Build a roof

How to Build a Roof - Sheathing the Roof

2007-09-27T21:50:00.000+02:00

It is assumed here that you will be applying a plywood, particle board or wafer-board sheathing. If you have chosen to use a rigid roofing (metal, wood shakes or shingles, tile, etc.) you can use 1 x 4 slats instead. With wood roofs, slats are a must to avoid rotting the wood shakes.

Plywood particle board or wafer-board roof sheathing is most commonly used, being low in cost and easy to apply. Choose an exterior C/D grade. Thickness will range from 3/8 to 3/4 inch depending upon local code*. When ordering the sheathing, divide the total number of square feet of roof surface by 32 square feet (a 4' x 8' panel) and add an extra 15% for waste. An air compressor with a nail gun will come in handy for nailing large flat areas like this.

Most Common Mistakes:

Not staggering the seams of the sheathing.
Aligning sheathing with the edge of the roof rather Than perpendicular to the rafters.
Attaching the sheathing wrong side up.
Inadequate nailing.
Panels not meeting in the center of a truss or a rafter.

Construction:

Check the rafter ends (tails) to be sure they are all on a straight line. If the walls are crooked, the rafter tails will also be crooked. Try to correct this problem; but if you are unable to, pop a chalk line across the rafter tails and trim them with your saw before attaching the sheathing. This is crucial because this building line will be a very noticeable one when viewed from below.
Begin applying the sheets from the bottom of the roof (the eaves) and work your way up to the ridge. The last course at the top may need to be rip cut if the roof is not in 4 foot increments. It is important here that the sheathing at the eave line be exactly perpendicular to the rafters so that the sheets will meet at the centers of the rafters it is even more important that it be perpendicular than that it is flush with the rafter tails. A tapered piece of sheathing can be cut to fill in at the eave if necessary.

Usually, code, which can vary locally, requires nails every 6 inches on the edge and 12 inches in the field. Pop a chalk line across the sheets to 'mark the centers of the rafters for a nailing guide.

Do not nail the edge rafters where the sheathing meets until the adjoining sheet is in place. This will enable you to move the rafter a bit if needed, so that the sheathing meets in the center of the rafter.
Stagger the joints of each course of sheathing. This can be done efficiently by cutting a panel in half and using these half sheets to start every other course. Special metal plywood clips will add stability to the splices where the sheets meet between rafters.
Carefully work your way up to the peak of the roof. Check for alignment and end support as you go. For safety, temporarily nail a 2 x 4 "toe board" horizontally across the lower panel of sheathing to brace yourself against as you add the second and subsequent courses of sheathing.

Sheath one slope of the roof at a time, ripping the top course to the needed width at the ridge. When one slope is completely sheathed, pop a chalk line down any slope edge (as in a hip roof) that needs to be cut at an angle. You may prefer to cut these panels before you nail them in place.

Set your circular saw to the correct depth and angle for cutting along the edge and saw off the excess overhang.
Repeat this process for each slope of the roof.

How to Build a Roof - Layout

2007-09-27T21:48:00.000+02:00

Just as you measured for spacing of the wall studs, you will need to measure for, and mark the location of, the roof trusses on the cap plate. Check your local building code* for proper size and spacing.

Most Common Mistakes:

Ordering inaccurate trusses.
Not accounting for overhang and rake rafters.
Placing the rafter on the wrong side of the layout mark.

NOTE: Rafters are DOUBLED to support Rake Rafter

Construction:

Beginning at one end, drive a nail 3/4" in from the end, hook your measuring tape to the nail, then measure and mark every 24" (or 16"). Place an X on the side of the mark nearest your nail. )
If, in your plans, you have an overhang (rake rafter) on either end of the garage, you will need to adjust the measurement to insure a sheet of plywood beginning at the edge of the overhang (rake) will end in the center of an interior truss.
Metal rafter ties make the installation of trusses easier and more secure.

How to Build a Roof - Framing

2007-09-17T09:02:00.000+02:00

Most Common Mistakes:

Placing the rafter on the wrong side of the layout mark.

Not plumbing the trusses.

Construction:

Very carefully lift one end of the rafter truss and carry it up the ladder. Rest it upside down next to the end set of metal rafter ties. Then place the other end into position on the opposing wall.

Slowly and carefully turn the truss right side up and slide it into place. You may find it helpful to nail a 2" x 4" to the truss as a leverage board to swing the rafter upright and into place.
Nail the rafter tie in place over each X where the rafter will connect with the cap plate.

