Room Area and Curtain Walls

Let’s take a look at a little known fact about computed room area when curtain walls are used. Below is a rectangular room with 4 basic walls. The Interior Fill subcategory under the Rooms category was checked to make the room area visible in a light cyan tint. In this case the area is calculated at the wall finish.

However Curtain Walls don’t have a “finish”; they just have a location line. So when using curtain walls that go all the way to the floor, area is computed up to the location line.

What does this mean? If you’re not aware of this fact, there’s a good chance your room area is overestimated. Personally I think putting the location line at the exterior (you have to specify mullion and panel offsets to move the location line to the desired location) makes a lot of sense from a modeling standpoint as you usually know the exterior line of your building. However that is the worst thing you can do for room area calculations, especially with thick curtain walls. So your options are:

1. Make the curtain wall Non-Room Bounding and draw in room separation lines where you need them (in the above example you would sketch them on the inside face). Now you can place your location line wherever you want.
2. Set your location line to the interior face of the curtain wall and leave it as Room Bounding.

My personal preference is #2 because most users forget and won’t bother sketching in room separation lines. Do I like how this particular aspect of curtain walls works? Nope, but I’ll deal with it!

Room Area and Curtain Walls

Spooky Spiders

I’m a day late to a Halloween-themed post, but that’s ok because what I’m talking about are the four-legged kind. Or three…Or two…

My good Italian friend Diego Minato of RevitLandia together with C.G.C. Tec, an Italian company specializing in glazed aluminum curtain wall systems, have released free Revit families of their products. They can be downloaded from here. You need to register for a free account before doing so.

Then you’ll be asked to fill in your name, last name, email address, re-enter the email address, password, re-enter the password and then scroll all the way down to the bottom to check the typical checkbox to accept the privacy policy. Finally click “Prosegui” (Proceed) to finish up registration. You’ll get an email confirmation with a link to activate your account.

At some point you’ll get to the download screen, where you’ll find a PDF tutorial (one in Italian and one in English), a video that shows how to put a system together (no audio or subtitles; also shows you how to schedule components), and a Revit project file containing all the bits and pieces – curtain walls, glazing, sealants, spider connectors and structural supports.

The system was put together very nicely. You have to model the glazing separate from the structural support system. This was done to circumvent the limitation posed by custom panels, which can only be rectangular. Hopefully you can still understand how to use it even though parameter names are in Italian. Spooky!

Spooky Spiders

The "I" in WALLS

BIM is supposed to put a lot of emphasis on the "I" - Information. Unfortunately, walls in Revit miss out on the "I" when it comes to spanning, support locations, scheduling/filtering Wall Function, displaying/scheduling attachment information (top of wall), displaying fire rating information graphically and tagging heights.

Spanning

Walls are made up of various components and their span characteristics vary. For example a stud wall built with a 24" on center spacing spans less than a similar wall built with 12" on center spacing. Currently, we can add a "Span" parameter to the wall category in a project or template. However, this on its own is not enough, as we'll see below.

Supports

Span and support locations are directly related to each other. Just because a wall is 30 feet high and it can span 16 feet, doesn't mean that it will fail, as long as it has intermediate supports that break spans at or less than the allowable span. Currently, we do not have the ability to model these conditions (unless we model each span as a separate wall, which is unproductive and not a realistic representation of how things are built), which occur a lot in our buildings such as high corridors, atria, etc. This applies to both walls and curtain walls. I envision this parameter being input in a graphical way in "sketch mode", where by default, the top and bottom sides of the sketch are "pinned" and the user would then sketch a "support path" with lines (pinned would be more typical) to break the span as required. In case a wall is spanning horizontally, the user could change the sides to define support locations and make the top and bottom as "free". When cut in section or plan, the wall would then display a user-defined "symbol" or graphical representation of a clip/support. A filter to highlight problem walls would also be required to check for span issues, with similar functionality to schedule and filter for span infringments.

Wall Function

Currently, we cannot filter or schedule Wall Function, which renders this parameter next to useless. We need this ability very badly. There have been many instances where I wanted to export a 3D model of Exterior walls and components only, and it is very frustrating to know that the model KNOWS which walls are classified as Exterior and which ones are classified as Interior, yet I have to go through each wall again manually one by one, and assign them to a unique workset so I can gain control over their visibility. EDIT: In Revit 2010, this is now scheduleable. Thanks factory!

