In the simplest terms - Logs rot because of water.
The rot organism needs four ingredients to begin degrading wood. It needs:
- Temperatures between 60º and 90º. This is why most of the active rotting occurs during our hot, humid Midwestern summers.
- Oxygen - rot needs it to get going. This is why wood that is underwater does not rot. There is not enough ‘free oxygen’ for the process to take place.
- A food source. This is what the rot organism eats - in this case wood- aka -Your house.
- Moisture content between 20% - 30% in the wood’s fiber. While this percentage varies from species to species, most wood will start to deteriorate at around 20% moisture.
Rot needs all these things to get going. If we can eliminate one of these ‘ingredients’ we can stop the rot process, which is easier said than done.
It is impossible to change the temperatures away from being 60-90° in the summer. As living organisms ourselves, we need oxygen too, just like rot. Rot eating wood is one of the laws of nature, so the only factor that we can control is - Water!
How do we keep a log home dry and stop rot?
1. Maintain a good finish on the exterior logs.
2. Have adequate overhangs wherever possible.
3. Have gutters in place and keep them working.
4. Free board - in other words - keep the house up off the ground.
5. Protect the lower logs around your decks.
6. The caulking and chinking between the log joints must be in good condition.
1. Maintain a good finish on the exterior logs. Log homes need to have a proper finish that can control moisture. First, modern log home finishes repel water (i.e. rain and condensation) from the outside. Secondly, they ‘breath’, which allows the moisture that is inside the logs to make its way out of the wood. The moisture content in a log varies based on the season of the year, how old the home is, and the current weather conditions. Log homes are different than other wood homes because they can actually soak up a lot of moisture in a relatively short period of time. For these reasons, it is extremely important that the finish on a log home be well maintained so that it repels water from the exterior surface of the wood and allows the wood to breath.
2. Have adequate overhangs wherever possible. The best way to stop water from getting into the logs is to keep it from falling on the logs in the first place. We recommend at least a 24” overhang on a single story log home and in this case, more is almost invariably better. On some lakeside gable walls for instance, we recommend five to eight feet of overhang. These overhang numbers are the two most important aspects to take into consideration when considering buying a log home. Are there adequate overhangs?
3. Have gutters in place and keep them working. Gutters often have to be retrofitted to an existing log home in order to keep the water that splashes off the roof to a minimum. The number one cause for having to replace rotten logs is due to splashing water from the roof onto lower logs. Gutters can be a reasonably economic part of the solution to controlling moisture.
4. Free board - in other words - keep the house up off the ground. Many times, this is a difficult thing to change because it can involve lifting the house and putting it on a new foundation. However, if you are in the design stage of building a log home, it is a relatively simple thing to raise the building above the surrounding ground (above grade) to prevent the water coming off the roof from splashing on to the lower logs. It will also help by preventing scrubs, tree roots, and simple soil moisture from making its way in to the lower logs.
5. Protect the lower logs around your decks. Water splashing onto lower logs is the #1 cause for log rot.
Decks have two ways they put the logs at risk. First, they reflect UV light and heat from the sun onto the logs, which in turn, causes finishes to breakdown faster. Second, they deflect water (splash) onto the logs effectively negating the “free board”. If you would like to know how to properly flash a frame deck to a log wall, check out this drawing.
File download: How to Flash a Frame Deck to a Log Wall PDF.
What to do? If you are in the design stage, we recommend having a limited amount of deck around a log home. Think about what deck space you are going to actually use and build those. On the decks that you do build or already have, make sure they are properly flashed between the logs and the deck itself. Keep in mind that while the logs elsewhere on the home are going to be re-stained every 2-6 years, the logs behind the deck are never going to get another coat unless the deck is removed. The area where the deck comes in contact with the logs must be completely sealed or it will rot.
This photo shows the back side of a log wall where the flashing was improperly installed. Water damage can begin quickly and eventually cause serious damage.
6. The caulking and chinking between the log joints must be in good condition. Most log homes require some sort of sealant in between the logs to prevent moisture from getting into the logs through the gap between each log. The width of the space between the logs is the main factor in determining if caulk or chink is required. (Click here for more information about Caulking and Chinking) It is also important to seal around all windows and doors. We recommend the use of modern chinking and silicon-based latex caulks.
Related Article
Preservation & Maintenance of Log Structures
Prepared by the Technical Committee of the Log Homes Council, Building Systems Councils, and the NAHB, this 14-page document is a must if you are contemplating designing, building, and living in a log structure. It compiles features and methods that will ensure the permanent quality of the log structure.
File download : Preservation Maintenance of Log Structures 10-15-03.PDF
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