How To Use A Speed Square (AKA Rafter Square)


How To Use A Speed Square (AKA Rafter Square)

Speed Squares are used for cutting rafters. They have been around since the early 1900’s. There are two types of speed squares: one with a sharp edge and another without.

The sharp edge type is better suited for cutting straight edges while the non-sharp edge type is best suited for cutting curved or angled surfaces such as rafters, joists, etc..

The most common uses for a speed square are:

Cutting rafters into lengths that will fit into the hole in your roof. Cutting rafters to length so they can be nailed down to support the weight of your house. Cutting rafters to make sure all joints are tight and no gaps exist between boards.

If you want to learn more about how to use a speed square, read on!

What Is A Rafter?

Rafels are pieces of wood that form the sides of a rafter. The term “rafter” refers to any piece of lumber that supports the ceiling above it. For example, if you had a 2×4 wall made up of 4 rafters, then those would be your ceiling beams.

The purpose of a rafter is to transfer the weight of the roof down to the walls beneath it. Typically, the walls will be made up of horizontal 2×4 or 2×6 boards. Most houses are built using this method.

Rafters are also used in other places such as lofts, garages, barns, or anywhere you need to support a ceiling.

How To Use A Speed Square To Cut Rafters

If you are using rafters to support your ceiling then you will need to cut those rafters to length. Most houses have a standard pitch: 12″ horizontal rise for every foot of run. If you have a house with a 6/12 roof then it means that for every 6 inches in the horizontal direction you will have 12 inches in the rise direction or vise versa.

The table below shows the rise and run measurements for various common roof pitches.

Common Roof Pitch Rise Run 6/12 6 12 8/12 8 12 10/12 10 12 4/12 4 12 2/12 2 12

How To Use A Speed Square (AKA Rafter Square) - Image

Calculating The Cut Length Of A Rafter

The first step is to measure the distance from your roof’s hole to the bottom of your desired rafter location. Let’s call this measurement “X”. Once you have this measurement, follow the chart below to find the cut length of your rafter.

Cut Length (in feet) = (X + 1) /2

For example, if “X” was 40 inches then the cut length would be: (40 + 1) / 2 = 20.5 or 20′ foot rafter.

The next step is to adjust this cut length by your roof’s pitch. If your roof has a 4/12 pitch (which is typical) then you need to add 5″ to the cut length. This will give you the total length of your rafter.

Total Rafter Length (in feet) = Cut Length (adjusted) + 5

As an example, if your cut length was 20.5 feet then your rafter’s total length would be 25 feet.

Using A Speed Square To Mark Your Rafter For Cutting

Now that you know your rafter’s cut and total lengths, you are ready to start marking your rafter for cutting. The first step is to place your speed square against the rafter so that it touches the top of your wall and the edge of the rafter. Next, rotate the speed square until the edge is aligned with your cut mark on the rafter.

How To Use A Speed Square (AKA Rafter Square) - Image

Now, from that angle, place the tip of the speed square’s long edge on the ground and push it past your rafter so that it runs parallel to your rafter. Now, draw a line down the edge of the speed square. This line will be at a 4:12 pitch.

Next, rotate the speed square so that the edge is again aligned with your cut mark on the rafter. Now, draw a line down the leg of the speed square. This line will be at a 8:12 pitch.

Repeat the process again by placing the tip of the speed square’s outside leg on the ground and drawing another line down the leg. This line will be at a 12:12 (flush) pitch.

These lines will indicate where you need to cut your rafter. Align your saw’s blade with these lines and cut your rafter to length.

Long Rafters

If your rafter is longer than 8 feet then you will need to take extra steps to ensure safety. Basically, you need to notch your rafter so that it doesn’t fall backwards and crush you. Use the diagram below as a guide when notching your rafters.

Notching a rafter

Make The Rafter Header

The next step is to make the rafter header. The rafter header is what the ceiling joists will rest on. Begin by measuring up from the bottom of your cut rafter and marking it at a distance that will allow you to place a 2×4 between the joists and the bottom of your rafter when they are installed.

Let’s call this measurement “A”.

Once you have marked the location, measure up another 2 feet and mark it. This is where you will place your rafter header.

Nail your rafter header in place between the marks using 16d nails.

Make The Rafter Tie

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The rafter tie will prevent your ceiling joists from spreading. Begin by measuring up 3 1/2″ from the bottom of each cut rafter and mark it.

From the top of each rafter, measure up 10′-2 1/2″ and mark it on all of the rafters.

Cut 2 pieces of 2×4 each 9′-0″ long and nail them between your top marks. These will be the rafter ties.

