Construction of a House Cont'd

Siding-
This house uses standard vinyl siding. The siding is made from thin, flexible sheets of plastic about 2 millimeters thick, pre-colored and bent into shape during manufacturing. The sheets are 12 feet long and about a foot high. You start at the bottom and the sheets interlock into each other as you go up. Because vinyl expands and contracts due to temperature and sunlight, it fits into deep channels at the corners and around windows and doors. The channels are deep enough that as the siding contracts it remains within the channel. The area extending out from the house under the roof is known as the soffit (parallel to the roof). The fascia boards are perpendicular to the roof. The soffit is perforated so that air can flow into the attic and up through the ridge vents to ventilate the attic. Note that all exposed fascia wood is capped with a sheet of painted aluminum that was bent into shape on the site. At this point, the house is "dried in," meaning that it is completely protected from rain. Now interior work can begin.

Plumbing-
Let's say you want to put a toilet in a house. Two-hundred or 300 years ago this was not an option -- everyone used outhouses. If you visit the governor's mansion in Williamsburg, VA, you will see that in the 1700s even England's high colonial governor used a pair of three-holer outhouses located at the back of the formal garden. Eventually, public water supplies and pressurized well systems allowed people to have indoor plumbing, and this allowed for the addition of indoor toilets. A toilet has to flush somewhere, so sewer systems evolved.
Why can't you run the sewer line from a toilet or a sink out of the side of the house so it spills on the ground? That certainly would be easy and inexpensive, but people learned fairly quickly that human waste spilled on the ground smells bad and leads to incredible disease problems. Septic tanks and sewer systems take care of this. The uniform plumbing code lists hundreds of rules for septic-tank installation. These rules ensure that tanks work properly over many years.
Once you have a septic tank in place, you can add sewer lines from the sink or toilet to the septic tank. Say you tried to put a pipe straight from the sink to the septic tank. The problem with this approach is that as the septic tank fills up with stuff, it produces a rather malodorous cloud of fumes. These fumes float from the septic tank up the sewer line to the sink and into the bathroom. Therefore, plumbing codes require a "P-trap" at every drain opening. You may have wondered why you find these funny loops of pipe under every sink in your house. The idea is that water gets trapped in the "P." This water blocks the fumes from the septic tank and keeps them from entering the bathroom. Unfortunately, a P-trap alone does not solve the problem because it turns out that the fumes in a septic tank are under pressure. The fumes simply bubble through the water in the trap and cause the same problem. Therefore, there is the concept of a vent pipe, which allows the pressure to escape. You may have wondered why houses have pipes sticking up out of the roof. They are vent pipes to relieve the pressure so that P-traps can do their jobs. It turns out that vents also break vacuums so water flows down the pipes faster. Besides covering P-traps and vent pipes, the uniform plumbing code specifies all sorts of other things:

• The required diameters for pipes
• The allowed materials for pipes
• The types of joints you can use
• The necessary supports for pipes
• The angle at which pipes must fall
• The longest distance for lateral pipes
• And on and on and on through hundreds of pages

When plumbers follow all the rules, they are able to create extremely reliable and safe plumbing systems. Over time, new rules get added as people realize funny little quirks and nuances. These new rules prevent problems in the future, and each one makes the code a little bigger and better. This is all a nice way to say that, even though plumbing looks simple in this section, there are many subtleties and nuances dictated by code that plumbers know and neophytes generally do not. (The same holds true for electrical systems, by the way.)

Construction of a House Cont'd

Porch-
The crew builds the porch, starting with the frame. The frame goes on top of short brick (or another sturdy material) pillars. Then a floor goes on top of the frame. That's it.

Windows and Doors-
Inside the house, things begin to look enclosed. The next step in enclosure is windows and doors. The windows and doors arrive in one shipment and are unloaded from the truck into a stack. Plastic stripping is stapled to the inside of all the window and door openings on the house structure. A common window used is a standard vinyl window. They are placed in each rough opening and stapled in place on the outside.

