ROOFS

Posted by on 21/ 11/ 15

I was in an office-supply house recently when a customer brought in a type­writer for repair. Folks were joking with him, wondering what he was doing with a typewriter in this time of computers. These days, in the world of roof trusses, cutting and building simple gable roofs on site has almost gone the way of the typewriter. Nevertheless, I still love the challenge of cutting and building (we call it stacking here on the West Coast) conventional stick-built roofs, whether the roof is a simple gable or a complex one with many different ridges, hips, and valleys coming together from every direction.

Now, of course, even the most compli­cated roof can usually be made by a truss company and shipped to the site ready to install. Trusses are labor-saving devices, and when you raise a truss in place, you are installing a ceiling joist and a roof rafter at the same time. Another nice part about working with trusses is that they are made from light­weight, kiln-dried lumber, so they’re lighter, easier to handle, and friendlier to the back. But be careful of the metal plates or gussets that hold trusses together. These are very sharp.

The main challenge in building most truss roofs is working high off the ground. An experienced carpenter can work off the ground like a space walker, often standing on a wall plate that is only ЗУ2 in. wide. Most of us can also learn how to do this, but as a beginner, go slow, take your time, and be careful. With practice, it becomes easier. If being up high on a wall is scary, work off a ladder or a scaffold and follow the safety guidelines on p. 123.

Where I live on the Oregon coast, simple gable roofs are found on about 70% of the houses, including mine. Other roofs aren’t quite so simple, but like learning to walk, learning to build a simple gable roof is the first step toward building those more complicated ones. What fol­lows are guidelines for building a simple gable roof, both with trusses and with conventional framing.

Cool Design for a Comfortable Home

Posted by on 21/ 11/ 15

■ BY SOPHIE PIESSE

Cool Design for a Comfortable HomeПодпись: Passive in practice. The author's house demonstrates passivecooling strategies that include east-west orientation, overhangs formed both by eaves and a second-floor balcony, and a vertical design that promotes good ventilation.

I live in North Carolina, and I love the look on people’s faces when I tell them that I haven’t turned on my first-floor air­conditioning in 10 years. There’s always a pause, and then they lift their jaw off the floor and ask me, "Really? How?"

As an architect who designs new homes, renovations, and additions, I encourage my clients to explore options for passive heat­ing and cooling and energy-smart design before we ever look at mechanically assisted options. To make your house truly energy – efficient, you must design it with the goal of using as little energy as possible. It’s great when people get excited about adding solar hot-water panels and photovoltaic systems, but before exploring any of that, you should first look at how you can design your new home or alter your existing home to reduce its energy needs. When your house natu­rally needs less energy, you can use smaller mechanical systems to support it. This saves money both up front and in the long run.

Passive Solar vs. Passive Cooling

When we talk about passive-solar design, we often focus on how it can help to heat your home. Passive-cooling design is really the opposite side of the same coin, using the properties of the sun to promote cooling rather than heating.

Passive-solar design can cut heating bills, but in the South and in many areas of the country, keeping your house cool in the summer is a bigger concern. Here, passive­cooling strategies become more important, and more economical. These simple design elements can save you hundreds of dollars every year in energy bills and also make your house more comfortable to live in.

Passive cooling refers to nonmechani­cal ways of cooling your home. It focuses on orientation and shading, air movement, thermal mass, and a tight building envelope. All these strategies can be complemented by mechanical means—from air-conditioning to ceiling fans—but these passive elements can also work successfully on their own.

While the potential for saving energy with any design-focused strategy is greatest when you’re planning a new house, several of the techniques I describe can be used when renovating or adding to an existing home. You may not be able to pick up your house and face it in another direction, but you can add shade structures and window overhangs, relocate window openings, and mitigate nearby "heat islands" (such as a driveway baking in the midday sun), all of which enhance your home’s ability to main­tain a comfortable temperature with less mechanical intervention.

So let’s take a look at how your house can work with the environment. By designing your home to work with nature instead of against it, you can benefit from lower energy bills, better daylighting, and greater indoor comfort.

