Tell any American that we wrap houses with paper during a new build without any sheathing behind it and they won’t believe you; that's right we still build new timber frame houses, and rather than making them durable and rigid with a hard sheathing on the outside, we compromise the structure to save a quick buck and just staple paper to the house. This paper is then expected to act as the all-encompassing weather-tightness layer to keep your insulation dry and frames from rotting. Then to add insult to injury we make all the structural bracing elements of the house out of a 10–13mm thin layer of chalk sandwiched between two layers of even less durable paper.
Ok, this paper on the outside of the house isn’t normal paper, it is tough to rip, but sometimes it is just made from plastic with tiny holes perforated into it. There is a great video from Matt Risinger showcasing why you don’t want plastic with holes punched in it as a building wrap, but these building wraps don’t add any airtightness, structural integrity, or soundproofing.
RABs are an essential component of a building’s envelope that can help improve its structural integrity, weather tightness, and energy efficiency. In New Zealand, RABs are not mandatory, but many experts think that they should be because they are a vital component to ensure the longevity of a house, especially in areas exposed to high wind zones or areas with high seismic activity.
Think of a house's framing like a floppy cardboard box, it is very easy to flatten when opposite sides of the box are open. When you brace a house you stiffen it and when you apply a RAB it is like you have closed and taped the sides of the box so it becomes extremely strong. If you try to brace a box from the inside it isn’t going to be as tough, this is why some RABs are designed to handle the 1 in 1,000-year seismic events.
Americans have been sheathing houses for over 80 years and over time they have moved from tongue and groove timber to plywood to OSB and now composite materials like fiber cement, here in NZ the majority of homes are built to a budget rather than built to last. One of the most popular products on the market is James Hardie RAB Board, which is a solid fiber cement pre-cladding but there are plenty of other brands that make RABs and they also come in different types of materials like OSB timber and PLY wood.
RAB boards provide superior weather-tightness by preventing moisture from getting in and allowing moisture vapor to get out and some RABs have a fire-resistance rating. Some RABs replace the need for paper altogether and you just tape the joins to make it 100% watertight.
In terms of construction and project management, builders love using RABs. It often allows construction to move faster, allowing builders to move to the inside of the house before the cladding is installed. Some RABs are so easy to install that the installation method is “score, snap and nail” meaning no special tools and since it ultimately gets covered with cladding the tape can cover any minor imperfections.
With its many attributes and benefits, RAB Board should be considered a mandatory component in new house builds in New Zealand. It’s a minor cost to have a RAB but it is well worth it for the benefits.
