BEFORE THE ARCHITECT – THE BIG PICTURES
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BUILDING ROOF DESIGNS, ROOF PLAN
Calculating roof pitch and slope are an easy part of building roof designs: rise in inches over a 12" run, or its equivalent. Calculating roof pitch and slope are akin to picking out which roof shingle manufacturer will get your business. These roof design steps are matters of reason and rote.
How about building roof designs themselves? There's hardly a client we've ever had at Before The Architect who could draw building roof designs to rest atop their floor plan. A few have even tried, and all have failed either a little (rarely) or a lot (common). And we get the best and brightest of clients.
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So what's the big deal? Essentially in building roof designs, don't start with a roofline, end with it. Play with it once you've laid out rooflines that work. Rooflines variously and easily lend themselves to architectural styles. English, gables. Dutch, gambrel. Contemporary, flat and shed among others.
In this case study, we had French Country Cottage house plans with which to work. Studying that style can tell you lots about how an in-style roof system should work: different slopes, some quite high; dormers (owing to the style's characteristic story-and-a-half structure wherein L2's perimeter sits inside L1's perimeter); mixed plans of gable, hip, and round top; etc. And these characteristics tell us, of themselves, other elements we could confront in building roof designs: roof crickets to wed differently sloped roof planes; possibly difficult roof drainage systems arising from eaves of different heights and unusually large watersheds to unusually small drainage areas; decisions about the extents of soffits both outwards from an exterior wall line and downwards along an exterior wall line, or in other words, the extents to which one will allow eaves at different heights over grade or relative to wall planes; conflicts with window and exterior door transoms and other over-window and over-door features, e.g., pediments, luminaires, etc.
French Country Cottage building roof designs are for their better part expulsive. Not splurgingly expulsive, but enough to run freely to exterior corners, exterior wall insets, rooms of substantially different sizes which rooms jut out from those that are proximate. Make an exterior corner and you make a roofline. An extensive French Country residence has lots of corners; an extensive French Country residence has lots of rooflines. Not quite organic, but not quite disciplined either. Complex. Let's see.
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Before The Architect designed this roof plan comprised of an extraordinarily complex set of building roof designs, as it also designed the house to go below it. The roof system involves -
 | about 30 flat segments |
| 7 different roof plane pitches ranging from a little over 4:12 to nearly 17:12; |
| 3 roof pitches given, and 4 derived; |
| 8 dormers of which 3 are shed and 5 are round top of 4 different widths, |
| a large round top roof over the entry stoop; |
| a mix of gables and hips and round tops and sheds. |
Here it is (in .pdf format) as presented in unique house
plans
prepared for bidding out:
There's quite a bit that's interesting about these building roof designs in these unique house plans. They identify many elements in building roof designs:
| pitches by major roof segment; |
| roof crickets; |
| roof vents to scale, based on details from another sheet in the plan set which specifies passive (and mechanical) venting environment; |
| soffit vents by location and number, based on details from another sheet in the plan set which specified passive (and mechanical) venting environment, including particular methodology for shed roof and certain other applications often passed over to the subsequent rue of owners unaware of the need to attend to such matters separately; |
| to-scale sites of dormers and skylights, the latter's profiles adjusted for the respective roof pitch of each (the needs for which either for emergency egress or natural lighting requirements are itemized and specified elsewhere); |
| annotations to help viewers get their bearings, e.g., rising ridge, triangulated wall, etc.; |
| specifications for watershed drainage by site of gutters, site of downspouts, and pitch of gutters - all based on extensive calculations elsewhere in the plan set (immediately preceding sheet) that defines watersheds into 9 distinctly different areas for application. |
The perimeter dimensions of this roof system are based on our floor plans. We start with the floor plan of L1, design a roof system that satisfies necessary and sufficient qualifications (principally of style), then figure out what space there is under that roof system to layout L2's habitable and unhabitable space. That layering on of rooflines, L2, L1 looks like this in plan view, given this color coding:
| primary rooflines are red; |
| secondary rooflines are blue; |
| tertiary rooflines are green; |
| dormers and skylights are black; |
| L2 is mid-gray; |
| L1 is light gray. |
Here's the working overlay (in .pdf):
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How does Before The Architect know so much about its roof layout? It's in a 3-dimensional drawing to-scale that's built precisely atop the L1 top plates' top of face. Remember that this is a story-and-a-half structure, so roof structures foot on L1 wall tops.
The purpose of the 3-dimensional drawing of our rooflines is:
| to cross-check ourselves that our floor plans are true; |
| to develop the roof plan in plan view - literally our 3-dimensional drawing laid flat; |
| to assist structural engineers with a set of essentially visual prompts as to roof element physical relationships both to each other and, by including below the rooflines the L2, L1, and foundation plans, to subordinate structures for subsequent amendment with posts, beams, and other buildups as load paths run from ridges to footings; |
| to provide the precise bases for elevations of roof profiles; |
| to reasonably closely determine the extent to which there's habitable space on L2 under that roof system. |
Here are four isometrics of the working overlay illustrated above.
| Note in each that rooflines run from the interior, top of face edge of top plates on L1, because that's as close as we can get at this stage as to the foot of a roof frame structure either that's truss-framed with its bottom of face line of the bottom chord at the edge point or the hand-framed rafter heel at the level cut of the bird's mouth. |
| Note in each that it is in wireframe and color-coded as above. |
| Be aware that these are working drawings right from our project file, not prepped for general presentation. |
| The black, angular lines and boxes emanating from the skylights downward are part of a natural light pattern study - those lines are the maximum boundaries of natural light's direct illumination on respective interior spaces. The rectangles on horizontal planes within each set of line-boxes is our reasonably close approximation of interior ceiling heights, or the extents of the skylight chases. |
| Soffits and overhangs are omitted from all the isometrics - added in elsewhere, in presentation pieces. |
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Postscript: One visitor has questioned the need for the humongous cricket that is identified as a roof plane in this plan. He could be right; he could be wrong. Whichever, it was good fun investigating the claim. Ultimately, this'd be the sole purview of the roof framers - no chance that this roof was truss-framed - who do what they have to with what they've been given including a whole lot of calculating going on. AG
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Before The Architect has not designed more complex rooflines. That's not because we couldn't; it's because nothing more challenging has come along yet.
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