BEFORE THE ARCHITECT – BLUEPRINT DESIGN CONSULTANTS
TIDBITS OF HOUSE DESIGN AND HOME BUILDING PLANS CONSULTING
Doghouse Dormers
Oh yeh. Oh yeh. Don't you know that it is a far better thing to doeth it right sooner even if it means a piece out of your own hide, because to maketh it right later can mean an even bigger piece out of your own hide. Thus spaketh the AG from the granite knee of been there, done that. AG
(If this is your first visit to Before The Architect, please consider spending a few moments looking over the Site Map, in order to get a feel for the architecture of the site itself.)
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Note: The As, Central GA
From: Before The Architect, Cumming, GA
Re: Companion Commentary to Coincident .PDFs
Date: August 11, 2003
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INTRODUCTION
Here's an interesting choice to make as between 2 types of doghouse dormers - that's the style of dormer atop our house (as opposed, principally, to shed roof dormers – typically flat-topped, pitched at about half the primary roof's pitch).
In the discourse to follow, dormers devolve to two types by size and roof pitch on the outside and two types essentially by interior ceiling height, angle, lighting, etc. with an inherent leeway of dormer placement in a roofline. If all that seems confusing, it can be. May your continued reading and close attention help to clarify and keep in mind the basics herein, since their understanding is crucial to the end-appearance of our house from both outside and inside. Herein under, we’re disclosing and discussing options available to us in dormer design in varying degrees based on dormer site and desirable interior appearance.
This Note is intended to introduce you to your options, to inform, to challenge. From an exterior vantage, we may have less latitude in dealing with the frontside dormers and, generally, with the primary roof dormers overall; we may be permitted variation in the exterior of the secondary roof dormers. On the interior, design options are broader throughout.
This Note is not intended in its entirety to direct a specific design course. We can guide you in related decisions; however, we will not direct you except by your leave.
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Dormer LOOK FROM THE OUTSIDE - Roof Pitch and Relative Size
This first point is about a rational to consider in respect to our dormers’ look from the outside – their look in both dormer roof pitch and dormer size.
Roof pitch on doghouse dormers can be a subject of some concern and debate in certain applications. Drawn elevations offer limited utility because they’re without perspective, operating on strict orthogonals and without the sense of depth and structural interrelationship that comes from parallax anglings on both the horizontal and the vertical. In other words, drawn elevations of dormers are even less helpful than views of a one-eyed bird frozen in flight.
Sometimes, the size and roof pitch of dormers is best resolved finally once the roof planes are framed up and a very rough-framed outline of dormers can be set atop to get a visual feel for what ought to be and what ought not. The latter-day deferral of decision-making herewith is an acceptable alternative for you in respect to this matter of exterior appearance.
This point is further developed now, so as to prepare you for whatever decision path you choose – deciding now or soon or deciding later on.
To our eyes, it usually looks best to pitch doghouse dormer roofs at the same pitch as that roof pitch of the main roofline facing us at gable end when we're looking at the doghouse dormer straight on. That is, it's almost always better design to give the eye what it's looking for - symmetry. Eyes and the mind's eye (the expectation of appearance herein) search out symmetry. Symmetry settles a lot of visual conflicts, and, short of symmetry, then proportion, balance (and, past that, light, color, texture, etc.).
This point becomes a matter of central interest on three counts:
1. From the frontside strictly, we have no gable end to catch our eye and to which to relate the dormers' pitch. Not to worry, we have a gable end pitch to set our eye to expectation as we approach the frontside of our house from left and from right - it's the primary roof pitch, currently 14/12. That is our suggestion for pitching the frontside dormer roofs, and appears to be consistent with the seminal drawing.
[I note editorially that our gable-end porch roof could easily qualify at a different pitch from all others for our house as our suggested porch design could be easily accepted as temporally antecedent to that of the main house, our porch being reminiscent of the central 19th century.]
2. From the left or right sides, we're looking at more dormers. From the left side, the only gable end reference we have is that primary roof pitch, and that would seem to settle it for how to deal with the left side's dormer roof pitch, again 14/12.
Here is where things get a little tougher. Because the roof pitch of the secondary roof on which the left-side dormers rest is 9/12, an exact copy of the frontside dormers will stand up and out more than those in the frontside. You may opt to reduce slightly the overall size of these side dormers relative to the front dormers.
Classically, it appears to us that most colonial dormers - particularly earlier ones - as this house of ours is intended to mimic in considerable measure - are smallish for the house roofs on which they rest, the glazes smallish, too.
I reckon that the smallishness of the dormer structure arises from a characteristic of the post-and-beam framing on which such dormers sat (and some still do), i.e., post-and-beam framing is inherently and substantially weakened by amendments to its planes, be they amendments to walls or roofs. Knock a corner out of a post-and-beam frame and rack the whole structure to ruination, even catastrophic failure. Knock a corner out of a more modern-day platform or even balloon frame and prepare to rebuild that corner. No rack. No ruin.
The smallish glass is an easy one. Glass cost a lot way-back when, and, compared to today's glazes, was brittle - not easily laid up in big sheets.
