Dips and Swales in Roof Surface


Many existing buildings, for various reasons, have dips and swales in the current roof decking. When re-roofing these buildings, the property owners seek products which can be installed over the uneven surfaces and which, hopefully, will not accentuate the negative aesthetics of the dips and swales.


Dips and swales can occur in roof decks for several reasons. One common reason is deterioration of the roof decking, often brought on by inadequate attic ventilation and sometimes by inferior quality decking or structural materials. In looking at these situations, it is important to determine and, if possible, address the root cause of the dips and swales. Correcting the situation will hopefully stop the problem from getting worse over time.


If necessary, consult with a structural engineer or contractor to determine whether complete decking removal and replacement is necessary. One thing they may wish to do is fastener pull-out tests to check the integrity of the decking. If the decking is deemed suitable to be left in place, there are many things to consider when looking at metal roofing options. Many metal roof profiles are designed for installation over horizontal purlins. Products of this type can help to minimize the appearance of dips and swales as the purlins may span the dips. Other metal roofing products attach directly over the decking or existing shingles (usually with an appropriate underlayment between the two). With these products, thicker metals and/or more heavily formed panel profiles will do a better job of going over the unevenness. Additionally, smaller panels which have more frequent overlaps, rather than very large or long panels, will have more allowance for the uneven decking. One thing to keep in mind, though, is that the strong horizontal lines of many metal shingle, shake, tile, and slate profiles can significantly telegraph the dips and swales, making them even more apparent. One big benefit of metal roofing on these applications is that the low weight of metal roofing can be beneficial in situations where the roof decking may be weak.