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- [Instructor] In this week's video, I want to dig a little bit deeper into the attach top and base command that's available for walls. So, with this command, you're able to take a wall and attach either its bottom edge, or its top edge to a geometry that sits above or below it. And, one of the most obvious use cases is this wall that we see right here in the foreground, by using the attach top and base, we're able to take this wall, and have it attach up underneath the gable end of that roof, and follow the shape of the roof.
The command to perform this action is right here on the ribbon, attach top and base, and if you wanted to remove that attachment, you have the detach top and base command right here. Now, what I want to point out to you about this feature is to exercise some caution if you are interested in the quantities of your wall. The quantities that are available to you are things like, the width, the length, the area of the wall, the volume of the wall, and the height. Now, of all of those that I mentioned, the width, the length, the area, and the volume, these are all pretty reliable.
So whatever number you see for those values, you can trust them. Now, most of those values are right here on the properties pallet, so if I scroll down with that wall selected, you will see three of the ones that I just mentioned right here, here's the length of the wall, the area, and the volume. To see the width of the wall, we'd have to edit type because the width is actually defined by the type, so that would be displayed in the type properties, rather than the properties pallet. Now all of those values, like I say, are pretty reliable, and you can trust what you see there.
But let's scroll up and take a look at the height values. Now first of all, height is a little bit tricker because height can be determined by a variety of things in Revit, as you're no doubt aware. So, the first thing is the base and the top constraints. So, this particular wall is at a base constraint of level one. The top constraint goes up to the high roof, and then, there are no base or top offsets being applied in this particular case, but we certainly could have values in there, either positive or negative, and that would impact the total height of the wall.
Now, beneath the top constraint, there's an unconnected height parameter, it's grayed out, and it reads 20 feet. Now the reason it's grayed out is because we have the top constraint. If we were to change this to unconnected, then this would become an editable value. It would still default to 20 feet, because that's how tall the wall was before we disconnected it. Now, what might surprise you is, if I change this top constraint, and I apply it by moving my mouse back into the view window, nothing appears to happen in the model.
Now, what I've done is, I've created a wall schedule, and you can see that tile next to this 3D view on the right hand side, and I've focused in on this section of the schedule right here, the exterior brick on metal stud stucco. So that's the type that's being used for this wall that we've currently got selected. You can see the name right here. So, if we look through the various entries here, we could see we have several instances of this wall type, and the one that we currently have selected is this one right here, that's 20 feet tall, and now says unconnected.
Now, to verify that, I'm going to click over here to deselect it, and then I'll come back into the schedule here, and I'll click that line item, and you'll see that it will highlight the same wall. So, the height of the wall, the unconnected height of the wall was unaffected by the change that we just made. And, in fact, if you were to change this value to really anything, I could change it to 30 feet, and apply, nothing will change in the model, because the unconnected height is really only applicable when you don't have the wall attached to other geometry, or to other levels.
So, by unconnecting it, we're saying let's disconnect it from the levels, but what that doesn't disconnect it from, is the roof up above. So, if I were to select this wall, and use the detach top and base command, and disconnect it from this roof, that is when it would finally display the unconnected height, and you see that we now have a 30 foot tall wall, and if we kind of zoom in here at the top, you can see we've got this little gap open there, because our ridge is a little taller than 30 feet.
So that's the only time when you can rely on that unconnected height value, which is, you know, a little bit concerning if, you know, a height is important to you to have reported somewhere. And the reality is, there's really no good way to get the heights of your walls reported, either in the properties, or in the schedule, and I suppose it's because there are so many things that impact the height, the level attachments, the connected capabilities to other geometry, like roofs and floors, and so on.
Now, I do want to point out one other thing right here, notice that when we did detach it from the roof, that actually had an impact on the area and the volume right here, so, if I undo that, I want you to watch these two numbers right here when I undo that. You'll see that those numbers become significantly smaller, and then if I redo it, they go back to being up near over 1,000. So, the volume and the area will always be accurate, so you'll be able to rely on those numbers, regardless of what the height says.
So really the only caution I'm giving you is to just take the height values you see here with a grain of salt, because they're not really that reliable by any measure. So, if you need the height of the wall, what are you going to have to do? Well, quite frankly, you'll have to just go to an elevation or section view, and measure it, and it'll put a dimension on there, and measure the height. Now of course, that does expose one of the issues why it may be difficult for Revit to report this value to us, is what is the height of this wall? Should we measure it up to the top of the ridge, should we measure it down here at the at the eaves, when this wall joins into this other wall, that has an impact there because of the sloping top, so, you'd have to make a judgment call anyway, in terms of determining how tall that wall really is.
Now another place where you're going to see this same kind of issue, is in a section view, so I'm going to open up this section right here, it's called section at offices, I'm going to zoom in, and I've got a similar condition here with these interior walls, they are currently attached to this floor. Now, how do you know if an element is attached? Well, unfortunately, if you go to your schedule, and go to fields, there's no field that we can add to the schedule that will report that information.
That information is simply not available to the schedule. So the only way that you'll know, is by selecting the wall, and looking at the properties pallet, and there's a parameter right here that says, "top is attached", and that will be checked, and it'll be grayed out. And that's the only way that you'll know, same thing with bases attached, that's also a read only parameter. It's currently not checked, so my base is not attached to anything, but my top is. So, you really just have to kind of investigate these elements, you know, exercise some caution when you're choosing to use that attachment feature.
Now, it's really invaluable for situations like this, where we have this gable end condition, I mean, the alternative to attach would be that you'd have to edit the profile, and model that manually, and then if the roof slope changes, you wouldn't get that change automatically. So really, I think the pros outweigh the cons for exterior walls like that one. But maybe for these interior walls, you might consider the alternative of detaching it from the floor, that pops it back up to its level attachment, and then whatever this thickness is right here, you could set that as a negative top offset, so negative one in this case, and that puts the top of the wall back in the same spot, but now, the unconnected height correctly reflects the actual height of the wall, and the floor no longer impacts the height of that wall.
So it's really a judgment call, it's up to you which feature you want to use, I think it makes a lot of sense for exterior walls to use the attach top and base, there really isn't a much better way to do that, especially with sloping roofs. But it's maybe, perhaps a little questionable with your interior partitions, and whether or not you should attach them to floor slabs. So just kind of keep all of that in mind, and particularly if you're interested in measuring the heights of the walls, you really don't want to rely on the values that come out of the properties, or the schedules.
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