| Home | DIY Log Cabins | Backpacking |
Once you reach the prescribed height called for in the plans, wall-building comes to a temporary halt. This height might be as low as 7 feet in an open plan where there will be no ceiling or upper story, or might go up to 8 or 8½ feet where ceilings or upper floors are involved. In high-posted rooms the height might even reach 10 or 12 feet, and there is also the possibility of two or more full levels in the same structure. In any case, at this stage of the construction structural cross-members are installed. Exactly how this is done depends upon the presence or absence of ceilings and upper floors, the layout of interior first-floor partition walls, the roof design, and whether or not visible logs are to serve as part of the decor. The basics of construction are much the same as for the first-floor frame, and can be done with logs only; beams, logs and dimension stock together; all dimension stock; or combinations of these. OPEN CONSTRUCTION Open construction simply means the absence of ceiling/floor at the normal second-floor level, with the living space carried through all the way to the roof frame. This is sometimes referred to as a cathedral ceiling design, especially where the open space is carried on past a full second-floor level and into the under-roof area, for a total floor-to-roof peak height of 16 to 20 feet or more. When open construction is used, it is usually necessary to place a number of tie beams across the narrowest dimension of the building—wall top to wall top, or at approximately the second-floor level (Fig. 7-1). In a log house these members are most likely to be fully-round logs, although beams are also sometimes used. They serve to stabilize the walls and prevent them from spreading out ward under roof loading. The usual method of installation is to form tenons on the tie log ends and fit them into matching mortises in the wall logs at the desired height. Then they are spiked securely in place. Another method that affords greater strength is to cut the tie log ends in dovetail tenons and fit them into matching dovetail mortises, locking the members solidly together. Spikes can be driven for added insurance. Fig. 7-1. Tie beams help to hold walls rigid and support the roof in open or cathedral ceiling designs. Where open truss assemblies are to be used as roof supports, the tie beams can become the bottom chords of the trusses. Depending upon the truss design, the tie beams might extend past the walls to the outside where they join the rafters, or they might be mortised or spiked into the wall tops with no overhang. They might also be installed as part of a preassembled truss, or installed first with the remainder of the truss being built up piecemeal. Further details are given in section 8. Tie logs or beams placed across a relatively narrow structure and not part of a truss assembly need not be especially heavy, because they carry no weight but their own. In a narrow structure, say 16 to 20 feet wide, tie beams could easily be as small as 6-inch, especially if several are installed. The wider the span, the heftier the log must be, if only to support its own weight without sagging. Also, greater lengths automatically mean larger logs in order to gain that length. A 9- to 10-inch diameter should be sufficient out to about 24 feet, about 12 inches for a 30-foot span, and 14-inch or greater diameter for 36 to 40 feet. Fig. 7-2. A tie beam with ridge log and/or rafter support. Some logs, and some species, are more limber than others. If some objectionable sagging appears to be likely, the problem can be taken care of to at least some degree by installing one or a pair of support poles in truss fashion when the roof is built (the additional roof loading this causes should be taken into ac count in the roof framing). Prop the sagging tie log up from below until it is level or even crowned upward slightly, but not enough to drive it out of its moorings. Secure a single sup port pole from the tie log to the ridge pole bottom, or angle a pair of support poles from the tie log to convenient rafter beams or purlins, or use some similar arrangement (Fig. 7-2). Of course, if there is a conveniently placed transverse partition wall, or an opportunity to set some posts, that can provide support from below. FLOOR FRAMING Floor framing is a good deal more involved than just setting a few tie logs. Framing for a second floor that will be part of the living quarters has to be every bit as sturdy as the first- floor framing, because it must carry a certain amount of both the live and the dead loads of the structure. Even though a portion of the second floor area might be unusable from a practical standpoint because of a low roof design, the entire floor framework has to be sturdy and substantial. Logs can be used for the entire job, flatted on top to receive the flooring. Logs or beams are used wherever the surfaces will be exposed and visible from below. Dimension stock is usually only employed when the en tire framing structure is invisible because of a first-floor ceiling; more about this later. The business of arranging a second-floor frame can be a tricky one, but the main thing to remember is to give the assembly as much support as possible. Not only must the floor bear weight, it should also be free from springiness and sag. Joists alone won’t do the job, except in a very small building, so this means