Dispelling the Myth: How to Actually Use Revit for HVAC Analysis

CARLOS ORONA: Welcome, everyone, for this session of Autodesk University, Dispelling the Myth: How to Actually use Revit for HVAC Analysis. In this session, we're going to be talking about calculations. We're talking about using Revit for performance calculations and HVAC tools.

I'm Carlos Orona. I'm principal implementation consultant with Autodesk. I've been in the BIM world for quite some time. In this session, I have been partnering with another colleague from WSP, Tim Faulkner, that we will be sharing information as far as what we have been experiencing and our insight into HVAC calculations and HVAC analysis using Revit. Now on this, I will go ahead and hand this over to Tim Faulkner. Tim, the floor is yours.

TIM FAULKNER: Oh. My name is Tim Faulkner. I'm working as a digital practice lead in mechanical engineering at WSP Canada. I started off in the industry as both a designer and then eventually progressed to a project manager working on health care facilities, net-zero product schools. It was fairly broad. And I'm currently involved in the development and deployment of digital workflows for mechanical engineering teams at WSP in Canada.

So, what you can expect is an overview of what you're going to see in this technical demonstration. So we're going to cover a few things. The first is going to be an introduction and review of current industry practices and the investigations and discussions that led us to look at Revit as a tool for HVAC analysis. We'll also see a background summary of fundamentals on how HVAC analysis in Revit actually works, a detailed breakdown of Revit HVAC analysis tools and interfaces, and how to leverage those various tools and interfaces as well as some of the lessons that we learned in the best practices that came out of our investigations.

So really, what we had to start with is how does HVAC analysis actually impact the engineering design process? So the current workflow for HVAC analysis is pretty typical across the industry. There's a lot of software programs and methods for performing one of the features, which is envelope load calculations, and they're fairly available and common.

So we have examples such as Carrier HAP, which is commonly used in Canada and North America, and North America in general, as well as Trane TRACE. You have IES-VE, virtual environment, eQuest, OpenStudio, and a number of other softwares. You also have Excel spreadsheets being used. And these can be commonplace for jurisdictional requirements in other parts of the world as well as sometimes it's the engineer's preference.

And for the energy analysis programs, most of them are compatible with what is called the gbxml or Green Building XML file format. And what that is, it is a recognized industry standard file format for how the files for energy analysis need to be structured. There are links below for further information, including softwares which support gbxml as well as the current gbxml schema.

And so where does heating and cooling analysis fit into the current HVAC analysis workflow? Well, this led us to have to go through a bit of a mind-mapping process where we really need to take a look at how does it work in conjunction with all the other decisions that we make as part of the design process. So what you're seeing here is one of three parts of a mind map where we basically broke down the entire mechanical engineering design process at a general level so it was easy enough to get a high-level overview look at but, as I'm sure as many of you can imagine, not too convoluted in detail.

So we have here are three fundamental pillars that go into the start of the design process, which is the heating and cooling design load calculation. There's the HVAC system strategy and the ventilation design mode calculations. And when it comes to HVAC, these are basically the core features that come together and tie it all together.

Which progresses into once you've completed those three processes, what you can expect out of that are the peak heating and cooling design loads for space, heating strategy, cooling strategy, your ventilation and control strategies, your HVAC system design parameters, and your peak ventilation design nodes for space, which really start to go into how you can actually design the individual spaces themselves.

As you can see here, we've gone into our actual system load calculations on a per space level, which is again fairly common. You see it typically in spreadsheets that teams have cultivated over time, whether it's a health care facility or a school. Some people rely on softwares like Carrier HAP to do their actual ventilation sizing. But generally, the process is the same. And the outcome of this is you have determined your maximum and minimum HVAC system loads.

You then progress into to your actual system sizing. A lot of you will be very familiar with this because this is your sum of air flows for an air handling unit, as an example, or the sum of heating loads for a boiler. After which, you are selecting your mechanical equipment where-- I mean, it's post located. You're coordinating with your stakeholders, culminating in the equipment's finalized, the location is finalized, and it's scheduled on a drawing.

So where does Revit and BIM fit into this process? So everything revolves around the GB XML file format. Whether you're using IES-VE, OpenStudio, Carrier HAP, Trane, or Autodesk, or Revit, Autodesk Revit, it all revolves around the gbxml. And so the summary of kind of what we found here is that Revit functions as a really good tool for producing that geometry for the gbxml file.

