US3884009A

US3884009A - Method of ventilating a roof system

Info

Publication number: US3884009A
Application number: US409849A
Authority: US
Inventors: Robert T Frohlich; John L Wright; Bruce A Blessington
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co Conn
Priority date: 1973-10-26
Filing date: 1973-10-26
Publication date: 1975-05-20
Anticipated expiration: 1992-05-20
Also published as: CA1007418A

Abstract

Moisture entrapped within roofing systems of the type wherein a layer of normally low-permeance, cellular plastic insulation board (e.g. foamed polystyrene) is employed in conjunction with at least one layer of moisture-bearing construction material (e.g. lightweight insulating vermiculite concrete) is made able to be vented from within the system by providing the board with a plurality of openings therethrough and further preventing the fluid construction material when placed upon the board from entering and filling the openings. Such prevention of filling of the openings may be accomplished by making the dimension of the openings such that the fluid construction material will not flow therein yet moisture will pass, or by covering the openings with a material (e.g. paper) which will prevent such filling, the material however being permeable by any moisture later entrapped within the roofing system.

Description

United States Patent [191 Frohlich et a1.

[ METHOD OF VENTILATING A ROOF SYSTEM [75] Inventors: Robert T. Frohlich, Bedford; John L. Wright, Duxbury; Bruce A. Blessington, Bolton, all of Mass.

[73] Assignee: W. R. Grace & Co., Cambridge,

Mass.

[22] Filed: Oct. 26, 1973 [21] App]. No.: 409,849

[52] US. Cl. 52/741; 52/302; 52/310 [451 May 20, 1975 1,965,839 9/1971 Germany 52/309 Primary Examiner-John E. Murtagh Attorney, Agent, or Firm-William L. Baker; C. E. Parker [5 7] ABSTRACT Moisture entrapped within roofing systems of the type wherein a layer of normally low-permeance, cellular plastic insulation board (e.g. foamed polystyrene) is employed in conjunction with at least one layer of moisture-bearing construction material (e.g. lightweight insulating vermiculite concrete) is made able to be vented from within the system by providing the board with a plurality of openings therethrough and further preventing the fluid construction material when placed upon the board from entering and filling the openings. Such prevention of filling of the openings may be accomplished by making the dimension of the openings such that the fluid construction material will not flow therein yet moisture will pass, or by covering the openings with a material (e.g. paper) which will prevent such filling, the material however being permeable by any moisture later entrapped within the roofing system.

11 Claims, 8 Drawing Figures 3.884..OOS

PATENTED W20 I975 SHEET 10F 3 FIG.

PATENTED HAYZU I975 SHEET 2 0F 3 FIG. 5

FIG. 4

PATENTEB MAY 2 01575 SHEET 30F 3 FIG. 6

FIG. 7

1 METHOD OF VENTILATING A ROOF SYSTEM BACKGROUND OF THE INVENTION This invention relates to improved ventilated insulated roofing systems. More particularly, this invention concerns roofing systems which employ as the insulation medium, or as a part of the insulation medium, a layer of normally low-permeance cellular plastic material such as foamed polystyrene, which systems are improved with respect to the ability to vent or release moisture entrapped within.

Insulation boards comprised of a normally lowpermeance, that is, usually less than about 3 to 5 perms, cellular synthetic resinous material such as foamed or expanded polystyrene, polyurethane, etc., have been widely employed as a thermal insulation medium in roofing systems, especially systems wherein the various components are installed or built-up at the job site. For instance, in US. Pat. No. 3,094,477 there is described a method of preparing a built-up roof wherein a board of foamed polystyrene is adhered to the structural deck and several layers of a bitumen and felt are applied above to provide the waterproofing membrane. One serious problem associated with the use of such low'permeance boards in the roofing is the entrappment of moisture vapor beneath the impermeable waterproofing. Such moisture vapor, especially on hot days, can cause the formation of bubbles and subsequent leaks in the bituminous waterproofing membrane.