Roofing-
This house uses standard asphalt shingles for the roof. The first step is to cover the roof with building paper (tar paper) .The shingles then go on very quickly (sometimes in less than a day). There is a vent along the peak of all the roofs that acts as a vent to allow hot air travel up and out of the house. This object is called a ridge vent. This vent replaces the triangular "gable-end vents" found in older homes. Ridge vents give better circulation (especially when cathedral ceilings are used) and also prevent bats and squirrels from getting into the attic. The aluminum flashing keeps water away from the walls at the points where the shingles touch the walls. At the edge of the roof, the shingles are cut off with about 2 inches of overhang.

Construction of a House Cont'd

Roof-
Some houses use trusses for the roof framing. Trusses are pre-fabricated, triangulated wooden structures used to support the roof. The alternative is to build up the roof's frame with 2x8s and 2x10s. Trusses are quite common these days because they have five big advantages from the builder's standpoint:

• Trusses are incredibly strong.
• Because they are built strictly from shorter lengths of 2x4 lumber, they are generally a lot less expensive than the alternative.
• You can have just about any shape custom-built, and this allows interesting features like cathedral ceilings at low cost.
• You can span a large distance with a truss and the truss transmits all of the weight to the exterior walls. Therefore, none of the interior walls are "load-bearing," so they can go anywhere and are easily moved later.
• Trusses go up quickly!

From the homeowner's standpoint, the one big disadvantage is that you don't have any attic space. C'est la vie...
Trusses come in several standard configurations:

• "W" truss
• "M" truss
• "Scissors" truss
• "Gable" truss

Gable trusses are used at the ends of the roof (the outermost trusses on either end). The vertical pieces are 16 inches on center so that siding can be nailed on. The left-hand side will provide a cathedral ceiling over the living room. Scissors trusses are used for the front room, and M trusses are used over the garage. Gable trusses are used at the ends of the three rooflines. The trusses are fist stacked on top of the walls, either by hand or with a crane. These trusses went up in about four hours. They are on 24-inch centers. The trusses are tied to the walls with small metal plates. Once the trusses are up, the roof is covered in plywood or OSB, which gives the roof tremendous rigidity. There are two small custom roofs in this situation: the roof over the porch and the roof over the breezeway. Roof framing without trusses is actually fairly complicated. The angles found in anything but the simplest roof become intricate.

Construction of a House Cont'd

Floor-
The framing crew is the next group of people on the site. They start by building the floor (unless the house uses a slab foundation, in which case the slab is the floor). The floor starts with a sill-plate made of pressure-treated lumber in direct contact with the bricks of the crawl space wall. One interesting thing to note is that this house literally "sits" on the foundation -- it is not held on or bolted on in any way. Then the floor is constructed on the sill with 2x10 lumber. The brick posts hold a beam that runs down the center of the house. The beam is also built from 2x10 lumber (three pieces thick).All of the "joists" (as the 2x10s in the floor are called) meet on the center beam. (In many houses the meeting of the joists is somewhat better organized!) A funny little cantilevered section of the frame will eventually hold the fireplace. Once the floor framing is complete, it is covered with 1/2-inch or 5/8-inch plywood or OSB (oriented strand board). And the floor is finished.

Walls-
The framing crew next starts on the walls. Walls are assembled on the floor...
...and then raised into place. The wall is made of 2x4 lumber and covered on the outside with an OSB sheathing. Using plywood or OSB as the sheathing gives the wall rigidity -- you may have seen diagonal pieces used at the corners of older homes (homes built before plywood was widely available). The plywood does the same thing, but it provides much more strength.
The 2x4s are placed on "16-inch centers," meaning that the center of one 2x4 is 16 inches away from the center of the next. In this wall, two things interrupt the consistent 16-inch pattern:

• Windows
  
• Special framing that will accommodate internal walls once they are built
  

The plywood will be cut out of the window openings as construction proceeds. Above the window is a 2x10 header, which is actually two 2x10s with a piece of 1/2-inch-thick plywood sandwiched in between and a 2x4 along the bottom. The reason why the header has plywood in the middle is simply to make the header as wide as the rest of the wall. A 2x4 is really 1-1/2 inches by 3-1/2 inches, and a 2x10 is really 1-1/2 inches by 9-1/2 inches. When you sandwich two 2x10s together they are only 3 inches wide. Adding the piece of plywood in between makes the sandwich 3-1/2 inches wide. A 2x10 header is a beam. The headers over all windows and doors give the wall enough strength over the window or door to support the roof. When a header spans more than 5 feet, you find double full-length studs on either side of the header instead of the single studs. All of the exterior walls go up following this same basic pattern. In the corners, the top plate on one wall overlaps the top plate of the next, and the walls are nailed together to bind the corner. Then the interior walls go up, fitting into the top plates of the exterior walls. Some houses have a garage and a breezeway connecting the garage to the house. The walls of the garage are built slightly differently (because the garage will have a slab floor). The walls are bolted directly to the brick foundation walls. The framers sometimes cover the outside walls in pink house wrap.

Construction of a House Cont'd

Basement-

A house with a basement starts with a hole about 8 feet deep. At the bottom of the hole is a concrete slab, and then concrete or cinder-block walls form the outer walls of the basement. Actually, a basement is poured in three pieces in most cases: the "beams," then the walls, and then the slab inside the walls. This approach helps keep the basement waterproof. The L-shaped piece is a steel reinforcing bar to bind the beam and the wall together.

Crawl Space-

A crawl space has several advantages over basements and slabs:

• It gets the house up off the ground (especially important in damp or termite-prone areas).
• It is a lot less expensive than a basement and comparable in price to a slab.
• Duct work and plumbing can run in the crawl space, meaning that they are easy to service and move over the lifetime of the house.

Most of the time, a crawl space is made of cinder block with a brick facing. Noticedthat the concrete work for the crawl space was not done with much precision at all. One of the neat things that the mason (bricklayer) does is carefully adjust the height of the cinder blocks and bricks with mortar thickness so that the crawl-space walls end up exactly level all the way around.
One problem that arises in crawl spaces and basements is dampness. In order to keep water out, perforated pipe and gravel are used in a trench around the crawl space to route water away. In a house with a basement, this same sort of drainage system is added along the bottom of the walls. The basement walls are then generally insulated with rigid foam board and then heavily waterproofed before dirt is backfilled against the walls.

The Construction of a House

This is giong to be a multi-part post, because it is so big.

The construction of a house is a very detailed, step-by-step process. This process is site preparation, foundation, basement, crawl space, floor, walls, roof, porch, windows and doors, roofing, siding, plumbing, rough plumbing, rough electrical, insulation, drywall, garage slab, and finishing up.

Site Preparation-
The first crew on the site handles site preparation. Often, this crew and the foundation crew are the same people, but sometimes not (especially if there are a lot of trees on the lot). Houses are generally built on a foundation that is either a basement, a crawl space or a slab. The site-preparation crew typically arrives on the site with a backhoe and/or bulldozer. The crew's job is to clear the site of any trees, rocks and debris, level the site if necessary and dig as necessary for the foundation being built. The example house shown here is built on a crawl space. For a crawl space, the site preparation crew digs a set of trenches and holes. Concrete is poured into these trenches and holes and will act as the interface between the foundation wall and the ground. The concrete in the trench is generally about 18 to 24 inches wide (45.72 to 60.96 cm) and 18 to 24 inches deep. Once it hardens, it forms a massive concrete "beam" on which the house rests. The width of this concrete beam is controlled by the compressibility of the soil. In light soils, the beam will be wider to try to spread out the load, while in heavy clay soils it can be narrower.
If the site slopes, the concrete beam is stepped. Concrete takes approximately four weeks to cure to full strength (depending on the weather), so once the concrete is poured nothing will happen for some period of time while the initial curing takes place. If this house had been built on a basement, the site-prep crew would have dug a square hole about 8 feet deep. If this house had been built on a slab, the site-prep crew would have trenched around the outside approximately 2 feet deep and then completely leveled the area for the pad.