that girders must be set as well. Girders should be at least 10 inches in diameter, more as the girder span increases. They are usually arranged to lie directly above and parallel with the first-floor partition walls, or so that they cross partition walls and receive some support from them. Failing this, post or column sup ports might have to be introduced at one or several points beneath them. Such supports should in turn be supported by a first-floor girder and preferably a foundation pier as well if the load is heavy. With the proper supporting arrangements, girders may intersect one another. Load-bearing partitions that bear directly on the second-floor frame, unless made of logs the same size as the wall logs and interlocked with them (not a common construction in this country (USA)), cannot as readily be used for support as they are in conventional framed houses be cause of the shrinkage problem. Girders should also be arranged so as to shorten the span of the joists as much as possible. The joists themselves should be of a mini mum 6-inch diameter, and in this type of construction are often placed on 24- or 30-inch centers. Joist diameter, joist spacing on centers, and joist span are all intertwined, so small joist diameters can be used with narrow spacing, large joists with wider spacing, and so forth. Logs and beams, whether girders or joists, are assembled with mortise and tenon joints. Straight ones are adequate, but dovetail joints will afford greater strength and rigidity. The logs should be securely spiked down. A considerable amount of notching is involved, and this is most easily done on the ground or the first floor, before the logs are raised. Accurate measurement is called for so that the notches cut into the wall logs at one side of the joist span will line up properly and squarely with those cut in opposite wall or girder logs and so that the joists, when set, will lie straight and parallel. Good craftsmanship is desirable, too, because many of these notches will be at least partly visible. Once the wall log notches are cut, the logs are installed atop the wall in the usual way. Then the girder ends are fashioned into tenons, mortises are cut for the joists, and the girders are spiked in place. Finally, the joists can be dropped into place from wall to girder or girder to girder. Girders and joists should be carefully aligned and leveled so that the floor surface will be level and smooth. This can be done with a little extra shimming and trimming as necessary. The process is the same as for the first-floor frame installation, except that any shimming should be kept invisible. Where girders are held up entirely by the wall structure and there are no supporting partitions or posts beneath them, as is often the case with small structures, no further treatment is necessary. As the walls of the building shrink and settle, the girders and consequently the joists will settle along with them. But where the girders rest upon walls, the situation is different. If the partition walls are made along with the shell and are of the same log materials, the settling rate will be about the same and so will the amount of drop. However, if the partition walls are of conventional stud construction, they will neither shrink nor settle and something is going to break or pull apart. This means that girders should not rest directly upon the partition walls at construction time, but should be spaced above them a distance equal to or a little more than the anticipated total settling. In order to provide support for the girders in the meantime, a series of shims can be in stalled at intervals between the top of the partition wall and the bottom of the girder (Fig. 7-3). They must be watched carefully and regularly, and adjusted periodically. If there is still a gap after the building has fully settled, shim wedges can be driven permanently into place. The same arrangement must be followed if the girders are supported by posts or columns. Otherwise, the posts can be driven through the floor, or the structure will come apart at some other point. If the partition walls are constructed of logs placed stockade-fashion, there will be little endwise shrinking and settling of these logs, so a settling gap must be allowed between partition and girder. If the logs are horizontal but smaller in diameter and/or of a different species than the wall logs, there will be some shrinkage and settling, but probably less than in the exterior walls. In this case, the settling space must still be incorporated between partition top and girder, but it can be a somewhat smaller gap. The second-floor frame can also be made entirely of dimension stock. Here again girders are used to provide adequate support and permit relatively short joist spans. This is even more important with dimension stock because of a lesser amount of strength and rigidity of individual pieces. Girders should be notched into the outside log walls, and must also be supported by posts or partitions to provide adequate rigidity. The joists are then set, usually on 16-inch centers, from wall to girder or girder to girder. The joists can be attached to the girder faces with metal joist hangers. Where the joists meet the wall logs, a dimension-stock header must be spiked to the logs. The joists are anchored to the header face with metal hangers. Again, the entire floor frame is supported at the outside edges by wall logs