Sweaters, Windbreakers, and Rain Gear

Posted by on 21/ 11/ 15

Don’t worry; we haven’t suspended our home­building work to look through the L. L. Bean® catalog. But what you already know about sweaters, windbreakers, and raincoats will help you understand the way sealing, insulating, and moisture-protection treatments work together in a house.

Start with a sweater and a windbreaker—just what you need to wear on a cold, windy day. A house exposed to frigid temperatures and icy winds also needs a sweater and a windbreaker. Insulation, exterior siding, and housewrap provide this protec­tion. In fact, housewraps like Tyvek and Typar act like a Gore-Tex® raincoat, blocking wind and water while still allowing vapor to pass through. This helps prevent moisture buildup, both in our clothing and inside the walls of a house.

As we work through the steps ahead, you’ll see that there are different sealing, insulating, and ventilation tasks that need to be done at different stages of the construction process. Pay attention to the tasks associated with each phase
of construction and your house will repay you with maximum levels of comfort, longevity, and energy efficiency.

Beyond Rome, The East And The Arab World

Posted by on 21/ 11/ 15

Beyond the Roman Empire – Persia and India

Between the Tigris, the Ganges, and the Oxus: multicultural influ­ences

The Indus valley had harbored the great “hydraulic” civilization of Harappa between the third and second millenia BC. This civilization would develop to have exchanges with the Mesopotamian millenia, and had extended its influence along the “lapis-lazuli route”, to the north of the Hindu Kush mountains in Bactria (Figures 1.3, 7.1). After the collapse of this civilization only the trading posts to the south remained, at and around the mouth of the Indus at Lothal. Development later continues in the Bactria – a pros­perous civilization grows on the banks of the Oxus and its tributaries, a civilization that uses gravity canal irrigation in the cultivation of terraces overlooking the rivers (Figure 7.2).

The ancient Indian civilization grew from Indo-European (Aryan) migration from the northwest in the middle of the IInd millennium BC. The earliest Vedic texts, written in Sanskrit around the 6th century BC, give us our earliest distinct portrait of the devel­opment of this civilization. The birth of Buddha is placed in this century at about 560 BC.

After the fall of the Persian Empire and the death of Alexander, all of the region from Mesopotamia to the borders of India becomes the domain of Seleucos, one of Alexander’s generals, and then of his descendents the Seleucids. In India itself the Maurya Dynasty, 313 to 180 BC, includes a period of unification from the Ganges to the Indus under the grand sovereign Afoka (about 269 to 232 BC). The development of writing first appeared in his reign, as did the humanistic principles inspired by Buddhism. Only the extreme south of India and Ceylon (modern-day Sri Lanka) are not included in this unification.

Around 250 BC the Parthians from the north of Iran push the Seleucids back toward Syria and settle in Mesopotamia. In so doing, they isolate Bactria and Sogdiana from the rest of the Hellenistic world. This is the beginning of the Greek kingdom of Bactria, destined to spread Hellenistic culture toward India. Around 200 BC, Bactria’s king Euthydemus and his son Demetrius set out to conquer large regions of India. These Indo-Greeks were subsequently pushed back out of Bactria by a people who are known to us through Chinese history as the Yuehzi. The Chinese, pushed to the north by the Xiongnu (fellow nomads of unsavory reputation and who were likely the ancestors of those whom we now call the Huns), try to form alliances with the Yuehzi. In the 1st cen­tury BC, the Yuehzi found the empire of the Kuchans, occupying all the high valleys of the Ganges and the Indus up until the 2nd century AD. The stability of the great empires across these centuries – Rome to the west, the Parthians and the Kuchans in Asia, the Chinese empire of the Han Dynasty to the east – favors development of the Silk Road.

Meanwhile in Ceylon there are many signs of active commerce with Roman merchants.

