Wednesday, September 21, 2022
HomeBuildHow To Build Roof Rafters

How To Build Roof Rafters

Build Your Own Roof Trusses

How To Build A Shed: Building & Installing Roof Rafters

The very first step for building roof trusses is to prepare a design layout that can be sketched by a professional architect or can also be done by using a software that is specifically meant to design a roof truss.

The second step in building a roof truss is to prepare the materials needed. These will include wood, a hammer, a saw, roof truss plates made from galvanized steel and galvanized screws of 1 ½ inches.

The wood needs to be cut based on the size of the roof and specifications in the design. It must also adhere to all the local building standards and codes. Most of the time, the sizes of the wood used range from 2×6 and 2×8 even though its thickness can be based on the weight that it will support and the overall size of the roof.

It is crucial that you use connector plates made from galvanized steel. It is a kind of steel that has a zinc coating and can prevent the occurrence of any corrosion.

The plates and the wood will join together in the shape of a triangle and will then be fastened together using galvanized steel screws, which arent shorter than 1 ½ inches in their length. Depending on the woods thickness, you might also want to use thicker screws.

If you want to build a roof truss with the use of other materials aside from wood, like steel, aluminum or tin, you will need to cut the material based also on the roof size and design specifications, just like with wood trusses.

Adding Fascia To Gable Ends

Anyway, moving on, we could get the fascia added at the gable ends, and first we snapped a chalk line and cleaned up the edge of the roof sheathing here, to make sure the fascia ran nice and straight.

Next, I got one of the fascia boards cut to length, making parallel angled cuts at each end, and the angle here once again matched the roof pitch.

I cut the board a hair long on the first try but, after taking a hair off, Erik got the board temporarily attached to the roof sheathing.

We repeated the process with the other board, and Erik actually fine tuned this board with his circular saw before attaching it to the sheathing.

Once both boards fit well, we ran more screws to attach the board to the sheathing more securely, as well as to the eave fascia, and we tweaked the boards as needed to get them in line with the edge of the sheathing, which we knew was straight.

We repeated the process at the other gable end and then we could move inside the house to finish the framing in the gable area. We actually considered leaving this area open and adding glass here to allow more light into the bedrooms but decided against it due to the cost of the glass, plus I would have had to run it by the HOA, and they probably would have denied because it doesnt match our main house.

How To Build Rafters For A Shed

Lets get down to business and build some rafters. Now that youve got a decent idea of how big your rafters are going to be, well go through how to build them step by step.

As an example, well use a 10×8 foot shed, with the span being 8 feet. The process will generally be the same for a shed of any moderate size, but be sure to use the rafter sizing calculator above to find the correct rafter length and size for your shed rafter project.

Well be using a ridge beam for this project, so each set of rafters will meet a horizontal 2×6 at the apex, which will run the length of the shed and connect to all of the rafters.

Remember that for rafters, youll always use a ridge beam one size larger. So in our case, 2×6. If you use 2×6 lumber for rafters, your ridge beam will be 2×8.

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Vs 26 Rafters: What Is The Difference

Depending on the pitch of your shed roof, you will choose between 2×4 or 2×6 rafters. But what is the difference? Simply put, it comes down to what is needed for your shed. The first thing you need to know is if your roof has a slope that is less than or greater than 3:12. This means for every 12 inches of horizontal run, a roof rises 3 inches. For those that are less than 3:12, 2×4 rafters are not strong enough. These are low-pitched roofs and 2×6 rafters should always be the choice of lumber.

When you want to make a truss you will always use 2x4s webbed together for strength.

While 2×6 lumber will cost you more money, it can be used for almost any type of shed. They can be spaced further apart than the 2x4s. But, if you live in a place that is not subject to strong winds or heavy snowfall, 2×4 rafters are the way to go. They cannot handle a heavy load like a 2×6 but can give you more versatility with the design of your roof.

Calculate The Length Of Your Rafters

Share Shed rafter design ~ Cerita kecil

Well be building a 4:12 pitch roof, with an 8 span with 1 of overhang. With this set of specs, we are looking at a rafter length of 5 3 ½. This total span is well within the load capacity of 2×4 rafters, but how far apart can we space the rafters?

If you look at our rafter spacing chart, youll notice that 2x4s can span an 8 gap on a 4:12 roof. However, youll also notice that that is only for #1 kiln-dried wood, which might not be available to most of us. In fact, #2 grade 2x4s seem to be more common.

Assuming then that we are using #2 grade 2x4s, well have to space our rafters at 16 on center. This gives us plenty of support for our roof without having to worry about snow or other debris caving our shed roof in.