Foundation-
Slabs, basements and crawl spaces are the three main foundation systems used on houses. In wet and coastal areas, it is sometimes common to put houses up on posts as well. The slab is probably the easiest foundation to build. It is a flat concrete pad poured directly on the ground. It takes very little site preparation, very little formwork for the concrete and very little labor to create. It works well on level sites in warmer climates -- it has problems up north because the ground freezes in the winter and this freezing can shift the slab at worst and at least lead to cold floors in the winter. Around the edge of the slab, the concrete forms a beam that is perhaps 2 feet deep. The rest of the slab is 4 or 6 inches thick. A 4- or 6-inch layer of gravel lies beneath the slab. A 4-millimeter sheet of plastic lies between the concrete and the gravel to keep moisture out. Embedded in the concrete is 6-inch by 6-inch wire mesh and steel reinforcing bars. You will often hear this sort of foundation referred to as a "floating slab" -- it "floats" on the soil, with the deeper concrete around the edge holding it in place. In northern climates, the concrete around the edge has to extend deep enough to remain below the frost line in winter.
One thing about a slab is that the sewer pipe, and sometimes much of the electrical conduit, has to be put in place before the concrete is poured. The sewer pipes are actually embedded in the slab.

The Old and the New...

The original World Trade Center was comprised of seven buildings. These were the Marriott World Trade Center (3WTC), the 4 world trade center (4WTC), the 5 world trade center (5WTC), the 6 world trade center (6WTC), the 7 world trade center (7WTC), and the two twin towers (1 & 2WTC). These 7 buildings housed such things as the United States Customs Service and the U.S. Commodities Exchange, the PATH station, office buildings, and underground shopping mall. Only three of these buildings still stood following the 911 attacks but they were subsequently demolished because they suffered a lot of damage.

The new site of the world trade center will contain 7 buildings again but these will be Freedom Tower (Tower 1) 200 Greenwich Street (Tower 2) 175 Greenwich Street (Tower 3) 150 Greenwich Street (Tower 4) 130 Liberty Street (Tower 5), and 7 World Trade Center. It is not known what these buildings will be used for as of yet, but it will probably house a few businesses just as it was before.

