Structural Help

Tile Roof Damage

2012-03-12

One or several roof repairs, recoverings, or replacements usually become necessary over the life of a typical structure. The word 'roof' in this context refers to the waterproofing assembly that is applied to the structural roof sheathing or deck, as opposed to the roof structure. The need for roof work may arise due to one or a combination of several factors. These include damage from hail, wind, or other severe weather effects; long term deterioration from normal exposure; and improper original installation. Any one of these factors may cause or contribute to a roof leak and interior ceiling stains. The 25% replacement rule should be considered prior to any roof being repaired recovered, or replaced. There are obviously many types of roof systems including asphalt shingles, tile, metal, wood shakes, membranes, and built up roof (BUR) to name a few. Membranes and BUR roofs are often found on flat roofs; shake, tile, and asphalt shingle roofs are found at sloped roofs. The focus of this discussion will be on concrete and clay tile roofs. Roof tiles are usually made from concrete or clay, and may be formed into an S, barrel (actually a two piece tile), or flat shape. Existing tile roofs have tiles that are either adhered to a rolled membrane with mortar or polyurethane foam, or mechanically fastened with screws or nails with or without wood battens between the tile and membrane. Very often the ridge tiles are adhered in an otherwise mechanically fastened tile roof.   WIND DAMAGE TO TILE ROOFS Tiles affected by wind are either broken, thrown, or visibly displaced. Wind does not gently pry roof tiles loose and leave them in place and not otherwise visibly damaged. Tiles may also be broken from wind born debris such as roof tiles and other objects.   LONG TERM DETERIORATION AND FLASHING FAILURES Roofing materials deteriorate with time and exposure. The rate of deterioration is largely a function of the type and quality of materials, installation methods, and the exposure conditions. Over time, deterioration increases the likelihood of leaks and may also increase the roof's susceptibility to wind and other damage. Flashings are applied at joints, intersections, and roof penetrations and are intended to prevent water intrusion. They are often concealed and made of sheet metal, membrane, or waterproof material. Roof flashing may fail due to improper installation or material, differential movement, long term exposure, or severe weather.   LOOSE MECHANICALLY FASTENED ROOF TILES: Concern sometimes exists over 'loose' mechanically fastened tile roofs. However, this is how mechanically attached roof tiles are supposed to be installed. When roof tiles are installed with screws or nails (mechanical fasteners) the fastener heads should not be driven flush with the top of the tile because doing so does not allow the tile to expand and contract due to environmental effects. In addition, it may cause the unsupported end of the tile to lift and be more susceptible to catching wind. Additionally, when mechanically fastened roof tiles are lifted by wind the tiles and nails do not fall neatly back into place. The Roofing Handbook by Robert Scharff and the editors of Roofer Magazine states the following:

"Do not drive home fasteners or draw the tile. Drive fasteners to a point where the fastener head just clears the tile so that the tile hangs on the fastener. When tiles are fastened too tightly, they lift up at the butt. This allows high winds to blow them off the roof or to blow water under them."