that are bound to settle. Therefore, a gap must be left between the supporting points and the girders to allow for this settling. Blocks or wedging can be inserted to provide temporary support while the settling continues, and rearranged every few weeks as necessary. When the settling stops, the final shims can be installed permanently. Another possibility that works quite well is to install a series of steel posts with adjust able screw-tops. These can be hidden inside the partitions or within hollow-box wood columns with the screw-tops protruding into the settling space above the partition tops (Fig. 7-4). Then all that is necessary is to wind the threaded heads of the posts down a turn or two every once in a while. The posts are adjustable through a wide range and can remain as permanent and extremely strong supports. Steel posts should be supported by first-floor girders and preferably foundation piers as well. This transmits all strain and pressure directly onto the foundation and ultimately onto the ground. The surrounding structure absorbs little, if any, of the strain. Fig. 7-3. One method of constructing a partition wall slip joint with shims. Fig. 7-4. An adjustable partition wall slip joint using a steel column with a screw-jack top. There are few second-floor frames that do not require some sort of an opening in them, except perhaps for some sleeping-loft designs. At the least there must be a hatch through which access can be gained to the attic area. There might be a chimney or a stovepipe or two that will pass through the framing, or there might be extensive ductwork. A 1½- or 2-story house requires at least one stairway, sometimes two. Wherever the openings are smaller than the distance between the joist faces, usually all that is necessary is to install trimmers to box out the desired size of opening. Where the openings are larger than the distance between joists, proceed in the same way as described for openings in the first-floor frame. CEILING FRAMING Wherever the first level of the building is solidly closed off from the second, be that roof space, attic, or full second floor, a certain amount of framing is sometimes needed to sup port a ceiling. The simplest method of doing so is to let the second-floor frame serve most or all of the purpose. Where the second-floor frame logs or beams are exposed to view from the first floor, all that is necessary is to install a deck-type floor at the second level, the bottom of which serves as the ceiling for the first level with no further construction needed. In such a situation, if the floor bottom (ceiling) and the floor-frame logs or beams are to be left natural or all painted or stained to the same color, the finish work can be done during the interior decorating process. If the ceiling is to be treated with one finish or color and the floor frame another, either or both can be treated be fore installation and then touched up afterward as necessary. Where a dimension-stock frame is used, a finish ceiling is almost invariably installed to hide the framing and present a more attractive appearance. If desirable, the same can also be done if the floor frame is made up of logs or beams. The materials most commonly used are ceiling tiles or sheets of plasterboard, though wood or other materials can be used. Once the floor frame is complete, and usually after the second-level flooring has been put down, a series of straps or furring strips of wood are attached at right angles to the joists (Fig. 7-5). The strapping is carefully shimmed or notched in to provide a flat and level mounting for the tiles or plasterboard. The strips are nailed entirely around the perimeters of the rooms or ceiling areas, with more strips spaced on 12-inch centers across the opening. Where the joists are on 16-inch centers, the strips can be inexpensive 1- x -2 S3S spruce or pine. As the spacing between joists widens out, thicker and/or wider stock should be used. When the ceiling area is fully strapped, the plasterboard or tile is secured directly to the strapping. Tile is installed with staples, plasterboard with special drywall nails or screws. An alternative system that can be used with tiles is to mount special metal runner strips in much the same way as the wood furring, and insert the tiles into them. Yet another possibility for many kinds of ceiling tile is a metal grid-work that is suspended on wire hangers from the joists. This system requires about a foot of open space between the joist bottoms and the finish ceiling level. Fig. 7-5. A cross section of a finish ceiling framework using strapping. Fig. 7-6. A cross section of a finish ceiling attached to the underside of the second-level flooring, between exposed floor frame beams. If the floor frame is constructed of beams or logs and it is desirable to cover the bottom of the floor above but at the same time expose the major portion of the beams or logs, other methods are effective. Where the beams are straight-sided, pieces of plasterboard can be cut and fitted tightly to the beam sides and nailed directly to the flooring above (Fig. 7-6). Cracks between the beams and plasterboard can then be filled with plaster or spackle, the indented nail or screw heads plastered over, and a finish applied—a time-consuming job. Or, you can put up prefinished lengths of molding, cut to fit, and then plug and touch up the nail holes afterward, which is much easier. Working with