The power of the Arabs rises in the near east during this time. In 640 AD the Arabs take Alexandria, occupying Egypt and destroying the Sassanide Persian Empire that had supplanted the Parthians from the 4th century BC. Having been confined to the Indus for a long time, the Arabs occupy Sind as well as Samarcand in 712, and in 751 they affront the Chinese armies on the Talas River to the northeast of Samarcand, in the loop of the Iaxartes (today the Syrdarya). This was an Arab victory in principle, but in reali­ty it marked the end of their expansion toward the east. With the decline of authority of the caliphs of Baghdad, the Ghaznavid Turks become the masters of Persia at the end of the 10th century AD. India collapses under their blows around 1000 AD, and all the north of the country is pillaged. Then successive waves of Mongols sack Mesopotamia in 1258 AD, and continue to ravage the north of India as far as Delhi in 1398 AD. Turkish-Mongol regimes control the sultanate of Delhi from the 13th century AD, and control the entire northern half of India until the 17th century, including the Ganges and Indus valleys.

Beyond Rome, The East And The Arab World

Figure 7.1 From the Syrian coast to the heart of China, in the ancient and medieval eras. Cities whose names are underlined are the great capitals: Ctesiphon for the Sassanide Persians, Balkh (Baktria) for the Greek kingdom of Bactria, Damascus and Baghdad for the Ummeyyades and the Abbassids, Pataliputra (Patna) for the India of the Mauryans and the Guptas, Delhi for the Turkish sultanate that dominates the north of India in the XIIIth century, Chang’an for China of the Han and Tang dynasties.

Figure 7.2 Irrigation of the plain of АЇ Khanoun in eastern Bactria, at the confluence of the Oxus (Amou Daria) and the Kokcha. АЇ Khanoun was probably the Alexandria of the Oxus. The map shows the population patterns and the traces of the principal irrigation canals during the time of the Greek kingdom of Bactria. These principal canals rise from the Kokcha and run along the plateau toward the north. The Oxus flows in an adjacent lower course, 20 m below the irrigated plain, which is why its water could not be used. After 37 centuries of irrigation using this same basic layout of canals, the plain returns to desert after the Mongol invasions of the 13th century AD (Francfort, 1989; Gentelle, 1989; Gardin, 1998). For an overview map, see Figure 1.3.

a. Beyond Rome, The East And The Arab WorldCanal trace dating from the Bronze Age (IIIrd millennium BC) passing by the Harapan site of Shortughai. It supported irrigation of 6,000 hectares of barley, wheat, lentils, and sesame.

b. Canal developed before or during the time of the Persian Empire (Figure 2.20)

c. New canal built in the time of the Greek kingdom of Bactria. It brings the irrigated area to

16,0 hectares. It is abandoned, and then restored with the same general alignment during the Islamic period.

Constitutive Modelling and Partial Saturation, Suction Coupling, Water Interaction on Mechanical Behaviour

Posted by on 21/ 11/ 15

Routine pavement design is based on an elastic calculation, with a resilient modulus. The design criterion is, typically, a limit placed on the maximum vertical strain. More elaborated models take into account the irreversible behaviour, e. g.:

• The Chazallon-Hornych model is based on the Hujeux multi-mechanism yield surface improved by a kinematical hardening; and

• The Suiker and Mayoraz elasto-visco-plastic models evaluate the irreversible strains on the basis of an overstress (Perzyna theory) which is the distance be­tween the stress level and a visco-plastic potential.

Each of these elaborated models is then based on a yield surface, a potential surface, a limit surface, in all cases a surface typical of the granular soil mechanics, with a frictional mechanism, possibly a cap contractive mechanism, a dependency not only on the shear/von Mise’s stress but also on the mean stress (p — q plane), and on the Lode angle.

How can we adapt these models to take into account the suction variation effects? For routine pavement design, only the elastic moduli need to be adapted. For the higher-level models, the yield surface and hardening mechanism also need to be adapted.

During the two last decades a number of models for partly saturated soils have been proposed (forareview, see e. g. Laloui etal., 2001). Most of them are based on the suction as an additional variable, with the same status as the stress tensor.

