BEFORE THE ARCHITECT – DREAM HOME DESIGNING BACKGROUND – UNIQUE HOME DESIGNING ARTICLES

By Before The Architect  Copyright 2005-2009

ATTIC VENTILATION SCHEDULES

Attic Ventilation Layout, Plan View

1)      Now, the tough shall get going

2)     Before The Architect address attic ventilation in at least three aspects

a)     Coded layout in plan view of each attic section to be ventilated

b)     Net Free Vent Area calculations for each designated area of attic to be ventilated

c)      Net Free Vent Area notes 

i)       Largely taken from Home Design Standards - Home Building Standards and

ii)    Adapted as needs be to a particular application

3)     Layout - the bones of the attic ventilation layout is a simplified, specialized roof plans in plan view

a)     Simplified by leaving out references made elsewhere in the plans set to ridges, valleys, eaves, slopes, and the like

b)     Specialized in that each attic area to be ventilated is codified for separate identification, calculation, and analysis.  This specialization includes, among others 

i)       A gable roof of a single ridge, i.e., intersecting gables get individual identifications

ii)    A “flat roof”

iii)  A hip roof

iv)   A dormer

(1)   Whether wall dormer or roof dormer

(2)  Is usually included into the larger roof section with which it is associated (but you’ll note that that total attic areas prescription for venting is prorated back to the dormers, too)

v)     A shed roof of whatever style

Comment: Roof design is where most clients hit the design wall first.  Lines of sight, efficient space allocation, improved functionality, better daylight and nightlight, safe and convenient traffic patterns, etc. come to a halt later on. 

Roof design bewilders most folks.

AG draws roofs in 3D right on top of the immediately subordinate floor plan, line by line, angle by angle.  This process assures that plates are where plates ought to be, that eave articulations, overhangs, valleys, ridges, and intersections involving over and under planes are properly represented.

Further, when it’s time to draw the elevations, this dream home designer literally tips up his 3D roof plans to the correct orthogonal and mask overrun rooflines.

This dead-reckoning technique in roof design is tedious, frustrating, and demonstrably accurate.

Usually, this dream home designer will include floor plans (walls only) overlaid by the Roof Plans lines, such that the rooflines are bold and continuous and each of the floor levels below it is in various grays and lineweights and styles.  This methodology has two benefits:

1. Obliges the designer to verify that perimeter walls are really lined up

2. Permits those working roof structure, floor structure, and foundation a literal opportunity to work out load paths, materials, and methods

4)     In this layout, we have, among others

a)     “Flat” roof to the far left and the backside and at the entry

b)     Wall dormers across the front

c)      An intersecting gable left and crossing and an

d)     “Underlapping gable on the right

e)     Plus several sheds in hip format

5)     This layout bears various markings that relate to the Attic Ventilation Calculations to follow, including among others

a)     Letter code for roofed-over attic area

b)     J-vents (the little rectangles) over the flat roofs (which vents are spaced in accord with the calculations)

c)      Circle references to exhaust fan siting

d)     Brackets at ridges to indicate extents of ridge vents for passive air movement

6)     In the Attic Ventilation Calculations, please note that

a)     Sections of column 1 relate directly to the layout coding

b)     Math is described at the top of each column, in the heading

Key:  APX=APPROXIMATELY; BEL=BELOW; BET=BETWEEN; BOH=BACK OF HOUSE; DBL=DOUBLE; DIA=DIAMETER; FOH=FRONT OF HOUSE; JST=JOIST; LF=LINEAR FEET; LOH=LEFT OF HOUSE; NFVA=NET FREE VENT AREA; SF=SQUARE FEET; SI=SQUARE INCHES

Comment: One might try to fault the old boy for going to such lofty ends as to layout the mathematical methodology for deriving materials and methods of applications.  Go ahead, make his day. 

There’s no miracle, mystery, or authority in sharing knowledge; there’s an honest effort here to disclose for one and all about how this dream home designer got from here to there involving a pervasively misunderstood and misapplied design and construction aspect of significant measure – attic ventilation. 

Furthermore, conditions of all sorts can change the underlying metrics; whereas, the principles and intents of the design remain stable and right there onsite for reference, review, and metric revision 

The reader – owner, residential general contractor, subcontractor, and supplier – can ignore, agree, or challenge.  That’s not on this dream home designer guy, that’s on the other guy.

c)      Applications are analyzed for both passive and active venting

d)     The comment column is specific and directive about both materials and methods, including the sheds

e)     Reading especially from column 7 and thenceforth to the right and comparing those notes and numbers to the preceding layout, one can discern the causal relationships between calculations and layout

KEY: DIA=DIAMETER; HGT=HEIGHT; HOR=HORIZONTAL; LF=LINEAR FEET; NFVA=NET FREE VENT AREA; OC=ON CENTER; SI=SQUARE INCHES

7)      The Attic Ventilation Notes 

a)     Address both materials and methods specific to this project

b)     Leave very little wiggle-room to misunderstand and misapply

c)      Of particular interest, this dream home designer references

i)       Higher-end soffit and ridge vents in expectation that their tolerances from ventilation specs will be narrower

ii)    Additional materials and methods for mechanical venting to include 

(1)   Heat sensor, thermostat, and humidistat

(2)  Specific switching and other wire prescripts

(3)  Specs for sealing the fan assembly from moisture intrusion

(4)  Caution not to defeat soffit vent intake with applications of gable or hip ridge vents 

Comment:  It has been Before The Architect’s experience from time to time to design solid partitions in attics to physically separate attic spaces in order to assure proper drafting evenly throughout each space.

d)     Of amazing note, consider the references to Cor-A-Vent for 

i)       Venting at flat roof perimeters

ii)    Most especially for venting at shed ridges

(1)   Before The Architect had to fetch about and think long and hard about how to ventilate a shed at its ridge, and they did in effective ways,

(2)  Albethey labor-intensive and crafted

(3)  Then came Cor-A-Vent’s approach, so simple and effective

e)     Before The Architect now includes the manufacturer’s section drawing of a shed ridge exhaust vent to illustrate application, as represented below

Comment:  He takes this moment to emphasize the importance of the Cor-A-Vent approach to venting at a shed ridge.  He has suggested one other methodology for venting at a shed ridge, which methodology, while potentially effective under most conditions and stupendously creative any time, was labor intensive.