Covering The Roof With Tar Paper

Tar paper will help to keep the roof dry along with helping to prevent the roof’s foam board from molding or rotting. Begin by cutting a piece of tar paper that is 6 feet longer and 6 feet wider than your ceiling’s measurements. In other words, if your ceiling is 10 feet by 12 feet then you would cut a sheet of tar paper that is 60 feet by 72 feet.

Begin by placing the tar paper under the first rafter and folding it into eighths. Next, fold the corners of the tar paper into the center of the roof. The idea is to create a tube with the edges of the tar paper wrapping around the sides and beneath the roof.

Once you’ve created the tube, staple the sides of the tar paper to the underside of the rafters on each end. You’ll need to use a flat head screwdriver to pull up the middle of the tar paper so that you can staple it down. Be sure that the staples go all the way into the rafter and not just the top or the roof sheeting will pull off when you try to roll it.

Roll the rest of the tar paper out and staple it down.

Installing The Roof Shingles

Start at the eaves and begin installing your shingles working from the bottom to the top. Begin by stapling the first row of shingles 6″ from where the shingle butts up against the bottom side of the roof sheathing.

Work your way across the row and stagger each strip so that no two shingles overlap.

Continue this process until you reach the ridge.

At the ridge, cut your first shingle in half and place one piece on each side of the peak.

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Now, cut all of your remaining shingles in half (You’ll have 40 left).

Begin installing them starting at the bottom and working up.

Stagger the seams with the first row.

Continue this process until you get 6 rows up.

Install the final row. You’ll only need to cut your shingles in half on the first and second row at the peak.

Nail down the rest of the shingles but only nail them 3/4 of the way. This will allow you to pop them up and add roofing cement under them for added water proofing.

Flip the roof so that the sheathing is facing up.

Installing The Soffit

The soffit will prevent air from getting trapped between the roof and the wall. Cut two pieces of 2×6 that are 6 feet long. These will be the top and bottom of the soffit.

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Cut two more pieces that are 4 feet 10 inches long. These will serve as the sides of the soffit.

Cut a 45 degree bevel on the top ends of the side pieces.

Connect your corners and nail everything together. You’ll need to use a scrap piece of wood to make sure that the angle remains consistent.

Connect your soffit to the house and brace it into place.

Covering The Soffit

The soffit will be covered in the same material as your roof. Start by cutting your tar paper so that it overhangs the eaves by 4″ on each side. Next staple the tar paper in place.

Covering The Soffit & Reroofing

Start by covering the soffit. Begin by cutting a piece of roofing that is 60 feet long and 6 feet wide. Begin installing it starting at a corner and working your way across the roof.

Overlap each piece 12″.

When you reach the middle of the roof fold the last row back under the next row and continue on.

Finish the rest of the roof using this method. It should create a nice finished edge on each side. At the gable ends, fold the extra length of roofing paper under the eaves.

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Nail everything down, but once again only nail it three quarters of the way down. This will allow you to lift up each strip and add roof cement or shingles under them later.

Finish The House

The walls are done and the roof is installed so now you’re ready to finish your shed!

You’re going to be putting wallboard on the interior walls and then taping and sealing the seams before painting it. Start by installing the wallboard.

Measure the wall, cut a piece slightly shorter than the measurement and then use a razor to cut a trough in the top horizontal edge that’s 1/2″ high and 4″ wide. This will allow you to fold it over the top of the wall and nail it in place.

Staple the wallboard to the studs 16″ on center. At the floor, leave a gap that’s equal to the thickness of the wallboard (usually 5/8″). At the top, overhang the wallboard 1-1/2″.

To tape and seal the seams you’ll need to cut strips of fiberglass mesh window tape (not wallpaper border!) that are 2″ wide and 16″ long.

Apply a continuous bead of acrylic caulking along the top edge of the wallboard and then position the tape so that 1/2″ is underneath the wall and the other 1/2″ is hanging over it.

Fold the tape over the edge and use a flat square-edged trowel to force the caulking into the seams.

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Continue along all the seams in the same manner. Allow the caulking to dry before proceeding.

When this is done, paint the entire inside of the shed including the ceiling with a good quality paint. (Remember to use flat paint on the walls and gloss on the ceiling!

You’re now finished with the inside of your shed. Be sure to clean it out on a regular basis.

On to the outside…

Weather-sealing The Doors & Windows

The first thing you should do is check all of your window and door frames for air leaks. Just push your finger up against them and if you feel a draft, you’ll need to weather-strip them.

For the door, just use some flexible foam weatherstripping. It comes with an adhesive on the back and you just peel off the paper and stick it to the door and frame.

For the windows you’ll need to get some strips of thin metal called window channel and hook it around the window frame like so. Then just put foam strips in the space.