So what we'll get into now is the actual Revit analysis tools and interfaces. It'll be a summary and kind of demo of all the various tools at your disposal within Revit, how they function, how they play together, and review the fundamentals of how does it all tie together. The first, we're actually going to take a look at the very basics. And that is, how does Revit actually produce the gbxml file? And it's not that far off of what we do in softwares like Carrier HAP or Trane TRACE anyways, and not that far off IES-VE, in that Revit only recognizes certain elements when generating the gbxml file.

Now, this can be done in a couple of ways. There's the conventional, sort of BIM project, where you have an architectural model that is being linked into the mechanical model and the architect has total control over those elements. But we've also looked at workflows where the architect is working in AutoCAD and the mechanical engineer is working in Revit. And there are workflows that still work with this. The caveat is that the mechanical engineer will be responsible for laying out the walls, these elements laid out here, which actually create your gbxml.

Now, the elements that are used in the gbxml, as you can see, you have spaces, walls, windows, doors, ceilings, roofs, and slabs. The reason for these elements is that they're the only ones that can be considered room-bounding and the only elements that the Revit processes for creating the gbxml file we'll be able to see. And we'll get into what that file actually looks like or how Revit sees that file later.

But as laid out here, only room-bounding elements will be recognized for when you are actually creating that gbxml file. Massing elements can also be recognized, but that's more of a niche workflow when you're in the very early design stages, you don't have a building, and you're looking to link something in, like a format model or a sketch it model from the architect, and you don't really have specific element information.

Now, we will be demonstrating this in the context of Revit 2020. Versions of Revit 2019 through 2021 are the same in terms of how they approach heating and cooling load calculations in HVAC analysis. And what occurs through this is that once your spaces have been created, it's a very straightforward button. We'll be showing that as well later where you go to your heating and cooling loads and you will get the interface popping up as to what your building actually looks like.

This is a preview of what it is. And that is essentially a 3D, simplified visualization of all the geometries that went into the gbxml. As you can tell, there are some elements we had off to the side as we were experimenting. But the green is your spaces. And you can see the surfaces of the walls in there.

A bit of a disclaimer. Things change a bit in Revit 2022. It doesn't affect too much in terms of overall workflow, but it's worth mentioning.

So in Revit a 2019 through 2021, the typical workflow for generating those HVAC analysis reports is accessed by the heating and cooling loads button under the Reports and Schedules tab. That heating and cooling modes button disappears in Revit at 2022. It's eliminated. That functionality then gets moved under the Energy Optimization tab. So the workflow is slightly different. It is just all roped under what is more of an energy model approach.

So what you'll see first when you check that-- when you click that heating and cooling modes button is, as I mentioned before, the model will generate a 3D visualization, a simplified visualization, of what does your gbxml file actually look like. If you've experimented with IES-VE, what you see there is quite similar. And we'll be doing a more detailed breakdown on the interface.

But as you can see, what you're actually seeing with this is a breakdown of all the spaces and the surfaces as well as the types of surfaces you're actually looking at. You can see here you have roofs, exterior walls, interior walls, floors, air gaps. It's quite comprehensive. And as you can see here below, you have a north-facing wall, east and south. So that's how all the data has been captured.

So what we're going to do next is we're going to actually cut to Revit directly. Now, this is the model we've created as kind of our pilot, just our test case. And it's a pseudo liquor store, for lack of a better term. Commercial facility.

This was the original basis. We just call it retail with an admin office area, washrooms, vestibule, retail area, shipping receiving storage, offices. As you can see, we've got windows. We have doors. There are internal doors throughout. It's a fairly straightforward project.

So now we're going to dive into the interface. Now, we're not technically going to start at the beginning, but we will start at the most relevant. And that is this heating and cooling loads button we've been discussing so far. And this is under report, under analyze, reports and schedules.

So this is the interface you saw here. For demo purposes, there were a few elements we had hidden away just for taking some screenshots and showcasing some things. One of them wasn't visible in the view I was deleting things from, but it is a wall, or sorry, a floor. So you can see that it does show up and that this simplified visualization does actually attempt to visualize the elements that get incorporated into the gbxml. If you're creating really complex wall geometries, those will get rendered, will get visualized within this. And it can start to make the process almost impossible.

