What you think is wrong…. may be right.


Troy Martsolf, an install and technical manager for the James Hardie Company has been running into problems with home inspectors making erroneous call-outs on James Hardie fiber cement siding installations, so he reached out to HouseTalk to see if we could clear the air on some common Hardie installation issues. This article and associated podcast cover our conversation with Troy about 5 primary installation callouts he wanted to discuss.

  1. Inlay Trim VS Cap Over or Overlay Trim
  2. Mixed up Climate Zones
  3. Pinbacks
  4. Over-driven fasteners
  5. Butt joint placement

1.       Inlay vs Overlay trim. 

This shows the cap over trim detail that has never really met code but is common practice. This photo is from a 2018 build. I often consider this detail, as Charles Buell says in our podcast, a sacrificial trim piece. Hardie is not concerned with wood trim, just their own products. In my opinion, this detail does not meet code but is a common practice that results in a higher-maintenance exterior. 

At James Hardie, they call this Butt To Trim vs Cap Over and according to Troy, there seems to be a pretty big gap in understanding the building science around both by the general group. In my own experience, builders and installation requirements have been skating a fine line with building code with the cap over trim detail, where horizontal flashings above windows and doors are not getting flashed, just laid over the top of the flashed window – see the photo above and the attached building code below. In my experience, it has been impossible to square these two things.

This shows IRC R703.4 Flashing Code

According to Troy, Hardie has recently developed an install method that they have tested in a weather chamber to roll out across HZ10 areas – see the attached figure #1. The purpose of this change is to address this poor cap over detail but still allow the easy installation of a cap over for three sides. James Hardie has not yet included this in the Best Practice guide and they may never include it in the Best Practice guide as they prefer Butt To (inlay) method above all others. To be clear Hardie supports both this new method and inlay trim, but prefers inlay. Some significant things to point out about each:

a.       No caulking is needed between the back of the trim and the gaps created by lap siding.

b.      ON HARDIE TRIM ONLY, an Inlay header is required over windows and doors. “We don’t get involved with wood trim install practices.”

Figure #1. This shows the weather chamber tested detail from Hardie. This is designed to replace the cap over detail. Please note this is for HARDIE TRIM ONLY. Not required for wood trim. 

c.       Inlay or Butt To trim requires a MINIMUM 1/8” gap from where the lap siding terminates to the edge of the trim for expansion. This is a MINIMUM. It could be as large as the installer sees warranted to stop expansion of house from buckling the siding.

2. Mixed up Climate Zones

“I often see wrong information provided by home inspectors. That is, someone might show an image from HZ5 to try and explain why the install in HZ10 is wrong. BE SURE YOU ARE REFERENCING THE PROPER CLIMATE ZONE.

Figure #2 shows the Hardie Climate Zones

3.       Pinbacks

Pinbacks at butt joints are for aesthetics ONLY. They are not required. Flaring out of lap siding at butt joints is not a quality issue if there is joint flashing present. Full-headed nails ARE ALLOWED for butt joint pinbacks however, this is not our recommendation. If a full headed nail is used for butt joint pinbacks they should not be into stud. That is, they should be placed far enough from the end of the lap pieces to allow the lap to pinned to sheathing only.

This shows face nailing that is well done
Note that this is far enough away it is likely off the stud.

4.       Overdriven Fasteners

As a rule, overdriven fastening is not allowed on our 5/16 products (lap siding/panel/shingle). All other thicker products, such as Hardie Trim or Aspyre allows for some over driving. Further, we don’t require caulking on nails heads, joints, or other holes/divots in our products. In fact, James Hardie’s position on caulking is less is better. We prefer that all fasteners be flush to the face of the product on our 5/16” product. With trim, the fastener is held by the friction between the shaft of the pin nail and the product, thus no head is required to achieve the proper holding power. Therefore, the requirement for flush fastener is less important than with 5/16” product. As long as the pin nail is not over-driven over half the depth of the product it is sufficient to achieve the desired holding power.

This fastener is over-driven and exposed – incorrect location

5.       Butt Joint Placement

James Hardie does not “require” a certain placement of butt joints. Specifically, butt joints over penetrations such as windows or doors. Hardie “recommends” no butt joints within 3”-6” from corners of penetrations. That is because most water intrusion results at corners of penetrations. Hardie would like to see no butt joints over penetrations but would support them as long as they are 3”-6” away from corners of windows. “I have seen some installers cut the Hardie at each side of the windows and make the butt joints at the corners. This is simply a bad practice regardless of the type of siding installed. However, 1 butt joint placed above the middle of a window header is “ok” provided they are 3”-6” away from the corners.


Thanks for reading and note that the information here was provided by james Hardie.