Why Do Log Homes Rot and How Can You Prevent It

by: Matthew Edmunds
Edmunds and Company Log Home Restorations, LLC.

Edmunds and Company Log Home Restorations

In the course of doing restoration work over the last twenty years, I have run into one prevailing misconception when it come to rot in log homes. People call us and tell us there building is rotting because of insects or that “dry rot” has “taken over. The bottom line is this – logs rot because of WATER! Moisture is what triggers the microscopic organism that is known as “rot” to start eating away at the wood. We need to use this fact to guild us when we consider what it means to properly maintain log homes. A quick lesson in the ‘science of deterioration’:

The rot organism needs four ingredients to begin degrading wood.

1. Temperatures between 60º and 90º. This is why most of the active rotting occurs during our hot, humid summers.

2. 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.

3. Rot needs a food source. This is what the rot organism eats – in this case wood or in more direct terms – your house!

4. Moisture content between 20% and 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 does. Rot eating wood is one of the laws of nature, so the only factor that we can control is the WATER!

All the things we do to prevent our log buildings from rotting needs to lead from this place: we need to keep the building dry. How do we keep a log home dry and stop rot? Here are eight things we recommend a home owner do to keep their building dry and prevent “rot”:

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 one of the most important factors 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 of rotten logs is water splashing lower logs from the ground or decks . Gutters can be a reasonably economical part of the solution to controlling moisture. It is not practical or necessary to have gutters on all log homes but if they are needed to remedy a moisture issue, they are an invaluable tool.

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 that is coming off the roof from splashing on to the lower logs. It will also help by preventing shrubs, tree roots, and soil moisture from making its way into the logs.

5. Protect the lower logs around your decks. Water splashing onto lower logs is the number one 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”.

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.

Click here for the proper way to flash a deck to a log wall (PDF)

6. The caulking and chinking between the log joints must be maintained 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.

7. Keep accessories, utilities, propane/oil tanks, and woodpiles away from the logs in order to prevent water from splashing on logs.

Keep these types of items away from your log home. While at first glance the convenience of placing these items under the cover of the eves of the house may seem like a good idea, it is not good for the logs. For one reason, the object may protrude out into the drip line causing water to splash back – wetting the logs.

Secondly, when the rain stops, these areas aren’t allowed to dry out quickly because of being blocked from the free flow of air around the logs. Logs that are constantly wet puts stress on whatever type of finish is on the logs and can cause this finish to breakdown faster. While it is certainly a difficult task, try your best to keep these items away from your logs. Keep the logs dry.

8. Pay particular attention to the logs underneath windows to prevent log rot below the window.

Make sure this seal is complete. Windows tend to concentrate water on the logs directly below them so it is very important to keep a close eye on these areas. Make sure that up-facing checks over 3/16″ are filled properly with caulking. Secondly, make sure the seal between the bottom of the window and the top of the log is tight. If there is a sill formed on the top of this lower log, make sure that it pitches water away from the window.

If you need help restoring your log home please feel free to contact us:

Matthew Edmunds – Edmunds and Company Log Home Restorations, LLC
76050 McKinley Road Washburn, Wisconsin 54891
Find out more at : www.restorelogs.com