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The Home Depot

Top Causes of Roof Shrinkage

Pro Referral > Home Guides > Roofing > Top Causes of Roof Shrinkage
Top Causes of Roof Shrinkage

Roofs are primarily made of lumber and are coated with a roof membrane before the tiles or shingles are installed over it. This membrane is called ethylene propylene diene monomer (EPDM) and is a very effective barrier against extreme temperatures and ultraviolet light. It is also quite resistant to puncture or penetration. Quite often, this membrane also shrinks leading to cracks, blisters, ridges, and splits on the shingles. There are many reasons why this occurs.

  1. research indicates that material, design, workmanship, or a combination of all these is responsible for the problems associated with EPDM.

    1.Different Kinds can be Purchased

    Studies by established institutes in the field of construction and roofing have thrown forth some causes for the shrinkage of EPDM as well as remedial measures and ways of prevention. Their research indicates that material, design, workmanship, or a combination of all these is responsible for the problems associated with EPDM. EPDM membranes are available in a variety of thickness as well as reinforced versions.


    EPDM can be installed in one of three ways—laid loose and held down with ballast, mechanically fastened to the roof with bars and buttons, or adhered to the deck. By imbibing some information about the reasons why these problems take place and learning ways of preventing them, you can safeguard the roof to a certain extent and also solve problems as soon as they arise.

  2. 2.Material

    During the manufacturing process of the EPDM membrane sheet, oils are added to enable mixing and processing of the ingredients with the EPDM polymer and carbon black. Only then will the membrane acquire all the desired physical properties. Hence, if the oil is lost at some point later it might lower flexibility and lead to shrinkage. Other factors that could lead to this are cross-linking or other molecular changes. In short, EPDM needs the oil to retain its shape and whenever heat or cold cause the oil to evaporate or harden, shrinkage can occur.


    EPDM shrinkage can be somewhere around one or two percent. If the roof is large this can account for several feet of shrinkage. Shrinkage is more common on larger buildings and when it has not been affixed properly.

  3. 3.Design

    The design of the securement detail of the roofing should be done keeping in mind the shrinkage limit of the EPDM. If the design does not have the strength to resist the shrinkage forces, it can lead to leaks when the flashing detail is pulled apart. There are two ways in which stress can get incorporated into the membrane—insufficient sheet relaxation before attachment and sheet expansion before attachment.

  5. 4.Venting

    There are opinions for and against venting of the EPDM membrane. It is uncommon in residential buildings and seen more on re-roofing projects. Absence of venting can cause the EPDM membrane to blow up due to the moisture that has been unable to escape. The decision to place vents or not is left to the roofing contractor and the manufacturer does not do anything about this.

  6. 5.Inspecting the EPDM

    The EPDM membrane must be regularly inspected for possible problems and action must be taken immediately if you find anything. Stains and signs of leakage are the most common issues that are likely to crop up. Residential roofing will have plywood decking with insulation below the decking. In commercial buildings, the insulation will be situated between the decking and the membrane. Small bubbles or wrinkles in the membrane are not a cause for concern, but if they are present on the flashings they must be checked thoroughly. Experts recommend semi-annual checks of EPDM as a precautionary method. Stable and legitimate care must be taken when manufacturing the membrane and there must be adherence to the necessary standards. Roofers suggest that this should be installed such that the membrane can relax at any temperature without deteriorating. The substrate of the roofing must also be checked thoroughly before the membrane is installed. If there is any damage to it, it must be reinforced beforehand.

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