Custom Home Design Program Series – Roof Plan Design Pictures & Text

INTRODUCTION

• This e-article is about designing a custom home Roof Plan, including pictures and text 

ROOF PLAN DESIGN – PICTURES & TEXT

Comment:  Nothing confuses and confounds more than a roof plan.  In this custom home designer's opinion, if it's not drawn in 3 dimensions, then it's not well understood. 

Again in this home designer's opinion, Autocad doesn't make it easy on the designer (as, for example, does Chief Architect):

• lines must meet exactly in lengths and vectors
• importing stock plan drawings can diminish or outrightly destroy isometric viewing
• standard views of objects can overwrite and otherwise bedevil perspective
• elevations can tease out tantrums of "what's that line?" and "is that in foreground or covered up?"
• hatches to get better sense of depth and pitch are limited to 3- and 4-sided flat planes. 

• Roof plans shall define 
  • slope
  • type
  • gable
  • hip
  • shed
  • round
  • valley
  • regular (default)
  • irregular
  • ridge
  • gable
  • hip
  • shed
  • rising
  • cricket siting
  • top plate lines relative to rooflines
  • cross-reference to identify attic ventilation requirements
  • cross-reference to identify water runoff requirements
  • depth of overhangs
  • rafter endcuts
  • square cut
  • level cut
  • plumb cut
  • flares

• Herewith, a Roof Plan sheet example, noting that no two are identical 

Roof Plan, Plan View 

KEY:

A = a 1-off study of section in elevation to clarify if not simplify the several relationships between house top plates and roof intersections, including statements of design objective and design guidance by way of commentary on how this section came to pass and why 

B = roof design and construction notes, including but not limited to: materials qualifications for lumber and sheathing; deflection performance limits; approval process; fastening generally; moisture barriers; bracing; fastening specific to roof trusses; raised heels; etc. 

C = specific guidance in re design and construction, including but not limited to: overhangs of eaves, rakes and gables - both main and dormer; rafter tail style; member spacing and in-line siting; sheathing thickness and quality; radiant barrier application.  Also: dimensions uninterruptedly between roof deck articulations at eaves, rakes, hips, and ridges; identification of elements including gable rake and gable ridge, eaveline, shed rake and shed ridge, raking cornice, regular and irregular valleys; slope rate and direction for each roof plane; roof finish clad; dormer framing method; primary and secondary ridges; rising ridges; intersecting ridges, roof-dependent top plates; etc. 

D = key 

E = notice of contractor's and supplier's responsibilities in regard to both design and construction 

Roof Plan Close-Up 

• Let's look more closely at a Roof Plan by reviewing a segment, this being of a 3-car garage by a porte-cochere to the right and a large motor courtyard above, bounded by a natural stone wall.

Roof Plan Close-Up, Garage, Plan View, Scaled 

KEY:

A = guidelines between floor plans, in order to orient users in structural alignments 

B = identification of cantilever soffits and dimensional extents 

C = dimensions between roof deck - not top plate - articulations 

D = roof deck perimeter lines 

E = intersecting gable identifying gable ridge, eaves, rakes, and valleys, plus cantilevers by site and extent, slope, and flare roof folds and slope 

F = fully-walled trash enclosure as outbuilding requirement of local community code, whether roofed or not - this one's not roofed 

G = note specifying construction treatment of returns in-style and generally at variance to (unfortunately) common practice  

H = note indicating design latitude still in-process with owners regarding whether to open the two roof dormers to the intrior as clerestories 

I = roof flare fold line and slope note 

J = note of roof dormer dimensions in footprint, arch type (segmental), individuated finish clad type (standing seam copper, stating seam spreads), major and minor arch axes, objective for slope 

K = dimensions from roof deck termini to dormer centerlines 

L = garage vehicle overhead door outlines 

M = slope rate and direction with note that such is typical unless otherwise identified, e.g., as in dormer identification (above) 

N = attic scuttle hole access dimensions and approximate site 

O = ridge lines 

P = outside edge of top plate line 

S = roof dormer overhang  

• Now, let's look at the Roof Plan as it is translated to the Motor Courtyard elevation . . . 

