Why Do Logs Rot?
In the simplest of terms - logs rot because of WATER!
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The rot organism needs four ingredients to begin degrading wood. It needs:
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. 7. Keep objects away from the logs to avoid water splashing back on them. 8. Pay particular attention to windowsills. 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.
Here you can see an example of a log that has begun to rot. In this case, an up-facing check (crack) allowed moisture into the log, then a build up of finish stopped the log from being able to dry out. A build up of finish (too much) can cause problems that are as bad as not having enough finish. 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. 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 to the right 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.
7. Keep accessories, utilities, propane/oil tanks, wood piles and
other 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
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 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. Rot was caused here by an improper seal between the window and the log.
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