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Outline of Article:

.Extra Steps for a Major Addition

Framing Tricks for Longer Walls

  • Assembling a Wall

Joining Interior and Exterior Walls the House Plumbing

  • Framing for Pipes and Fixtures
  • Installing a Branch Drain
  • Running Supply Pipes
  • Venting the New Drain
  • Plumbing for an Overhead Addition

Roof Trusses for a Wide Span

  • Raising the Trusses
  • Connecting to a House Roof
  • Framing Above Interior Walls

107--- [Prefabricated roof trusses]

Extra Steps for a Major Addition

The job of erecting a major addition may seem forbidding at first glance, However, the components of the addition-foundation, floors, walls, and roof-though larger than those described in Sections 2 and 3, demand no new skills and surprisingly few additional techniques, Foundation and floors: Depending on the width of the foundation and the interior floor loads, such as walls and bathrooms, you can build floors of I-beam joists. Consult a dealer to find out the correct size and spacing of the I-beams for your project walls: Exterior walls may be so long that they must be raised in sections and spliced together, but the splices are matters of simple carpentry. And building the second story of a two-story addition is no different from raising wails atop a garage.

Interior partition walls, usually not necessary in small additions, are almost always built into large additions, and they must be spliced to the exterior walls.

- Roof: For wide additions, prefabricated, easily installed roof trusses can be substituted for the ceiling joists and rafters used in small additions.

- Utilities: You may want a bath room in a large addition. Putting in the new pipes presents no unusual problems for the initiated home plumber.

Supplying electricity, heating, and cooling is another matter. For electricity, it’s likely that you will need a subpanel in the addition, wired to the main service panel in the house. From this unit you can run branch circuits through the addition as shown.

The chances are great that your furnace or air conditioner does not have the capacity to heat or cool the addition. You may choose to re place your old system with a larger unit that can serve new pipes or ducts running into the addition. Or you might consider installing separate heating and cooling plants for the addition alone.

Some of these jobs, such as in stalling a central air conditioner, require licensed technicians, and all of them require a good deal of expertise. With this in mind, you may decide to hire professionals to do the work.


Anatomy of a two-story addition.

The block foundation of this four-room addition to the back of a two-story house supports I-beam floor joists. On the second floor, the I-beam directly under the interior partition wall is doubled to carry the extra weight of the wall. To stabilize the partition wall on the first floor, it’s fastened to the second-floor joists. Roof trusses bear on the outside walls of the addition, and the partition wall on the second floor is secured to the trusses.



Tricks for Longer Walls

Framing Tricks for Longer Walls

The elements of a long wall are identical to those of a short one-top and sole plates with 2-by-4 studs spaced 16 inches apart, or 2-by-6 studs every 24 inches. However, a few special techniques, which are outlined below, are required for the installation of a large addition's long walls.

Walls Built in Sections: For economy and handling safety, assemble walls in sections that don’t exceed 16 feet in length. A doubled top plate ties the sections together.

If you plan to attach an interior wall to an exterior one, nail a special stud assembly into the exterior wall frame. The interior wall is nailed to the assembly and the subfloor, then further tied to the ex tenor wall of the addition with a doubled top plate that runs across the intersection.


Safety goggles protect your eyes when you are working with hammers, saws, and power tools. In an en closed space, earplugs muffle the noise of power tools to a safe level.



Doubling u top plate for strength.

Connect adjoining wall sections with a second top plate that overlaps each wall section-and any joints in their top plates-by at least 4 feet. If necessary, force the upper plate to align with the lower ones by toenailing at an angle through the side of the upper one into the top of the lower one.

Tie wall sections together at a corner by extending the upper top plate of one section across the joint and butting the other upper top plate against the first.



1. Making nailing assemblies.

• Cut three studs and assemble them in a U shape, with the sides of the U nailed to the bottom (left).

• Before raising the exterior wall section, butt nail the assembly between the top and sole plates. Position it where the interior wall will meet the exterior wall, and with the opening of the U facing outward.

2. Connecting the walls.

• After raising the framing for the exterior wall, set the interior wall in place. Nail the sole plate to the subfloor, and the end stud to the nailing assembly.

• In the upper top plate of the exterior wall, cut a gap the width of the bottom of the U in the nailing assembly. Double the interior-wall top plate with a board that runs from the outside of the exterior wall, through the gap, to the end of the interior wall.