rounded logs is more difficult because their sides are far more irregular and the pieces of ceiling material must be bowed or bellied down in order to slip them up between the log sides where they meet the underside of the upper floor. If the spaces between the logs are narrow, plasterboard can’t be used because it won’t bend sufficiently. Fiberboard or insulating board of one sort or another, especially if very thin, can be used successfully and installed in much the same way, but by using mastic or construction adhesive instead of nails or screws. Cracks along the edges cannot be successfully filled with most fiberboards, so a small molding must be in stalled to hide the gaps. If only a portion of the log or beam frame is to show, the job is a bit easier. Each nailing space between joints should be boxed around with nailing strips of 1- x -2 stock. On flat-sided beams they can be tacked in place at any appropriate distance above the bottom face, de pending upon how much of the beam is to be visible. On logs the nailing strips should be se cured just above the average greatest width of the logs so that the ceiling panels will fit into place at the narrowest point between two logs and show a minimum crack. Panels of plasterboard or insulating board are edge-nailed to the nailing Strips, and the nail heads and joints are then covered with a small wood molding (Fig. 7-7). Where the plans call for a first-floor ceiling but no floor above, or only a small section or two of flooring to provide service crawlways or extra storage space, the ceiling framing can be done a bit differently. All that is really needed is enough of a framework to holdup the ceiling itself and also tie the walls of the building together. Logs can be used for this purpose and so can beams, though the expense would be greater. Because the framework would be hidden anyway, dimension stock is probably the best choice. For a lightweight tile ceiling all that is necessary is a series of 2- x -6 joists secured on 16-inch centers. A plasterboard ceiling is much heavier, and so requires 2- x -6s on short spans, or 2- x -8s or 2- x -12s on longer spans. With either stock the joist bottoms should be strapped with 1- x -2s—shimmed and/or notched to pro vide a level frame—on 12-inch centers. The joists are attached to the sidewalls by spiking headers to the logs and using metal joist hangers, or they can be notched into the wall logs. Depending upon the spans involved, girders and supports must also be installed to keep the spans short and give the overall frame work sufficient strength (Fig. 7-8). Fig. 7-7. One method of installing a ceiling between partially exposed floor frame logs or beams, in cross section. Fig. 7-8. Ceiling strapping applied to a typical dimension-stock floor frame. If a suspended ceiling hung in a metal grid is called for in the plans, even less framing is required if there is to be no floor above. Just install enough tie logs or beams to keep the walls square and plumb and the structure in tact. The ceiling grid can be suspended by wires from the tie logs and whatever else hap pens to be handy, even roof rafters. A suspended grid tile ceiling is so lightweight that it won’t impose any appreciable strain on a well-constructed building, especially where heavy log framing is involved. At this stage of the construction, only the structural members (girders, joists, tie beams, temporary or permanent supports need be in stalled. Strapping is left until work begins on the interior, and ceiling tile or plasterboard are among the last items to be installed. The same is true of suspended metal grid ceilings. Girder support posts or columns can be installed now or later. Interior partition walls are sometimes built before the second-story frame is begun, and sometimes not until the shell has been completed. In conventional platform framing, interior partition frames are almost always erected first so that portions of the second-floor frame can be anchored and supported by them. However, in log construction it is often just as easy to build these partitions later. Temporary supports can be stood in place under girders if necessary until the shell is complete. LAYING FLOORING The second-level flooring is best laid down as soon as the floor frame is finished. This helps to tighten the structure up and keep it well aligned, and also affords a convenient platform from which to work while completing the upper story and roof. And, the working conditions are a lot safer than trying to trod around on planks or loose chunks of plywood. The general procedures for laying flooring are the same as for the first-level floor. If the underside of the floor will not be visible from the first level, a subflooring or sheathing of plywood, or a layer of boards, can be laid. If the second level is designed only as a dead-storage attic, the single layer of sheathing is probably sufficient. If designed as living quarters, the subflooring is covered with an underlayment or a finish covering, or both. At this point in the construction, only the subfloor is laid. When the underside of the flooring will be visible from the first level and actually constitutes the ceiling, an added measure must be taken in laying the flooring. Decking or deck planking is frequently used for this purpose, though other types of boards or special plywoods could be used as well. In most cases the flooring material is laid with the best