General Information
Because there is a Difference


Designing Your Roof How and why

The eaves and rakes (gable-end roof overhangs) of a house can be intensely expressive design features. But expressive of what? Answering such questions is the task of a lifetime. Two difficulties thwart easy answers. First, it is not possible to associate a particular feature with a particular expression. If you could, there would be plenty of information telling you, for example, the exact effect of various overhang designs. The meaning of a detail depends on its context. A given roof under different sets of circumstances can give multiple different looks and impressions, like a hat, or a head of hair. The second reason we can’t work up simple formulas is that the "expression" we are seeking is not a bunch of words, like "Beautiful" or "light" or "sober" or "delicate" but something visual and tactile that defies expression in words. That is why artists (architects are artists, too) often resort to poetic language to explain the intent of their work. Hard and Fast rules may be impossible, but we can make some progress toward understanding how to make building features expressive, through examples. Manipulating a Simple Idea Walls and roofs are doing different visual things, because they have different relationships to gravity: Walls push up against the force of gravity while roofs press down on the walls. If you visually express this simple idea, you are in sync with what is going on physically, and this gives you a leg up in your detailing. So it is with a bungalow, which expresses a realistic idea: The roof is so heavy that it is all the walls can do to hold it up. The low eaves express that the roof is almost too heavy to lift, and the long overhangs dramatize the effect, maybe to the point of melodrama, by making the roof appear even bigger than it is. Now simple is not always better. We have remarkable abilities to hold subtle contrasts in mind, and we enjoy the mental games required to balance conflicting images. Visually, brackets and exposed rafters say a bunch of contradictory things. They are needed because there is a lot of weight to hold up. However, the roof is lighter because he have eliminated its mass and replaced it with a skeleton. The skeletal, bracketed roof is more like the way animals and plants are made and less like a rock, so we can say with justification that it is more "organic". A Drama of Contrasts, What if we Sharpen the pitch? Much of the gravity of the bungalow design depends on the low pitch: The roof seems so hard to lift that we could only get it up a little. The gable under a steep roof has a lot more energy, "achieving" more by elevating the ridge much higher.

Roof forms are developed for practical and visual reasons. In many instances, those forms become associated with specific styles. Sadly, this has led designers to choose a roof form because it "looks authentic" or because it creates a particular effect. I prefer to look at roof forms as a kit of tools, there for our use, with nothing to prevent us from mixing and recombining them, as the designers of the late 19th century were wont to do. Design a roof to enclose living space, in contrast to a roof that simply sits above the top floor like an inappropriate hat. Roof Form follows wall height, when designing multistory homes, It is often necessary to check for head room at the outside wall. The height of the outside wall is the most important factor in working out the roof. For example, a staircase might rise up along an outside wall, then turn to clear the roof. Working between section and plan views, You would have to determine how many stair risers fit before the headroom ran out.

What About the Cracks in the Timbers?

People who are experienced with wood are familiar with the term checking. For the benefit of those who do not know of this term it refers to the natural linear cracking which occurs during the drying process of larger timbers. Checking occurs when timbers dry and shrink faster on the outside than at the core wood. This can take place at any time in the life of a timber when it takes on large amounts of moisture but is most likely to occur in new wood being dried for the first time. As wood loses moisture to the surrounding atmosphere the outer cells of the members lose their moisture at a rate which is more rapid than the cells on the interior of the piece. As the outer cells lose moisture and try to shrink the inside core stays the same size causing the surface membrane to tear in order to allow the outside cells to shrink. The more rapid the drying rate the more likely the piece is to show checking. In sawn lumber and timbers controlling the rate of drying will eliminate or minimize checking. Many monumental buildings with great historical value have been constructed in such a way as to exploit the natural beauty of large sawn timbers. In these structures, seasoning checks are as an inherent part of the natural beauty of the structure and timberwork. One of the major advantages of utilizing a multi-ply beam system on the ridges and purlins of our Post & Beam homes is the fact that checking cannot penetrate through more than one individual member of the beam due to their individual grain patterns. Structurally checks affect the shear parallel to the grain strength of the lumber Therefore engineering of timberframe structures allows for this predicted and expected structural weakening therefore in a Post & Beam building when there are checks these have been allowed for in the engineering of the structure. All of which means you can relax and enjoy the individuality of your home without worrying about the structural integrity. The longer the wood has been in service the stronger it becomes therefore the checking should it increase in future years does not decrease the strength of the structure. Posts are not weakened to any measurable extent by checking there checks are strictly a visual concern not a structural one.