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What Is The Difference Between Ceiling Joists And Rafters

Rafters and joists are both used in the construction of buildings, but they have a few differences. Its essential for those who work in the construction industry to understand the difference between the two, and its also useful for homeowners to have a basic understanding in case repair and maintenance are needed.


Lets start with joists. They are parallel horizontal beams that run across an open space. They join the opposite walls in a building to support both the ceiling below and the floor above. Theyre usually made from timber, and they come in a variety of widths .


On the other hand, rafters run diagonally from the wall plate to the apex of a roof structure. They form the foundation for attachment of the roof boards onto which the final roof covering is fixed. They are typically about 8-10 inches wide.

The main difference between joists and rafters is that joists are usually more horizontal to the ground while rafters are used for steeply sloped roofs.

Stair Gauges Lessen The Chances For Error

The most useful accessories for laying out rafters are a pair of tiny clamplike devices called stair gauges . Each gauge is a small hexagonal nut with a slot through the middle and a thumbscrew for securing it to the square. Clamped to the legs of a framing square at rise and run points, stair gauges act as stops to ensure that the rise and run settings remain consistent throughout the layout process. As the name implies, these little gadgets also are handy for laying out stair stringers.

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Making Your Own Trusses

While most trusses are manufactured by small, local manufacturing companies for lumberyards and home improvement centers, you can build your own trusses on site. Its a good idea to do this before beginning framing of the home, so that you have the full slab available for laying out and assembling the trusses. If you are building a home with a basement, then assemble the trusses on the floor, before the interior walls are framed.

Making your own trusses is still considerably faster and easier than building a stick roof, if your homes design allows for it. If you make your trusses in advance, as I am recommending, be sure to store them somewhere where you can keep them off the ground and cover them with a tarp to keep them from getting wet.

To make your trusses, youll want to lay out the truss design on the slab or floor and possibly attach some blocking to help you locate the individual pieces. Make a first truss, calculating the angles for your cuts and the overall dimensions for each part. Then you can cut the material in mass, saving time.

One-half inch CDX plywood can be used for the joining plates or gussets, nailing them to the 2x 4 pieces being used to make the trusses with 6d coated box nails. Dont be stingy with the nails, as they are the main thing holding the truss together.

Sizing Roof Rafters Example 2

How to build a shed. (Cut and assemble Roof Rafters)| Paulstoolbox

Now lets try another example, but this time a span will be given and you must select the correct size lumber to be used given the following scenario:

Question: When the ceiling is not attached to the rafters and where Hem-fir #3 roof rafters are to be spaced 12 inches on center supporting a snow load of 30 psf and a dead load of 20 psf, what is the minimum allowable rafter size when required to span 14-0 in length?

First step, lets collect all the given information within the question:

  • Ceiling not attached to rafters and a snow load of 30 psf: Use Table R802.4.1
  • Roof Rafter Spacing: 12 inches
  • Species and Grade: Hem-fir #3
  • Roof Rafter Span: 14-0

Now lets find the minimum allowable rafter size given the above scenario:

Therefore given the above example, the minimum allowable rafter size for Hem-fir #3 lumber spanning 14-0 is a 2×10 since it can span 14-5. A 2×8 member for example cannot be used since it can only span 11-9.

To Learn more about the design and construction of wood roof framing, be sure to check out Section R802 of the 2018 International Residential Code .

Fun Tip: To learn how to easily size ceiling joists, be sure to check out this POST.

Hopefully given the above examples you can find it easier to size wood roof rafters per the Tables within the International Residential Code.

In conclusion, lets take a quick second to answer some common frequently asked questions related to roof rafters.

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Selecting The Right Type Of Truss

  • 1Measure your structure to determine how big your truss needs to be. Trusses can be built in many different shapes and sizes to accommodate the dimensions of various structures. Before you can begin plotting the exact specifications of your truss, find the overall length and height of the structure being reinforced.XResearch source
  • A truss for a gable roof on one side of your home, for example, might need to be 15 feet long and 46 feet tall.
  • The dimensions of your structure will determine the angles formed by the trusss top and bottom beams, or chords. On a relatively shallow roof, for instance, the upper and lower chords may meet at a 30-degree angle on each side.XResearch source
  • In some cases, building codes may dictate the size requirements of a truss for a certain type of structure. Be sure to consult your local building codes before you begin drawing up plans for your truss.
  • 2Use a simple king post truss to reinforce small, lightweight structures. A king post truss design features a single vertical joist that runs through the center of the triangular frame. This style is useful for framing structures that dont require quite as much support as structures that bear more weight.XResearch source
  • A king post truss may be all you need if you’re looking to add some extra stability to a garden shed or gable roof.
  • Because of their complex configuration, Howe trusses tend to be difficult to plan and assemble, and are most often reserved very large load-bearing structures.
  • How To Build Roof Trusses For A Garage

    If you want to know how to build roof trusses for a garage, you must ask a professional about the right support of the roof as well as its weight.

