Home Construction Shop and Guide

Hello everyone , welcome to Home construction shop and steps to Hand cut a basic Gable end roof. For the layman a gable end roof is depicted below. Note the ends are straight up and down as opposed to a cottage style roof or a Hip roof as it is referred to sometimes, where all side of the roof are sloping.. The Gable end roof is fairly easy to build but is still a fair amount of work.

In his section of  Steps To Hand Cut a Gable Roof  the Home Construction Shop will cover the the procedure to measure and layout the rafters in your home construction project.

One of the most important tools to cut a roof is a framing square, here are some basic components of a framing square below. The shorter thinner measure of the square is known as the Tongue. This is the side that the lesser measurement of the pitch will be gauged when layng out the rafter. In a 7/12 pitch roof you would use the 7 inch mark  on the tongue measure. The longer , thicker measure of the square is known as the Blade. The larger of the measurements is gauged on this side. In a 7/12 pitch roof you would use the 12 inch mark on the blade measure. Always remember to gauge your measurements using the values on the outside of the square.

The first step in your home construction project of framing your roof , is to calculate the span of your rafters. The length of rafter is determined by two factors.

1. Roof  Pitch – This is ratio of horizontal length to vertical length. For example if the roof pitch is a 7/12 pitch. Which will be indicated in the drawing. For every 12″ of horizontal length or ” run” there is 7″ of vertical height or “rise”. The diagram below depicts this

2. Structure width- This is the width of the building as determined usually by the shortest span , or as indicated in the building drawings. This measurement would be taken from outside of the framing on one side of the structure to the out side of the framing on the other side. The diagram the Home Construction Shop shows below depicts this measurement.

By dividing the span of the structure in half  we will be able to calculate the run of the rafters. As the Home Construction Shop depicted above , a span of 24 ft. divided in half will give the run of the rafter which is 12ft. Knowing , both the pitch and the run of the rafters it is easy to calculate the height that the roof will be from the top of the Wall to the very peak of the roof.

Since the pitch is 7/12, then for every 12″ or 1ft of run , the roof will rise 7″, so…. if the run of the rafters is half the span of the structure , 12ft as depicted above, then the roof will rise 7″ x 12 ft = 84″ or 7ft. I know this is not easy math for some but at the Home Construction Shop we feel its good to go through to get the easier picture and a full understanding.

Lets say that the span of the structure was 32ft. Then the run of the rafters would be 16ft. With a 7/12 pitch the rise of 7″ for every foot, then we would calculate 7″x16ft.=112″ or 9ft. 4″

I hope you are still with me so far.

Now that we have our run for the rafter lets go through the steps to layout the proper length of  the rafter. There are a couple methods of laying out the rafter. The quickest way at the Home Construction Shop would be to use trigonometry and the Pythagorean Theorem. This methods is calculated using the equation ( a2 + b2=c2).  Below is a video with a bit of a math lesson showing  how to calculate the Pythagorean Theorem, assume that the letter X in the video is the rafter, lets have a look and then plug our own numbers in.

So , if we plugged in our numbers we could find the length of the rafter, lets see;

(A) squared will represent the height of the roof from the top plate to the peak and we figured out that with the 7/12 pitch and half the span of the building at 12ft. A rise of 7″ for every 12″ or 1ft. would equal 84″ or 7 ft.

(B) squared will represent the half span of the building which is 12ft.
(C)  squared represents the rafter. So..

(A) squared = 7′
(B)  squared=12′
(C) squared=?
7 squared =49
12 squared=144
49+144=(C) squared
193=(C) squared
the square root of 193=c
c=13.9ft. or 13′ -10 7/8″

Once this measurement is achieved all you would have to do is mark your ridge cut and then measure down the rafter stock , 2×6 or 2×8 whatever you are using for your Home Construction roof framing project and mark the outside edge of the building or structure line , this is where the birds mouth will be cut out. See the first diagram below.

NOTE: In the second diagram below, the measures on the square are doubled  12″  on the tongue as shown and 24 ” on the blade. Here the diagram shows an 12/24  pitch setting on the square.  This is the same as a 6/12 pitch. Doing this gives you the full use of straight edges across your rafter to scribe or mark

The final mark on the edge of the square represents the outside of the structure and the plumb cut of the birds mouth. To mark out the birds mouth take note on the diagram below the the Home Construction Shop has provided.

Once you have the outside structure edge marked , take your square and flip it the opposite way with your measures still on the outside of the square but set on the top side of the rafter as the Home Construction shop has shown in the top diagram. Now slide the square so that the width measurement of the exterior wall top plate sits at the outside structure mark. In this top diagram it is showing using 4″  measured on the inside of the square. This measurement  represents the wall thickness where the birds mouth will sit on a 2×4 top plate, 31/2″ for the plate , and a 1/2 ” wall sheathing. Once this is marked remove the section shown.

Next step in your Home Construction roof framing project is to layout the overhang. View the diagram below

Once again with the square flipped and the gauged measures on the top side of the rafter, align the outside edge of the tongue with the back of the birds mouth as shown in the top diagram. Mark off 10 1/2 ” to represent the overhang. Now flip the square back over and align your tongue at the 10 1/2″ mark that you made with the pitch settings aligned with the bottom of the rafter as the Home construction Shop has shown in the bottom image.

The final cut is the fascia cut. The length of the fascia cut is determined by the width of the fascia. If you are using 2×6 for fascia the length of the fascia cut should be enough to account for soffit and fascia board.  So,  5 1/2″  for the 2×6, subtract 1/2″ – 3/4″ for soffit and fascia flashing = 4 3/4″ – 5″

Here is a sectional view of the components of a hand cut roof below.

Well… I hope you have gotten a layman’s understanding of everything here. If you have difficulty , feel free to comment and leave an email and Home Construction Shop will be gladly to help more. Continue browsing the Home Construction Shop to learn how to measure your rafters using the square and the step down method. A little bit more time consuming but not difficult. S o c’mon in to the Home Construction Shop.