  LOOSE MORTAR SET ROOF TILES: There is often concern over the condition of mortar set roof tiles being loose in place with the bond failure plane between the tile and the mortar (as opposed to between the mortar - membrane). Mortar set tiles become loose for a number of reasons related to original installation, such as improper mixing and application of the mortar at the time of construction, misplacement of the mortar, or insufficient mortar under the tile. Many roof tile manufacturers require that the tiles be wetted prior to being placed on the roof. If not the tiles may be too dry and may absorb moisture from the mortar. If this happens the top portion of the mortar loses water and the hydration process may be cut short. As a result of incomplete hydration the top portion of the mortar is weakened and susceptible to premature bond failure. Roof tiles may also become loose due to the expansion and contraction forces that occur from exposure over time. This is usually in conjunction with a weak mortar bond that allows environmental stresses to have an effect on the bond. The following excerpts were taken from an industry sponsored report: TECHNICAL PUBLICATION 155 titled “The Loss of Bond Between Roof Tiles And Mortar on Pitched Roofs” by Professor Wilson C Barnes, AIA and Jose Mitrani, P.E., dated November 12, 1994.  This technical publication was a research project sponsored by The Building Construction Industry Advisory Committee under a grant from the State of Florida under the Department of Education.
  1. In recent years it was evident that problems existed with clay and concrete tile bonding to mortar in newer installations. Many tile roofs appearing tight at the time of installation were discovered later to have suffered a loss of bond between the tile and setting mortar. Often, this was occurring shortly after installation.
  2. The problem had been identified prior to Hurricane Andrew and many segments of the construction industry were experiencing woes arising from this phenomenon. These ranged from the simple issuance of code violations to lawsuits for large sums of money.
  3. The Dade County Board of Rules and Appeals began addressing loose roof tile in 1987, and its Roofing Committee has been working with industry since then on the problem. Respected and licensed roofers had noted the loss of bond problem as being prevalent even in tight quality control situations. In the fall of 1991, the Board agreed on certain material and procedural changes that would provide more satisfactory installations in the short term while industry research and product improvement could be carried out.
  4. The report presented to the Roofing Committee of the Dade County Board of Rules and Appeals Board by John Pistorino cites the following items which are discussed as reasons for the lack of bond between clay or concrete tiles and mortar. The word lack is used intentionally to emphasize, that in many cases breakdown occurred before a bond had opportunity to form:
    1. Poor workmanship.
      1. Improper mix of cement, sand, and water for mortar resulting in strength of less than 1800 psi.
      2. Drying out of mortar before application.
      3. Walking on tile prior to set-up of the mortar.
      4. Not keeping tiles cool during curing of the mortar.
      5. Not enough mortar being used.
      6. Improper placement of mortar paddies.
    2. Incompatibility of materials.
      1. Tile is so dense and smooth that mortar will not adhere.
      2. A bond breaker used to release the concrete tile from the steel form during production may affect the adherence of mortar to the tile.
      3. Tile shape and interlocking may cause movement similar to expansion and contraction of concrete decks creating a shear plane at the mortar interface.
Because of this problem the building code was changed in the mid 1990s to require a structural foam-type adhesive or epoxy mortar be used.   CRACKED MORTAR SET ROOF TILES: Excluding tile breakage due to impact, the condition of mortar set roof tiles being cracked is usually the result of foot traffic, restrained thermal movement and other environmental effects. Just as wind does not gently pry tiles loose from their mortar paddies, wind also does not crack tiles and leave the tile or tile pieces in place. Cracked tiles of this nature are typically randomly distributed throughout the roof area.   TESTING APPLICATION STANDARD (TAS) 106 The "Standard Procedure for Field Verification of the Bonding of Mortar or Adhesive Set Tile Systems and Mechanically Attached, Rigid, Discontinuous Roof Systems", or TAS 106, is referenced by the Florida Building Code as an uplift test protocol for tile roofs. The scope of this TAS is "...a product application quality control test to confirm: 1) sufficient bonding by the mortar or adhesive to the tile and underlayment in a mortar or adhesive set tile system; or 2) effective mechanical attachment of components within a rigid discontinuous roof system." Occasionally a TAS 106 test is conducted on an existing roof and a failed test result is cited as evidence of wind damage. However, the TAS 106 is not applicable for evaluating whether or not an existing roof has been damaged by wind for the following reasons: Tile uplift tests and other roofing uplift tests, such as the bell chamber test, are applicable to newly installed roofs. These tests do not provide guidance regarding wind damage and they do not provide any information about the condition of the roof the day prior to the wind event. There are no tests or other procedures, other than visual inspection by a qualified professional, that can provide a determination as to whether or not a roof was damaged by wind. In addition, uplift tests conducted at older roofs may result in roof damage by the testing itself.