looked at Building Construction Illustrated, Site Planning and Design Handbook and Fundamentals of Building Construction yesterday, all 3 discuss soil types a la USCS, which means none of them have "loam" as a single type of soil - you can have loamy clay, loamy sand, etc, but there is no plain "loam" mentioned in any of the 3 that I could find.
Welcome! It's easy to get caught up on this kind of thing, your time is usually better spent on knowing the adjacent topics as well as you can!
Best,
Ralph, the Amber Book Team
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