Tapping the House Plumbing

Installing plumbing in an addition can be a straightforward job if as is often the case, the pipes can conveniently be run into the existing plumbing system. Local codes permitting, use plastic pipe and fittings—light weight, inexpensive, and easy to work with—in the smallest permissible sizes. (The drainpipes shown are cast iron, so adapters are necessary.)

- Keeping It Simple: In a ground- floor addition, the work is easier if your house has a basement with a concrete-block foundation wall and your addition has a crawl-space. More complex are installations involving slab foundations or those with walls of poured concrete.

Drains must run underneath a slab, and a concrete wall can be weakened if a hole is made for pipes to pass through. In such cases, you may want professional help. Plumb a second-story addition bathroom directly above an existing one, rerouting vents for the lower bath room as shown.

- Sloping Drains: Plot new plumbing in a ground-floor addition from the addition’s main drain (the drain of a toilet in a bathroom, a sink in a kitchen or a wet bar) to the main stack of the house. The new lateral drain line must drop inch per foot; if a long run of pitched drainpipe would be an obstruction in a finished basement, you can box it in or run it along a wall and build a partition to conceal it.

- The Sequence of Work: Under- floor plumbing is easiest to install after the addition joists are in place but before the subflooring is nailed down. Locate the positions of the new fixtures and predrill holes for pipes in plates of wet walls. Then run the pipes into the addition, stop ping a few inches above the wet-wall sole plate. After the subfloor is complete, extend pipes laterally through wet-wall studs to fixture locations.

CAUTION---Solvents in the materials for joining plastic pipe are toxic and flammable. Be sure to provide good ventilation.

Old plumbing and new.

This drawing shows in principle how house plumbing can be extended to a ground-level addition (brown) and a shed dormer (purple). For clarity, only the house plumbing serving a bathroom is shown. Supply pipes carry hot and cold water to the fixtures, all of which drain through a waste stack—also the main stack in this illustration—into the sewer. Above the fixtures, the stack functions as a vent, letting air into the system.

branch runs through a sleeve in the common wall to the main stack. New supply lines, ex tended from old ones at the point nearest the addition, also pass through the sleeve. The considerable distance to the house plumbing re quires installing a new vent.

In the dormer, a new vent line for the down stairs washbasin connects to a stack extension upstairs. The original bathtub vent is disconnected and runs up to the extended stack. Supply for the upstairs bathroom is through vertical extensions of supply pipes.


  • Hammer and cold
  • chisel
  • Level
  • Pipe cutter
  • Plumb bob
  • From the new ground-level bathroom a waste
  • Hole saw
  • Electric drill and bit
  • Saber saw


  • Framing lumber
  • PVC and CPVC pipe, fittings, and adapters
  • PVC and CPVC primer and cement
  • Applicator brushes
  • Plumber strap iron
  • Common nail
  • Finishing nails
  • Mortar
  • Brick chips
  • Gate valves
  • Insulation (tubular rubber or foam fiberglass batts)
  • Pipe hooks



A wet wall.

An extra-thick wall, framed with 2-by-6s, accommodates a 3- or 4-inch waste stack through holes cut in the top and sole plates. Horizontal runs of supply pipes and drainpipes will pass through holes drilled in the studs. Supports for fixtures, called cross pieces, are nailed between studs at the height specified by the manufacturer. (Use 2-by-6 lumber for tub faucets and washbasins, a 2-by-4 for a shower head.) Tub and shower crosspieces are recessed to accommodate faucet and shower arms; a washbasin crosspiece is set flush with stud edges (inset) to accept washbasin mounting brackets attached after the wallboard has been installed.

Supports for a tub.

Doubled joists-I-beams with wood filler between them in the illustration at right-bear the consider able weight of a tub filled with water. Headers assembled from two 2-inch boards frame an opening where the tub overflow pipe and drainpipe will connect to the drain system. Additional filler inserted between I-beam flanges at header locations pro vides backer blocks for joist hangers that support the headers.

A crosswise closet bend.

To make room for a toilet closet-bend assembly that runs across floor joists, a gap is cut in the intervening joist. Backer blocks in the I-beam webs help support headers, as described above. The closet-bend assembly is supported from below by a crosspiece nailed between the headers.


1. A route to the foundation.

• To locate and mark the point at which you will break through the common foundation wall, first determine the location of the main fixture drain in the new plumbing.

• Test-fit an elbow to the drain assembly—in this example, a closet bend for a toilet. Support the elbow temporarily, placing the top of the elbow at least an inch below the joists.

