US3538666A - Fire-retardant wood roof assembly - Google Patents

Description

lNov. 10, 1970 J. E. DALY rAL 3,538,666

FIRE-RETARDANT WOOD ROOF ASSEMBLYl Filed July 1, 1968 WML/AM J. OBELEY :lr-United States Patent O U.S. Cl. 52-409 3 Claims ABSTRACT F THE DISCLOSURE A tire-retardant Wood roof assembly has a top layer of wood shingles or shakes which have been treated to render them fire-retardant, an intermediate, non-flammable metal foil layer, and a subdeck of untreated wood. The inflammable intermediate layer cooperates with the treated wood to protect the untreated subdeck from ignition.

BACKGROUND OF THE INVENTION While one of the oldest forms of roofing material for homes or the like is the wood shingle or shake, wood decay and combustibility resulted in increased use of synthetic materials and a decreased use of wood. Recently, more careful selection of proper types of Wood such as cedar or the like, coupled with new methods and formulas for treating wood to render it lire-retardant, decay-resistant, and the like, have caused a renewed interest in wood shingleand shake-type of constructions. Architects have, therefore, returned to wood roof designs, particularly in mediumto high-price housing Where aesthetics, as Well as functionality, are desired in the home. This use of wood has resulted in some very beautiful housing designs, bringing out all the warmth and natural beauty of wood, which characteristics synthetic materials cannot match.

However, approval of such constructions by tire insurance underwriters has presented problems. Homes constructed with such roofs are relatively costly; they are more often located in wooded areas where re can be a problem; the wood shingles or shakes which have been treated to render them lire-retardant do not, as a result, become tire-proof or incombustible; and, due to their constant exposure to the elements, including rain, lireretardant treated wood may lose some of its resistance to lire. While the subdeck, which is not exposed to the elements, could also be constructed of lire-retardant treated wood, this would add considerably to the cost of coustruction.

Quite surprisingly, it has now been discovered that a wood roof assembly can be constructed which will meet the rigid tests accepted by the re insurance underwriters and building code authorities without constructing the entire roof assembly of lire-retardant treated Wood.

SUMMARY OF THE INVENTION In accordance with the invention, a nre-retardant wood roof assembly comprises an outer layer of wood which has been treated to retard the spread of lire, a non-tiammable metal foil interlayer, and an inner wood layer. The interlayer acts to isolate the treated layer from the inner layer.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cut-away perspective view of a roof-deck assembly constructed in accordance with the invention.

FIG. 2 is a fragmentary cross-sectional view of a shake roof.

FIG. 3 is an exploded cross-sectional View of an alternate construction.

DETAILED DESCRIPTION Referring now to FIG. 1, a wood roof assembly 2 is shown having an outer layer of wood shingles 4, an interlayer of foil 6, and a wood subdeck 10.

The wood outer layer of shingles or shakes is constructed using wood which has been treated to render it fire-retardant. The particular treatment used must also be substantially non-leachable, i.e., leach-resistant since the shingles or shakes will be exposed to the leaching eifects of the weather. Such results can be obtained using treating compounds containing phosphate and cyano-yielding ingredients. Shingles or shakes so-treated are available from the Koppers Compay as Non-Com exterior treated shingles or shakes.

As stated above, the invention can employ either shingles or shakes, the distinction between them being one of thickness and moreover of manufacture. The shingle is severally a tapered rectangular member of varying length and Width usually tapered from about a g thickness to about 3/8" to 1A. Usually, both planar surfaces of the shingle have been sawn. The shake, in contrast, is a thicker shingle having a taper such as, for example, from 1A" to up to l-|, but also usually having one sawn and one split planar surface. The shake is usually installed with the split face up so as to preserve the desirable rustic appearance.

The subdeck can be constructed of conventional wood materials such as either planking or plywood sheets over a stud substructure. In accordance with a preferred embodiment of the invention, the subdeck is constructed to leave little, if any, gaps between adjoining planks or plywood sheets. The tight surface prevents the passage of air from beneath the subdeck to the upper or outer surface of the subdeck. This has been found to be beneficial in preventing combustion of the subdeck by transmission of heat from the outer layer when the outer layer is exposed to flame. It is believed that the absence of gaps in the subdeck inhibits combustion of its outer surface by starvation of air.