So as a breakdown of the interface, a lot of this is going to look very similar to what you would see in other softwares. You have the building type, which I'm going to cut to shortly to explain what function this is. But you can see courthouse. We have hospitals, manufacturing facilities, et cetera. Fairly typical.

You have your location. In this case, we've selected Toronto, Ontario because of an obvious bias. You have a default city list. So again, it's fairly distributed over North America.

You have the weather. But you do have the opportunity-- it says use closest weather station. You do have the opportunity to override those values directly yourself if, say, it's a more remote location. And set your design temperatures as well.

And then you can define a number of sites in this project and you can manipulate that accordingly as well as control your rotations. But otherwise, it will read the project's rotation within the site. You also have your ground plane, which in this case we've set to level one. We are going with a one-story building just for the sake of this demo and keeping it simple. You have your project phase, which we've only got existing in new. But obviously, if you have more complicated project phases, the gbxml file will only recognize the phases that you're looking at.

Sliver space tolerance. As you can see here, you have these gaps in between spaces. Silver space tolerance affects what size of a gap actually gets recognized. So if you had a long, narrow kind of channel through your building or, say-- that would be the first example. It would be a long, narrow channel through your building or two buildings that are separate but side-by-side. This will govern what actual sliver space tolerance does the model kind of fill in and assume has some kind of a wall in between and which ones are actually a gap between buildings.

You do have building envelope, which I'm going to cut to this just to showcase something here. But building envelope is how Revit actually analyzes that building envelope. There are functional parameters in room-bounding elements which dictate if that element is an internal or external element. And we'll get into that later.

But as you can see, if we switch to identify exterior elements, looking towards the top left of the building there, wall has changed color. That is because we intentionally made those walls internal to showcase this feature. So from here, it act-- Revit basically says, OK, this is roughly what the outside of the building looks like as opposed to reading purely based on the elements. And then you can set the analytical grid cell size from there.

Building service, it's a building-level identification of how that building is being supplied with your HVAC services. You can see several examples here. Again, this is quite typical for what we would see.

Schematic type I will get into after this. But essentially, it's how you're defining the U values, R values, and absorption values for all the elements that would be recognized in the gbxml file. There's a hierarchy we're going to kind of get into after this. But for now, what you can do here is you can basically override everything for the entire building for those circumstances where it's very early stages or you're missing a lot of information and you just want to go with a very basic level as per code or an assumed value.

Building infiltration class, which being-- Revit being closely aligned with ASHRAE, is more about how much leakage do you have. You don't really have as much opportunity for manual input. But for now, this usually works. And then your report type, which we'll get into later, as well as load credits.

Next piece of the interface is when you actually go into your spaces. So here, you only see spaces. It purely just changes the color coding. And analytical services gives you that view where you can actually start to look at what are the surfaces you're seeing.

Now, when you get into the space level, you have the other features of your interface, which are your space type. So you can-- if any of you have actually dabbled in spaces in Revit, you are familiar with space types. This is where you can start to put in override values, which are driven on a space-type level.

So audience seating area for an exercise center, you have the area per person, which those can be linked to ASHRAE 62.1 values or any other industry-assumed values, principle heat gain per person, latent. These are all fairly typical values that would go into a heating and cooling load or energy analysis. And you have your various options for creating spaces.

You do have the construction type. So this is another feature where you can control this in a more granular level. We'll get into that more later.

People. So this is the number of people in the space. It will default to your space type, but you can also specify of the number of people manually or the area per person directly, as well as heat gain values. You can do space type or specified. And the electrical loads, all fairly similar, as well as break down a contribution to plenum.

Now before we do more of a deep dive on the hierarchy of how information gets passed around through spaces in Revit, we are going to go and dig into one of the probably least experimented with or understood aspects of it. And that is, when you're at the very start of a project, how do you actually set it up for HVAC analysis? Now, it's not as challenging as one would think.

The key feature here is when you go under MEP settings and you go into building slash space type settings. This is where you would manage, again, your various building types, your space types, fairly typical. And then there's another feature under project information. It gets into a lot more granularity. So under project information, where you would have your typical, again, not necessarily HVAC analysis-oriented features, you have energy settings.