The so-called Barcelona Basic Model – BBM, proposed by Alonso et al (1990) is probably one of the best known. It is now the reference for most new develop­ments in mechanics of geomaterials under partial saturation.

The BBM is based on the well-known CamClay model. It is written within the framework of the independent stresses state variables p — q — s defined in Section 9.5.

The BBM yield surface depends not only on p — q stresses but also on the in­dependent stresses state variables p — q — s. Two lines are added with respect with the modified Cam-Clay model. On a wetting path (a loading path along which the suction decreases), the Loading-Collapse, LC, line allows a normally consolidated material to support irreversible plastic strains and hardening, and the plastic slope to depend on the suction level (as there will be an increase of stiffness with suction). For low stress level, the cohesion only depends on the suction level. For the case illustrated in Fig. 9.10, a capillary cohesion is postulated, which depends linearly on the suction. Eventually, under very high suction (a consequence of the drying process) irreversible strains may also occur. This is at the plane SI in the figure – the suction increase surface.

However, neither do the BBM, nor the other published models, introduce any suction dependency into the elastic moduli formulations.

From this illustrative model, it appears that building a coupled model for re­peated loading and suction variation on granular soil material needs the following developments: [23]

• Using the generalised effective stress or the net stress approach allows develop­ing coupled moisture – mechanics models to be developed.

• For any development an experimental basis will be needed to calibrate and vali­date the models.

9.5 Conclusions

This chapter deals with the constitutive modelling of the effects of water on the me­chanical behaviour of pavements. It has been shown that routine pavement design is based on an elastic calculation, with a resilient modulus. The design criterion is, typically, a limitation of the maximum resilient vertical strain. Such design ap­proaches do not model in a realistic manner the observed irreversible behaviour seen as rutting and as other forms of distress. To achieve a design approach that can replicate more closely the observed behaviour is likely to require use of the concepts of elasto plasticity and visco-plasticity. More elaborate models of soil and granular material will be needed to take into account these concepts and several approaches have been reviewed that attempt to do this.

At present few of these newer approaches explicitly include the effect of wa­ter pressures and suctions within the soil or aggregate pores, so the chapter has discussed how the available constitutive models could be improved to take into ac­count suction and suction variation effects. Some research topics have, also, been suggested to enable further development.

INSIDE

Posted by on 21/ 11/ 15

Sealing, Insulating, and Ventilating a House

The old house I was born in still stands out there on the prairie. When I was a child, the house was simply unheatable in the wintertime. We defi­nitely spent more dollars trying to heat the house than we did on the mort­gage. Nowadays, the house has new doors and windows, insulation in the ceiling, and a real heating system—not just an old iron stove in the kitchen. But there are still plenty of cracks and gaps in the walls for those ever­present western winds to howl through.

Thankfully, we don’t build houses like we used to. Today, there are materi­als and methods available that allow us to design and build energy-efficient houses that hold heat during the winter and keep it out during the summer.

But attaining high levels of comfort and energy efficiency is not always a simple feat. In fact, it can be the most technically complex aspect of building a house.

The products that we use to seal, insulate, and ventilate houses may do more harm than good if they’re not installed correctly. Common problems include poor indoor-air quality, peeling paint on interior and exterior surfaces, moldy bathrooms, and rotten wood in walls and ceilings (see the photo on p. 196). Sometimes we solve one problem (such as cold air infiltration during winter months) and cause another (high concentrations of stale, humid indoor air, for example). And thanks to the significant climate differences in this vast country of ours, what works in Maine may be ineffective in Texas.

