September 1995 Edition

Lapped Siding Problems

We have lapped siding on our house and it is beginning to decay at the bottom lip of each board and at the joints.  How can we tell if the siding is defective or if it just was not installed correctly?           
You have just asked one of the questions even the pros are having problems answering. First of all, there are two different types of composition siding that have been used around Atlanta. The first is commonly called hardboard siding which most people identify with the trade name “Masonite”. The second is a relatively new product called OSB siding and is manufactured with the process called “Oriented Strand Board” which uses wood chips. Both products can fail in the same manner.           
Unfortunately, most siding is improperly installed. The manufacturers print very good installation instructions, both in English and Spanish. However, most installers just do not read them. Even when the manufacturers go out to the field to train the crews, they return in a few weeks to find different people. The turn over is quite great.           
Here are a few of the proper installation techniques that we just do not see very often in the field:
The bottom course  should never touch the concrete foundation or it will absorb moisture from the concrete and this will cause the siding to deteriorate. The siding should be a minimum of 1/2” from any masonry or concrete product. Metal flashing is sometimes used to protect the siding  where  it  meets the foundation. Some builders use foam board insulation for the bottom board and paint it to match the siding. The foam board will not be affected by the moisture. However, it is soft and is easily damaged, especially by grass trimmers. Some builders are now using wood trim boards which seems to be a better solution to the problem. Time will tell just how well they stand up to the elements.
The local building code and the manufacturer both require the siding to be a minimum of 6” above the ground. This prevents moisture and rain from damaging the bottom board. We continually see the siding actually buried in the ground or mulch and ground cover piled against it. The end result - siding decay.


The installers are very good at cutting the siding to the exact length needed without allowing for proper expansion. As the boards expand, they warp or bow. With tight butt joints, it is also impossible to fill the joints with caulking to prevent moisture from entering into the ends of  the  boards. 
The net result is delamination at the butt and end joints. The manufacturers are aware of this problem and have manufactured metal trim pieces to cover the butt joints and end joints. However, they are not very popular here because visually they look like vinyl or aluminum siding which just is not well   accepted   in   the Atlanta area.
The next area to cover is the intersections of vertical walls or chimneys and the roofing shingles. As we have mentioned before, if water comes in contact with the siding, it will deteriorate.  Some  installers  are  very  good about cutting the bottoms of the boards to perfectly fit against the roofing shingles.
This will cause the siding to wick up the water and deteriorate. Also, it makes it impossible to seal the bottom lip. When the siding is held off the shingles by 1” to 2”, the bottom lip can be properly sealed. The exposed flashing may be painted also.
Incorrect nailing will cause deterioration around the nails. If the nails are recessed, they must be caulked to prevent the moisture from entering the siding.
Finally, all of the siding must be properly sealed. A minimum thickness of 4 mils of paint is required over all exposed surfaces. This means “two” full unthinned coats of paint are required. Most painters only apply one coat since the siding comes primed from the factory. Rarely do we see the bottom lips properly sealed.
Even if the siding is properly installed, some of the material in the Atlanta area has been found to be defective. Most manufacturers will stand behind their products. If you think your siding is defective, first try to find out who is the manufacturer. Sometimes their name will be printed on the back side, if you have an extra piece,  or contact your builder. For Georgia Pacific Corporation call (770) 441-5000, for Masonite call (404) 237-2738, for Louisiana Pacific Corporation call (800) 648-6893.

 (Drawings courtesy of Masonite, A Division of International Paper)

If you have a question, change of address, comment, home tip or would like to send Home Tips to your clients, send your letter to Home Tips, Christian Building Inspectors, Inc., 3697 Habersham Lane, Duluth, Georgia 30096. You can E-Mail your questions to us at We reserve the right to edit questions for length.

Quote of the Month

“Cherish your visions and your dreams as they are the children of your soul - the blueprints of your ultimate achievements.”
- Napoleon Hill

A Tip Of The Hat To:

Toni Farrell Itkin

Buckhead Brokers Realtors

Atlanta, Georgia

**** Thank You****