Attachment

When you attach the top of a wall to a roof, ref. plane or other element that it can attach to, the parameter "Top is Attached" is checked (read only). Similarly when the base is attached, the parameter "Base is Attached" is checked (read only). Once more, these parameters are not scheduleable or available for filtering. When documenting how walls are to be built, firms have come up with various ways to communicate intent, so I'm pretty sure there is no consensus over how it's done! So I can only relate to our rationale. We like to document how tops of walls are to be built on our code review sheets. These already outline fire rated walls (more on this below), which obviously go to deck. We are then left with walls that go to deck for acoustic reasons and others that only go to 8" above the ceiling. So we chose to tackle the latter with a note that says something on the line of "Undesignated walls go to 8" above the highest ceiling on either side of the wall" and then we designate a "fire tape" for "Unrated walls to deck". In some rare cases, we reverse this reasoning if there are a lot more walls to deck for the sake of keeping the drawings devoid of excess clutter. Currently, Revit does not allow for a BIM way to document this and we desperately need it so we can model every wall how we want it to be built, with the graphical representation becoming a direct extraction of what we model. Currently it is very hard to justify the extra effort since we would have to supplement this information via "2D drafting" techniques, regardless of how we model the walls.

Fire Rating

Walls do have a parameter for fire rating, but once again they fall short of letting us communicate this on paper documents correctly. If we used color prints, then this would be less of a problem, however we're not there yet. Users have used filters and special cut patterns to communicate this information in a BIM way. However, this mostly works on small buildings. If you have an overall plan on a code review sheet with a scale of 1/16" or smaller, then it becomes hard to see what the rating information is if you use the cut pattern technique (especially on 4" walls). Obviously, the "fire tape" method is a pure drafting technique. I'm not an advocate of trying to force drafting vernacular on BIM, but we probably all agree about the need for a clean, graphic way to communicate this information. Unless we're offered a good alternative, we're stuck with doing this in an un-BIM-like fashion, which doesn't do us any good for progressing the BIM cause. We will be experimenting with a number of techniques such as tagging fire rated walls and halftoning all those that are not rated. This still leaves the issue of non-rated walls to deck unresolved.

Heights

Wall heights are difficult in Revit, especially when wall tops are attached to multiple roofs at varying heights. It's not an easy problem, but needs resolved nonetheless. Revit currently reports the Unconnected Height in the Properties Dialog, which in the real world of construction has zero relevance! It cannot schedule this parameter and the closest one can get to finding the Height of a wall, is to schedule the Area and Lenth and add a calculated parameter that divides Area by Length to find an average Height. Unfortunately, when wall tops and bases are attached, the Unconnected Height becomes a worthless parameter, as the reported information is of no use. At the moment we can be disciplined and model each wall separately if the height varies, and then give an explicit height (unattached top). The problem is that we lose the productivity gained by attaching the top of a wall so that when the attachment point moves, the wall adjusts accordingly and is then able to potentially identify whether it violates span limitations (see above). It is next to impossible to estimate quantity and cost if you cannot determine actual heights!

The "I" in WALLS

Where's my curtain wall grid?

Curtain walls are one weird family. Don't get me wrong, I like how easy they are to "design" them. They are very flexible and you can add/subtract grids, move them around etc. Obviously, they could be better, but on the whole they're great.

Why do I think curtain walls are weird? Mainly because you cannot turn off their visibility like any other object in Revit, as the different components that make up a curtain wall are scattered around under numerous categories: Walls, Curtain Wall Mullions and Curtain Panels. Personally, I think it's time that these categories are re-visited.

My suggestion is that there should be a "Curtain Wall" category with at least the following subcategories:

1. Panels
2. Mullions
3. Grids

This way, users can turn off curtain wall visibility at one go just like other object categories, and can also have a logical number of subcategories that users would find more "natural" than what is currently implemented.

So now back to the original question. Grids are controlled by the Wall category, so if you're trying to move mullions around and cannot seem to be able to pick the grid that controls mullion location, check that the Wall category's visibility is turned on. This catches a lot of users by surprise when documenting/designing curtain wall elevations in views with applied view templates that might turn off the wall categories. Once again, with the current implementation, if a wall surrounds a curtain wall and we want to turn them off for documentation purposes, we have to manually override the visibility of such walls or use the linework tool to turn wall linework to invisible lines. Now that's weird!

Where's my curtain wall grid?