    Trusses are utilized for stabilizing and supporting the walls, particularly in huge buildings that have more than one to two stories.

    Usually, roof trusses are triangular and can be installed easily. Another advantage of roof trusses for a garage roof is that they are practical and can be used with several materials.

    Learning how to install roof trusses for a garage roof isnt hard, particular if you follow particular hints and tips.

    • Cutting the Timbers

    The first thing you should do when building roof trusses is to cut timber panels to the garage roofs size. Measure the roofs span and check with the building project and plan.

    Before you buy timber panels, you must also take into consideration the weight theyll be supporting. The reason behind it is that this will help you know their thickness. More often than not, you will have to purchase 2×8 timber panels and cut them to the size if required.

    • Securing Timber Panels Together

    Utilize the connector plates when securing timber panels and creating a triangular shape. For securing the panels and maintaining the triangular shape, use screws.

    • Adding the Brace
    • Securing the Trusses
    • Attach the Roof Trusses

    When attaching roof trusses to roof frame, make use of deck screws. The majority of professionals would suggest or recommend you to brace trusses.

    • Extra Tips to Remember

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    Measuring And Marking The Birdsmouth And Tail Cuts

  • 1Measure the diagonal of the rafter. Start this measurement from the top of the cut you just made. When the rafter is installed, this top/long end will be at the peak of the ridge beam. Hook your tape measure on to the rafter, and measure the diagonal rafter length that you calculated earlier. Use your pencil to mark the length directly on the rafter.XResearch source
  • The diagonal measurement is the full length of the rafter, minus the overhang. Measuring the diagonal will allow you to make the tail and bird’s mouth cuts in the correct locations.
  • In this example, the diagonal measurement that you found earlier was 39.81 inches .
  • 2Position the framing square to make the birdsmouth cut. Align the framing square so that the stair gauge that youve placed on the tongue of the framing square is on the pencil mark you made to indicate the full diagonal length of the rafter. Hold the long end of the framing square so that the other stair gauge is also resting against the rafter this will ensure that you mark the tail cut at the correct angle.XResearch source
  • Use your pencil to trace the full length of the tongue along the width of the rafter.
  • 3Determine the depth of the birdsmouth cut. This is relatively simple: measure the full width of the outside wall. For most buildings, the birdsmouth cut is 4 inches deep.XResearch source The width of the 2×4 used to frame the outer wall measures 3.5 inches , and the outside sheathing measures 12 inch .XResearch source
  • Difference Between A Rafter And Truss

    Barn Roof Construction

    Rafters typically use larger wood beams and do not have any sort of framework other than the beams themselves. A rafter beam is usually larger than a 2×4 large homes may have rafters that are 2×12 or more!

    A truss, on the other hand, is only made up of 2x4s and is often pre-fabricated in a factory. Trusses use webs of 2x4s within the truss structure to support the roof. Trusses are held together with steel gussets and are staples of home construction.

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    What Is Rafter Spacing

    Rafter spacing is the distance between parallel rafters or roof joists. It is measured from the center of one rafter to the center of the next, also known as on-center, which makes it easier to determine the number of rafters based on the buildings length. The typical on-center spacing, according to the International Residential Building Code , is 12, 16, 19.2, and 24, which means the actual space between the rafters is 10.5, 14.5, 17.7, and 22.5.

    Rafter joist spacing is only one aspect of roof design and building that affects the span, along with load variables, wood species, and grade. The greater the space between rafters, the shorter the distance they can span. Thicker dimensional lumber, such as 2x10s and 2x12s can span further at 24 centers than 2x4s or 2x6s at 12 spacing for comparable wood species, grade, and load variables. So, always check the prescriptive code tables, or with a Structural Engineer before building.

    Sealing The Roof With Zip Tape

    With the roof sheathing on, the only thing left to do to get the roof water tight was seal up the open area where the ridge vent will be installed. Since I knew this roof wouldnt have shingles installed for at least a month, we went ahead and ran a strip of the 9 wide ZIP tape along the entire ridge, and this 50 foot long roll was perfect for this roof.

    Now, because I know someone is going to say adding this tape doesnt allow ventilation, we will be cutting away this tape from the ridge vent area before adding the roofing, this was just a temporary solution to get the building dried in.

    It was also at this point that the fire Marshall came out to tell me I wasnt allowed to have a fire on site, even though I wasnt burning anything besides non-treated wood and was just trying to create an area for us to get warmed up while working. Thankfully, they were really nice about it and just told me not to do it again, but it seems awfully silly to send these bits of scraps to a landfill when they could be burnt for warmth.

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