I'm going to edit. You do choose how the energy analytical model is done. So if you're in mode, generally conceptual masses and building elements is the best way to do it. Conceptual masses, again, are those masses that get pulled in if you generate a model that is something, like, say, form it or sketch up where you're just taking basically boxes and you're using that to kind of represent your building. And building elements, again, are actual the walls, windows, doors, roof, ceilings, floor, slabs, et cetera.

Ground plane. Again, this overlaps with the other interface we saw for the heating and cooling load calculations, project phase. You have the analytical spatial resolution and surface resolution. The perimeter zone depth, for those of you familiar with going for LEED certifications, the perimeter zone depth is how far it looks in from the perimeter of your spaces, 15 feet being a very common practice.

Perimeter zone division. That's if you want to separate it. If you don't want to separate it, that tick box is there. Average vertical void height threshold. Again, these are all fairly straightforward interface values.

One of the things you do have with this is a fairly-- actually, fairly comprehensive breakdown of what all those values mean. So if you go to the Revit help site, it's just following that link, it will take you to a breakdown of what these are all-- what these values all mean, what they represent. You can see here parameters on division, if you want to divide it, if you don't want to divide it, depending on how your space is done. If you have large open office areas, this is how you would achieve it. And you can get a great deal of information from this site.

You also have your advanced options here, where you can get into a greater degree of granularity. You also a few more options where, if you're looking at target percentage glazing, target sill height. A lot of this is when you're at the beginning stages of project, you don't have that many elements in the model, and you want to start doing the early-phase analysis. Again, building type. You have the building schedule options, for example a 24/7 facility, 24/6, 24/5, k-12 school. There are some preliminary values already in place for you.

Your HVAC system. Again, a great deal of options. Very similar to what we would see for other softwares. Our outdoor air information. This is on a building-wide level. So it's not space-by-space.

Your export category, whether you're taking rooms or spaces. Generally for engineering, we take spaces. And then, realized elements are conceptual types, schematic types, and detailed elements. So your schematic types, again, this is if you want to override all of your assumptions for the whole building. So doing this here will make every exterior wall an eight-inch, lightweight concrete block regardless of what the architect has fed in for those values. Whatever the wall is-- regardless of whatever the wall is constructed from.

Now we're going to go back. What we're going to discuss next is a bit of a breakdown of the hierarchy of how all this information flows within Revit. So what you see here is really how the information cascades.

You start with the building type, which sits at the top. You have the schematic type. Now, this doesn't interact much with building type, but you would have seen it earlier.

Space type, the individual spaces. And the element. And this is kind of how all the information passes. Similar to those of you familiar with the visibility setting hierarchy within Revit, it's a bit of a similar principle.

So with the building type, what you see here is this overrides essentially everything. It will take all the square footage of your building, all the spaces. It cares less about that and just applies the same value to everything. When you're in the very early stages of project, this has a lot of value because it basically ensures you at least have something in place. So you're not just taking an empty value where it's not getting factored in. It's being overridden with what is a best practice assumption for the entire facility.

You have your schematic types, which as I mentioned before, this is where you can start to set things at the building level when you don't necessarily have-- you may not have confidence that the elements, the construction of the elements within the architect's Revit model, or rather, the architect, your model, you're not confident that they're as accurate as you think they will be.

So for now, you want to play it conservative, whether it's assuming it's a minimum per code or there is an agreed-upon value that you can currently assume. You have your space type settings, which is where you can start to go and set things on a space level. So every space that is the same type will get the same value. It will feed through and it will supersede whatever is being driven on a building level.

You have your individual spaces. This is a screenshot of the property's palette for spaces in Revit. A number of you would have seen this before where you get into the energy analysis values of the zone can be default. We'll talk about zones later. We don't intend to cover them as much with this session, but there is a reason for that.

You have-- you can select it as plenum, occupiable. The condition type, so you can go to heated and cooled. We'll demo a bit more on this later. The space type, construction type. You control a great deal amount of information on an individual space level, not just by space type.

And then lastly, you have your elements, which is very basic wall. What is that wall actually created out of? You would go into structure and edit. And that is where you start to go and select what is actually-- what are the components that make up that wall. And then looking at heat transfer coefficients, as you can see there, those values are calculated based on what information is passed through.

So cutting back to Revit, we'll get into a bit more of a deep dive as to how that hierarchy plays and how we've learned to use it. So as a quick breakdown of the user interface for spaces, just before we expand on other things and get into kind of some of the nitty gritty value items that we really want out of Revit. So this is the screenshot of the interface I showed previously where you can see, again, zone default that we're not getting into those, plenum, occupiable, et cetera.

