5 keys to drafting home addition floor plan

Tips from an architect

Editor’s note: This is the second in a two-part series. See Part 1 here.

Last time, we looked at all the un-sexy preliminary steps that are necessary en route to designing a home addition. Not one them, you’ll recall, involved any drafting of plans: Rather, there was lots of preliminary wish-list making (creating the program), fact-gathering (the survey), and ensuring that what you want to build conforms to local zoning codes (your conference with the local planner).

Now, armed with the confidence that your scheme won’t get blown out of the water by unanticipated restrictions, you can move on to the next step:

1. Measure your existing house and draw the floor plan to scale, whether on paper or using a consumer-level drafting program — there are lots available at a reasonable price. Take your time and measure very carefully, as the success or failure of some areas can often come down to mere inches.

2. Using this existing floor plan — and following the planner’s guidelines for the area that’s buildable — determine how the addition will adjoin the existing house. Don’t settle for a half-baked solution such as simply passing through a bedroom — provide a proper hallway even if it means having to recoup the lost space someplace else. At this stage, you’ll be wasting your time if you’re making neat, careful drawings. Just hang loose, drawing rough bubble-shaped rooms on inexpensive tracing paper, and going through as many different solutions as you can.

3. Still using rough bubble diagrams, determine the ideal solar orientation for each of the new spaces. Typically, major living areas such as family rooms should face south where they’ll get maximum sun. Kitchens and breakfast rooms ideally face east to southeast, while bedrooms are faced to suit the sleeper’s preference for morning sunshine or the absence of it. The least important rooms, such as the garage, secondary baths, laundry rooms and the like, are given the least desirable northern orientation. Don’t expect perfection, but remember that a decent attempt is better than nothing.

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4. Only now should you begin sketching out some preliminary drawings using straight lines. Whether you’re working on paper or computer, pay careful attention to crucial minimum dimensions such as the width of hallways (rock-bottom minimum: 3 feet wide), stairs (ditto), clothes closet depths (2 feet minimum), and kitchen aisles widths (4 feet minimum). You’ll be sorely tempted to cheat on these minimums in order to wedge in just a few more of the features you crave — but don’t: You’ll end up with a nonfunctional and obviously amateur plan. It’s far better to err on the generous side.

5. When you think you’ve accommodated everything you want — or you’ve tossed out the spaces or features that simply don’t fit — you can finally begin drawing "hard-line" drawings of your floor plan. Note how many steps were necessary before even getting to the drafting phase that most people consider "architecture."

It’s the willingness to lay all this often tedious groundwork that’ll separate your thoughtful, well-designed end product from standard amateur-hour bungling. Whether you choose to tell admirers how much work your project entailed or whether you claim you shook it out of your sleeve is up to you.

Read Arrol Gellner’s blog at, or follow him on Twitter: @ArrolGellner.

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