| Owner/ Builder |
||||
|
|
|
Timber Frame Questions and Answers |
|
|
|
|
|
Q: How does timber framing fit in a green building environment? A: Use local materials. That to me, is one of the major components of a sensible building system. In New England, where I live, our forests are mature again and we have plenty of good timber that can be sustainably and selectively harvested and processed at local sawmillls. Portable sawmills are also very popular that can go right into the woods. All of this avoids the transportation costs, embodied energy and fuel associated with materials shipped from far away, and it supports the local economy. Even with certified timber I would hesitate to buy it if it came from across the country. So for you folks out in the desert or plains without trees, I suggest you look to one of the earth based building systems using local materials, at least for the walls, if you're trying to be truly green. Timber frames also are valued more highly, are usually inside the building envelope, and are thus cared for better than a light-framed house. So they will generally last for centuries, as opposed to less than 100 years for a typical modern house. Thus, for about the same amount of framing wood, you get a house that will last 2-3 times longer. A: The majority of contractor-built timber framed homes use Structural Insulated Panels (SIPs) that get nailed onto the outside of the frame. (SIPs can be the subject of a lot of debate - they have some advantages from a green standpoint - but we'll save that for later.) These go on very fast, thus saving labor (=money), and make a very energy-efficient envelope. But if you're doing your own labor, there are other alternatives such as light framing and Larsen trusses nailed outside the frame that allow you to use conventional insulation or sprayed-in systems, or you can use strawbale or slip-formed earth systems. One thing that is common to all of these systems is that they are outside the timber frame, thus keeping the frame exposed to the warm interior where it is protected. This is important in a cold climate; burying the frame in the wall could cause condensation and rot if the sealing details are not done well. This is not as big an issue in a dry or warm climate, but you still have the problem of finishing your infilled wall up against the sides of the timbers that you avoid by putting your wall outside the frame. Q: I'm looking for a primer on building with roundwood. That is, I would like to learn how to do framing with non-milled poles. You will occasionally see beautiful natural buildings (cob, strawbale, slipstraw, etc.) that are supported in this way. I have yet to find a guide that addresses joinery and design. A: Log Construction Manual by Rob Chambers, available from the International Log Builders Association. And the three part series of articles on scribing that appeared in the quarterly journal Timber Framing from the Timber Framers Guild. Q: I am currently in my final year at Kingston University London, and am undertaking my Degree in Residential Property. As part of my final year project I am compiling information for a dissertation. The title for this dissertation is, "Timber Frame Housing, a time effective solution?" The research looks into the time comparisons between timber frame and masonry construction. In order to undertake this research, I have decided to compare two case studies, one of which looks at Masonry construction and a similar one which used Timber Frame. A: The term "timber frame" outside of North America generally refers to any form of wood framing, and usually means light framing with lumber (2-4 inches thick). In North America our term "timber framing" means framing with heavy timbers (5" or more thick) and traditional wooden joinery. "Post and beam" can use heavy timber and metal connections. So I think the timber framing you are studying in Britain is really light frame construction. I suspect there are some inherent problems in comparing masonry to wood construction that go beyond the bottom line of time and materials costs. It's literally like comparing apples and oranges. In our area of New England wood construction is preferred because of availability of local materials, energy efficiency and performance, the local skills pool. In areas like Florida (with termites and hurricanes) or the desert Southwest masonry is preferred. From a green standpoint, my priority is to use local materials and local skills, and support the local economy. I suspect the scarcity of wood in Britain led to the predominance of masonry construction there. Q: Several years ago I was offered a very unusual gift, a free cottage. The owners of the neglected structure were elderly and were glad to pass it along us. It's quite a charming little place, although there is no foundation (the north end has a cinder block in each corner; the south end was likely on a tree stump at one point, but now is slowly settling into the ground.) There is virtually no insulation (nor furnace or A/C, either) with 1/4" gaps surrounding some