In accordance with the invention, a non-flammable interlayer is installed between the subdeck and the outer treated wood layer. In a preferred embodiment, the interlayer comprises steel foil which is about 2 mils in thickness and which has been coated on both sides with a film to protect the foil against corrosion. Foils of other materials can also be used.

The outer treated layer of wood, when exposed to flame, in accordance with the invention, cannot transmit the flame through the non-ammable metal interlayer to the inner layer of non-treated wood. However, some degree of heat can still be transmitted through the metal foil. The close iitting joints of the subdeck prevent air from reaching the interface between the subdeck and the interlayer. Since little, if any, air is present, ignition of the subdeck by the transmitted heat is inhibited because no oxygen is present for combustion even should the temperature become high.

As stated previously, either shakes or shingles can be used to construct the tire-retardant wood roof assembly of the invention. When using shakes, it is preferred to include a Waterproof, non-ammable interlayment between layers of shakes and over the interlayer of nonilammable material. Preferably, this waterproof interlayment comprises an asbestos felt material such as, for example, Nicolet Asbestos Felt No. 411, an asbestos felt material about 1&2-1/16 thick interlaced with liber glass marketed by Nicolet Industries. This additional layer is beneficial when constructing a shake roof assembly for several reasons. The thicker shake is usually not as well treated with tire-retardant materials as is the shingle (due to the increased thickness). Also, the geometry of the surface of the shake deck increases the heat intensity of burning materials which may ignite the roof by falling thereon. This greater heat intensity could, if the additional asbestos layer be absent, transmit suicient heat to the subdeck to char through the subdeck and, therefore, eventually ignite the subdeck in spite of the preferred relatively air-tight construction of the subdeck. Finally, the geometry of the shake makes it somewhat more susceptible to penetration by rain; and, therefore, the waterproof layer tends to protect the interlayer and the subdeck from such effects.

It should be noted here that the waterproof interlayment between the layers of shakes does not replace the non-flammable interlayer located between the shakes and the subdeck but merely supplements it. In actual burning tests, after the overlying shake has burned up and the waterproof interlayment is exposed to wind, the interlayment can become brittle and be blown away. This would expose the subdeck if the non-flammable interlayer was not used.

Referring now to FIG. 2, the waterproof interlayment 20 is, for example, usually laid to overlap the row of shakes 30 beneath it by about 4 and extends beneath the row of shakes 32 laid over it by about 14" while about 10 of shake is exposed in each shake row. Thus, the width of each layer of waterproof interlayment is great enough to insure overlap and thus insure no moisture penetration.

The wood shingles, however, need not be installed with a waterproof interlayment. Their geometry (sawn on both planar surfaces) and their close spacing (about exposure) provide a roof which is waterproof without supplementary materials.

To further illustrate the invention, 4 x 4 inclined test roofs Were constructed using 1/2" plywood as subdeck. Steel foil having a thickness of 2 mils and having a film of polyethylene of about 1 mil thickness on both sides was laid parallel to the line of overlap of shingle in 24 wide strips with 2" of overlap at the seam. Treated shingles and treated shakes were then respectively applied to the roofs having the steel foil. The shingles were nailed to the roof allowing a 5 exposure. On the test roofs using shakes, the shakes were installed with exposure. An interlayment of Nicolet Asbestos Felt No. 411 was applied to one test shake roof installed over a steel foil covered test deck and another shake test roof was constructed using only the steel foil. The asbestos felt was applied in 18" wide widths. The first layer of felt was applied flush with the bottom of the deck, a row of shakes installed thereover and then the second layer of felt, installed to overlap the shake row by 4". This procedure was repeated for each row of shakes. Control roofs were constructed in the same manner using respectively only shakes or shingles over the subdeck.

To test the roofs under tire conditions, test re brands to be ignited and placed on the roofs were then constructed using clear grained Douglas r tree free from knots and pitch pockets as follows: Class A brands consisted of a grid 12" square and approximately 3" thick made from 36% x 12" strips placed 1A apart in criss-cross form at right angles and nailed at their intersections using a 3d finishing nail. The dry weight of the brands was 2000i 150 grams at the time of test. The Class B brand consisted of a similar but smaller grid 6" square and 3 thick constructed from 18% x BA1" x 6" strips. The dry weight of the finished Class B brand was 500i50 grams at the time of test. These test brand sizes and constructions were in accordance with underwriter laboratory suggested procedures to obtain respectively Class A or Class B fire rating.