If you have a door that opens outwards, you’ll need to do something a little more to prevent the wind from catching it. Just take a 4-ft. length of 2×4 and saw a V-notch at the bottom that’s 1″ deep and 1-1/2″ wide like so.

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Nail the stop to the inside of the door near the top edge and then put a latch on it so it’ll stay in place. Just make sure the latch is on the same side as the hinges.

You’re done with your shed for now, just make sure you clean it out on a regular basis.

Making Sure The Roof Doesn’t Leak

The first thing to do is to seal up any holes you find in the roof. The asphalt shingles are usually nailed down with rounded edges so you don’t need to do anything there except check for any loose ones and replace them if necessary.

Plywood roofs just need to have any loose pieces patched and then sealed.

Metal roofs need to be caulked as well, but you’ll need to use special metal roof sealant because the others won’t work.

Also check for any bowed or curved shingles and replace them right away. Once a roof is really bad, it’s almost impossible to fix it.

After you’ve done all that, you’ll need to install some vent pipes. The rule of thumb is that you need one vent pipe every 10 feet of run (from the soffit to the ridge) and 1 vent pipe for every flat roofed room that’s less than 800 square feet.

Your house should already have these, but check to make sure. If it doesn’t, just get some 4″ galvanized vent pipe and connectors (use high quality stainless steel ones if you’re going to be installing them in a high wind zone).

Make sure you get the kind that have the screen in them, some don’t. You’ll need to get connectors to go with them as well.

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Check out your local building codes because you may need flashing for the corners. You may also need roof jacks to support the added weight of the vent pipes.

Installing The Gutters And Soffits

Gutters and soffits are pretty easy to install. Just make sure you get all the parts you need because they’re all a little different. Most are made of aluminum, but some are made of plastic.

The plastic ones aren’t very durable though.

The first thing you’ll have to do is to install your fascia. This is the board that goes along the very top of the roof. Your soffits will be attached to this and your gutters will hang from this.

The rule of thumb is that it should be at least 3″ in from the edge of the roof.

After that’s done, measure the height of your roof (all the way across). The gutters will hang down 1-1/2″ for every foot it measures. Make sure you mark where the soffits are going to be located before you start running your gutters.

Now you need to get a few tools together. You’ll need a hammer, a pair of pliers, a handsaw, and a screwdriver. That’s pretty much it, unless you want to include some measuring tools.

Begin by installing your gutters. Most come with instructions, but here are the basics of what you need to do.

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Begin by finding the midpoint of your roof starting at the fascia and working your way across. Mark this point. Then measure 8 feet out to each side and make marks there.

Now you’ll connect the dots by using your pliers to crimp a connector onto the gutter strap. Now snap the connector onto the bottom of the gutter and use your pliers to crimp it onto the roof.

Continue all the way across.

Next you’ll do the same thing for the other side, but you only need to go about halfway. You’ll see what I mean when you get there.

After you’ve got one side done, do the other side.

Now start putting in the soffits.

The soffit should be located right below where the ridge vent is going to be installed (you haven’t installed that yet, right?

).

Install the soffits by using the soffit support to connect it to your fascia. Use pliers to crimp the metal support onto each one.

Continue all the way across until you’ve got it all done. At this point, make sure everything is straight and that none of the edges are sticking out. Take the handsaw and trim the edges if they are.

If this is a flat roof (like most garage roofs), then you’re done!

Installing The Ridge Vent

The ridge vent needs to be installed before you can finish up the roofing. It’s not a difficult process, but it does require two people.

The ridge vent is what connects all of your rafters together and provides the opening so that water can freely escape from your roof. It’s also what the soffits will hook into.

You’ll need your handsaw for this step.

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Find the middle of your roof by measuring the length and width of the roof (divided by 8) and make a mark. Now measure halfway in both directions from that point and make marks at those points as well.

Connect the three points with a straight edge and saw the ridge vent to fit. It should be big enough for a person to walk on top of the roof if necessary.

Make sure it fits nice and snug into all of the rafters. Using a pry bar, gently bring the sides of the ridge vent outward so that it expands into the rafters.

Now use your pliers to fasten down the ridge vent. Use three nails on each side.

Take a step back and marvel at your beautiful workmanship!

Installing The Roof Shingles

The hardest part of installing asphalt shingles is getting up on the roof! Once you’re up there, it’s pretty easy. The exposure can be a little unsettling if you’re afraid of heights, but take a deep breath and just keep telling yourself “everything is secure” and “you won’t slip”.

The first thing you need to do is to apply the underlayment. This layer goes underneath the shingles and is what protects the roof from the sun as well as holds all of the shingles down securely.