of the windows. Obviously, attempting to make this northern Indiana structure a year-round residence is well beyond my ability and hiring professionals is beyond our budget (and likely significantly more expensive than rebuilding.) However, it is built with old-growth actual-sized lumber. I came up with the crazy ideal of recycling the entire building. Literally, taking it apart and rebuilding with as many existing materials as practical. Potential recyclables: studs, flooring, roof planks, interior appointments. Required replacements: foundation, roofing, windows, insulation. I have talked to several people familiar with the building trades and the unanimous advice has been to tear it down. My goal would be to make this 1920's 20' x 40' structure in northern Indiana a year-round residence. The floor joists have rotted and the floors are soft in many places. In the late 1960's the previous owner dealt the the problem by placing plywood on the floor. This distributed the weight but did not help things in the long run. The building is Kellastone, a forgotten style where a stucco-like finish is applied and small stones (or in some cases glass) are embedded into the mud. This made for an economical, durable and attractive finish. Some of the interior walls are intact and remain quite nice. The building is framed in old growth actual sided lumber, although the studs and rafters are 2x4's 3' oc. When looking into the attic it looks like it should not be sturdy, however, the building has been sitting there nearly 90 years and a straight roofline remains. To preserve the structure I would need to replace a significant amount of the low-lying lumber, jack it up and pour a foundation under it. Then insulate and replace the many windows with energy efficient replacements. Is this practical? What is a good next step? A: If the wall framing and roof framing is good and straight, it still seems to make sense to me to preserve the structure, support it on cribbing and pour a new foundation and frame a new floor, then lower the existing frame onto it. This would preserve the Kellastone system, which seems of great value, although it doesn't address the lack of insulation, which sounds like it would have to be blown in. Someone knowledgeable would have to visit the site in person. Not being familiar with the stucco system you're better off consulting with someone local who is. Q: I would like to build a new timber panel /or beam house. I read about insulation material "neopor" and I would be glad, if you would give your opinion about this synthetic material. A: I am not familiar with this material so have no opinion. Our material of choice for insulation in Massachusetts is blown in or wet spray cellulose, with Structural Insulated Panels (SIPs) second. Q: What is the best way to get the bark off of timber and why is it advisable to do this? A: (Kelly) It is easiest to debark trees when they are still wet with sap, since the bark will often peel off by just pulling on it; once they are dry, it is often necessary to use a draw knife, or some similar tool to debark them. Leaving the bark on can provide a place for insects to reside, either living there before or after installation. Also the bark is much more likely to shed debris over time. Q: Why do you ignore log home structures as a natural alternative? Built with standing dead wood the structure is masssively energy effecient, is a huge carbon sink, and left to to decay in the forest re-emits the carbon it absorbed when living. I would love to know why a sip panel is promoted and a log wall is not. A sip carries a huge carbon footprint during the manufacturing process. The efeciency of both walls are the same but the log wall is purely a natural fiber and a sip is a massive synthetic. Don't understand your rational. A: (Kelly) I like log homes, and in some circustances it makes a lot of sense to build them. This is generally true when there is a local source of surplus logs that need to be thinned sustainably from the forest. Otherwise, to harvest logs just for a log home when it is necessary to either cut down productive forests or to ship the logs much distance it doesn't make sustainable sense. It takes a lot of logs to build a log home. Another issue with log homes is that they do not naturally provide very much insulation, compared to many other materials. I feel that too often log homes are promoted as natural alternatives without attention to these factors, so in the interest of saving our forests (which sequester much CO2 and provide needed habitat), I have not devoted much attention to them. I do adovocate the use of logs for timber framing under similar circumstances. I don't really promote SIP's; I only recognize that they have a place in the realm of sustainable building, just as log homes do. Q: My two sons and I are building a triplex in Crystal Beach Florida. We want to go as green as we can and stay within a budget. What is the best product to build with in Florida? We are in a flood zone area and need to build 12 feet above the ground. A: (Kelly) If