Lap siding and the ‘blind nail’ - Installing Lap Siding Tips

Siding never gets the attention it truly deserves. At face, it is a pretty easy task. But if you don’t follow the correct install methods, it can easily damage itself.

 For this current project, the old wooden composite lap siding has begun to rot. It is easy to say that wood will eventually rot. But once the boards are removed and the backside is examined, you can see water is only accessing the bottom portion where the nails were placed on every course. 

 When installing lap siding, the fasteners are ‘blind nailed’ by fastening at the top of the board. The next course is then lapped over the fasteners, so that water does not have a way to come in contact with the hole that was created. It is only on the last course, that the fastener are applied on the face. This last course is generally protected by the soffit, where the smallest amount of water ever arrives. If at any point that a board needs to be face nailed (which is common on individual board replacement), then a high quality caulking needs to be applied and maintained over the life of the home.

 This really only covers the fastening portion of lap siding. There is still more that needs to be taken into account when installing. This involves cutting, stud layout, tolerances, spacing, and painting. There is always more in depth approaches to the exterior protection of a house, but at minimum always make sure to hire a contractor that is going to follow manufacture specs for installing.

The old lap siding was face nailed at the bottom on every course. The holes created by the fasteners, can allow water to find its way in and behind where it can keep the siding damp enough for mold growth. To prevent this, nails should be set flush to the face of the board as much as possible. Additionally, a high quality caulking should be used to seal these areas and be kept up with a normal paint schedule.

Here is a rear view of the old lap siding. You can see the rot and water marks from where the nails had been set. Along with unprimed cut ends, the only thing that could have helped was a more intensive painting approach to prevent water intrusion.

Here shows the proper way of attachment. The fasteners are set at the top of the board with the following course hiding the nails below. This is called ‘blind nailing’. The trick is to set a 1” starter stripe behind the first row, so that every course above follows a tight seal.