Plan Highlighted in Elevation, Garage, Facing from Motor Courtyard, Scaled 

Plan Highlighted in Elevation, Garage, Facing Obverse of Previous, Scaled  

• Note well that in these last two pics, the letter symbols are the same as in the Roof Plan; see how many correlate –  

KEY:

B = roof cantilever and extent 

G = note specifying construction treatment of returns in-style and generally at variance to (unfortunately) common practice  

H = note indicating design latitude still in-process with owners regarding whether to open the two roof dormers to the interior as clerestories 

I = roof flare fold line, slope 

J = roof dormer arch per Roof Plan metrics note 

K2 = cross-check on roof dormer placement by centerlining to Garage vehicle door parting walls 

M = roof slope 

O = ridge lines 

P = outside edge of top plate line 

R = roof rake and raking cornice trim notes 

S = roof dormer overhang per Roof Plan metric 

T = cross-reference to detail of return 

• A Roof Plan is based atop the top plates on which the roof rests whether sawn or trussed
  • in a single-story home, that'd be the wall's top plates
  • in a two-plus story house that'd usually be the uppermost floor's wall's top plates
  • in a story-and-a-half, that'd usually be the first floor's wall's top plates 

• A Roof Plan is essential to developing a
  • Watershed Plan
  • Elevations (exterior)
  • Whole-House Section(s)
  • Roof Overlay 

• A Roof Plan shall include overlays, in order to give contractors and engineers a head start in reckoning load paths and bearings 

Roof Plans, Plan View, Overlays, Scaled 

• Where Roof Plans fail
  • commonly, Before The Architect discovers stock plans with Roof Plans, if at all, then inaccurate
    • drawn and texted slopes can be in conflict
    • overshadowed roof profiles in elevation are not left behind, but brought forward
    • roof layouts, particularly in elevations, suffer from the same laxity of exactitude that many elevation occasion generally
    • dimensions are forced
    • dimensions are locked and then the underlying layout changes without commensurate change in dimension
    • difficult relationships, notably in this designer's experience in regard to rafter and truss rests, are
      • unnoted
      • incorrectly noted
    • roof planes that are never, ever going
      • to intersect fully
      • to intersect where they're supposed to
      • to intersect at all 

Comment:  An unpleasant consequence of poorly defined, complex roof structures arises when Before The Architect, in consort with clients, alters perimeter lines and a proportionally similar appearance of the roof in elevation is still desirable. 

• The worst Roof Plan in a stock plan gave rise to this study, the point of which was to convey the intricacy and interrelationships of 4 different roof structure rests – two at Front Of House, two at Back Of House – that, in the original, were totally blown 

Primary and Secondary Roof, Section in Elevation, Scaled  

• It might be instructive to review just how much prescript and prescript needed, in this home designer's opinion, to communicate design and construction targets to the guys who'd ultimately be designing and constructing 

Guideling Text Accompanying Immediately Previous Section in Elevation

DATA ARE APPROXIMATE AND SHALL BE CONFIRMED AS ACCURATE OR REVISED BY OTHERS, INCLUDING BUT NOT LIMITED TO GENERAL CONTRACTOR, FRAMING CREW, AND ROOF TRUSS ENGINEERS BEFORE EXCAVATION. 

OBJECTIVES:

1. DETERMINE KNEE WALL HEIGHTS TO ROOF SEAT, IN ORDER TO HIT PEAK TARGETS OF OLD HORIZONTAL METRICS AND NEW VERTICAL METRIC WHILE KEEPING KNEE WALLS BELOW PORCHES' OVERRUNS USING ORIGINAL SLOPES AND TOP PLATE HEIGHTS.

2. PROVIDE A BASIS OF SHARED UNDERSTANDING OF THE DESIGN ESSENTIALS TO PRIMARY AND ABUTTING SECONDARY ROOF STRUCTURES OF THEMSELVES AS REPRESENTED IN ELEVATIONS AND ROOF PLAN AND AS A BASE POINT FOR POSSIBLE REVISIONS DONE BY OTHERS, E.G., ALTERED HEEL HEIGHT FROM 7 1/2LI AS-DRAWN. 