INSIDEINSIDEПодпись: 1 Seal Penetrations in the Walls, Ceilings, and Floors p. 196 2 Insulate the Walls, Ceilings, and Floors p. 200 3 Install Vapor Barriers (if Necessary) p. 207 4 Provide Adequate Ventilation p. 210 INSIDEAlthough there is no standard approach to building a tight, comfortable, and energy-efficient house with good indoor-air quality, it’s not difficult to achieve those goals if you understand how a house works in terms of insula­tion, airtightness, and ventilation. This is especially true with the basic, afford­able houses that Habitat builds. This chapter explains the concepts, materials,

Подпись: Habitat houses are affordable now and later. At Habitat, we believe that affordable housing goes beyond cost- effective construction using durable materials. A house should be afford-able to build and affordable to maintain. Energy efficiency is a must. A house that costs hundreds of dollars to heat and cool is not affordable. Подпись:

and techniques to make your house comfort­able, healthy, and energy efficient no matter what the temperature is outside. To expand your knowledge, see Resources on p. 279.

Before we dig into the technical details, here’s a final thought to keep in mind as you tackle the sealing, insulation, and ventilation work on your building project: Try to keep everyone aware of these important issues.

When houses were built with simple materials, they were both leaky and energy inefficient. People working in the trades didn’t really need to understand the work of those preceding or following them. To build a safe, energy – efficient, nontoxic house, everyone involved in its construction must have more knowledge and work together. Otherwise, a house that was perfectly sealed and insulated can be left riddled with holes by a plumber, electrician, or heating contractor who was “just doing his job.”

Effective Stress Approach

Posted by on 21/ 11/ 15

The constitutive models introduced in the previous sections express the constitutive stress-strain relation of the material. As soon as the water is involved, the material has to be considered as a multi-phase porous media with two phases: the solid matrix (for which we introduced the stress-strain constitutive relations) and the water phase. The two phases are coupled since the pressure acting in the water may affect the mechanical behaviour of the material. Also, the material deformation may modify the pressure in the water. Such hydro-mechanical coupling is well represented by
the Terzaghi effective stress concept for saturated conditions (when water is filling all the pores) (Terzaghi, 1943). It shows the importance of the consideration of the water phase in the analysis of the mechanical behaviour of the material.

In the case of non saturation (water is no longer filling all the pores) the effective stress, expressed as a function of the externally applied stresses and the internal fluid pressures, converts a multi-phase porous media to a mechanically equivalent, single-phase, single-stress state continuum (Khalili et al., 2005). It enters the elastic as well as elasto-plastic constitutive equations of the solid phase, linking a change in stress to strain or any other relevant quantity of the soil skeleton; e. g. see Laloui et al. (2003). As a first approximation, let us consider a force Fn applied on a porous medium (constituted by a solid matrix and pores) through an area A. In this case, we can define a total stress:

If we consider only the part of the load acting on the solid matrix (and deforming it), we may define an effective stress as the part of the load acting on the solid area (XSi) (Fig. 9.9):

The effective stress may be simply defined as that emanating from the elastic (mechanical) straining of the solid skeleton:

ee = Cea’ (9.18)

in which ee is the elastic strain of the solid skeleton, Ce is the drained compliance matrix, and a’ is the effective stress tensor.

In a saturated medium, the effective stress is expressed as the difference between total stress, a, and pore water pressure, u (Terzaghi, 1943):

Fig. 9.9 An illustration of inter-granular stresses

a’ = a — u (9.19)

In an unsaturated granular material with several pressures of different fluid con­stituents, the effective stress is expressed as:

n

a’= a — ^2 amumI (9.20)

m = 1

in which am is the effective stress parameter, um is the phase pressure, and m = 1, 2,… n represents the number of fluid phases within the system. I is the second order identity tensor. This equation is close to the one of Bishop (1959) for a three – phase material (solid, water and air):

a’ = (a — Ua) + X (Ua — u) (9.21)

where u is the pore water pressure, ua is the pore air pressure, x is an empirical parameter, which has a value of 1 for saturated soils and 0 for dry soils. It represents the proportion of soil suction that contributes to the effective stress. Several at­tempts have been made to correlate this parameter to the degree of saturation and the suction (Bishop, 1959; Khalili & Khabbaz 1998). As the parameter x seems path-dependent, several authors, starting from Bishop and Blight (1963), proposed the use of two sets of independent “effective” stress fields combining the total stress a, and the pore-air and pore-water pressures, ua and u (Fredlund & Morgenstern, 1977). In the literature the net stress a = a — ua and the suction 5 = ua — u are com­monly chosen (Alonso et al, 1990). In general, this net stress concept will be defined in invariant terms using the independent stress variables p(= (ai + a2 + a3)/3), q and 5.