How important is my Foundation?

Most early deterioration problems arise when builders fail to recognize that the soil surrounding a foundation is responsible for the majority of foundation failures. Even foundations built with good materials and first rate workmanship will fail if poor soil conditions are not considered.

Preventing Frost Damaged Foundations

Water expands in volume by about 10% when it freezes, and can exert pressures of up to 80,000 pounds per square foot as it expands. If wet soil below a footing is allowed to freeze, significant heaving will occur, causing damage to the structure above. For a frost heave to take place, three conditions must be present:

  • 1. a frost-susceptible soil
  • 2. a source of water
  • 3. freezing temperatures
  • Eliminate any one of these conditions and you’ll eliminate frost heave. To avoid frost heave in colder climates, footings are placed below the frost line. But this alone doesn’t prevent frost problems altogether. Soil tests and good drainage are the best protection against settlement and frost heaves

    What About Foam Block Foundations?

    The makers of foam foundation forms want you to believe that the fourth little pig, had there been one, would have built his house out of polystyrene and concrete. Flip through any building magazine and you’ll find that the manufacturers of rigid foam concrete forms are spending a bundle on ads extolling the virtues of their products. Is it time for you to jump in and try one of them? Maybe. Builders I have talked to have been very successful in their use and intend to keep on using them. But they also noted that foundations and walls built with foam forms cost more, and that using these products involved a learning curve. Most foam forms fall into one of three categories: molded, stackable blocks; sheet foam panels; and largecore molds. Stackable blocks typically have 2 or 3 inch thick expanded polystyrene sidewalls held apart by molded foam crossmembers, or plastic or metal braces. They interlock with teeth, grooves, or Lego-like knobs. Horizontal rebar is laid over the metal or plastic cross-members every one to three courses, depending on the product; vertical rebar spacing varies with the block design and the height of backfill. The finished assembly gets braced with 2 x 's and the concrete placed with a pump truck. Sheet foam systems resemble traditional concrete forms. They consist of 8 inch high by 4 foot long strips or 4 foot by 8 foot sheets of expanded or extruded polystyrene foam connected by plastic or metal ties (some builders report that the expanded poly is more dimensionally accurate and easier to work with). Concrete is poured into the space between the foam walls just as with wooden forms. You can place concrete without a pump truck, and you only need rebar where building codes or good construction practice would require it for a conventional foundation. Sheet forms can be ordered assembled from some dealers, or you can assemble them on site. Large sections are stitched together quickly at butt joints by wrapping polypropylene bailing twine around plastic tie plates. Mechanical ties are also available. Large-core molds produce what is essentially a concrete post-and-beam structure (Sounds Good to US!!!). The long cores in the foam block are aligned, then filled with rebar and concrete. Some of these cores run horizontally, some vertically. Large-core molds use less concrete than the sheet forms or blocks. Foam forming systems have simple but important rules that you’ll need to follow for a successful job.

    These include:

  • Securing wood guide plates to the footing
  • Starting lay-up at a corner
  • Staggering block joints
  • Stacking cavities directly above one another
  • Using adequate bracing
  • Bracing is one of the most critical elements of a good job. Requirements may vary dramatically between manufacturers so follow directions for the individual brand you are using. Though they don’t save money, stackable foam blocks form and insulate in one step. They are lightweight and cut with a handsaw. Polystyrene forms simplify foundation work, but you have to brace carefully, watch the concrete mix, and be prepared for small blowouts.

