When most people build a log home, they are extremely concerned with the insulation
values of the log wall. If you have read my previous article, then you already know this. What most people overlook however is that the largest loss of energy from a log home is usually around the windows and doors. Second only to the roof. New construction techniques have all but eliminated energy loss through the roof, now windows and doors are the weak link in the system. Typically when a log home is stacked, the logs are allowed to run partially through the window and door jambs to be cut back after the logs are stacked. Once all the logs have been stacked, the builder will come back and cut out the excess log and install window and door bucks. These bucks are usually 2x material being the same width as the logs are thick. The builder will usually apply foam or log caulk to the buck and install the header buck, then the two side bucks and finally the sill buck. Once this is complete, the builder will install the windows in one of two ways depending on the type of window.
For a wooden window, the builder will usually trim out the exterior of the window and after applying a liberal amount of caulk to the window buck, he will nail in the window from the outside. For an aluminum window with nailing flanges, he will caulk the buck, nail in the window from outside and then he will trim out the exterior. If the window is not under a porch or an overhang, he will then make a drip edge and install it above the window and caulk it to the log. Now, this method does work, but it is likely as not to leak. If you are building a new log home and are at this stage, you can test your windows by taking a water hose and spray the windows from an angle directing the water behind the trim. Odds are you will have a leak!!! Occasionally, the supplier of your log home will have a method of installation differing from this procedure, but odds are it is not much better and can be tested in the same way.
Doors are installed in basically the same manner, logs are trimmed back and a buck is installed. Beyond this the builder will usually trim out the exterior of the door (often removing the existing brick mold and replacing it with the same trim as the windows.) Then he will slather the buck and threshold with log caulk, press the door into place and after plumbing the hinge side and making sure all the margins are equal, he will nail the door into place. This will often provide the same result as the window installation and can be tested in the same manner. Once your home is complete and you have moved in, do not use the water method. You can test the openings with a compressed air hose while someone on the inside tells you if you have a leak. (Being careful not to blow out the foam insulation) There are a few log home manufactures who have this system down to a science, however, you will find that the majority does not.
The best method for installing windows and doors begins with the stacking of your log home. Build all of your bucks before you begin stacking. (Note: Few if any builders will be willing to do the extra work without you specify what you require before it is bid, either way it will result in extra costs on your end) Once all of your bucks are built, go around them and mortise them at least 3/4″ in the center of the buck with a 1/2″ router bit. Then figure where in the wall they are going to go (Example: three inches into the third log course and two inches into the ninth) so that you do not stack through them. Paint this information on the sub-floor at each location. Set the door bucks before you begin stacking and kick them off to keep them plumb and square. Now, as you begin stacking, as you come to a door or a window, you can cut the log to the exact length and mortise the end of the log with the same 1/2″ router bit. Install a 1/2″ plywood spline (make sure to use plywood as a 1/2″ board will simply split under the pressure) into the buck making sure to caulk liberally in the mortise of the buck and the log. You can use a continuous spline the length of the buck or you can make your splines as long as each log is tall or the height of two logs. However, using the spline method often makes stacking a little more difficult, yet it is worth every minute of extra work.
Using the splined buck method not only seals the bucks as you build, but it makes for a straighter and plumber log stack. Once you have your logs stacked you have almost all of the hard weatherproofing done. Now, when you get ready to install the windows, you are pretty much back to the original method. However, there is a way to improve this process as well. Whether you have a wooden window or an aluminum window with nailing flanges. You want a water tight seal all the way around. The best method for this is to leave the buck back the thickness of your trim from the face of the logs. If you have the foresight to do this, you can set your wooden window in temporarily and mark around it which will tell you how much wood to take off the face of the logs. Remove the window and either cerf cut your logs on the end as you stack or put up temporary guides for your router so that you can remove the excess wood (keep in mind that you do not want to go any deeper than the thickness of your trim). Once you have removed the excess wood, caulk behind the trim and install as you normally would. This should leave the face of your trim flush with the face of the log.