• With a carpenter’s square, mark the foundation opposite the elbow’s center. Measure the distance from elbow to foundation, then lower the mark inch for each foot of the distance.

• With a hammer and cold chisel cut a hole through the foundation, centered on the mark and big enough to accept a short length of 8-inch- diameter PVC plastic pipe as a sleeve.

2. Running drainpipe into the addition.

• Have a helper in the basement of the house slide a 4-inch drainpipe through the sleeve and into the crawl-space of the addition.

• Test-fit the pipe into the elbow on the closet-bend assembly and suspend the pipe from the joists with plumber’s strap iron nailed to the joist or—for I-beams—backer block at 4-foot intervals. Attach the strap on one side of the pipe with a 2.5-inch common nail and on the other with a 2.5-inch finishing nail to permit later adjustment of the slope.

• Extend the drainpipe to the main stack in the house.

3. Adjusting the pitch.

• Tape a small block of wood to one end of a level to make it read true at a pitch of inch per foot. For a level 2 feet long, attach a block that is 0.5 inch thick; for a 4-foot level, use a 1-inch block.

• Starting at the closet-bend assembly, set the level on the drainpipe and correct the pitch by

adjusting the loops of strap (for clarity, existing drains have been omitted).

4. Connecting to the main stuck.

• Unscrew the cleanout plug in the main stack and replace it with a threaded plastic adapter. Fit a plastic Y to the adapter.

• Slip an elbow onto the drainpipe and test-fit - a vertical run of pipe into the Y, taking care not to reduce the slope of the drainpipe.

• Cement a test cap to the other opening of the Y. Remove it after you test the system, and re place it with a cleanout fitting.

5. Setting the sleeve.

• Fill around the pipe sleeve with mortar and brick chips.

• Recheck the slope of the drain, and replace the finishing nails on one side of the plumber’s strap iron with 2.5-inch common nails.

• Check your local code for regulations on testing the system.



Tapping the lines.

Though the supply-pipe routing shown here may not match the layout of your own house, this method of construction works in any pipe route.

• Shut off the water supply and drain the runs of hot- and cold-water supply pipes that are closest to the sleeve in the foundation wall.

• Install a T fitting in each of these pipes so that the supply lines into the addition will be at least 4 inches apart.

• Install new CPVC pipe at the Ts—with adapters if necessary—then cement a CPVC gate valve Onto each one.

• Extend the pipes through the sleeve and into the addition crawlspace, on opposite sides of the drain pipe.

Insulating the pipes.

• In the addition’s crawlspace, slip insulation over the supply pipes.

• With pipe hooks, secure the insulated pipes to backer blocks on I-beam webs, slanting the pipes slightly so that they will drain into the house.

• Pack insulation loosely into the sleeve, and insulate between joists and around drain traps with fiberglass batts.

• Cement a 4-inch to 2-inch reducer to the sanitary T on the closet-bend assembly, unless local codes prohibit 2-inch vent pipes. In that case stand a short length of pipe in the sanitary T.

• Extend supply pipes above floor level.

• Complete the addition’s subflooring, framing, and sheathing; then install horizontal piping through studs to bring all the new plumbing to the fixture locations.

PROTECTING PIPES IN COLD CLIMATES: Where winter temperatures fall below -10°F. supply pipes require more than foam or rubber insulation. One approach is to attach a thermostatically controlled electric heating cable to each pipe. Fasten the cable to the pipe with all-weather electrical tape, then wrap the pipe with i-inch fiberglass insulation t and secure the insulation with more tape. A prerequisite to this procedure, however, is to use copper piping instead of plastic, which heat from the cable may melt.



Raising the stack.

• To locate the point where the vent stack will pass through the top plate, drop a plumb line from the plate to the center of the stack (left).

• Mark the position of the string, and with a hole saw, cut an opening slightly larger than the vent pipe through the top plate and into the attic.

• Determine where the stack will pass through the roof, and after marking the location with a *-inch hole, cut a corresponding hole in the roof with a saber saw.

• Extend the stack through the roof.

= TRICKS of the TRADE: A Flashlight Alternative =

Dropping a plumb line to establish a straight line for a new vent pipe from a tight attic space through a roof can be awkward. An easier alternative is to shine a narrow-beam flashlight on the roof to establish where the hole should be cut. Simply plumb the vent stub and place a wood block on it. Then turn on the flashlight and set it on the block. Drill the marker hole for the vent at the center of the beam where it hits the roof sheathing.



