Reroofing With Slate
In old Oriental rugs, rare oil painting or ageing houses alike, we are consciously or unconsciously aware of the effect of time. The contrasting colors of the rug are softened, those in the painting slightly dimmed, and the house has been toned so that the materials blend as one. We would instantly resent the insertion of fresh, new colors in the rug or painting. Yet some people thoughtlessly reroof their houses with a roofing material which cannot help but be incongruous and unharmonious with its surroundings. The ageing exterior walls and the profuse foliage of the trees and vines call for the use of materials which quickly become a part of the composition.
Slate possesses qualities which make it at once suitable for reroofing any type of building. It is a product of nature, obtainable in neutral or colorful, permanent or weathering tones, which quickly assumes the characteristics of age, blends with the natural surroundings, or by proper selection will conform to any desired color scheme. Its texture meets the demands of any design. Its cost is only slightly more than the less permanent roofings.
Slate, being a hard, dense stone, is fireproof, storm. proof, permanent, and cannot warp or curl. Reroofing with slate settles the replacement problem for the last time and assures economy in maintenance and lowest insurance rates.
A reasonably smooth under surface is essential to the proper laying of any roof covering. Where the old roof covering presents a fairly even surface or can readily be made so, the slate may be laid directly on top of it. This procedure has been common practice for years, produces satisfactory results, and the old roofing possesses some insulating value.
For high-grade work, it is strongly recommended that the old roof covering be removed. This insures proper examination of roof construction, rafters, etc. It permits of moving shingle laths or roof boards to proper spacing for slate, renewing broken ones and nailing all solid. In sections where heat conservation and the keeping out of air is an advantage, it allows the filling in with new roof boards between the lath so that the under surface may be solidly sheathed, smoothed and covered with at least a 14-pound asphalt felt. Should a responsible slate roofing contractor's inspector recommend the removal of the old covering, the cost of this adds only a small amount to the entire cost of the new slate roof.
For a slate roof of commercial standard thickness slate, roof construction conforming to good engineering practice for roofs of lighter materials will usually be found adequately strong. This applies both for new construction and for reroofing, and will be found discussed in detail on page 34.
The reroofing data which follows was originally published by the National Slate Association under the title of "Hints to Roofers on Reroofing with Commercial Standard Slate." Since much of the information therein must be considered by the architect in recommending a new roof covering in alteration work and by the owner in deciding on the type of roof, it is reprinted here in the hope it will prove of value.
When the Old Covering is Removed
The removal of the old covering has the advantage of exposing the sheathing or roof lath and permitting a thorough inspection. Any broken boards or lath should be replaced with new whole material and all loose boards should be securely nailed in place. Boards originally so laid that the joints were not broken over bearings should be taken out and replaced or short rafters or blocking cut in to act as a bearing. In localities where the saving of heat is essential and roof lath has been used, if the lathing is not to be removed, new boards should be used to fill the space between the old lath. Both should be of the same thickness to provide a reasonably smooth surface.
It is important to go over the roof and remove or drive "home" any projecting nails and cut down any warped or raised edges or ends of sheathing or lath. Before laying the felt, thoroughly sweep off the sheathing to remove all chips, blocks and loose nails.
When the Old Covering Remains
Where the old roof covering is allowed to remain, see that any low spots or loosened areas are filled up and made secure. Where possible to do so, inspect the sheathing or lath from the under side and repair all broken or loosened boards. In ordering nails, make allowances for the thickness of the old roofing and use a nail of sufficient length to secure thorough penetration into the roof boarding.
Note the width of the roof boards or lath spacing and order slate of proper length to secure a nailing which will avoid the joints. The following table will be useful in this connection:
Heavier Rafters Are Not Required
Rafters adequate for wooden shingle roof will be of sufficient strength for slate of commercial standard (3/16") thickness.
It will sometimes be found that the rafters of old buildings—and some not classed as old—while of ample strength to support the present roof covering, were not designed to carry the additional snow or wind load recommended by present-day engineering practice or required by the local building code.