While one person holds a 4'-8' level against each truss and holds it in position, another person nails a temporary brace to the unit across the sloping top chord.
Continue this procedure until all rafters are up and in pla

How to Build a Roof - Felt

2007-09-16T08:29:00.001+02:00

Applying the Roofing Felt

Roofing felt acts as a waterproof barrier between the sheathing and the roofing material (shingles, etc.). We recommend using 15-30 lb. roofing felt. It is necessary to apply the roofing felt (tar paper) to a clean, dry surface immediately after the sheathing is completed to protect it from the weather. If, however, this is not possible and the sheathing gets wet, allow it to dry for a couple of days before applying the felt so as not to trap any moisture that may cause damage to the sheathing. Felting applications vary according to the type of roofing so determine the proper application before beginning.

Most Common Mistakes:

Applying felt to a wet surface.
Not overlapping the layers.
Not applying smoothly.

Construction:

If you have chosen to apply a metal drip edge along the eaves, this must be in place before laying the felt. A drip edge is usually made of 26 gauge galvanized steel with a top flange of 3 to 4 inches that extends in from the roof edge.
In heavy rain or snow areas we also recommend eave flashing, a strip of smooth or mineral faced roll roofing. This is cut to extend from the edge of the roof to a point 12 inches inside the wall line. Place the lower edge of the strip even with the drip edge.
The roofing felt is then applied in accordance with the type of roofing to be used. We will assume here that you are using asphalt shingles.
Snap horizontal lines on the roof sheathing to align the upper edge of the felt. Snap the first line at 35 and 5/8 inches above the eave. (The 36" felt should overlap the eave by 3/8".) Snap succeeding lines at 34 inch intervals, assuring a 2 inch overlap of each course.
The felt must be flush at the rake (side) edges, have 4 inch overlaps where two pieces are joined, and 6 inch overlaps on hips and ridges.
Ensure that the felt lies flat and smooth before securing it.
Tack the roofing felt down with 1/4" staples using an air compressor with a pneumatic stapler, a hammer-tacker, or a staple gun every 12 inches.

How to Build a Roof - Checklist

2007-09-16T08:28:00.000+02:00

Tools:

Canvas Nails Belt
Tape Measures: 33' and 16 to 20'
20-24 oz. Framing Hammer
16 oz. Claw Hammer
Combination Square
Carpenter's Framing Square
Carpenter's Level
Nail Puller
Set of Wrenches
Hacksaw
Screwdrivers
Electric Drill
Circular Saw
Chalk Line
Sturdy Ladder(s)
Saw Horses
Carpenter's Pencils and/or Felt Tipped Pen
Hand Saw
String
Plumb Bob

Clam
Air Compressor w/Nail Gun and Staple Gun
Finish Hammer
Nail Set
Caulking Gun
Chisel
Tin Snip
Blueprints
Insurance

Materials:

Pre-fabricated Roof Trusses
Exterior Plywood
Scaffolding
Metal Flashing
Drip Edge
Tarpaper
Composite Asphalt Shingles
Staples
12 GA. Galvanized Roofing Nails
Metal Fasteners
Rafter Ties Plywood
Sheathing Clips

How to Build a Roof - Introduction

2007-09-16T08:17:00.000+02:00

-hese pages detail the building of a roof. Just think of building a roof as being made up of many, small, easily accomplished steps.

Safety:

As you exercise your do it yourself skills, develop safe work habits and stick to them.

Work patiently. If you become confused, frustrated or in too much of a hurry, chances are greater that mistakes will be made or that accidents will happen.
Read and follow the specific safety rules of every tool and material you will be using.
Unplug tools when changing blades or making adjustments.
Wear heavy soled boots on any construction site; rubber soles when working on the roof; gloves while handling lumber; and protective eyewear whenever power tools are in operation.
Wear ear protection when using power tools as some operate at levels that can damage hearing.
Tie long hair back so as not to catch it accidentally in power tools.
Keep work surfaces and traffic areas free from scraps and debris.
Select the appropriate tool for the job and keep all tools sharp and in good working condition.
If an object is too heavy or awkward, get assistance in moving it; bend from the knees when picking up large and heavy items.
Hard hats are recommended when working under or around overhead construction.
Use scaffolding when working on high places. The added stress of manipulating heavy and unwieldy tresses and sheathing can cause you to lose your balance. Be careful where you step; move slowly and with caution. Be sure no one is standing below the work unless absolutely necessary.
Be extra careful working around glass - one wrong move can cause serious injury and/or necessitate replacing a costly item.
Use the proper protection, take precautions and plan ahead. Never bypass safety to save money or rush a project.

*Check local building code and permit requirements before beginning work.