Freedom Tower

1 World Trade Center, or the Freedom Tower, is the main building of the new World Trade Center complex currently under construction in Lower Manhattan in New York City. The tower will be located in the northwest corner of the 16-acre (65,000 m²) World Trade Center site, bound by Vesey, West, Washington and Fulton streets. Construction on below-ground utility relocations, footings, and foundations for the 1,368-foot (417 m) Freedom Tower began on April 27, 2006. On December 19, 2006, the first steel columns were installed in the building's foundation. Three other high-rise office buildings are planned for the site along Greenwich Street, and they will surround the World Trade Center Memorial, which is currently under construction. The area will also be home to a museum dedicated to the history of the site. The Freedom Tower's program includes 2.6 million square feet (241,000 square meters) of office space, as well as an observation deck, world-class restaurants, parking, and broadcast and antennae facilities, all supported by both above and below-ground mechanical infrastructure for the building and its adjacent public spaces. Below-ground tenant parking and storage, shopping and access to the PATH and subway trains and the World Financial Center are also provided.
An 80-foot-high (24 m) public lobby topped by a series of mechanical floors form a 200-foot-high (61 m) building base. 69 tenant floors rise above the base to 1,120 feet (341 m) elevation. Mechanical floors, two floors to be occupied by the Metropolitan Television Alliance, restaurants and observation decks culminate in an observation deck and glass parapet that mark 1,362 feet (415 m) and 1,368 feet (417 m) respectively — the heights of the original Twin Towers. A shrouded antenna structure supported by cables, engineered by Schlaich Bergermann & Partner rises to a total height of 1,776 feet (541 m), which is symbolic of the year the Declaration of Independence was signed (July 4, 1776). The tower rises from a cubic base whose square plan—200 feet by 200 feet—(61 m by 61 m) is almost as wide as the 208-foot (63 m) Twin Towers. The base is clad in more than 2,000 pieces of prismatic glass; each measures 4 feet by 13 feet 4 inches (1.21 m by 4.06 m) with varying depths. It has been designed to draw upon the themes of motion and light; a shimmering glass surface drapes the tower's base and imparts a dynamic fluidity of form whose appearance will reflect its surroundings. Just as the rest of the building, the base will serve as a glowing beacon. Cable-net facades on all four sides of the buildings, again designed by Schlaich Bergermann, measure 60 feet (18 m) high and range in width from 30 feet (9 m) on the east and west sides (for access to the restaurant and observation deck, respectively) to 50 feet (15 m) on the north side and 70 feet (21 m) on the south for primary tenant access, activate the building at street level. Though not occupied by office space, Freedom Tower's observation deck is set to be higher, at about 1,362 feet (415 m). Currently, the Sears Tower, Shanghai World Financial Center, and Taipei 101 have occupied floors higher than Freedom Tower. International Commerce Center, Chicago Spire, and the Burj Dubai will have roofs and floors higher than Freedom Tower's highest roofs and floors.

World Trade Center

The World Trade Center (sometimes informally the WTC or Twin Towers) was a seven-building complex in Lower Manhattan (New York City) that was destroyed in the September 11 attacks. The World Trade Center was designed by Minoru Yamasaki who used an innovative tube-frame structural design for the twin 110-story towers. The elevator system in the towers utilized large-capacity express elevators which went to sky lobbies, along with local elevators serving individual floors. In gaining approval for the project in the early 1960s, the Port Authority of New York and New Jersey agreed to take over the Hudson & Manhattan Railroad which became the Port Authority Trans-Hudson (PATH). Groundbreaking for the World Trade Center took place on August 5, 1966. The North Tower was completed in December 1970 and the South Tower was finished in July 1971. Construction of the World Trade Center involved excavating a large amount of material which was used in making Battery Park City on the west side of Lower Manhattan. The complex contained 13.4 million square feet (1.24 million m²) of office space. An observation deck was located atop the South Tower, while the Windows on the World restaurant was located at the top floor of the North Tower. With construction of 7 World Trade Center in the 1980s, the World Trade Center had a total of seven buildings but the most notable were the main twin towers which were each 110 stories tall. During a press conference in 1973, Minoru Yamasaki was asked "Why two 110-story buildings? Why not one 220-story building?" His response was: "I didn't want to lose the human scale". When completed in 1972, 1 WTC became the tallest building in the world, unseating the Empire State Building after a 40-year reign. 1 WTC (the North Tower, which featured a 360-foot (110 m) high TV and radio antenna added in 1978, stood 1,368 feet (417 m) high at the top of the roof. With the 360 ft antenna, the highest point of the North Tower reached 1,727 ft. 2 WTC became the second tallest building in the world when completed in 1973. The observation deck was 1,362 feet (415 m) high. The World Trade Center towers held the height record only briefly. Chicago's Sears Tower, finished in May 1973, reached 1,450 feet (442 m) at the rooftop. Of the 110 stories, eight were set aside for technical services (mechanical floors) Level B6/B5, Floors 7/8, 41/42, 75/76 and 108/109, in four two-floor areas evenly spaced up the building. All the remaining floors were free for open-plan offices. Each floor of the towers had 40,000 square feet (3,700 m2) of space for occupancy. Each tower had 3.8 million square feet (350,000 m²) of office space. Altogether the entire complex of seven buildings had 11.2 million square feet (1.04 km²) of space.