I’m interested in including material quantity reporting as a project requirement for the general contractor. Does anyone have guidance/ideas/examples of such requirements:
In specifications issued by the design team?
In the contract between the owner and general contractor?
This is a big topic, and different approaches may be needed for different types of materials. I’m especially interested in structural materials but welcome any resources or thoughts generally applicable to this topic.
General contractors or material suppliers: how would you react to a specification requirement to provide actual supplied quantity of materials to the design team? How would you react to an owner-driven requirement to provide this same information?
The purpose is to help to close our gap in understanding between our quantity estimates during design and the actual quantities used (due to various unknowns and waste that occur anywhere between design and construction). I’m sure there has been some research already done on this topic, too, so any links are appreciated!
Hi Eric - can you elaborate a bit more on you material quantity estimating process? Is that something you are doing internally or is extrapolated/derived from owner/GC pricing exercises.
@jgarcia is on the CLF Chicago committee and works at a GC. I’m curious what her thoughts are on this request. It seems like a small ask, from my perspective.
@ScottFarbman Sure, happy to elaborate. I’m a structural engineer and am approaching this from a designer’s perspective. We typically model projects in Revit, and we can use Tally to perform an LCA or simply pull material quantities directly from Revit for other purposes. I don’t simply trust the quantities coming from a Revit model, but understand there are all kinds of reasons that the quantities as modeled in Revit are not accurate. Some inaccuracies are very obvious; if we don’t model the metal stairs because it’s not in our scope to design them, we know the model is missing that material. Some are more subtle; if a shallow foundation is poured with earth forms in competent soil, the actual size of that foundation is going to be somewhat larger than the perfect rectangular prism in the Revit model. I believe it’s my responsibility as a designer performing an LCA to understand these inaccuracies and account for them to a reasonable degree.
But then there is waste that occurs downstream during fabrication and construction, which I know much less about. I know that waste is accounted for to some degree within an EPD or within an LCA tool. I don’t have a great understanding of this (and am afraid the answer is something along the lines of “it depends on the PCR for that particular category”), so I would like to learn more about that generally, but I see a couple of benefits of trying to obtain final material quantities on a specific project:
I assume that waste factors in an EPD and/or LCA tool are based on pretty blunt average numbers from industry wide research (except in the case of a product specific EPD which should have a higher degree of accuracy for that product). I’d like to have some specific examples to better understand material waste on the particular types of projects I typically work on.
For every model inaccuracy I am aware of (e.g. the stair or foundation examples above), there is probably another type of inaccuracy that I’m not yet aware of. Such inaccuracies may not truly be “waste,” but just a lack of understanding on my part about how something gets fabricated or installed. I recently found that drilled piers on a project had about 30% greater concrete volume than modeled due to the increasing diameters of casing segments used from rock to surface. (And that is independent of another potential major source of inaccuracy - bearing elevation assumed in Revit model vs actual bearing elevation in the field). Is this extra concrete due to telescroping casing waste? It seems wasteful, but I’m not sure I would call it “waste.” Should it be included in an LCA? 100% yes! Should we be aware of this extra concrete and consider it foundation design decisions? Yes!
So back to the original request … if we can get some truly “accurate” final quantities from the GC/suppliers on a project, we can compare this with our best guess design quantities considering all of the inaccuracies we already know about. Then, any final quantity that is much larger than expected is either:
an opportunity to gain a better understanding about construction and use more realistic material quantities in future LCAs, or
an opportunity to reduce waste somewhere in the process of construction.
I am certain many people have thought about this topic, and I know other structural engineers have even performed some version of a study like this. So I’m just hoping to benefit from others’ experience about what has worked well or what has been challenging when trying to obtain quantities.
Finally, I have multiple motivations for bringing up the topic:
General personal interest
A specific project that I want to obtain quantities for and use as a case study (hoping to include cladding & finish materials as well in coordination with the architect and owner)
A desire to make the SE 2050 LCA Methodology Guide (currently in development by members of the SE 2050 Subcommittee) as relevant and helpful as possible. While there is no way the guide can be 100% comprehensive, we do want to include as much high-quality, specific advice as possible to structural engineers who are performing LCAs on the structural scope of their projects. So if anyone wants to chime in with “we did a detailed study of estimated vs actual steel connection material, and here is a link to the published study,” that would be awesome!! Also, feel free to share ideas for the SE 2050 LCAMG by emailing database@se2050.org, but share any good info in this forum, too, if appropriate.