Another way to describe the behaviour is to use the “saturated effective stress” a’ = a — uw and the suction, 5 (Laloui et al., 2001). This combination has the advantage – among others – of permitting a smooth transition from fully saturated to unsaturated condition.

Continuing with the approach having two sets of independent stresses, the strain rate obtained for the elasto-plastic behaviour may be decomposed into elastic and plastic parts:

є ij = єу + єp

each of which results from mechanical and suction variations, as follows. The elastic increment єe. is composed of a mechanical and a hydraulic strain increment:

(9.23)

where ej is the elastic mechanical strain increment induced by the variation of the effective stress a’, 1 eevh is the reversible hydraulic strain increment, Ee is the classical elastic tensor and к is a proportionality coefficient which describes the hydraulic behaviour.

Similarly the plastic strain increment is also deduced from mechanical and hy­draulic loads by considering two plastic mechanisms derived from two yield limits:

(9.24)

pm

Where eij is the mechanical plastic strain increment, associated with the mechani-

1 ph

cal yield surface and з eV is the hydraulic plastic strain increment, associated with the hydraulic yield surface.

Using an effective stress approach together with the non-linear models presented in the preceding section allows users to partly take into account the moisture varia­tion effects on mechanical behaviour. However, more fundamental modifications are probably needed. The next section indicates some tools to advance in that direction.

Unidirectional Slip Bases

Posted by on 21/ 11/ 15

Unidirectional slip bases for small sign supports consist of inclined slip bases, as shown in Fig. 7.18. The upper support piece is made from rolled-steel shapes, standard pipe, or structural tube. The base of the support assembly is inserted into a concrete footing to prevent movement of the anchor assembly.

The upward thrust obtained from the inclined slip base design is important to the proper action of a single-support sign system. The upward thrust causes the sign panel and support to rise and rotate when vehicle impact separates the mechanism. The sign panel and support stay together as a unit, which passes up and over the vehicle and lands behind it. This action is obtained only when the support is impacted from one direction. An impact from the opposite direction actually pulls the sign support down­ward, causing the support and sign panel to rotate toward the vehicle. Inclined slip bases should not be used where impact from more than one direction is expected. Horizontal slip bases will separate when impacted from the front or the rear but will not provide the uplift capability obtained from inclined-base designs. A typical design for an inclined slip base is provided as Fig. 7.19.

Horizontal slip bases, discussed in Art. 7.5.2, are not recommended for single sign supports. When impact can be expected from more than one direction, a multidirec­tional slip base design should be used.

CEILING JOISTS FOR A GABLE ROOF

Posted by on 21/ 11/ 15

The saying, "They don’t build them like they used to," is often true when it comes to ceiling joists. And it’s just as well. I have remodeled many an old house that had ceiling joists that were sagging from the weight of time and heavy plaster. If you live in an old house,
look at your ceilings—especially in large rooms—-and check to see if they sag in the center.

Once the walls have been plumbed and lined, ceiling joists can be nailed to the tops of the walls in preparation for installing roof rafters (see the drawing on p. 132). In factory-built roof trusses, joists are part of the truss (see Chapter б for more information on roof trusses). Joists nail to the top plates of the walls and help tie the house frame together. Roof rafters nail into both the plates and the joists, forming a truss that helps keep the roof from sagging under heavy loads like wet snow.

CEILING JOISTS FOR A GABLE ROOF

Laying out joists

Lay out the walls for joists just like you laid out the rim joists for the floor (for more on this, see Chapter 4). Hook a long tape on the end of an outside wall and mark 1 б in. o. c. (or 24 in. o. c.) the length of the building. Just like the floor joists, make an X beside the mark to show where the joist will nail.