To your condition type, this affects how Revit carries the information. If you're doing-- using Revit for heating and cooling load calculations, it's how that information gets passed around. Obviously, for an unconditioned space, it's going to accumulate some heat or lose heat as the day progresses or if it's nighttime.

And then it will affect that-- the adjacent spaces. If you're familiar, for those of you familiar with Carrier HAP, Carrier HAP doesn't really have the same 3D aspect to how you assemble the gbxml file. So Revit does take that into account on some level.

You have your space type, as I showed you before. And then this interface here with people, it's the same interface shown under the heating and cooling loads button where you can control by space type or specified. Again, just to recap, here, under details, where you go into your spaces and you select the space, these interfaces are all the same. So you make a change here, whether you make a change from here or in the Properties palette for the space itself, it will be the same.

And so really the kind of capstone feature of why we chose to go this way is the goal here for us is to eliminate how much information has to be passed from one platform to another. And so really what that culminates in does it-- is can you get these values using the heating and cooling load calculations in Revit? And really, that gets to this here, this last feature, which is the report type.

So we're going to demo a few report types for you right now. One, this is to showcase. It is quite quick. And then also get into what they really capture so that engineers and architects can understand what value, what information is provided and then hopefully understand how to use it.

So we'll go with a detailed report. Simply press and calculate. It will run. And the report appears. If we had information populated like project name, address, et cetera, that would all be pre-populated, as well as the report type.

Latitude and longitude stays as well as calculation time, for those of you concerned about having a continuous record of the design process. This has a lot of appeal because you can see exactly when that report was done. And it shows up under reports, load reports here. This is the one we just ran. So you actually have the opportunity to keep that catalog of reports within the model.

You do have all your design input values. So your summer dry bulb, wet bulb, winter, wet ball-- sorry, winter dry bulb. And your mean daily range. We have the building type, area volume. As most engineers are primarily interested in, you do have your peak values, so your peak cooling total load, when that peak load occurs, heat cooling sensible, heat cooling latent, maximum cooling capacity.

So we won't dig too much into airflow. For this particular project, we didn't actually look at sizing the load calculations based on airflow. Right now, we're just looking at peak heating and cooling values. But if one was so inclined to take that approach, you could. It would be very similar to how you would use any other software for doing those ventilation calculations.

Again, you get your peak heating values, your design values. You have values pulled together, check sums. So you can kind of take a brief look at OK, what is the overall building look like.

And then you get into your breakdowns. So there's a level summary. We only have one level. Obviously, you would see more if you had additional levels. We have the area and meters squared. Again, it can be changed.

The volume, your peak values for that level. Again, if you have more levels, you will get separate breakdowns. And the same thing can go for zones, although with zones you get a little more information as to what is air being supplied at, your set points. It gets much more into what you would expect from the system sizing feature in something like a Carrier HAP.

But again, all the information is presented front and center. It's very similar to other platforms that would be used. So you get the breakdown of all the components that went into this, your wall exposures. It's summarized. You can get a general look at OK, if you're really-- if this was done by, say, an engineer in training and it's the engineer of record on the project who wants to just go ahead and take a look at the high level values, this is where they would find them.

And just for the sake of demonstration purposes, if you look at the simplified report, you will get the zone summary. But it's quite basic. You're really only looking at simple information for spaces.

Standard report gives you just a little more granularity where you start to see more things like second metrics. You actually get the components for everything and how much has an impact of what exactly. And then detailed, of course, being the most information. You get your breakdown in a space-by-space level. You have your summaries per space, individual information within that. And you will get that for every single space in the project.

Now, the kind of capstone piece of why we actually wanted to look at this approach, and there's really no better way to showcase it than this, is if we go to our spaces. Prior to running calculate, these parameters would have been empty. And just as a case of demonstrating it, I will go ahead and override these values here to ones that are not at all applicable.

And this is an important feature in how this actually works is that if I were to go and recalculate my heating and cooling load values, one, it will generate another report. But more importantly, the design heating load and design cooling load values for the space have been updated. So these are the peak values that you would be expecting to get out of a report from, say, Carrier HAP, IES-VE or Trane TRACE.