COMMENT:  THIS DESIGNER WENT TO THESE ANALYTICAL LENGTHS EVENTUALLY - AMONG OTHERS PRECEDENT - IN ATTEMPTING TO REDESIGN THE ORIGINAL FOH APPEARANCE SUBSEQUENT, NOTABLY, TO REDESIGNED EXTENSIONS OF THE GARAGE WING OUTWARDS, FIRMLY HOLDING TO AN 18LI OUTSET OF ROOF PRM TO PLATE PRM AND A 7 1/2LI HEEL, RELIANCE ON A CANTILEVER ROOF STRUCTURE FOR ALL MAJOR PLANES AT THE PERIMETER, AND A REVIEW OF ORIGINAL ROOF PLAN MATERIAL WHICH WAS, IN THIS DESIGNER'S OPINION, UNHELPFUL OVERALL.  IN OTHER WORDS, THE HOME GOT WIDER, MAKING THE SECONDARY CROSSING RIDGE, AND, DERIVATIVELY, THE PRIMARY RIDGE HIGHER.  REGULARIZING SOFFIT STRUCTURE AND HEELS, TAKEN TOGETHER, FURTHER RAISED THE ENTIRETY OF THE ROOF NOT QUITE 6LI.

        THE KEYS TO UNDERSTANDING THE TWO MAJOR PIECES OF THIS ROOF SYSTEM ARE THAT - A) IT RESTS AT FOH AND BOH ON PLATES EACH OF TWO DIFFERENT HEIGHTS, AT FOH IN-LINE AND AT BOH OFFSET; B) THE PRIMARY ROOF MUST PEAK AT WHATEVER THE RIDGE HEIGHT IS OF THE CROSSING SLOPE.

        THE ORIGINAL'S SLOPES ARE MAINTAINED WITH THE SEMI-EXCEPTION OF THE 12:12 HIP NOW AT BOH WHICH WAS 10:12 IN THE ORIGINAL WHEN IT WASN'T 12:12 - BOTH REFERENCED.  THE ORIGIN OF THE GARAGE-SIDE LEG OF THE FOH'S LARGER DORMER REMAINS UNCLEAR. 

• Where a Roof Plan succeeds
• when its construct agrees with
• Watershed Plan
• Elevations (exterior)
• Whole-House Section(s)
• Roof Overlays
• Floor Plan perimeter rests
• 3-dimension version of the roof overall 

Roof Plan Vector to Elevation, Front Of House and Floor Plan, L1, the Last Two (Vectored) in Plan View, Scaled 

• such agreement arises conclusively by straight-line vectors to
  • eaves
  • valleys
  • peak
  • ridges

     
     
• An example of Roof Plan vectoring is in the immediate pic Roof Plan Vector to Elevation, Front Of House and Floor Plan, L1, relating
  • three sheets
    • Elevation, Front Of House (top)
    • Floor Plan, L1 – Text Version (middle)
    • Roof Plan (bottom)
  • two ways
    • top plate articulations, red
    • roof ridges and peaks, green 

Comment:  Please note that all three sheets are not to be published in the same scale; the Elevation will go 1/4 linear inch:1 linear foot, while the other two will be plotted at 3/16 linear inch:1 linear foot.  They're all three drawn in 1/4 linear inch:1 linear foot, but framed differently, in order to plot similarly on ARCH D (36 linear inch x 24 linear inch) in landscape.

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Comments on this article: (2 total)

» left by Teresa Ortiz ^(11,162)
Teresa Ortiz (1 year 218 days ago.)

And I thought you just had to slap some shingles on it and call it good. Thanks again for a great layout. This is great information for someone pursuing such a project.
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» left by Ralph Pressel ^(48,060) (1 year 218 days ago.)
Dear Teresa,

Delighted you appreciate this article for its usefulness.

Indeed, there's even more to roof design than is in this article, including active or passive attic venting, compensating for rainwater runoff, maximizing daylight intrusion in summer and winter, let alone home design style, proportion, balance, interior space needs, advanced structure and substrates for certain finish clad, trimming over-roof elements with true masonry, etc.

Thanks for your interest in our work.

Ralph


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