The problem of moisture entrappment can be of all the more concern in roofing systems such as that described in U.S. Pat. No. 3,619,961 to Sterrett et al. wherein a layer of the foamed insulation board is employed in conjunction with a layer, more often a number of layers, of a moisturebearing material such as lightweight insulating concrete. The foamed board enhances the thermal insulation of the system without adding appreciably to the weight of the roof. The insulating concretes are generally mixtures of Portland cement and a lightweight aggregate such as expanded vermiculite or perlite, fly ash, etc. Whereas, the water to cement ratio for structural Portland cement concretes lies generally between 0.4 and 0.7, a typical water to cement ratio for such lightweight insulating concretes ranges in excess of 2. This excess mix water employed to render the material sufficiently fluid for placement can easily become entrapped beneath the waterproofing in these systems by the impermeable foam. In the Sterrett et al. patent, the problem of venting such entrapped moisture is solved by grooving a number of the lateral surfaces of the plastic foam insulation board which act to convey the moisture around the board and eventually outside the roofing system. In another previous system wherein the foamed insulation board has been sandwiched between two layers of lightweight insulating concrete, holes have been provided through the layer of foam insulation and the fluid concrete from the upper layer allowed to flow into and fill up the openings. In this system, the bridges of concrete formed in the foam layer serve chiefly to key the upper layer of concrete to the lower layer and as passageways for moisture since the concrete itself is moisture permeable.

SUMMARY OF THE INVENTION While the aforementioned previous systems have met successful commercial acceptance, there remains a need for a more efficient manner of venting moisture entrapped in roofing systems of this type. In the present invention, it has been found that highly efficient venting of moisture entrapped within a roof system wherein at least one layer of moisture bearing construction material such as lightweight insulating concrete is employed in conjunction with a layer of normally impermeable cellular plastic insulation board, is obtained by providing a number of openings extending through the board of a dimension selected such that passage of moisture therethrough is allowed, and thereafter insuring that the openings are not penetrated and filled by the layer of construction material. Thus in the present system, there is provided a direct, unobstructed passage for flow of moisture through the cellular insulation.

Filling of the openings in the cellular board by the moisture bearing construction material is prevented according to one embodiment of the invention by proper dimensioning of the opening at the face of the board upon which the construction material is to be placed. In this embodiment, the opening at such face is dimensioned such that passage of moisture therethrough is permitted yet fluid construction material such as insulating concrete is prevented from substantially filling the opening. The precise geometrical shape selected for the opening is not critical and any desired shape may be employed so long as the construction material is prevented from filling the openings. Preferably, the opening will have at least one cross-wise dimension not exceeding about 0.37 inch. Thus for openings of circular configuration for example, the cross-wise dimension or diameter should not exceed about 0.37 inch in order to prevent filling thereof. In a preferred embodiment of the invention the openings are made to have an elongated, generally rectangular slot-like configuration approximately O.25 inch wide by approximately 2.25 inches long. The total open area calculated as a percentage of the area of the surface of the board, should be at least great enough to allow drying of the wet construction material within a season. Generally, an open area equivalent to at least 0.5 percent of the total surface area of the board should be used. A board having an open area above about 50 percent of the surface of the board is mechanically weak and has a significantly reduced insulation value. It is preferred that the total open area of the board fall within from about 1 to 4, more preferably about 2 to 3 percent of the surface area of the board.

Prevention of the filling up of the openings by the fluid construction material applied over the board is accomplished in another embodiment of the invention by providing a layer of a moisture-permeable material such as paper over the openings before the fluid material is applied. In this embodiment, the maximum size of the openings is not critical as in the above embodiment since the permeable material will prevent the filling of the openings. The material, because of its permeability will however pass moisture therethrough to the openings. Any moisture permeable material having the requisite strength to prevent the concrete from entering the openings may be used for this purpose. In addition to paper, specific examples include woven and non-woven fibrous materials of glass, cloth or synthetic resinous material such as nylon.

BRIEF DESCRIPTION OF THE DRAWINGS In the attached drawings:

FIGS. l-3 are perspective views, partially in section of roofing installations according to various embodiments of the invention;

FIGS. 47 are perspective views showing various alternative insulation board constructions for use in the systems of FIGS. 1-3;

