I work at a developer and am trying to underwrite a site. Looking for advice on how you decide on a development program and massing. In this case, mid-rise multifamily, sunbelt.
I’m assuming 85% site coverage (for setbacks), 85% building efficiency, dividing building footprint sf by avg. unit sf to get units/floor, then multiplying by number of floors to get total unit count.
How do you guys approach this? Does anyone use SketchUp/ or just have a prototype they use/ etc?
I have seen multiple methods, but here's the way I have been taught, which is good enough to use for a preliminary underwriting. We don't need to refine the details of the building layout until we know it's worth pursuing.
I start with a satellite image of the subject property, ideally one where the lot lines are easily identifiable (GIS or even just Google Maps). After checking zoning regulations for setbacks, FAR, density, etc., you can have an idea of where your building envelope can fit within the property. Seems like you're already doing this part.
Considering site coverage ratios is important, but using them without visualization may overlook the layout of the subject property and the feasibility of the building design. Our typical double-loaded corridor multi product has 30-foot deep units with a 5 ft corridor between, meaning the width of a building is 65ft. For single-loaded corridors (wrapping a parking garage, etc), width would be 35ft. Parking spaces are 9 ft wide by 20 ft deep, with 20 ft wide driveways required between double-loaded parking lanes. So, 60ft minimum width for parking lots / garages. Helpful if zoning includes parking requirements.
Start drawing rectangles with a 65ft width for the building, 60ft for parking. If you have access to Bluebeam Revu, you can use the measurement feature. If not, Google Maps measurement feature will give you a good enough estimate for a first pass (right click - measure distance). Consider building shapes that your shop has built in the past - bar, C-shaped, L-shaped? Is parking below a podium? Garage? Surface level?
Once I have the layout, I figure out how many stories we can build, now I have total building square footage. Divide it by 1,000 to get rough estimate for total number of units. We use 1,000 sqft per unit based on our unit mix, including common areas and amenities. This is assuming the building is at least 100 units. That's enough to run a prelim proforma for us, then we will refine the program with our architects once we determine if it's worth pursuing.
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