    Insulation Techniques

    Batts are carefully manufactured to have a specific insulating value as indicated by the rated R-value. To keep its R-value, however, a batt must not be compressed or crushed during installation. Batts should completely fill the stud cavity, fitting snugly against every piece of framing, the sheathing and the drywall. If they don’t fill the space evenly, or if they get crushed, you lose R-value. For example, when a standard 6 1/4 inch thick R-19 batt is compressed to fit into a 5 1 /2-inch-deep 2x6 stud cavity, its R-value drops to just under R-18. (although the R-value per inch of a batt actually rises slightly as it is compressed). Higher density batts are rated to deliver R-21 in 5 1 /2 inches. Voids are another common problem. Even tiny voids can cause heat loss, because they allow air to move around inside the stud cavity. If a batt is stapled to the sides of studs, crushed, or cut short, air can rise up the warm side of the cavity and fall down the cool side. Heat rides on this convective loop, actually traveling around the insulation, significantly eroding the R-value. That takes care of your everyday stud bays. But you also need to know how to deal with the pipes, conduits, wires, and other obstacles that potentially cause breaks or crushed insulation.

  • Electrical boxes - To prevent compression. First, work the batt behind the box. Then slice into the batt around the box so that the fiberglass can fluff up to each side of it. When you finish, only the material behind the box is actually compressed.
  • Narrow bays - To insulate undersized cavities, cut the batt for a tight fit. Crushing a batt into place will inevitably leave voids.
  • Plumbing bays - Some places are too tight for batt insulation to do a good job. Use foam board to insulate behind plumbing, electrical panels, and heating ducts in outside walls. Cut the foam to fit precisely, or use foam sealant around the edges.
  • Wiring - Electrical wires are common obstacles to a good insulation job. It’s tempting to shove the batt behind the wire, but that crushes much of the insulation and leaves voids. There are two easy ways to fit batts around electrical wires:
  • If the wire is near the end of the batts, split the batt by hand and drop it over the wire. Ask that the electrician help out by running the wires about 4 inches above the plate.
  • If the wire is not near the end of the batt, cut the batt about half way through at the same height as the wire.
  • Vapor barriers - One essential element of the moisture protection system is a vapor Barrier. Vapor barriers help protect wall framing from decay caused by condensation. There are several types of vapor barriers to choose from. Be careful to install the vapor barrier in a way that doesn’t interfere with the wall insulation. There are three installation options:
  • Face stapling - Staple the flanges of Kraft-paper or foil-faced batts to the surface of the stud facing the inside of the house. Side-stapling compresses the insulation.
  • Friction Fit - Since the new high-density batts are more rigid than older batts and won’t settle over time, there is no need to staple the flanges at all. This saves installation time and allows drywallers to use panel adhesive on the face of studs.
  • Plastic sheets - Some insulators prefer to install unfaced batts and staple up clear 4- or 6-mil polyethylene sheets. Staple the plastic to the top and bottom plates. At seams, overlap the sheets 3 inches and staple both sheets to a stud.
  • Polystyrene Insulation

    Granby utilizes the dual zone insulation technique when designing our homes this technique allows for R-11 or R-12 of fiberglass insulation in the 2x4 wall system. As well as R-5 to R-8 of Polystyrene sheet insulation over the exterior of the wall. This system keeps the wall warmer than a single zone insulation of the same R-factor. Prevents cold spots at the location of the studs and posts, electrical boxes panels etc. The polystyrene ensures that the cold air cannot invade at the places where the fiberglass insulation gets inadvertently bunched or compressed. The second advantage of dual zone insulation is that the heat loss due to convection within the wall is cut down severely. This can occur in a fiberglass insulated wall which has been allowed to retain any of its airspace or where the fitting has been less than perfect.