3. From the right side, we've got the same issues as on the left both in cause and effect. That the eye also sees a shed roof (over the sunroom) pitch at lesser degree than any other it looks at is irrelevant - that shed roof pitch is substantially lesser to the point that to mimic it in any of our dormers would herald a design disaster and, of itself, that pitch serves to identify a shed or porch or later extension or covering to more steeply roofed structure. That is, the shed roof distinguishes an interior space easily recognized and visually accepted on its own.
What's more central to our concern on the right side follows.
Holding true to our rationale in b. above, the Bed 2 back-facing dormer roof would pitch at 14:12 to ape the currently 14:12 primary roof on which it rests, as would the 3 side-facing dormers resting on the 9/12 roof over the L2 long hall and Bed4. So far, so good.
Still holding true to the permissible rationale of b. above, we might reduce the overall size of these dormers to be more proportional as described above. Therefore, standing on the back deck and looking up, we could be viewing dormers of two different sizes – proportional, yes; same size, no.
Please keep these optional differences in mind as design and, possibly, construction progresses.
Reprieve
By way of leaning on our own understanding, we think it’d be meet and right to offer the eye two sizes of dormers on the two axes of primary and secondary roof lines, that is, larger on the primary and smaller on the secondary.
A design characteristic of colonial houses is that they were built on as time passed. In ours, the secondary roof (and subordinate structure) is logically an addition to the primary roof (and its subordinate structure). Conditionally, the same can be said of our porch roof over the sunroom (conditionally, because that roofline could be precedent to either the primary or secondary roofline). So different-sized dormers on secondary vs. primary would not be without warrant. That a carpenter decided to hold (or, for that matter, relax) the primary roof pitch in the secondary dormer roof pitch would not be out of keeping with architectural development of things residential including the structure we’re representing. That a carpenter decided to alter dormer sizes between segments of a house built in stages divided by years would be similarly appropriate and understandable. Still, it would not be beyond imagination for a carpenter to copy primary dormer height and width to the secondary roof’s dormers inch for inch and let the secondary’s lower slope extend the surface area of both dormer walls and rooflines versus the primary’s.
Conclusion
In essence, you’re pretty free to do as you choose with our dormers in terms of both roof pitch and dormer size subject to notions of common sense and visual appeal, and are herewith offered bases of awareness and choice in these regards.
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DORMER LOOK FROM THE INSIDE – DORMER CEILING STRUCTURE
This second and last point about dormers is this: You have a choice to make about the distinctive look of our dormers as viewed from the interior; essentially, whether you desire the dormers’ ceilings to be flat or vaulted [note, I did not write “cathedral”, as I am not suggesting that our the dormer ceiling rafters be exposed to their sheathing or its equivalent]. This interior look has no direct bearing on our exterior look addressed above (aside from the wiggle-room in siting the dormers by height on the primary and secondary roof planes – see below).
I have included within the email that contains this .doc 2 .jpg files depicting your choices structurally better than I can. [The .jpg files are digital photographs from Framing Roofs: The Best of “Fine Homebuilding”; For Pros by Pros, by The Taunton Press, 1998, specifically in an article “Framing Doghouse Dormers: Two ways to frame a basic gable dormer” by Scott McBride, pp.36-41. Excellent piece. Excellent reference book. Excellent magazine.] Each .jpg portrays the same doghouse dormer structure in size, and each varies only in interior layout and, in these examples, roof penetration over gable eave height.
In the so-called Valley-Rafter Method, the dormer ceiling is vaulted presumably (though not necessarily) all the way back to an existing, interior, flat ceiling. Its major design elements are 2 –
1. Opportunity to run a dormer starting from fairly low on a roofline while still offering a sense of height to the dormered space;
2. Diffusion of light to the interior.
In the so-called Valley-Board Method, the dormer ceiling is flat presumably (though not necessarily) in-plane or close to it with a predominant, proximate, interior, flat ceiling. Its major design elements are 2 –
1. Opportunity to run a dormer starting fairly high on a roofline, offering a continuity of ceiling height throughout the dormered space and that to which it is proximate.
2. Focused light, more or less at standard, interior window height.
Reprieve
Not much to reprieve with this one. The Valley-Board Method in common application probably predates the Valley-Rafter Method simply for the relative complexity and sophistication of the latter’s structure. From the outside where community appearances count, this distinction is moot.
Conclusion
The differences in dormer structure addressed herein can be seen as reasonable options to serve different purposes in our design, either one possibly suitable to our interior look, and, the potential for dormer height on roof aside, should be virtually indistinguishable from the exterior.
Moreover, the two dormer structures can be mixed and matched interior-wise, depending on the height at which we decide to begin penetrating our roofline and, somewhat independently, the height at which we decide to exit the dormered ceiling at its ceiling apex as it abuts the ceiling height of the interior room with which it is associated.
Interior variations can offer interesting opportunities for the use of both natural and artificial lighting, principally in dramatic applications in the dormer space itself. These opportunities in respect to natural light are enhanced by the East and West exposures of the side-facing dormers.
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EPILOGUE
I respectfully defer for now on matters of trimming the dormers on the outside. This is a subject entirely unto itself for some later date of exposition.
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