FIG. 8 is a perspective view, partially in section, of a roofing system employing the board of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now specifically to FIG. 1 of the drawings, subdeck 1, which is typically comprised of substantially rigid galvanized steel sheeting often corrugated or formed as shown in FIG. 2, is secured to and supported by structural frame members (not shown) and has apertures 2 therethrough to provide an egress for moisture to the atmosphere below. Subdeck 1 can of course, be composed of a material other than metal, e.g. wood or structural concrete, and also may be planar instead of corrugated or formed. A layer of normally impermeable foamed polystyrene board 3 is placed adjacent the metal deck. The thickness of the board is generally from to 4 inches. The board shown in FIG. 1 has circular openings 4 therethrough having an approximate diameter of about 0.25 inch. Layer 5 of expanded vermiculite-Portland cement lightweight insulating concrete is cast while in a fluid, plastic state over the board 3 in a thickness of from about 2 to 8 inches. Because of the relatively small size of openings 4, the fluid concrete does not fill the openings. After sufficient hardening of the concrete layer 5, a layer 6 of waterproofing material, for example bitumen and felt, is applied. Excess moisture from the concrete layer 5 is permitted direct passage through the board 3 and out through openings 2 because of the void spaces 4 maintained in the board. As an alternate or additional method to the use of openings 2 for conducting the moisture out of the roofing system, an air-space or air spaces between layer 5 and waterproofing 6 can by provided for, and such made to communicate with the atmosphere outside of waterproofing 6. One method of accomplishing this is to place a layer of felt having particles of for example, gravel embedded therein, adjacent the surface of layer 5 beneath the waterproofing. The particles prevent full contact of the felt with the surface of layer 5 and thereby provide air spaces which act as channels for passage of moisture from layer 5. These channels in turn can be vented through the waterproofing to the atmosphere for example, by placing one or more conventional roof vents through the waterproofing and into the layer of channels.

In FIG. 2, an additional layer 7 of lightweight insulating concrete is first applied to the corrugated subdeck 1 and the concrete screeded to the height of the corrugations so that essentially only the valleys of the corrugations are filled. The layer 7 of insulating concrete provides a flat surface for the board 3 and also provides additional thermal insulation to the finished roofing structure. Ideally, a number of the openings 4 will become aligned with the apertures 2 in the subdeck for direct venting of moisture, but this is not necessary since the concrete itself is moisture permeable.

In FIG. 3, the openings 8 are of relatively larger size than openings 4, for example, of at least about 0.5 and preferably from about 1.5 to about 3 inches in a crosswise dimension. Since the plastic concrete layer 5 would normally fill up openings of such dimension, a layer of permeable Kraft paper 9 is provided between the board 3 and the concrete 5 to prevent the concrete fron entering the openings. Since the paper is permeable by moisture it will permit the passage thereof into the voids 8. If desired, the insulation board 3 of FIG. 1 having the smaller diameter holes 4 therein can be provided with a layer of paper (shown in FIG. 4) to insure that the voids 4 are not completely filled during the placement of the concrete layer 5.

In FIG. 5, there is shown an insulation board useful in the roofing system of the invention wherein the board 3 has both openings 4 dimensioned as in FIGS. 1 and 2 and the larger openings 8 dimensioned as in FIG. 3. When employed in the systems shown in FIGS. 1 and 2, a portion of the concrete from layer 5 will fill the larger sized openings 8 but not the openings 4. Bridges of concrete are thus formed in the openings 8 which in the arrangement of FIG. 1 would provide additional support to the upper layer of concrete 5 when workers installing the waterproofing 6 walk on it. A further advantage obtained is that the bridges serve to key the upper layer of concrete to the foam 7 thereby enhancing the resistance of the upper layers to lifting by abnormally high winds. The resistance to lifting would be especially improved by the use of the board of FIG. 5 in the system of FIG. 2 since the upper concrete layer would not only be keyed to the foam but also the lower layer of concrete 7. A further advantage offered by the formation of such bridges of concrete in the foam is that in the event a fire below the roofing reaches an intensity sufficient to burn out the foam layer, the bridges assist in maintaining the integrity of the roofing system.

In the embodiment shown in FIG. 6, the openings in the insulation board have an elongated, generally slotlike configuration about 0.25 by 2.25 inches. The openings are preferably staggered as shown. Because of the relatively narrow width of the slots, the concrete will not fill up the openings when poured. The use of openings having this configuration minimizes the opportunity for blockages of the opening as a result of the opening being aligned directly over an imperforate portion of the metal subdeck. For example, in FIG. 8, the board of FIG. 6 is shown installed in a system having a corrugated metal subdeck, the board being placed such that the openings 10 extend longitudinally at an angle to the lengthwise direction of the corrugations. The use of the slot configuration in this instance has an advantage over for instance circular openings, in that assurance is obtained that the opening will not be entirely blocked off by alignment over an imperforate portion of the apex 11 of the corrugation. The slotted board may also be provided with the large diameter openings 8 as shown in FIG. 7 to permit the formation of bridges of concrete through the board as described above.

The insulation board of the invention is as aforementioned preferably comprised of foamed polystyrene, especially foamed polystyrene board often called bead board prepared by molding expandable particles or beads of polystyrene in a closed cavity. The heat employed in the molding operation expands and fuses the particles into a lightweight, cellular, relatively rigid board. Cellular plastic boards wherein the plastic particles are alternatively or additionally bonded by a method other than fusion, for example by a latex or a hydraulic cement such as Portland cement binder, are within the scope of the present invention.