Joists tie into the roof rafters and some­times need to be trimmed a bit to follow the slope of the roof. If you are using 2×8 joists and 2×6 rafters, for example, the joist ends need to be clipped, as shown in the drawing above. Otherwise, they’ll stick up above the slope of the roof. Remember to mark and cut your ceiling joists with their crown up.

Use a 2×6 for the first ceiling joist, laying it flat on the end wall. If the end wall is built of 2x4s, cut notches 1V2 in. wide and 20 in. long in the ends of the 2×6
and nail it flush to the outside. As shown in the drawing above, the notches leave room for the first set of rafters to be nailed to the plates. If the end wall is of 2×6 construction, nail a 2×4 flat onto the plate, ЗУ2 in. in from the outside. This leaves room for 2×4 gable studs to be nailed under the rafter. The part of the flat 2x that hangs over the inside edge of the plate provides backing for ceiling drywall.

Installing joists

With the crown side up, start nailing the joists on edge at each layout mark with a 16d toenail in each side. Where joists lap over an interior bearing wall, nail them together with two 16d nails and toenail them to the wall with one 16d nail on each side. A joist that passes over any other wall is secured to the plate with a 16d nail on each side. This helps hold the building plumb and strengthens the entire structure.

Catwalks are seldom required by code. They are usually a 1×4 or 1×6 nailed flat to the ceiling joists in the middle of the span (see the photo on p. 140). They help keep joists upright, free from twists, and properly spaced and also make it safer to walk when stacking roof rafters. Mark a layout at either 16 in. o. c. or 24 in. o. c. on the catwalk before securing it with two 8d nails per joist.

When joisting for a second floor or any ceiling that will be covered with drywall, backing has to be nailed on all walls that run parallel to the joists. Usually this can be accomplished by nailing a 2×6 flat on the top plate of a 2×4 wall and letting 1 in. hang over on both sides. Or you can nail a 2×4 on top of the plate (see the drawing at right). This is a good place to use up shorter pieces of 2x stock, crooked studs, badly crowned joists, and lumber with large knots. Nail the backing down every 16 in. with 16d nails directly over the wall studs.

Framing headouts in ceilings

A joist or two will have to be cut to allow access to the attic. Most codes require this access to be at least 30 in. by 30 in. I like to put these access holes in an out-of-the way place, like in the ceiling of a closet.

Once the ceiling is joisted, lay out the location of the access hole right on the joists, allowing an extra 3 in. to leave room for the 2x header joists (see the drawing at right). Support the joists that will be cut by nailing a flat 2x across sev­eral joists, then make the cuts in the ceiling joists and nail in the headers. Cut 141/2-in. blocks to nail to the header between the joists to help support the cut joist.

Подпись: INSTALLING DRYWALL BACKING Подпись: FRAMING AN ATTIC ACCESSCEILING JOISTS FOR A GABLE ROOFOnce the walls and ceiling joists are in, you’re ready to turn your attention to the roof.

Sealing, Insulating, and Ventilating a House

Posted by on 21/ 11/ 15

THE OLD HOUSE I WAS BORN IN STILL STANDS out there on the prairie. When I was a child, the house was simply unbeatable in the wintertime. We definitely spent more dollars trying to heat the house than we did on the mortgage. Nowadays, the house has new doors and windows, insulation in the ceiling, and a real heating system— not just an old iron stove in the kitchen. But there are still plenty of cracks and gaps in the walls for those ever-present western winds to howl through.

Thankfully, we don’t build houses like we used to. Today, there are materials and methods available that allow us to design and build energy-efficient houses that hold heat during the winter and keep it out during the summer. But attaining high levels of comfort and energy efficiency is not always a simple feat. In fact, it can be the most technically complex aspect of building a house.