you need to build that high off the ground, probably the best approach is to build with tall piers or poles so that any flooding that does occur will not adversely affect the structure. I would recommend a wood pole or timber frame structure, since it can easily be adapted to this need. Q: I'm having a hard time locating a 16 inch post. Even the used telephone poles are only 12-14 inches .....got any ideas where else to look? A: Try a sawmill or a logger. There are plenty of 16" trees out there. Q: My wife and I intend to build a number of timber framed structures on our homestead 15ac in Georgia, and are examining different techniques for doing so. We have considered both traditional timber framing and pole framing with embedded poles, and we're exploring a variety of infill methods as well. In the square timber world, the extreme cost of large dimensional lumber worries us. However, it occurred to me that composite box posts or beams could be made from "normal" 2x stock that might serve well. If the joints were both glued and screwed, it seems to me that such a member might be quite strong - perhaps even approaching the strength of a solid single member. Furthermore, since it is essentially a pair of L-girders joined together it might span space well when used as a horizontal beam. The additional side piece would make it less efficient perhaps than an I beam, but it should be similarly strong or stronger. Also, if the joints between the ends of the 2x stock pieces are staggered along the length, in theory, a beam of virtually any length required might be constructed. Finally, one might be able to use the center channel as a race for wiring. Does this seem to you like it would be a practical approach? A: You can't approach the strength of a solid timber using the methods you describe. Glue-lams can but only when they are made in a controlled environment with strict quality control and proper arrangement of the "plies". If you stagger the joints you have still severed the grain in each piece and that cannot be considered a structural continuous beam, even if glued and screwed. When you consider all of the extra labor required to assemble these built-up members, and the cost of the glue and hardware, it's hard to imagine it would be worth it. But mostly I question your assumption of the "extreme cost" of large timber. Local timber purchased from a sawmill will almost always be less expensive then buying the equivalent volume of dimensional lumber at a lumberyard; less sawing required. (By the way, "timber" is anything 5" or larger in both dimensions; "lumber" is 2"-4" in either dimension.) I can only think you are looking for timber from a lumberyard rather than going to a sawmill, of which there should be many in Georgia. All lumber will have some degree of twist, crown or cupping. No matter how slight, this will fight you during assembly and probably prevent a bomb-proof glue joint. When they build a gluelam in a factory, the material is all jointed straight and true and then immediately glued together under immense pressure. Small built-up beams of say, 2-2x4s or 2-2x6s in an 8-10' length might be doable with little fuss, but bigger than that.... If you were somehow able to calculate the strength of the built-up beam (and some of that, in smaller sizes like 2-2x8's, is in the building code), you would need to have a bigger beam than one using solid timber to reach equivalent strength. And then there's aesthetics (if you care about that). It's hard to make a built-up beam look as good as solid timber, in my opinion. Also, consider all the metal you'll have to avoid when doing any drilling, sawing or fastening of finish materials. Your building inspector, if you have one, will be the final word. Try contacting the Holder Brothers in Georgia if you want to source timber. www.holderbros.com. They may be of help. Q: What would you go with for natural insulation for walls with Timber Frame roofing? What is your take on earth walls vs straw/clay walls (especially in hot and humid weather) and which one will do very well in humidity? I plan on getting an AC/Heater central system but will the use of it decrease significantly with earth or straw/clay walls? Is there an alternative to AC/Heater central system I should look into? A: I only have experience with straw/clay, and it seems to work well for this northern climate. You should contact natural builders in your climate to find out what is time-tested there. I think any kind of high-mass wall would help moderate temperature swings, and the use of any AC/Heater system would decrease with increased r-value. But the key is to get the mass heated up (or cooled down), and I don't recommend high-mass walls unless you have extra solar gain to store. In our new england climate, I prefer high r-value over mass, and thus thick walls of cellulose. Alternative AC/Heater systems is a pretty broad question. Again, high r-value can decrease the need to think about alternatives. It's possible to design a house so well insulated that you don't need a system. |
|
|