And the best feature of this is that, for those of you who have dabbled in creating schedules in Revit and really dug into that, this allows you to easily create ventilation calculation schedules. And a lot of engineers are-- prefer to use their own Excel spreadsheets to do those calculations rather than relying on something on what's baked into softwares like Carrier HAP or Trane TRACE. So this actually means that the information is just front and center and ready to be used. As you can see here, we have a space schedule. We don't have that parameter shown at the moment. But again, fairly straightforward.

If you were to go to design cooling load, design heating load [INAUDIBLE] for pressing the button a little bit too soon. Those values have been passed through. They are ready to be used for whatever purpose you see fit.

So the last thing we're going to get into is really more of a deep dive on what lessons did we learn out of this. There were a few things. We went quite far into this to go and take a look at this and what can be done. If you take a look at the write up, you will see a bit more detail on those case studies and exactly what happened. But I will be cutting to Revit periodically to go and show how some of these work.

So the first thing is, and I think I've tried to hammer this home a bit earlier, is that schedules make busy work easy. As you can see here, if you try to do all of this through the interface, it's not exactly friendly towards mass data population.

For those of you that have plugins or created plugins where you can use-- you can temporarily export to Excel and control the information that way, this is your best bet for doing mass data entry and managing that information really, really quickly. Things start to change when you look at schedules, as I'm sure we're all aware. But that also rings true for heating and cooling load calculations in Revit.

Void spaces. So a void space is not just a space that's completely empty, but also where architects have left rooms, say, inside a shaft. And it's this large, empty kind of area. You usually want to avoid them.

But there's other void spaces in areas you wouldn't expect. We had a really interesting case in a long-term care facility where we had one space-- and I'm sure some of you may have seen this problem. We had a space that just didn't show up in the view for some reason.

And any time we placed that space, it was on level one, it still wouldn't show up. And what we found was a floor with a top elevation of six millimeters and a thickness of one millimeter. So it's a floor, but you have this five millimeter empty gap underneath. And the space-- and floors were set to room-bounding. And so the space was five millimeters tall.

And that's kind of the extent of how Revit actually works. This floor turned into this magically floating floor. And it was effectively making that one space impossible to capture within this workflow.

So it starts to break down what kind of elements, things you can actually look for, the typical first offenders. Which is, if you want to get a good gbxml file out of the Revit model and you're working with an external architect, the key is going to be to focus on those elements and make sure that a box is a box. It's not like you have layers of things tucked away. And always to keep things simple.

The other aspect, and funny enough, it was the same project. We had an example where an architect cut a hole out of a wall to make room for a plenum, or the structural, the-- rather, structural supports that were going to keep that louver that were going to create the opening to have a mechanical louver and then a plenum behind it. And we-- again, we couldn't place a space in that room because, effectively, the space is empty. It's just open. The wall is open.

So that's another thing to keep an eye out for is that it will mess with your calculation values, and that it will basically just see this nice open gap, which most buildings don't have a large-- in that case, it was a six foot by three foot hole. And so the thing to remember is that break into is always the best approach. You would need to coordinate with architects for this. And the key is to try and find if there's usually a better way to do things. But break into is generally the best approach.

And the last item is that plenums are tricky to model. Now, a really common practice within the industry is that we don't separate the plenum, the ceiling plenum, from the space itself. And that's generally to keep things simple. Otherwise, it would be really challenging to go and try and manage that information using Carrier HAP. It would be, to be perfectly blunt, a nightmare.

And so what you actually have to do with that process is create a separate level just for your ceilings and then place your spaces on-- your plenum spaces on that level. And you would check them off as a plenum and make them unoccupiable. And then what will happen is that for the spaces on your floor, when in your actual rooms, they will see to the underside of the ceiling. And then the plenums-- the spaces in your plenums will see to the underside of the slab above. And you would actually have to manage those levels.

From our experience, we've opted not to go for this process on most of our projects. Part of the reason for that is that with increasingly complex buildings, ceiling heights change frequently. And it's difficult to try and manage all those levels simultaneously, especially when you're looking at a 2D-- when you're looking at a floor plan from the top down. And how do you actually try and gauge this? And you get these kind of mishmash of puzzle pieces together.

So what we found is that it's easiest just to go from finished floor to finished floor. Spaces can quite easily see the slabs, so you actually get the correct volumes you're looking for and you get the correct surfaces. And thank you, everyone, for attending.