Sketching Massing Alternatives in Three Dimensions

This exercise explores techniques for translating the massing regulations provided in a zoning regulation into three-dimensional building envelopes and specific massing alternatives. Massing regulations are one way that cities regulate the character of neighborhoods. By specifying the unbuildable margins of property parcels, known as setbacks, and maximum height limits, each parcel has a unique three-dimensional potential zoning envelope that defines the extent the extent of the buildable area above each parcel. The zoning ordinance also typically specifies a maximum ratio of the useable floor area of a development to the area of the development's parcel, floor to area ratio or FAR. There are often several potential massing alternatives that might be specified to fit a building of a certain FAR into potential zoning envelope. This exercise provides some techniques for visualizing and presenting the regulatory envelopes and potential development scenarios for a neighborhood in Boston's North End.

This tutorial will introduce a very simple, yet powerful 3d modeling tool, Sketchup. We will use the most basic drawing techniques, which are covered in the video Sketchup Tutorial 1 which is available on-line at The Sketchup Tutorials Page Keep in mind that this tutorial makes use of audio, so plug in your headphones, or you will be missing a lot! Wherever more detailed technical information is required, we will refer to applicable documentation in Sketchup's on-line help, with references highligted like this.

The importance of Learning to Navigate in Sketchup

The key to success in any editing tool is to feel comfortable with placing your cursor in a specific location and creating and moving geometry exactly where you want it. Naturally, if you don;t get to this level of comfort, you will not have fun with modeling in sketchup. The interface is probably the most intuitive of all 3d editing interfaces, yet people aren;t born with an understanding of sketchup. This is why you should go through the first six of the short video tutorials referenced with the sketchup 5 videos.

Understanding how to Organize Your Work in Sketchup

Simply making shapes in sketchup is fairly easy, but after your model has more than a few shapes in it, you will find that it can be very difficult to understand what shapes you are selecting and editing. A good model may have different alternatives in it that share a context, but that you may want to selectively turn on and off. Without understanding how to use Layers and the object Outliner to organize your model, you will get very confused and frustrated by sketchup. To understand this, take a look at tutprials 11 and 20 in the with the sketchup 5 videos.

The Boston Zoning Ordinance

We are intested in exploring the potential alternative massing scenarios for some parcels near the Paul Revere Mall in Boston's North End. To begin, we will find the apropriate articles of The Boston Zoning Ordinance. In particular, in particular, we are interested in the map that covers the North end Neighborhood District Which tells us that our parcels are in the MFR zone. Then we need the applicable dimensional requirements for this zone, which are found in Article 54 of the zoning ordinance in Table C, which is near the end of the article.

Table C specifies the dimensional requirements as follows:

• Building Height Maximum: 55 feet
• Floor Area Ratio: 3.0
• Front Yard Minimum Depth: None
• Rear Yard Minimum Depth: 12 feet
• Side Yard Minimum Width: None

Lot Dimensions

The next step in determining the building potential for the lots in question is to figure out the exact dimensions of our parcel. For this, we have an image of the parcel boundaries with a graphic scale. In this case the image came from the cities GIS, but it could have just as easily have come from any scaled map that we may have scanned. You can download the North End parcel image by right-click this link and "Save Target As". It will be helpful if you create a new directory in the C:\temp folder to hold your work for this project.

First we bring the zoning map into sketchup, and scale it to real-world dimensions. For future reference we sketch in the fountain from the aerial photo. We can now sketch in the building lot and get its dimensions and area. Subtracting backyard setback yields the dimensions and area of the buildable area. The buildable envelope is an extrusion of the buildable area to the allowable height limit.

We will use Sketchup to begin exploring the dimensions of thsi parcel and the lot above it.

Drawing in Setbacks to Establish the Potential Footprint

The allowable building footprint is determined in our case by the edges of the parcel minus the reqired backyard setback, (12 feet). So in this case, we can simply make a new polygon which occupies the back 12 feet of the parcel.

Establish the Potential Zoning Envelope

The zoning ordinance specifies the maximum building heiight. This information, combined with the building footprint, tells us the potential buildable envelope. We can easily visualize this in Sketchup by extruding the building footprint polygon.

Developing a potential Massing Proposal

There are many possible ways to create a building with a given FAR. We know the area of the parcel is 722 sqaure feet. our Floor Area to Lot Area ratio is 3.0. This means that our building may have 2066 square feet of useable floor space. If we use the maximum building footprint (494 sq ft) as the basis for our floors, then one potential massing scenario would have 4.2 floors in a perfectly rectangular building.

The simplest buildout scenario creates a simple four story building Or we can use more of our envelope with a five story building Now we can compare the effect of shadows of the four story scenario with shadows of the five story scenario (October 3 at 3:00 pm.)

Of course, there is always more than one way to do it. Rather than making all of our floors have the same footprint, we can make a building that has the same floor area but is taller, by adding terraces. This may also allow for a less imposing appearance fromthe park. Fopr example, we may have 2 floors at 494 sq feet, and two floors of 400 sq feet apiece, and cap it off with a penthouse of 278 sq feet. This scenario will take more advantage of the height envelope, and will provide some nice outdoor areas for residents of the building. But what will be the shadow impacts on the park relative to our more compact scenario?

Shadow Study Animations

By setting pages in the Skethup View->Tourguide options, we may save particular shadow settings. Then, exporting an animation will morph our shadows from one season or time to the next. These anaimations can be exported as avi files:

• 5 Story Scenario, 2:00 January to December
• 4 Story Scenario, 2:00 January to December