The openings in the polystyrene board can be cut through the board in any desired manner. For instance. the openings may be cut, bored or melted in an already formed board. Alternatively, they may be formed by placing appropriate sized dead-heads in the board molding equipment.

It is claimed:

1. The method of constructing a ventilated, insulated roof comprising the steps of providing a subdeck of substantially rigid metal sheeting having a non-planar surface and apertures therethrough for permitting passage of moisture, casting a first layer of fluid light weight insulating concrete over the metal subdeck, placing a plurality of normally low-permeance insulation boards comprised of cellular plastic material over said first layer of concrete, said boards having a plurality of openings therethrough of such dimension that passage of moisture is permitted yet substantial filling of the openings by fluid concrete placed thereon is prevented, casting a second layer of said fluid concrete directly upon said boards and thereafter placing a layer of waterproofing material over said second layer of concrete, whereby moisture from said second layer of concrete can be directly vented through the vacant openings maintained in said board, through said first layer of concrete and out said apertures in said corrugated sheeting.

2. The method of claim 1 wherein said openings have at least one cross-wise dimension not greater than about 0.37 inch.

3. The method of claim 1 wherein said openings are circular and have a diameter not greater than about 0.37 inch.

4. The method of claim 1 wherein said openings are in the form of elongated, generally rectangular configuration and have a width not greater than about 0.37

inch and a length of up to about 2.25 inches.

5. The method of claim 1 wherein said openings are in the form of elongated, generally rectangular slots having a width of up to about 0.37 inch.

6. The method of claim 1 wherein said boards have additional openings of sufficient dimension that said second layer of fluid concrete will enter and substantially fill such openings.

7. The method of constructing a ventilated, insulated roof comprising the steps of providing a layer of substantially rigid subdecking material, placing a layer of normally low-permeance insulation board comprised of cellular plastic material over said subdecking, said board having a plurality of openings therethrough of such dimension that passage of moisture therethrough is permitted yet substantial filling of such openings by a fluid moisture-bearing construction material placed thereon is prevented, said board further having additional openings therethrough of a dimension such that said construction material will flow into and substantially fill these openings, casting a layer of said fluid moisture-bearing construction material upon said layer of board whereby the openings through the board able to be filled are substantially filled by the construction material, and thereafter positioning a layer of waterproofing material above the layer of said moisturebearing construction material.

8. The method of claim 7 wherein the total area of the openings in said board comprises from about 0.5 to about 50 percent of the surface area of the board.

9. The method of claim 7 wherein the total area of the openings in said board comprises from about 1 to about 4 percent of the surface area of the board.

10. The method of claim 7 wherein said subdecking material has apertures therein to permit moisture from said openings to pass therethrough.

11. The method of claim 7 wherein said board is comprised of foamed polystyrene.

Claims

1. The method of constructing a ventilated, insulated roof comprising the steps of providing a subdeck of substantially rigid metal sheeting having a non-planar surface and apertures therethrough for permitting passage of moisture, casting a first layer of fluid lightweight insulating concrete over the metal subdeck, placing a plurality of normally low-permeance insulation boards comprised of cellular plastic material over said first layer of concrete, said boards having a plurality of openings therethrough of such dimension that passage of moisture is permitted yet substantial filling of the openings by fluid concrete placed thereon is prevented, casting a second layer of said fluid concrete directly upon said boards and thereafter placing a layer of waterproofing material over said second layer of concrete, whereby moisture from said second layer of concrete can be directly vented through the vacant openings maintained in said board, through said first layer of concrete and out said apertures in said corrugated sheeting.

4. The method of claim 1 wherein said openings are in the form of elongated, generally rectangular configuration and have a width not greater than about 0.37 inch and a length of up to about 2.25 inches.

7. The method of constructing a ventilated, insulated roof comprising the steps of providing a layer of substantially rigid subdecking material, placing a layer of normally low-permeance insulation board comprised of cellular plastic material over said subdecking, said board having a plurality of openings therethrough of such dimension that passage of moisture therethrough is permitted yet substantial filling of such openings by a fluid moisture-bearing construction material placed thereon is prevented, said board further having additional openings therethrough of a dimension such that said construction material will flow into and substantially fill these openings, casting a layer of said fluid moisture-bearing construction material upon said layer of board whereby the openings through the board able to be filled are substantially filled by the construction material, and thereafter positioning a layer of waterproofing material above the layer of said moisture-bearing construction material.