The test roofs were then exposed to tire using the following underwriters laboratory suggested procedures: (1) An artificial air ow simulating a 12 m.p.h. (1056 fpm.) wind was set up using a fan set at proper speed and spacing. The actual velocity was measured with a volumeter at 1050 fpm. (2) The roof deck was placed in an inclined position such that the rise overrun was 5/12 (20 for 4' section). (3) Class A and Class B brands were respectively ignited by holding the brand over a gas burner until they burned freely in still air. The approximate ignition time was 5 minutes for Class A brand and 3 minutes for Class B brands. Each brand was rotated above the flame so that each of the six sides was ignited.

The flaming brands were then applied to the roof decks and allowed to burn freely in the 12 m.p.h. wind. The test in each case lasted until there was no longer any evidence of glowing on the test roof, or until failure occurred. The results were tabulated as follows:

The pass or fail rating of the test is based upon examination of the subdeck during the test. The appearance of sustained flame on the underside of the subdeck is rated as failure. In each test roof, the treated shingles or shakes were selected as nominally treated shakes or shingles representative of the results of commercial treatment. The test results indicate that the wood roof deck assemblies made in accordance with the invention with a non-llammable interlayer are capable of passing Class B standards, while the addition of an asbestos felt interlayment between layers of shakes enables the shake roof to meet Class A standards.

FIG. 3 illustrates an alternate embodiment of the invention wherein the non-flammable interlayer 6' is preconstructed into the subdeck 10. Wood plies A, B, and C, for example, laid cross grain to one another and bonded together as is conventional in the construction of plywood. In accordance with this embodiment of the invention, non-flammable interlayer 6 which can be steel foil or any non-flammable material, but preferably metal, is bonded to the surface of ply C. Ply D is then bonded to non-flammable layer 6'. Ply D, in accordance with the invention, has been treated to render it lire-retardant. The wood roof assembly constructed in accordance with this embodiment of the invention comprises subdeck 10 installed with treated ply D facing upward. The treated shingles or shakes are then installed directly upon the subdeck, the non-flammable barrier being integral with the subdeck. When shakes are used in this embodiment, the use of a waterproof, non-flammable interlayment between the shake rows of asbestos felt or the like is preferred. The installation of the non-flammable layer such as steel foil or the like, integral within the plies of the subdeck, simplifies installation of the roof and prevents accidental damage to the foil layer. By only treating outer ply D with tire-retardant salts, less salts need be used resulting in considerable economic savings over treating the entire subdeck.

Thus, the invention provides a tire-retardant wood roof assembly wherein only the wood outer layers above a non-flammable interlayer need be treated to retard lire. Thus, a safe wood roof capable of withstanding fire is provided enabling the construction industry to install eyeappealing wood shingle and shake structures without risking denial of re protection.

What is claimed is:

1. A tire-retardant wood roof assembly comprising:

(a) an outer layer of wood that has been treated with chemicals to retard the spread of lire on said outer layer;

(b) an inner layer of wood comprising a plurality of wooden members that are tightly abutted to form a continuous surface;

(c) a continuous interlayer of steel foil between said References Cited inner and outer layers of wood; and b UNITED STATES PATENTS d said ti htly abutted wooden mem ers of said inner 8,957 8/1958 Babcock 52-478 assembly to the lnterface between said inner layer 5 3 383 274 5/1968 C 161 403 X and said interlayer of steel foil; said interlayer 0f 1627027 5/1927 Fn 5 2 478 Stel COIllpletely isolating any flame from Said Fletcher mi inner layer of wood, should any iiame penetrate 1599417 9/1926 Jorsch 52 588 through said outer layer and said interlayer of steel 1967611 7/1934 Finck nn- 52 404 foil preventing the passage of air from above said 10 839;739 6/195g Adams 52 407 assembly to said inner layer of wood 3,202,567 8/1965 Muri 161 403 whereby ignition of said inner layer of wood is prevented.

2. The tire-retardant wood roof assembly of claim 1 FOREIGN PATENTS wherein said steel foil interlayer is of about two mils in 924,987 1963 Great Britainthickness. 15 507,299 1954 Canada.

3. The tire-retardant wood roof assembly of claim 1 JOHN F MURTAGH Primary Examiner wherein said outer layer of wood comprises a plurality of wooden shingles or shakes that are disposed edge to edge U.S. C1. X.R. in rows which overlap one another. 161-220, 403

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