Roof vent structure for plastic membrane roofs

A vent structure for use with plastic membrane roofs has an elongate vertical tube with a base flange to which membrane material may be heat welded. An overhanging tube cap has generally radially extending, vertical, venturi passage-creating fins which converge inwardly and enhance the pull of moisture entrained air from the tube when wind currents blow between the cap and upper end of the tube.

BACKGROUND OF THE INVENTION 
The present invention relates generally to roof ventilating devices, and 
methods of constructing and utilizing them in typical flat, or near flat 
roofs, of the type used mainly for commercial and industrial buildings. 
Such roofs consist of a structural roof deck, normally covered by a vapor 
barrier on top of which is insulation and an impermeable synthetic plastic 
roofing membrane of the type disclosed, for instance, in the present 
assignee's U.S. Pat. No. 4,652,321, wherein the membrane consists of a 
woven polyester core fabric encased in a thermoplastic, synthetic plastic 
sheath, which typically may be polyvinyl chloride. With insulation 
sandwiched between the vapor barrier membrane and the outer roof surface 
membrane, a water and vapor trap may be created which tends to wet the 
insulation, which then no longer can provide adequate heat flow 
resistance, and tends to physically degradate. Water present in the 
materials from which the roof is constructed, or water entering through 
the top via leaks, or from below as vapor, are typically the sources of 
the moisture which tends to collect. 
In the past, a variety of breather vents have been proposed to alleviate 
this problem, as exemplified in the following listed patents: 
______________________________________ 
Re.31,549 
Ballard et al 
4,484,424 Logsdon 
3,238,862 
Smith et al 4,512,243 Ballard et al 
4,184,414 
Jarnot 4,593,504 Bonnici et al 
4,189,989 
Maze 4,622,887 Peterson 
4,214,513 
Ballard et al 
4,706,418 Stewart 
4,386,488 
Gibbs 
______________________________________ 
With effective stack venting, such wet roofs can be dried over a period of 
time, and the present vent structure has been conceived to enhance the 
elimination of moisture from such roof systems. 
As noted in an article entitled VENTING OF FLAT ROOFS, by M. C. Baker and 
C. P. Hedlin, in the "Canadian Building Digest", U.D.C. 69.024.3: 697.92, 
on page 176-2, "Two transport mechanisms can be in effect in moving 
moisture through breather vents: the convective moving of air carrying 
vapor; and vapor diffusion. In addition, wicking along the insulation 
fibers may help to move moisture laterally through some types of 
insulation." The article points out that wind can cause a pressure 
difference which creates convective air movement, as can stack effect, 
which can be created if some vents are higher than others. On most flat 
roofs, however, all vent openings will be at approximately the same level, 
and there will generally be only small pressure differences from wind. 
Diffusion, the second transport mechanism involves the movement of water 
vapor through the insulation to the outside under a vapor pressure 
difference. The article notes that stack venting is logical for new roofs, 
as well as wet roofs, and may well take care of small quantities of 
construction moisture that would otherwise be trapped in the system, as 
well as small quantities that might get past the vapor barrier. In 
addition, such vents tend to relieve vapor pressure generated under a 
heated roof surface. 
SUMMARY OF THE INVENTION 
The present invention seeks to speed up the drying process. 
It is a principal object of the invention to provide a roof vent structure 
which more effectively dries both new and existing roofs than prior art 
structures. 
Another object of the invention is to provide a moldable, two-piece plastic 
vent structure which can be readily assembled on the roof in a manner 
which permits shipment of the parts separately, and removal and 
replacement of the hood or cap portion of the vent structure for 
inspection purposes. 
Still another object of the invention is to provide a vent apparatus of 
sturdy and reliable character, which can be relatively economically and 
rapidly fabricated of a thermoplastic plastic, rather than metal. 
Other objects and advantages of the invention will be pointed out 
specifically or will become apparent from the following description when 
it is considered in conjunction with the appended claims and the 
accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now more particularly to the accompanying drawings, and in the 
first instance to FIG. 1, the roof, generally designated R, which is 
disclosed, may typically consist of an interior metal building deck 10, 
supported on roof purlins 10a, which form the upper roof-supporting 
surface of a typical commercial building's frame structure. Typically, a 
near impermeable vapor barrier sheet 11, covers the surface 10 which, of 
course, also could be wood decking, and rigid fibrous or foam insulation 
boards or blocks 12 are provided between the barrier sheet 11 and the 
outer roof covering membrane, generally designated M. Membrane M has an 
opening 13 cut in it, to receive the novel vent structure, generally 
designated V, and it is to be understood a number of such breather vents V 
will be used in appropriately spaced apart relation on a typical roof R. 
As FIG. 2 particularly indicates, the insulation board 12 also has a 
circular opening 14 cut in it, which typically is filled with a loose 
fibrous insulation material 15 to facilitate air flow movement in the 
direction indicated by the arrow x to the vent structure V and to provide 
a weep sink. 