or finish side down, so care must be taken not to scratch or gouge the visible surface as the material is installed. Pieces should be carefully fitted together to show a minimum of joints, and nailing carefully done so that none miss the mark and show from below. If the upper surface of the flooring material will also be a finish floor surface, as is sometimes done with thick decking, all the pieces must be blind-nailed to maintain a presentable appearance. It is a good idea to cover the floor surface with building paper, plastic sheeting, or sheets of plywood for protection from mechanical damage as construction continues. If another layer of flooring such as underlayment or a finish covering will be added later on, slight mechanical damage won’t matter. Water might, though, no matter the arrangement. There is always the possibility that an untimely rainstorm could leave watermarks or stains on the visible surfaces, upper or lower. If the finish is to be natural, these stains will be difficult to remove, especially on the underside of the floor. Covering the whole flooring area with plastic sheeting and keeping the floor clean of debris and saw dust is a good idea. In many house designs only a portion of the second-floor level is given over to living quarters, with the remainder being storage or just crawl areas under eaves. The flooring should be installed in such areas as well—not just in the living area—in order to strengthen the structure and also to provide a platform for storing goods or for crawling around on service missions. Underlayment and/or finish flooring is put down later, in the living quarters only. SECOND-STORY WALLS As soon as the tie beams and/or second-story floor frame is complete, construction of the shell can proceed. In some instances the side- walls need no further attention, and the roof rafters rest upon them approximately at the second-floor level. In other designs one more course or round of logs may be laid on the side- walls to form the top plate, upon which the rafters will rest. Inmost designs, there are end walls that must be carried up higher to form a partial or full second story, and to conform to the roof design. Five of the most common roof styles are shown in Fig. 7-9. All of these end-wall configurations (or combinations and variations) are put together in pretty much the same way. There are two general construction methods you can follow: full-log, or dimension-stock framing. In full-log construction the courses are simply built up in the same way as the first- floor walls were, except that at one point or another there are no longer any corner joints to fashion. With the gable style roof the log outer ends must be cut to an angle that matches the roof pitch, and the logs must be accurately trimmed to form a smooth and continuous face that will match the rafter levels and present no gaps. The situation is much the same with the gambrel roof end walls except that at a certain point on each side the roof pitch, and thus the log-end cut angle, changes from relatively gentle to relatively steep. Setting the logs for a shed roof is done in much the same way. The principal difference is that a course of logs must be laid along the front wall first. Then an end-wall course is joined to the front-wall course, with the back ends cut to match the angle of the shed roof (Fig. 7-10). Another front-wall course follows, and so forth, until the full height of the front wall is reached and all of the end-wall courses are laid. The saltbox in effect is nothing more than a gable style with mismatched roof sections and an off-center ridge line; the pitches of the sections may be the same, or different. Depending upon the roof line, wall construction may be the same as for the gable end walls, with the log ends cut to a steep angle at one end and a gentle one at the other. Or, the saltbox style could be used Where the front wall and thus the starting point of one roof section is elevated above the floor level while the rear roof section meets with the floor level. In that instance, the lower portion of the end wall is assembled as though it were a shed roof style, while the upper portion resembles a gable end wall. Whatever the configuration of the roof lines, the wall logs are all assembled, joined as necessary, secured, and sealed just as the first-floor wall logs are. Window and door openings are also handled in the same way. Dimension-stock construction of end walls that rise above a top plate is most often done at this stage, though some builders prefer to wait until the roof frame is finished. Then they build up the end walls to suit the roof shape by simply boxing in the open area with a frame work that is later sheathed. Either way works out fine, though most people consider the former method to be the easier. Fig. 7-9. Some of the roof lines frequently used in log houses. Construction of dimension-stock walls is undertaken in the same fashion as for any conventional platformed assembly, with some variations introduced where logs are part of the scheme. The sole plate, studs, and top plates of 2- x -4s or 2- x -6s are laid out on the second- level floor and nailed together. The top angle of the studs and the lie of the top plates match the pitch and placement of the roof. Door and window openings are framed in the conventional manner. When the assembly is completed, it is stood up in position and nailed in place (Fig. 