New pipes above old ones.

The simplest plumbing scheme for an upstairs addition is a vertical extension of the pipes downstairs (dark blue). Water-supply lines can take any convenient route, but drains and vents have stricter requirements. As shown here, several new pipes are needed, some to serve the fixtures upstairs (green) and others to reroute, vent, or drain lines for the tub and washbasin on the lower level (light blue).

Pipes for the upstairs fixtures connect to a waste stack-and-vent extension in stalled through the addition roof. The extension begins with a closet bend that also accepts the drain line for a shower or tub. Branching up ward from this pipe is a vent line for the shower and toilet; it’s connected to a sanitary T installed high on the stack extension. A washbasin drain line enters a sanitary T placed above the closet bend.

Downstairs, the washbasin drain and tub vent are disconnected from the stack (dotted lines) and the sanitary Ts capped. A new Y low on the stack accepts washbasin wastes through a pipe that extends upward as a vent, ending at one side of a sanitary cross. A new vent line for the downstairs tub connects to the other side of the sanitary cross.


Roof Trusses for a Wide Span

Prefabricated trusses allow you to roof an addition more than 18 feet wide, without the interior bearing walls that are needed to support lumber joists and rafters over a similar span. Built in a factory, trusses require less time and skill to install than standard roof framing.

- Ordering Trusses: To allow time for fabrication, order the trusses 3 to 5 weeks before you need them. Give the supplier a set of working drawings for the addition, with precise figures for the slope of the addition roof, the heel height of the house roof, the width of the addition including sheathing, and the length of the addition (less the house-roof over hang, if any). If the addition roof must match the slope of the house roof, some suppliers may want to take the measurements; others will ask you to do so.

- Different Framing Methods: In a one-story addition without interior walls, you can carry one truss at a time inside, lift its ends onto the top plates, and tilt it upright in a single, simple operation; begin with the end truss, then work toward the house. When an addition has interior walls, trusses cannot be carried in side. Slide them up an outside wall (or hire a crane) and stack them fiat atop the addition. Tilt them upright as needed; in this case, it’s easier to brace the first truss to the house and work outward. Still other adaptations are required for a two-story addition.

If the addition roof meets the original house roof, a ridge beam and jack rafters mate new with old.


  • Tape measure
  • Hammers
  • Level
  • Mason’s cord
  • Chalk line


  • Roof trusses
  • 2 x 4s
  • 1 x 6s
  • Rafter ties
  • Common nails (3.5”)

Roof Trusses

SAFETY TIPS --- Put on soft-soled shoes to move about the roof and scaffolding, and protect your eyes with safety goggles when you are nailing. A hard hat is essential gear whenever you work with un secured trusses and braces overhead.



Roof trusses, composed of pieces of lumber called chords held together with metal plates, are available in many shapes and sizes. The simplest trusses frame a gable roof above a flat ceiling. The ceiling shape is defined by the bottom chord of each truss, and the roof by the top chords, which intersect with the center chord at a section called the apex. Other designs provide attic space within the trusses or combine different ceiling and roof shapes. The truss at the end of a roof has additional framing: cripple studs to sup port sheathing and an opening for a vent.

Measuring to match a slope.


• To determine the height of an existing attic or overhead crawl- space, hook the end of a tape measure over the top of the ridge beam, let the tape hang vertically, and measure to the bottom of the joist below . For a truss- framed roof, measure from the top point of a truss to the underside of its bottom chord.

• Determine the width of the space by measuring between the outside edges of the top plates that support the joists or trusses. There is no need to include exterior wall sheathing in this measurement; the small amount that it adds to the width of the house is insignificant when calculating the roof slope.


1. Positioning rafter ties.

• Starting 2 feet from the end of the addition farthest from the house, mark positions for the trusses at 2-foot intervals on the top plates of the side walls. Mark the position of the truss nearest the house so that the truss will rest in front of the house fascia board.

• Nail rafter ties to the top plates on the house side of each mark.

2. Securing the nailers.

To create a nailing surface for the end truss, fasten a row of 2-by-4 nailers to the top plate of the end wall with 3k-inch nails. Use a scrap 2-by-4 as a spacer to position the nailers 1.5 inches back from the outside edge of the plate, and make sure the ends of the row are flush with the out side edges of the side-wall top plates.

3. Preparing for the end truss.

• Find an end-wall stud about a third of the way in from a corner.

