Building Confidence
| Volume 16 Issue 3 ISSN 1923-7162 |
Welcome to Dave's Shop Talk's Home Improvement Newsletter of questions from our members on their construction projects, a Tip of the Month and a home remodeling article, both from our website at http://daveosborne.com.
Tip of the Month
Safety Tip: Don't use a grounded power tool outside in the rain without proper grounding. All outside plugs should be a GFCI (Ground Fault Circuit Interrupter). All power tools used outside should be plugged into one of these receptacles with a 3 wire grounded plug on the extension cord on both ends.
And a Bonus Tip:
Safety Tip: Before changing bits or blades, be sure the power tool is disconnected from the power cord. Before reconnecting be sure the wrenches and adjusting keys are removed from the power tool, and the guards are in place.
Ask Dave!
I've had a few questions on the operation of our stair calculator:
Why can't I use a rise greater than 7 3/4" as allowed by the code?
We changed this feature to allow any rise or run outside of the building code. In using this calculator it is IMPORTANT that you know and follow the Building Code requirements for stairs in your local area. This Stair Stringer Calculator will let you enter any size stair for planning purposes ONLY. It is NOT an invitation for you to ignore your local Building Code.
I want to have the first step from the upper floor even with the floor. How do I use the Calculator to do this?
I don't know why anybody would want to start their top step flush with the top floor. It seems redundant to me. I always make my steps drop down 1 riser from the upper floor. I agree that there is usually more than one way to do something, so I have relented and helped people with their set of stairs that they want to have flush with the upper floor or deck. I do this in the following way:
After finding the total rise from the top of the floor to the bottom floor, go to our stair calculator and enter in your total rise and desired rises and runs. Click Calculate. Write down your rises and runs along with the number of each. The stair calculator will give 1 more run than rise, as shown, like it was designed to do:
To have the top tread flush with the top floor or deck, we need to trick the Calculator. Add 1 rise to your original Total Rise. The original in our example is 62, so add 1 rise of 6 7/8 = 68 7/8. Reload 68 7/8 into the Calculator Total Rise box, leaving your other original entries as they were. Click Calculate. and Get the drawings. You will get this drawing:
We tricked the Calculator to give us a new stringer, we just need to fasten it into position, 1 stair tread thickness down from the top of the floor. The bottom end will have 1 tread thickness remove from the bottom, as normal. The stringer is level and flush with the top floor when the treads are installed. The bottom drawing shows this which I manually "photoshopped"!
There you go! You can use our Stair Calculator to make a stringer flush with the top floor. If you are having trouble with the Stair Calc, just email me with your question and entries and I'll "photoshop" your own custom drawing.
Dave
Feature Article of the Month
(taken from our website: DaveOsborne.com)
Tables 1: Rafter Tables
Rafter tables are commonly imprinted on the steel square (carpenter square, rafter square, framing square). I've revised it a bit to include angles of the side cuts for hip and valley and the jack rafters.
For info on how to use these tables see Rafter Tables on the Framing Square.
The angles shown are to be used with the popular compound miter or cutoff saws.
Common Rafter
The common rafter is one of a series of lineal structures extending from the fascia of the overhang to the top of an exterior wall to the ridge board of a roof. The angle given for a common rafter is called the plumb cut, since the ends are vertical or plumb. The plumb cut on a common rafter is at the ridge, the bird's mouth on the wall and at the fascia.
| Roof Pitch: | Length per Foot of Run | Angle of Plumb Cut in Degrees |
|---|---|---|
| 2 in 12 | 12.16 | 9 1/2 |
| 3 in 12 | 12.37 | 14 |
| 4 in 12 | 12.65 | 18 1/2 |
| 5 in 12 | 13.00 | 22 1/2 |
| 6 in 12 | 13.42 | 26 1/2 |
| 7 in 12 | 13.89 | 30 1/4 |
| 8 in 12 | 14.42 | 33 3/4 |
| 9 in 12 | 15.00 | 37 |
| 10 in 12 | 15.62 | 39 3/4 |
| 11 in 12 | 16.28 | 42 1/2 |
| 12 in 12 | 16.97 | 45 |
Hip & Valley Rafter
The hip rafter is the structural board which forms the hip at an outside corner of the roof and is installed between 2 common rafters at the ridge. The valley rafter is the structural board which forms the valley at an inside corner of the roof. Both the hip and valley rafters form a 45 degree angle, compounded with the slope of the roof. The angle or plumb cut for a hip or valley rafter, given in our table, is taken from the rafter square based on the slope of the roof and diagonal. If the common rafter has a slope of 5" in 12", the hip or valley rafter has a slope of 5" in 17". 17" is the diagonal of a 12" square. The compound angle for the hip or valley rafter is the plumb cut, given in the table, and the degree on each side of this cut, on both ends, as In the table.
| Roof Pitch in Inches | Length per Foot of Run | Angle of Side Cut in Degrees | Angle of Plumb Cut in Degrees |
|---|---|---|---|
| 2 in 12 | 17.09 | 44.9 | 6.7 |
| 3 in 12 | 17.23 | 44.6 | 10 |
| 4 in 12 | 17.44 | 44.2 | 13.2 |
| 5 in 12 | 17.69 | 43.8 | 16.4 |
| 6 in 12 | 18.00 | 43.3 | 19.4 |
| 7 in 12 | 18.36 | 42.7 | 22.4 |
| 8 in 12 | 18.76 | 42.2 | 25.2 |
| 9 in 12 | 19.21 | 41.5 | 27.9 |
| 10 in 12 | 19.70 | 40.7 | 30.5 |
| 11 in 12 | 20.22 | 40 | 32.9 |
| 12 in 12 | 20.78 | 37.1 | 35.2 |
Jack Rafter
There are two types of jack rafters: the hip jack and the valley jack. The hip jack is a short rafter that spans from the wall plate to a hip rafter. The valley jack goes from a valley rafter to the roof ridge. Each jack rafter has the same side cut and plumb cut on the hip or valley rafter and the same angle as the common rafter at the ridge or fascia. The side cut is the angle given in the table, the plumb cut is the same angle as in the table for the hip or valley rafter.
| Roof Pitch in Inches | Difference in Length on 16" Centers | Difference in Length on 24" Centers | Angle of Side Cut in Degrees |
|---|---|---|---|
| 2 in 12 | 16 1/4 | 24 5/16 | 44.6 |
| 3 in 12 | 16 1/2 | 24 3/4 | 44.1 |
| 4 in 12 | 16 7/8 | 25 3/16 | 43.5 |
| 5 in 12 | 17 5/16 | 26 | 42.7 |
| 6 in 12 | 17 7/8 | 26 7/8 | 41.9 |
| 7 in 12 | 18 1/2 | 27 7/8 | 40.8 |
| 8 in 12 | 19 1/4 | 28 7/8 | 39.8 |
| 9 in 12 | 20 | 30 | 38.7 |
| 10 in 12 | 20 7/8 | 31 1/4 | 37.4 |
| 11 in 12 | 21 3/4 | 32 5/8 | 36.5 |
| 12 in 12 | 22 5/8 | 34 | 35.9 |
Dan and I thank you for your interest and support of our Website.
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Hi, I'm Dave Osborne. With over 50 years experience as a journeyman carpenter, foreman and contractor in heavy construction I enjoyed working with apprentices and sharing the tricks of the trade that others shared with me. Now I get emails from Members all over the world and we include many of my answers in our Free Monthly Newsletters. Some of my answers include drawings and instructions specific to a project, but may also answer your questions. I use correct construction terminology, so you can confidently inform your building supply dealers or contractors exactly what you need.
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