This is one of the most frequently asked questions when visiting homeowners who are interested in replacing siding with HardiePlank siding. It is an important part of the decision and will ultimately determine how successful the installation and longevity of the project will be.
There are two options for this: Remove the siding and install Oriented Strand Board (commonly referred to as OSB), or to use the existing siding that's on the house now as substrate (or layer beneath the top surface) underneath the HardiePlank siding. The main concern to understand is that the HardiePlank siding is going to be on the house for a very long time. In most cases, HardiPlank lasts on a house 50+ years. Above all, it is extremely important that there is a substrate, whether it's new OSB or existing siding in good integrity, installed directly to the studs underneath the HardiePlank siding. So how do you decide?
Using Existing Siding for Replacing Siding
The best place to start is to closely examine the existing siding to get a good understanding of what condition it is actually in. According to the best practices manual from James Hardie, existing siding can be used as a substrate as long as it is in good condition, meaning that it is not warped, bowed, curling, delaminated, or rotting.
This is the main task to tackle to make sure that there are no preexisting issues on the home. It's important to find out more about the home to gain an understanding of any prior water infiltration issues that have happened or any interior water leaks in the past. It's also to important to note any repairs that have been done because of either of these problems. If there have been any previous water infiltration issues, whether interior or exterior, it is always a recommendation that the siding be taken off so the studs and wall cavity can be inspected to make sure there is no damage.
Other issues that are important to address are possible rodent nests or damage from woodpeckers or other birds. If none of these potential problems are present, the existing siding is probably fine to use as the substrate. The benefits of using existing siding as substrate are cost savings on your project as well as shortened project time.
Using New OSB for Replacing Siding
If a home has suffered from any of these issues, it is always better to remove the existing siding and inspect the wall cavity and other areas to make sure there is nothing that is being covered up. Removing existing siding and installing OSB has several benefits, such as having brand new substrate on the home and the ability to inspect the wall cavity and all framing, insulation, and structural integrity of the home before replacing siding. One major stipulation with the James Hardie siding warranty is that it specifically states that if any project is not installed according to the best practices standards, the warranty on that material is null and void.
Work with a contractor that you trust to give you the information and recommendations that are best for you and the needs of your home and not best for his company's agenda or gross profit margins.
If you have any further questions about installing James Hardie siding on your home, please feel free to comment below or contact us directly. You can also take a look at some of our other blog posts on HardiePlank siding.