InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or tamko shingle warranty pdf discussed at this website. This article discusses how to prepare an existing asphalt shingle roof for a roof-over or for re-roofing with new asphalt shingles. This article series discusses best practices in the selection and installation of residential roofing.
We also discuss Proper asphalt shingle roof preparation for a roofover job. Roof-over details for multiple layer asphalt shingle roofs. Characteristics of asphalt shingle roofing materials. We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need. If the roof is structurally sound, most building codes allow for two layers of asphalt shingles and some allow for a third on roofs with a 5:12 or steeper pitch.
Roofs that already have two layers of 2 shingles should not be roofed again. Shingle Type Recommendations for Re-Roofing Asphalt Shingles The heavier the shingle on the new layer, the less likely it is that irregularities in the surface below will telegraph through. Laminated or other heavy-textured shingles work well, as they do not need to be carefully fitted to the existing shingles, and the irregular texture will conceal any small bumps or dips from the original roof. More warnings are below at “When is it Dangerous to Roof-Over Existing Roof Coverings?
If removal of shingles is required on some sections of a roof-over job, be sure that you properly build-up or shim meeting points between the removed-shingle area and the rest of the roof, so that the roof surface remains both cosmetically acceptable and so that you do not create a wear point in the new shingles that have to lap over these roof shingle thickness transitions. Clip any curled shingle corners and remove any curled tabs, replacing them with new shingle scraps as shims. Install new drip edge on rakes and eaves. Specialty drip edge profiles designed for retrofitting wrap around the exposed roof edge, leaving a neat protected edge. When is it Forbiden or even Dangerous to Roof-Over Types of Existing Roof Coverings? The question of when is it necessary to tear-off an existing roof-covering vs.
Strip Hard-Roof-Coverings: Model building codes address the easy part of the question: we do not put a new layer of roofing material over rotted, damaged roof decks, nor over wet roofing, nor over hard-material roofing such as slate, fiber cement, clay tiles, or wood shake roofs. Limit Number of Roof Covering Layers: Local building departments in many jurisdictions will permit multiple layers of some but not all roofing materials. Most won’t permit more than three layers of asphalt shingles on a roof. The issues are with nailing security, wind uplift, shorter life of asphalt materials over an uneven surface, effects of moisture trapped between roof layers, and possibly fire and roof covering weight loading safety concerns.
The contractor won’t want to warrant the entire roof against leaks if she is repairing only a limited area of it. Don’t even think about roofing-over a structure whose roof deck is in the condition shown in our photograph at left. But a careful inspection may be required to detect more subtle but dangerous roof deck conditions. 4″ plywood had been used for roof sheathing and we already had a concern about the nail-holding ability of that material to prevent a roof blow-off. We had also seen evidence of prior leaks on the north slope of the roof. But we failed to spot badly damaged roof sheathing in one area of the roof. After our in-attic inspection, our worker who weighed the least, D.
See ROOF SHINGLE TEAR-OFF PROCEDURE FOR HOMASOTE PRODUCTS , reproduced with permission of the Journal of Light Construction. See “WHEN REROOFING, SHOULD YOU TEAR OFF OR RECOVER? Smith, director of NRCA’s technology and research, originally published by the NRC’s Professional Roofing magazine. This article concludes that in some roof jobs a roof re-cover approach can be a viable operation and re-covering existing roof surfaces has been successfully used on many roof jobs, but it involves greater risks than a tear-off.
If laying three-tab shingles over three tab shingles, it is important to nest the new shingles against the old to create a flat surface. Even before installing the starter strip or underlayment you should install drip edge flashing along all roof edges. After that, shingling should proceed normally, fitting each course up against the bottom of an existing course. Nesting each new row below an existing one keeps the new nails 2 inches below the existing, which will help minimize any splitting of the sheathing.
Flashings for Re-Roofing Asphalt Shingles Depending on their condition and accessibility, some flashings can be reused. New shingles may be able to tuck under existing step flashing, chimney flashings, and front-wall flashings. If they are deteriorated, they must be replaced along with vent boots. See FLASHING ROOF WALL DETAILS and FLASHING ROOF-WALL SNAFU for specifications of roof-wall flashing and for some photo-examples of troubles with existing step and counter flashing when re-roofing an existing structure. Unless a metal valley flashing is used, the first step is to line the existing valley with a new underlayment consisting of either 90-pound roll roofing or a more durable modified bitumen membrane.