When existing roof appears to sag or gives indication that existing supports are not adequate for the present roof covering, it would be unwise to replace the old covering or cover with any new material without strength. ening the roof supports.
To aid architects and owners in overcoming such conditions, we would be glad to advise methods or send blue prints of drawings which the Structural Service Bureau has prepared showing methods for strengthening roof construction. It rarely occurs that conditions are such that the entire roof construction must be removed and replaced with members of larger size or different arrangement.
How a Northern Roofer Lays Slate Over Shingles
"In regard to the over-shingles work, will say that it works out very satisfactorily. Occasionally I have a job which is badly cut up with hips, dormer windows, etc., which should be stripped, and I do that. But the average roof lays very nicely over shingles with slates 18" or longer, and valleys go in well over shingles. Short slates do not lay well over shingles, as the slate necessarily rests on the shingle butts and it should span at least two courses of the wood shingles.
"I lay the American method entirely, and do overshingles work for about 25% more than the cost of stripping and reroofing with wood shingles. A 6d nail is used, which goes through the old shingles and into the roof boards. I also punch four holes in the slate instead of only two, as sometimes we don't get good nailing and have to use the other pair of holes."
Another roofer, who has made a specialty of overshingle work secures better results where the old surface is more or less uneven, with slates 12" and 14" long. He says, "They lay well and fit the contours much better than the larger sizes and further they are less liable to breakage where carpenters, painters and others must use the roof." The Association partial payment plan makes reroofing with slate conveniently financed.
Making Additions or Alterations to Slate Roofs
Once a slate roof is properly laid it will be permanent and require little or no upkeep or care. However, houses are sometimes enlarged or remodeled. In such cases it is often necessary to join a new and old roof or to remove and alter sections of the existing roof.
It is desirable and necessary that the altered or additional roof match the existing one in both shade and texture. To obtain this result, it is advisable to secure slate of the same quality and color as the original slate. Slates from some quarries weather, that is, the color as first quarried will differ from the permanent shade resulting from a few months' exposure to the weather. Other slates are permanent or unfading and do not mellow on exposure but retain the original natural shades.
To match slates that are unfading, requires unfading slate of the same shade or slate which will weather to the desired shades. If the slate on the roof has already weathered, it can be matched with unfading slate or with weathering slates which will mellow to the desired effect. Securing slate from the original quarry, reduces trouble about matching or colors. However, in many remodeling jobs, the slate has been on the roof for many years and no record of the quarry from which it came will be available.
An experienced slate roofer can usually identify slate as to producing vein but in case of doubt samples may be submitted to the Association for classification.
The best method of procedure is to remove small adjoining sections and relay, mixing some new slate with the old. This will prevent a clear line of demarcation where the new work adjoins the old and the completed roof will at once present a satisfactory appearance.
In minor alterations such as adding or removing a dormer, the old slate which is removed can be used again. In dormers and other projections, the lights and shadows will differ from those on an expanse of roof, making it easier to add new slate which will be unnoticed. For example, new slates could best be used on cheeks of a new dormer using old slates on other parts. Some roofers buy up a number of old roofs from buildings which are being torn down and thus obtain old weathered slate in their yards which can be readily matched with the slate on the roof when minor alterations are made.
However, due to unavoidable causes, slates are sometimes broken on the roof. The broken slate can be repaired by the Slate Roofer. The best method is to first remove the broken slate, cut the nails with a ripper and remove any remaining small pieces of slate. Insert new slate and nail this slate through the vertical joint of the slates in the overlying course approximately 5 inches from the head of the slate, or 2 inches below the tail of the second course of the slate above; over this nail insert a piece of copper approximately 3 inches in width by 8 inches in length. The piece of copper should be inserted under the course above, lengthwise, so that it will extend a couple of inches under the succeeding course, thus insuring a proper lap and protection throughout the exposed joint in which the nail is driven. This small piece of metal should be first bent slightly concave or convex which will insure its remaining tightly in place.
When making alterations to a slate roof, only responsible and experienced slate roofers should do the work. If other workmen are required to use ladders or scaffolds on slate roofs, boards should be used under the legs or uprights to distribute the pressure.