Measure the roof and cut pieces of underlayment to fit. Use the staple gun to fasten them down to the roof making sure to stagger the seams.

Now you’re ready to start putting on the shingles! Start at the eave and work your way from the bottom up. Make sure that you stagger the joints as you go, but don’t worry too much if you mess up.

The next row you put on will cover it.

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Continue putting on the shingles and stopping occasionally to cut more as you need them with your handsaw.

Note: Whenever you’re done applying a certain number of rows, take a level and make sure the roof is still sloped the right way. Usually, you want to have about six rows that are fully secured before moving on.

Tip: It’s best to put the bottom rows on first and work your way up. That way, it gives you more room to maneuver up top.

Installing The Chimney

The chimney is probably the most important part of the roof since that’s what keeps the whole thing from falling down! It also adds a nice finishing touch at the top.

Start by using your pliers to bend the flashing into an “L” shape. The straight part will go on the roof while the longer part with the bend will overhang the edge of the roof, but still be anchored down to the top of your wall.

Now take the piece you just made and put it up against the corner of the roof. Hold it in place and use your pliers to dent all around it so that it sits snugly on the roof.

Take the flashing that you cut for the front of the chimney and fasten it to the bottom of the bent flashing. Do this by darning it into the valleys between the shingles and then using your pliers to crimp it tightly.

Use your pliers to bend all around the bottom edge to form a tight seal where the flashing meets the roof.

Cut a piece of flashing that’s about 5 feet long and make an “L” out of it again. Place the flashing underneath the bottom edge of the chimney flashing and fasten it in place with dabs from your pliers.

Go around the entire chimney and form tight dabs all the way around it with your pliers.

Cut four strips of flashing, each about 2 feet long. Lay them side by side under the chimney and fasten them in place by crimping them tightly with pliers.

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Now take the piece you made in the last step and place it right on top of the ones you just laid. Form tight crimps all around the edges to seal them into place.

Cut a long piece of flashing and make an “L” out of it. This should be a little longer than the chimney is wide.

Place this piece on top of the one you made in the last step and fasten it in place with dabs from your pliers.

Do the same thing you did in the last step all the way around, but this time with strips of flashing about an inch wide.

Cut a little “V” notch into the top of the flashing at the back side of the chimney. This is so that water will run off the back side instead of working its way behind the flashing and leaking through the wall.

Now cut a small piece of flashing and form an angle on one end. This will go at the bottom of the back side of the “V” notch you just made.

Do the same thing all the way around, forming tight crimps with your pliers.

Cut a strip of flashing and form an angle on one end. Place this piece at the bottom of the front of the “V” notch. Form tight crimps all the way around with your pliers.

Do the same thing on the other side, making sure both angles go up against the horizontal piece you added in the last step.

Cut two more pieces of flashing and form angles on one end. Place these pieces on the bottom edge of the “V” notch and fasten them in place with crimps from your pliers.

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Do the same thing on the other side. These pieces will extend beyond the bottom edge of the “V” notch.

Cut a small piece of flashing and fasten it to the top inside edge of one of the angle pieces you just added. This will direct the water to flow off to the side instead of down behind the flashing.

Cut another small piece and place it at the top inside edge of the other angle piece.

Now do the same thing all the way around, forming tight crimps with your pliers.

Cut a small strip of flashing and place it at the bottom edge of the back side of the chimney, right at the bottom corner.

Do the same thing on the other three sides. This will direct any water that makes it down behind the flashing off toward the back side of the chimney and out from under it.

Now take your pliers and form tight crimps all around all of these strips. This will lock them in place and keep water from seeping behind them and leaking through the wall.

Cut a piece of flashing about 6 inches long and bend a small tab on one end. This will go on the bottom edge of the flashing at the back side of the chimney.

Do the same thing on the other three sides, placing them at the bottom corners. These will keep water from working its way down the back side of the flashing and leaking out from behind it.

Now take your pliers and make crimps all the way around each one to lock them in place. This is very important, because without this step, the water would still leak through and cause major damage to your wall and ceiling.

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Now go back over all of your work with a metal detector. You don’t want to miss any spots.

If you find any, go back and add some more flashing.

That’s it! You’re done and your chimney is protected from the elements and should last for many years to come.

Allow everything to dry for a day or so. You can then go back and caulk all of the joints with high-quality silicone caulk.

You’re Done.

It may not be the most exciting part of your wood burning experience, but protecting your chimney is one of the most important things you can do. It’s definitely worth the time and effort. You’ll save yourself a lot of hassles and heartaches in the long run.

Be safe and be smart. Have fun!

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