    EPS is Expanded Polystyrene, a downstream petrochemical product from styrene Monomer, which in turn is made from benzene and ethylene in a weight ratio of three parts to one. EPS beads are composed of a styrene polymer containing a blowing agent and which will, when subjected to heat, expand up to 40 times their original volume. Expanded polystyrene consists of in excess of 96% air and is therefore an excellent, lightweight insulation material. Following expansion, the beads can be either directly shape mounded into special products, or molded into blocks. After a suitable curing time blocks are cut into sheets. One of the outstanding properties of EPS as a building material is its excellent thermal resistance. It has a maximum R Factor of 0.61 to 0.74 per 25 mm thickness. Because EPS insulation has a cellular structure containing only stabilized air, because it has a low moisture vapor transmission rate, because it is dimensionally stable and does not "settle", and because it is dust free, it will not deteriorate over time but retain its original insulation value. EPS delivers constant R values for the life of the building. EPS is easy to install because of its light weight and because it is clean, is not irritating to the skin, it does not give off gases, and it can be cut on site with a knife or saw. Furthermore, EPS does not support bacterial growth and it will not rot or decay. As with all organic materials, EPS insulation products must be considered combustible, but they do not constitute a fire hazard if properly used or installed. The material contains a flame retardant additive to inhibit accidental ignition from small fire sources. Extensive research programs have been conducted overseas to determine if thermal decomposition products of EPS present a toxicity hazard. The test results have revealed that these decomposition products are decidedly less harmful than those of burning wood and certain other conventional building materials. Gases released during combustion are predominantly carbon dioxide and, to a lesser extent, carbon monoxide. A current report comments that the toxicity of the gasses associated with the burning of EPS is no greater that those associated with timber. EPS has a low water vapor transmission rate. It has no capillary action. However, it must not be considered as a vapor barrier in the same sense as polyethylene film. It has excellent breath-ability characteristics and allows moisture to escape from a wall or floor element, and does not form vapor dams. In spite of the low moisture transmission rate, it is still proper to use a vapor barrier under conditions of high humidity and high temperature differentials. Normally, the vapor barrier should be installed on the warm side of the structural component, with insulation as near as possible to the cold side. Of all materials used for insulation applications, EPS is one of the most resistant to the adverse effects of moisture. Condensation, which may build up within any insulation material under critical vapor flow conditions, only marginally affects the thermal performance of EPS. Even if condensation develops through improper use EPS will retain its dimensional stability and superior insulation values.

    Manufactured Joist Information

    Now it's easier than ever to design and build better floor systems. You will have fewer problems with squeaky floors and ceiling sheet rock cracks. Manufactured joists are environmentally friendly due to their utilization of otherwise useless wood cuts. The manufactured joist system also means better overall floor and roof framing than dimensional lumber allows. Better Framing Doesn't Have to Cost More building with manufactured joists actually cost less than conventional framing methods when the resulting reduced labor and materials waste are considered. There is less sorting and cost associated with disposing of waste because you order only what you need. At the same time the longer lengths help you get the job done faster, while they cost no more. As an added Bonus manufactured joists are Environmentally Sound. Floor and Roof systems built with the manufactured Joists require about half the number of trees as those built with dimensional lumber. This makes your Granby a home both you and future generations will be proud to own. Floor and Roof Framing with manufactured joists makes sense as they are Light in weight, but heavy-duty, manufactured Joists have a better strength to weight ratio than dimensional lumber. Knockouts can be removed for cross-ventilation and wiring. Ceilings Framed with manufactured joists are more trouble free due to the consistent size of the joists. This consistency helps keep sheet rock flat and free of unsightly nail pops and ugly shadows, while keeping finish work to a minimum. The dimensional stability of wood I-joists and their resistance to deflection convinced us to use them. Wood I-joists take some getting used to. While they perform better than sawn lumber in most cases, wood I-joists require special attention in handling, cutting, fastening and bracing. Here are some of the things we’ve learned in years of working with them. Storage and Handling require special attention. You need to handle wood I-joists carefully, beginning with the way they’re stored on your site. The availability of long lengths is one of the attractions of using wood I-joists. Please keep wood I-joists on edge while moving or storing them. Because if they’re handled while lying flat (both individually and in bundles) they can bow severely. This is especially true when long I-joists are lifted at the center with a standard forklift. Severe bowing, even for a short time, can cause splits in the flanges and webs that weaken the structure of the joist. Plan to be on hand while they’re loaded and unloaded. At the site, keep the stack of joists off the ground with a 2x4 every 8 feet or so. Stack the joists on edge (one next to the other or nested) and nail a 2x4 or a piece of strapping across the tops to keep the whole row from falling over). Finally, be sure to cover the stack to protect the joists from the weather: Wood I-joists are more susceptible to water damage than sawn lumber. Crosscutting a wood I-joist is tricky because the surface isn’t flat. Try using scrap plywood to make a two-layer template that can be inserted during the cut. Manufactured joists once in place have marvelous Longevity and are a suitable joist for a post and beam Timberframe home where the frame can last for centuries. ***