Hi Eric. There’s a lot to unpack there, but let me see if i can help with some parts of it. We’ve been working with our contractors on some of our projects to obtain quantities of major elements. One project I’ve been working with has contractor take offs for procured volumes of concrete (by volume), steel (by weight), and cementitious fire proofing (by number of bags and coverage area). Trying to work these numbers back into Tally has been quite the headache, so let me share some of the things we found. With steel, our procured numbers were about 5% more than what came out of the Tally model. We assume that this is probably correct, as we’re not modeling all the connections and minor details. Concrete was a bigger delta. The total volume modeled by Tally was about 12% less than the procured amount, and given concretes impacts, this has a substantial affect on the final numbers. When we go to validate our final numbers, we’ve started to selectively remove/modify the tally data for the concrete to match the procured amount and mix specific EPD. Cementitious fire proofing opened up a whole other can of worms. You are correct to assume that Revit take offs can be questionable, and Tally can exacerbate this if you’re not careful. We found that our tally fireproofing numbers were 4x higher than the actual procured amount. I spent more time than I care to admit digging into the numbers, but I believe there are two reasons - Tally’s baseline assumption for density is significantly higher than the product we’re using, and because the tally material definition seems to include the top part of the flange if you set the application to by area instead of by the specific beam shape. I say seems too because I’m just testing different scenarios and trying to dig out the algorithm based off the numbers and my (limited) experience with bug testing. So yes, if your contractors are willing to work with you, it’s a good way to dial in your models. I’ll have to check if we’ve requested this in the specs, but for the most part, I know project team members have sent out requests when the question arises and our contractors have been generally willing to provide them.
On the EPD front, I just saw on a Nucor hot rolled steel epd that it assumes a quantity of 1.07 metric tons of steel to create 1 metric ton of fabricated product, and that A1 includes the impacts of the full 1.07 metric tons. I’ve also seen additional waste material totals for install on carpet epds, so there is some consideration with waste. I would assume waste in the factory is more consistent than waste in the field though, so you’ll have to consider it by material for now.
Something you might be interested in, as it does touch on construction waste. We recently had several contractors present on tracking A4 and A5 impacts on projects. These presentations are up here:
Steel: 5% seems about right for connection material, stiffener plates, etc that most likely weren’t included in the Revit model. I’ve heard numbers in the 5-10% range thrown around and even 10-15% for some steel projects. Anecdotal info like this is helpful.
Concrete: The 12% extra you found doesn’t surprise me at all. And it is so dependent on the type of element. For the earth-formed foundations and drilled piers I mentioned above, the actual concrete could be much more than 12% over the modeled volume. But a large mat foundation with steel formed sides should have an actual volume of concrete very close to the modeled volume. A very large industrial slab on grade that requires many several full trucks to pour should have little extra concrete.
But a small slab on grade that has thickened slab edges all around that aren’t modeled could have a relatively large actual/modeled ratio. There is a great need for well-reasoned guidance about actual vs modeled concrete volume for all kinds of structural components.
Fireproofing: this is a very helpful watch-it for fireproofing in Tally.
I look forward to watching the A4/A5 recorded webinars - thanks for posting the links!
Hi Eric,
I’ve also found contractors to be happy to provide material quantity information from the field. They generally have this information readily available since they pay based on the actual quantity.
Regarding requirements to provide quantity data in contracts, I’ve seen that for some projects. One recent California project comes to mind where it was required in the sustainability spec. I think that’s a good approach. If contractors are required to provide this data regularly, e.g. monthly as part of a progress pay application, it’s more likely to be good quality information.
Concrete volumes for underground work can certainly be much higher than theoretical. It depends a lot on construction method and ground conditions, but I’ve certainly seen 20-30% overages for slurry walls. It’s also important to account for concrete that needs to be removed as part of construction. This could be for a pile capping beam, secant piles, slurry walls (depending on joint arrangement) etc.
Also, feel free to share ideas for the SE 2050 LCAMG by emailing 