7-11). If a large ridge log is part of the plan, a saddle notch is framed into the peak of the end- wall assembly to receive and support it. A solid or built-up post is included in the assembly directly below the saddle to support the ridge log sturdily (Fig. 7-12). If log purlins are to be used, frame in more saddles at the appropriate locations to hold them. Note, however, that in some designs the ridge log or purlin logs might lie fully above the top plate of the end-wall assembly and rest on them, rather than being en closed in saddles. The exterior of the end-wall frame can be covered with a variety of siding materials. A sheathing of plywood might first be attached to the frame, but sometimes is not. The finish siding might consist of log slabs or split half- logs laid up horizontally and spiked to the framing members. Log facing can be applied vertically by first nailing blocking sections between the studs to which the vertical log sections can be spiked. Conventional siding materials can also be used, such as horizontal clapboards, vertical weathered barn boards, cedar shingles, or exterior-grade siding ply wood in any of several types. The bottom edge of the siding should lap down over the top log course an inch or so and be sealed off. Any kind of interior finish can be applied. STUB AND FULL WALLS One-and-a-half-story is the term given to those houses that have low roof lines but still contain a certain amount of living area located beneath the highest portion of the roof. The standard Cape Cod design is an example. In some cases the roof joins the wall at the second- floor level. In other cases, however, stub or stem walls are installed to elevate the entire roof structure somewhat above the second-floor level. Stub walls may be anywhere from 1 or 2 to 5 or 6 feet high. Beyond this approximate point they are considered full walls. Fig. 7-10. Setting end-wall logs in a shed roof design. Fig. 7-11. A dimension-stock framework for the end wall in a gable roof design. The assembly can be built on the floor and erected in one piece. Fig. 7-12. A dimension-stock end-wall framework for a gable roof design with the ridge log and center support framed in. Stub walls are constructed in exactly the same way as the first-floor walls and are really just a continuation of them. Once the second- level floor is built, the walls are just carried up further to the desired final height. The top course of side stub walls then becomes the plate course that supports the roof framing. The stub walls can be of varying height or the same all around the perimeter of the structure. In the case of a saltbox style with a raised front roof, there might be only a stub wall at the front, for example, or there could be a tall one at the front and short one at the rear. All manner of combinations are possible. Full walls are those built to full height, usually 6 feet or more, as used in a house that contains two full stories with the roof beginning at the third level. These walls are also constructed in the same fashion as first-story walls, with door and window openings provided for in the same way. Upon reaching a prescribed wall height, a third-level floor frame or suit able tie beams are installed along the same lines as described previously for second-level arrangements. KNEE WALLS Knee walls are a form of interior partition walls, installed to separate usable living space from under-eave crawl or storage areas in story- and-a-half structures with low roof lines (Fig. 7-13). These walls are set at right angles to the roof rafters and may be 3 to 5 feet or so high. Fig. 7-13. A cross section of Jog and dimension-stock knee walls. In conventional construction knee walls are almost always installed after the shell has been completed and as a part of the interior work. However, in some types of log construction it is easier to lay up knee walls after the second-level flooring is complete and before the roof framing beings. If the knee walls are to be made of dimension stock, they might be best installed after the roof rafters—whether log or dimension stock—are in place, but before the roof sheathing is applied, if the knee walls are log and locked into the end walls, they must of course be laid up together. If the knee walls are log but not integrated with the end walls, they can be laid up before the rafters are set, then the top course of the knee wall can be appropriately flatted or notched to receive the rafters. Thus the rafters will help stabilize the knee walls, while the knee walls serve as bearing points for the rafters. The knee walls might also be arranged to lie directly beneath purlin logs in that type of roof construction. When built in that fashion, knee walls can become an important structural part of the building rather than tacked-in, hide-it panels. Here again, log construction of knee walls is similar to exterior wall construction. Differences lie in that the logs need not be of as great diameter, nor need they be splined or fully sealed. They should be ruggedly secure for stability, with the ends carefully matched and mated to whatever cross-walls they butt up against. If the storage or crawl spaces they close off are unheated, the back side of the knee walls should be covered with a vapor barrier and suitable insulation, if the climate warrants it, and the seams and butt joints caulked to pre vent drafts and keep out insects. PREV: The Walls © CRSociety.net |