The vent structure V, is fabricated in two component parts and, as shown, 
these parts include an upwardly extending open-ended tube 16 formed at its 
lower end with a radially outwardly extending flange 16a having three 
downwardly directed dimples 17 providing a stable tripod support of the 
vent structure V on the insulation blocks 12 under membrane M. A skirt 18 
of the same roof membrane material is heat-welded to the flange 16a, and 
it is the skirt 18 which is lap welded then to the membrane M radially 
outwardly of the flange 16a. Typically, the membrane skirt 18 is heat 
welded to the flange 16a at the factory. The membrane skirt 18 is heat 
welded to the membrane M at the time the vent structure V is installed in 
the roof. 
As FIG. 2 indicates, the tube structure 16 has a convergently upwardly 
tapered peripheral wall portion 19, with an inturned flange 20, 
terminating to leave a sizeable top opening 21 in the upper end of tube 
16. The lower end of tube 16 is open to the space 22, provided above the 
insulation blocks 12, by positioning dimples 17. 
A cap or hood, generally designated 23, is provided for the upper end of 
the tube or stack 16 to prevent the entry of rain, snow and the like, and 
comprises a top wall 24 spaced above the inturned flange 20, which has a 
downwardly divergent peripheral wall 25 extending generally parallel to 
wall portion 19 to a distance overhanging about half of wall 19. 
Integrally provided in the hood or cap 23 are uniformly spaced, vertically 
extending radial fins 26 which, when the cap 23 is in installed position, 
extend somewhat inwardly of flange 20. The fins 26, as FIG. 2 indicates, 
are integrated with the walls 24 and 25 to rigidify them, and have two 
additional functions. They function to vertically space the hood 23 from 
the flange 20, and are, as will later be described, also mechanisms for 
enhancing the moisture-removing function of the vent. 
As FIGS. 3 and 7 indicate, a series of bayonet-type slots 27 are provided 
at uniformly spaced circumferential intervals in the flange 20, and have 
reduced width portions 27a and expanded width portions 27b. Dependent from 
each of the fins 26, is an integrally formed lock leg 28, including a 
shank portion 28a and an enlarged hook portion 28b, which is adapted to 
initially pass downwardly through the expanded portion 27b of an opening 
27. As indicated by the chain line position 26' of one of the fins 26 in 
FIG. 3, upon rotation of the duct or cap 23 in a clockwise direction, as 
indicated by the arrow y, the shank portion 28a is received within the 
reduced size portion 27a of slot 27, and the enlarged end 28b engages 
under the flange 20 in the manner indicated in FIG. 6 in chain lines. 
Pilot surface 29 deflects the shank portion 28a radially outwardly at the 
time of entry into the reduced size portion 27a to cause the hook 28 to be 
tightly held in slot portion 27a under tension. Each of the fins 26 is 
provided with a dependent lock leg 28, and the cap is rigidly locked in 
position by the legs 28 when the duct or cap 23 is rotated in a clockwise 
direction to the position indicated in FIG. 3, and can only, with the 
imposition of considerable manually exerted torque, be rotated reversely 
to unlock the cap. 
THE OPERATION 
In operation, at a proper location for installation of a vent structure V, 
an opening 13 is cut in membrane M. An opening 14 of smaller dimension is 
then cut in insulation board 12, and filled with a loose fibrous 
insulation material which provides a wicking effect. The opening 14 may 
aptly be termed a weep sink or weep hole which promotes diffusion of water 
vapor through the insulation. With the skirt 18 in lifted position, the 
vent structure V is vertically tilted and moved in a direction to slide 
the forward dimple or dimples 17 under the membrane M and then slid 
reversely to a position in which all the dimples 17 are supported on the 
insulation board surface 12 surrounding opening 14, as shown in FIG. 2. 
The skirt 18, which is welded to the flange 16a only at its inner annular 
edge from, typically, location W-1 to location W-2, is then released to 
overlap membrane M and is heat welded to the membrane M at location W-3. 
On a windy day, an air stream traveling up between the walls 19 and 25 is 
converged by the fins 26, such that its velocity is increased, and a 
venturi suction is created tending to pull an air current upwardly out of 
the tubes 16. The air pulled upwardly out of tube 16 is a moist, rather 
than dry, air, if moisture is present in the space 22 and/or the weep sink 
14, and this air is then moved outwardly. 
The wind stream, whose velocity is increased by the fins 26, travels 
rapidly across the top of the stack 16 without any appreciable loss of 
velocity to the radially opposite fins 26, and downwardly between the 
walls 19 and 25, as indicated by the arrows z in FIG. 2. Because the fins 
26 project radially inwardly of flange 20 approximately only a third of 
the distance to the center of stack 16, they are able to provide the 
convergent effect necessary, without cross-blocking air currents entering 
at the same time from between neighboring fins. 
When no wind is blowing, the vent structure V is in a state of equilibrium, 
except in the wintertime when the interior of the building is being heated 
and there is some transfer of heat by the insulation which creates a stack 
effect and aids the drying process. 
In the summertime, because the membrane M typically is white in color, the 
insulation 12 does not operate as a heat sink, and vent structures V 
remain in a state of equilibrium. 
While one embodiment of the invention has been described in detail, it will 
be apparent to those skilled in the art that the disclosed embodiment may 
be modified. Therefore, the foregoing description in all aspects is to be 
considered exemplary rather than limiting in any way, and the true scope 
of the invention is that defined in the following claims.