Normally when an owner purchases his windows and doors for a new log home, they give little or no thought to the depth of the jambs. The depth of the door and window jambs should be the same as the thickness of your log. If you have an eight inch log (nominally seven and a half inches) then you want your windows to have that same depth. Often a homeowner will discover that his windows are standard (four and a half inches) and that they are going to have to build extension jambs. This is a costly process that can easily be offset by ordering the correct jambs to begin with. Remember, if you are going to flush your trim to take the thickness of the trim off the depth of the jamb. (Example: Seven and a half inch log and three quarters of an inch trim, then you would want your jambs to be six and three quarters) If you decide to use any of these processes it is imperative to have the exact window and door openings before you begin construction. I have seen well qualified builders have to go back and cut out the top or bottom bucks in order to get his openings correct. Most builders will want to measure the windows and doors before they begin.
Most log homes are kiln dried to a nominal seventeen percent moisture content. Even the driest of logs will eventually settle to some extent. You will find that the finest log home manufactures allow for settling in the design of their homes. This brings us to allowances for windows and doors to settle. Before about five years ago it was common to leave at least an inch below windows and door bucks to allow for settling. This made it even harder to seal the openings against wind and rain. Now it is more common to leave the settling gap at the top of the window or door. The theory behind the switch is that if an opening is going to leak then it is more than likely to leak at the bottom so it makes better sense to leave to gap at the top. It is my belief that if you have built with kiln dried logs then you need no more than a half an inch of settling space above your opening (this is a personal preference, I recommend using the manufactures specifications in any case). This is above the buck not the actually unit. You can still do this and still spline the buck. In fact, if you are planning on leaving a settling space, I would definitely spline the bucks.
Wet logs or air dried logs require more settling space than kiln dried. This can be calculated depending on how moist the logs are when they are being stacked. If you are planning on using green logs (which I do not recommend) then the spline method is almost out of the question as you will experience too much movement to control. Also, if you use any of these methods with anything other than kiln dried logs, do not flush mount your trim as the shrinkage will cause the trim to buckle and pop out. Leaving you a mess to deal with. If you decide to build with wet or green logs or even air dried (standing dried included) then you would do well to consult an architect who specializes in log homes to help you with your window and door openings. This being the case, most people who use these types of logs do so to save money and any money saved will be spent in builder and architectural fees. Not to mention constant repair and reworking finishes to compensate for shrinkage.
Finished homes with leaky openings can be fixed, although it is not always a simple process. Using the air testing method, find out which if any openings leak. If a window or door does not leak, don’t take it apart until you have to, unless you want to be proactive. You can always test the openings again every year and fix as necessary. Once you find a leaky opening, pull off the exterior trim. Using a log caulk that expands and contracts with the logs (do not use commercial grade silicone) caulk along the edge of the buck where it meets the logs ( in most cases, you can find a log caulk that matches the color of your home or your trim). If it has already been caulked there, remove the existing caulking before you begin. Then caulk the along the edge of the buck and the edge of the window where the trim overlaps, keep a wet rag and bucket of water handy to remove any excess caulk. Then reinstall the trim while the caulk is still wet. Do not allow the caulk to begin setting as this can leave an opening for wind or rain. If there is no drip edge above the window trim, now is the time to install one. Using the same type of material, bevel the edge of your board so that the trim sits at a thirty degree angle over the top piece of trim. Then rip the drip edge to where only about an inch of material overhangs the trim. Now cut in a one eighth inch rip the length of the drip edge about one eighth of an inch from the edge. This will break the surface tension of the water and allow it to drip instead of just working its way back to the trim. Now cut the drip edge so that it is 1/4″ longer than the top piece of trim on both ends and nail in place. Finally caulk along the top of the drip edge where it meets the log wall. If you follow the instructions correctly, you will have an even more efficient home that will remain comfortable year round.
This same method of splining the bucks can also be used wherever you have two logs butting each other in a wall. This is much more efficient and stronger than the peg method. This is the third article in a series that I am writing for Associated Content. If you would like diagrams or plans on how to install windows and doors properly in a log home, feel free to contact me here at associated content. Keep coming back as I plan to write many more articles on log homes on everything from site preparation and delivery to everyday maintenance. Thank you for reading.