Roof Design

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This house design project case study is about residential home roof design.  Not just any residential roof design - not just any residential roof, and not just any home design.  

It'll take some explaining before you'll understand well what you're looking at in the 3 sheets we first drew for our clients in re residential roof design planning.  Please be patient there's a lot to learn in this house design project. 

Residential roof design offers no mercy to novices - roof line design, roof deck design can vex.  The AG has been quoted on this:

If you can't think easily and every which way in three dimensions, swear off  home design involving roof planning.

This residential roof design is to rest atop a 2-story custom home for which Before The Architect had been commissioned to assist in home design consulting, home designing, and home drawing.  Our clients had done a lot of homework before we ever met them, hand-drawn plenty of home floor plans, and had finally hit the wall of inexperience.  That's when we were invited to help.  Indeed, this residential roof design is very basically of their doing.  In all cases, we strive to know what's on our clients' minds, that is, we begin each day knowing that we don't know better than our clients about what they want, what they envision, what they expect.

We'll only address roof design of this home plan here, leaving other aspects of this construct to other house design project case studies.  Still, it's worth noting that by the time we got to a roof design Before The Architect had already alerted our clients that they'll need a structural engineer to hold up the home we're designing, and that prompt was in no small measure founded in our forecast of the roof itself - large, irregular, tall in some parts, uncommonly overhanging - over a home on a hillside of hard clay and granite, with walls of glass on the one whole side with the best views.

This roof design is of parts in which roof line design and roof deck design generally rule -

---a main roof gable

---3 intersecting roof gables

---a porch shed roofing rimming the entire perimeter of the home at L2

---a porte cochere at L1 for drive-thru and L2 for roof of 2 roof gables sections offset at 45 from one another, and one offset 45 from the home.

The gables are all to be sloped at 8/12, and the porch roof at 2/12.

On their own, the gables are not a special challenge.  Their three intersections are below the main gable's ridge, and all intersections are at right angles.

The porches all 290 linear feet of them are another matter entirely.  You see, we took as our home design specification that all porch ceilings, soffits, and eaves clear around the home stay at a one level on the horizontal.  (We'll explain that decision in the next paragraph.)  No big deal, you say?  Well, please consider these home design characteristics: 

Overhangs range from 2'-4'

Porch depths range from 3' to 9'-6".

For those nimble of mathematical mind, you can start to visualize the problem here.  For those in need of a brain booster (as we were early-on until we figured it out precisely), the problem here is that the porch ridges attach to the home at different heights over grade.  (In fact, our roof design specification of level ceilings, soffits, and perimeter eave profile were borne out of this realization.  Our choices were:

  1. either to hold the porch ridges stable at a height and let the porch ceilings, soffits, and eaves go up and down from place to place on the porch as joist and rafter runs varied
  2.  or to hold the interior ceiling stable (and with it the porch roof soffits and eaves. 

We judged that the former was a visually goofy option.  (In our analysis of joint heights where porch roof ridges meet main roof gable ends and gable eaves, the total range of height differences is a whopping  14- 11/16" which would have been in our frame of reference intolerable.)  We chose letting the porch ridges run their own courses.  Our primary home design motive was to maintain symmetry from within and its overhang and eave kicker from without.  Our secondary motive was given to us by the building site - most of the changes in porch ridge height to gable ends and gable eaves were on sides of our house open to the down-slope of the site, i.e., essentially out of human view.)

This first pic identifies the scope of the roof  in terms of ridges and valleys of different sorts, dimensions for important widths and lengths, and a host of textual references to the roof and its locale, including, importantly, passive venting specifications.  This pic is illustrative of the basic work we do in roof plans.  Subsequently, we will further define rafters, joisting, sheathing, blocking, and bracing, and other home building elements including specific prescriptions for EPDM application particularly at the porch roof area, nailing patterns, etc.  This pic as it stands is more than we see from virtually any of the plans that come to us.  This PDF offers a huge amount of information on 1 sheet and bears careful scrutiny.  As a very helpful hint, take a heavy look-see at the detail home drawing in the upper right of this sheet there's the secret to all 3 sheets - setting a baseline for laying out the porch ridges.

 Roof Design Home Plan Pic, Sheet 1 of 3, in Plan View, in PDF

Next, elevations.  These are standard home drawing when appended atop elevations of a home.  In this instance, the exterior appearance of the home was still under investigation by our clients, so we show only the roof in 4 standard orthogonals.  Later, we attach these roof elevations to full-house elevations.   Note our extra effort in subtitle notes to make sure that residential contractors have a head start on dimensioning their work at the application level.  These are the sorts of forethoughts and assists that demonstrate the bridge between our home design and home building backgrounds.  Those data in the subtitles are crucial references to setting out work on-site.

  Roof Design Home Plan Pic, Sheet 2 of 3, in Elevation, in PDF

Finally, perspectives.  We don't offer perspectives of home designing elements, unless we reckon they'll benefit our clients majorly one way or another.  This roof is sufficiently complex to check on perspective whether what folks saw in 2D they see in 3d, too. 

Now, the AG doesn't think much of common isometric in perspectives on two different bases:


Most in perspective are at 45 angles that completely obstruct right-angled vertical lines in the distance.


Most in perspective turn down a pic too far for visual interest unless you're a fly-by crow.

The AG gets around both of these long-standing objections by


Turning front-facing elevations short of the 45 standard, i.e., at 40, 140, 220, and 320.  The AG thinks the difference is a bid deal- seeing all the lines you can see.


Dropping down an elevation by only 10.  The AG thinks that this perspective is more realistic than what crows see.

Take a look for yourself.

  Roof Design Home Plan Pic, Sheet 3 of 3, in Perspective, in PDF

You see, by the time our clients go over these 3 sheets in full size and carefully, there'll be little room for doubt that either what they envisioned is what we have designed and drawn or not.  In the latter case, there'll be more work to do, which work will be represented similarly.

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