Batten vs. Batten-Less
Stone-coated steel was developed in New Zealand over 50-years ago and even today this market as well as others in the Pacific Rim use very little solid sheathing (Plywood or OSB sheathing) across the roof deck. This, unique construction practice enabled stone-coated steel panels to gain strong market share as they were easily mounted on “Battens” (usually 2'X2' wood strips) that spanned the rafters and provided front and back fastening points for each stone-coated steel panel. As these types of products were introduced to North America the 'batten' application was modified to accommodate applications over existing roofs such as Asphalt or wood shingles and even wood shakes. In these installations a batten grid consisting of '1X4 Counter-battens' (running vertically as a support batten) and '2X2 battens horizontally across for the stone-coated steel panels to be fastened to. Metro developed “Direct-to-Roof-Deck” installation methods using its existing designs and after extensive testing concluded the 'batten-less' application over solid sheathed roof decks provided exceptional wind uplift performance, just what the market needed to ensure protection against Florida and other gulf state's hurricane prone areas.
Whether a roof is installed on battens or batten-less really depends on the climate & roof design. To explain why climate has a bearing on the application method; let's assume the home is in south Florida (West Palm Beach), this market is considered by the building code as a severe wind region Known as HVHZ (High Velocity Hurricane Zone) and in some areas roofs need to withstand winds of up to 150-mph. In this case Metro has proven in numerous scientific tests at independent Laboratories (Underwriters Laboratories, UL) that the highest performing wind uplift system is a Batten-Less install method which uses two fasteners in an 'X' pattern.
On the other hand if your home is located, say in Texas around the Dallas area not only is hail a concern (All Metro products are Class-4 Impact rated) but also usually the roofs are very steep and here is where a batten system can provide a benefit to the Installation process as the batten grid forms a ladder across the roof area to make the install process a little easier.
The best way to install all stone coated steel panels is BATTEN-LESS. The main reason why is wind resistance. This installation is more walkable and hail resistance. It does not waste a bunch of needless wood framing in an attempt to achieve a slightly more energy efficient roof system. Battened installations are only slightly better than batten-less installation when it comes to energy efficiency as documented in independent testing done at Tennessee’s Oakridge laboratory in 2006 and 2007. The marginal increase in energy efficiency does not offset the loss of wind and hail resistance, walk-ability and the ecological downside of using lumber which comes from trees that must be cut down to make this lumber. It must also be mentioned that the quality of 2x2 and 1x4 lumber that is typically used is an extremely cheap grade of lumber and coupled with the weaker nails that usually driven through the panels into this weak grade of lumber makes for an even weaker installation to boot.
There are times when it is necessary to utilize batten framing in the installation of a stone coated steel roof such as going over wood shake or wood shingle, asbestos fiber cement shingles and when the home does not have an attic or vaulted ceiling.
It is also a good idea sometimes to utilize a batten frame work underneath a Standing seam roof. There are pros and cons to all installation chooses. A homeowner simply needs to get themselves well educated and pick the best installation to meet their project needs.
Either method can be used to meet all building code requirements across North America and both methods (Batten or Batten-Less) can meet the new California Title-24 Energy code exception, due to providing a minimum 3/4" air-space above the roof deck sheathing which ensures the roof meets the new California Title-24 Energy Code requirements providing a truly green roof for the 21st century.