FACT
Many homes that had original wood shingles need to be re-roofed each year.
ANALYSIS
The owners of homes with wood shingles often desire to maintain the distinctive natural beauty of their homes. Additionally, wood shingles are often installed over spaced sheathing (lathe boards) rather than over solid decking. This spaced sheathing needs to be considered when choosing and installing the new roof. Additionally, it must be kept in mind that wood shingles over spaced sheathing are a very breathable roof and that eliminating that breathability may bring ventilation concerns.
SOLUTION
Particularly with higher profile metal roofs, such as shake and tile facsimile products, installation over wood shingles is not uncommon. Most manufacturers will suggest a maximum thickness of 3/4” to determine whether the old shingle should be removed. (Keep in mind that, with many roof systems, both metal and non-metal, if the wood shingles are installed over spaced sheathing, their removal will often require the installation of solid decking.) If the wood shingles are installed over spaced sheathing, only roof systems that can be safely secured through the wood shingles and into the lathe boards beneath them should be installed over them. This is achieved either through the use of Fastener Clips that can be situated over lathe boards or through the installation of vertical purlins followed by horizontal purlins (these installations can also allow installation over thicker wood shingles and shakes). Ventilation issues do become a concern whenever the natural breathability of wood shingle installations over spaced sheathing is taken away (see Technical Bulletin #15). In these instances, more attic ventilation will need to be added.
