FAQs

There are two general choices when it comes to installing that is used beneath metal roofing. The choice is between installing the metal roofing panels over battens or over solid decking. Some of the original installations of metal roofing were over battens. Battens “strapping” they are small boards that run horizontally across the trusses of a structure; they typically are spaced a specified distance apart one from the next and then the metal panels are installed over them with an open space to the attic to allow proper ventilation. Over the years, a problem has developed with metal roofing installed over battens. That problem is the accumulation of condensation on the back side of the roofing panels. Condensation wasn’t an issue with the early metal roofs, nor is it usually an issue with larger buildings as the metal roofing wasn’t installed over existing roofing.

There are a couple of reasons for that and they both stem back to what causes condensation. Condensation occurs when warm, moist air collects in a space and then has contact with a cool surface. Obviously when temperatures drop at nighttime the back side temperature of metal roofing drops as well. If warm, moist air contacts this, the “dewpoint” will be reached and condensation will develop. If installed on batten there needs to be ventilation and airflow between the existing roofing and battens . If that moisture is not adequately vented outward and it is instead offered the opportunity to come in contact with the cool underside of a metal roof therefor condensation and other problems will occur. Condensation concerns over the years manufacturers of metal roofing and certified installers shy away from recommending installation over battens and instead recommend solid decking with approved underlay. Many non-certified installers may recommend this option not for proper install but profitable gains or just from not enough understanding of installing steel roofing.

The reason condensation is not an issue when metal roofing is installed over solid decking is because of these factors. Quality underlayment should always be installed between the metal roofing and the solid decking or between the metal roofing and any existing shingles that the installation may be occurring over. This underlayment protects the decking or old shingles from any condensation which may occur on the back of the metal roofing. Polymer-based synthetic underlayment should be used on the back side of the metal roofing so it will protected from condensation which may develop between it and the underlayment. This airspace helps prevent trapping of moisture and encourages moisture to escape from the seams between the metal panels. Metal roofing should always be installed over solid decking to avoid dangerous and damaging condensation issues.