The products that we use to seal, insulate, and ventilate houses may do more harm than good if they’re not installed correctly. Common problems include poor indoor-air quality, peeling paint on interior and exterior surfaces, moldy bathrooms, and rotten wood in walls and ceilings (see the photo on p. 194). Sometimes we solve one problem (such as cold air infiltration during winter months) and cause another

1 Подпись: STEP BY STEPSeal Penetrations in the Walls, Ceilings, and Floors

2 Insulate the Walls, Ceilings, and Floors

3 Install Vapor Barriers (if Necessary)

4 Provide Adequate Ventilation

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Sealing, Insulating, and Ventilating a House

Подпись:Подпись: Helping HandПодпись: Habitat houses are affordable now and later. At Habitat, we believe that affordable housing goes beyond cost-effective construction using durable materials. A house should be affordable to build and affordable to maintain. Energy efficiency is a must. A house that costs hundreds of dollars to heat and cool is not affordable.

(high concentrations of stale, humid indoor air, for example). And thanks to the significant climate differences in this vast country of ours, what works in Maine may be ineffective in Texas.

Although there is no standard approach to building a tight, comfortable, and energy – efficient house with good indoor-air quality, its not difficult to achieve those goals if you understand how a house works in terms of insulation, airtightness, and ventilation. This is especially true with the basic, affordable
houses that Habitat builds. This chapter explains the concepts, materials, and tech­niques to make your house comfortable, healthy, and energy efficient no matter what the temperature is outside. To expand your knowledge, see Resources on p. 278.

Before we dig into the technical details, here’s a final thought to keep in mind as you tackle the sealing, insulation, and ventilation work in your building project: Try to keep everyone aware of these important issues. When houses were built with simple materials, they were both leaky and energy /«efficient. People working in the trades didn’t really need to understand the work of those preceding or following them. To build a safe, energy – efficient, nontoxic house, everyone involved in its construction must have more knowledge and work together. Otherwise, a house that was perfectly sealed and insulated can be left riddled with holes by a plumber, electrician, or heating contractor who was “just doing his job.”

Sweaters, Windbreakers, and Rain Gear

Don’t worry; we haven’t suspended our home – building work to look through the L. L. Bean catalog. But what you already know about sweaters, windbreakers, and raincoats will help you understand the way sealing, insulating, and moisture-protection treatments work together in a house.

Start with a sweater and a windbreaker— just what you need to wear on a cold, windy day. A house exposed to frigid temperatures and icy winds also needs a sweater and a windbreaker. Insulation, exterior siding, and housewrap provide this protection. In fact, housewraps like Tyvek and Typar® act like a Gore-tex® raincoat, blocking wind and water while still allowing vapor to pass through.

Materials CODE REQUIREMENTS FOR INSULATION

MOST LOCALES have an energy code that defines how well insulated your house must be. Check with the building inspector in your community for this information. Rather than requiring so many inches of fiberglass or rigid foam, these codes define insu­lation requirements in terms of R-value, or resist­ance to heat flow. The higher the R-value, the greater the insulating value. For example, code may require that exterior walls be R-ll or R-19. As it turns out, a 2×4 wall with fiberglass insulation designed for a 3V?-in. wall has an R-value of 11. A 2×6 wall with 5Уг-іп.-thick fiberglass has an R-value of 19. Don’t try to stuff R-19 fiberglass batts into a 2×4 wall, though. Carpenters say that’s like trying to stuff a 1000-lb. gorilla into a 500-lb. bag. It just doesn’t work.

Remember—code requirements set minimum standards. As far as building materials go, insulation is relatively inexpensive, so it’s often cost effective to install more insulation than what is required by code. A house with lots of insulation (in the attic, for example) will not only reduce your heating bill for years to come but may also save you money up front by reducing the size of the heating or cooling system you need to install!

This helps prevent moisture buildup, both in our clothing and inside the walls of a house.

As we work through the steps ahead, you’ll see that there are different sealing, insulating, and ventilation tasks that need to be done at different stages of the construction process.

Pay attention to the tasks associated with each phase of construction and your house will repay you with maximum levels of comfort, longevity, and energy efficiency.