• Hold a 10-foot 2-by-4 stop against the wall so that it projects 6 feet above the top plate, and secure it with at least four 3.5-inch nails driven through the sheathing into the top plate and the stud.

• Mount a second stop the same way, placing it at a stud about a third of the way from the other corner of the end wall.

Working on the ground, sheathe the end truss. Cover the rectangular ventilator framing, then cut through the sheathing to make the opening for the ventilator.

4. Erecting the end truss.


• With two helpers, lift the ends of the end truss, apex down, onto the top plates of the side walls,

• Roll the truss upright as shown above, fitting the bottom chord between the stops and the 2-by-4 nailer installed in Step 2.

• Shift the truss as necessary to equalize the over hangs at the sides, then nail the top chords to the stops and the bottom chord to the nailer.

• From outside, fasten a long 2-by-4 brace to the ventilator framing, use it to plumb the truss, then nail it to a 2-by-4 stake in the ground (opposite).

5. Laying out the overhang.

• With a helper, stretch mason's cord between a nail hammered partway into the overhang of the installed truss and a nail in the house fascia board positioned so that the cord is parallel to the addition.

• Erect the next truss as in Step 4. Align the overhang with the string guide, then nail the bottom chord to the rafter ties.

6. Aligning the trusses.


• Nail a 1 -by-6 brace to the middle of a top chord of the end truss. Mark for the second truss 2 feet along the brace.

• Hold the truss at the mark and nail the 1 -by-6 to it. Add a 1 -by-6 brace on the other side of the roof.

• Put up all but the last four trusses.

• Lift those trusses onto the side-wall top plates and lean them against the house.

• Anchor and brace the trusses as you did the others—unless the addition runs into a house wall. In that case, nail the last truss to the wall.



A temporary truss brace that runs to the ground is impractical on a roof over a two-story addition Instead, you can brace the trusses against the end wall To do so, complete Steps 1 and 2, then set a truss at the first rafter tie that is farther from the addition end wall than the height of the truss. (In the case of 7-foot high trusses at 2-foot intervals, this would be the tie 8 feet from the end wall) Nail two 2-by-4 braces between the bottom chord and the nailer on the end wall, then plumb the truss and nail another brace between the top of the center chord and the end wall. Working toward the house, erect additional trusses, installing truss-to-truss braces as you go. Finish the job by removing the three end-wall braces and erecting the outer trusses, bracing each of them to the standing trusses.


1. Marking the ridge beam.


• Snap a chalk line on the house the center of the addition.

• With a helper, turn a long 2-by-4 on edge, and center one end on the chalked line, the other on the apex of the nearest truss. Then level the board by moving it along the line.

• Set a scrap of lumber on the roof against the 2-by-4 and use the top of the scrap as a guide to mark the board for a diagonal cut.

2. Securing the ridge beam.

• To make the ridge beam, Cut along the diagonal marked in Step 1, then trim the other end of the 2-by-4 so that the beam fits between the roof and the face of the truss.

• Butt-nail the ridge beam to the truss so that the top edges of the beam meet the top edges of the top chords.

• Secure the other end of the beam by nailing through the roof and into a rafter or a bracing board.

• Nail a 2-by-4 across the top chords of the truss and under the ridge beam to support it (inset).

• Attach 2-by-4s to the top chords of the truss nearest the house to help place the roof plates and jack rafters.

• Install the plates and rafters, then re move the extensions and sheathe the roof, detaching the 1 -by-6 braces from the top chords as you go.

• Finish the roof.



1. Putting up Trusses.

• Mark the positions of the trusses on the side-wall top plates, but don’t install rafter ties at this stage.

• Lift the trusses over the end wall and stack them three high atop the side walls and partitions.

• Raise the truss nearest the house, plumb it, and brace it with a 2-by-4 nailed to the house root Secure the truss to the top plates with rafter ties.

• Erect the other trusses in the usual way, but work from the house toward the end of the addition.

• Sheathe the roof, removing braces as you work, and add the roof covering.

2. Attaching to partitions.

When the trusses have settled under the load of the roofing, fasten the bottom chords to the top plates of the partitions as follows:

• Where a partition runs perpendicular to the trusses, toenail the bottom chord of each truss to the top plate of the partition.

• If the partition runs parallel to the trusses and between two of them, butt-nail 2-by-4 blocks between the bottom chords at 4-foot intervals, and nail through the blocks into the top plate of the partition.


Friday, April 4, 2014 20:35 PST