Roof pitch calc. and culvert type/depth?

[TC18guy]

4/12 pitch means 4' Vertical per 12' Horizontal. All you need to do is divide 4/12 then multiply by your Horiz. dist. to get the height.

4/12 * 2' = 0.66' * 12"/1' = 8" i.e. at 2' spacing every perlin is 8" longer than the one before it. You will need to take in account your overhang though. So with a 1' overhang you will be 4" at the wall, 12" at your first 2' spacing, 20" at your next, etc. you should be 3'-8" high at the peak.

 

[tc35dforme]

Can't dispute the calcs.... but I always thought a purlin was a member than ran perpendicular to the rafter ( or trusses top chord ) that was generally used for attachment of roofing or sheathing /forums/images/graemlins/confused.gif.

 

[cj7]

You may want to check with your township on the culvert size. They may have a min they want and a distance back from the road. Also make sure that there are not any other utilities where you need to dig. I am sure there is a number you can call and the comanies will be notified. Around here it is a $1000.00 fine if you did not call and damaged something.

I just installed a 12" smooth bore culvert (plastic). We dug an 18" wide ditch and backfilled with 2A modified. There is about 6" of 2A on the top. My excavator suggested that we let it settle for a few weeks with light duty traffic before bringing a tri-axle across it. There is not much drop on mine it alomost looks level as it is at the low spot of all surrounding ground. It works fine.

 

[johnday]

TC35; You are right about the purlins, but you have to know the lenghth of your rafters and space the purlins appx 24" OC. You would divide the rafter lenghth by 24" and add one purlin for the right spacing. CAUTION; I used 24" spacing just as an example, check wiyh your local BI to see what HE wants. /forums/images/graemlins/smile.gif

 

[California]

Roof pitch calcs: Looking back over the posts here I see a lot of variation in terminology. It helps to define terms: 'Rafters' run down from the roof's ridge to the 'plate' (the top of the wall) and usually extend a foot or two beyond to put the drip line beyond the wall.

A 'purlin' is a timber added between two rafters, or across the top of the rafters, for example to support long panels of corrugated roofing on a big barn. 'Jack studs' rise vertically from the end plate to the end rafter on a simple roof where the roof's ridge is as long as the building. (or next-to-last rafter if the ridge overhangs the end of the building).

The calculations giving rafter length for any given rise are stamped on the side of the traditional (16"x24") framing square. Buy a new square that includes the manual to explain what the stamped tables mean. Be sure to add the overhang when calculating the length of lumber you need.

A rafter table book will be needed for more complex roofs. For example length of the ridge for a hip roof (a roof that slopes down to meet all four walls), the length of its hip (corner) rafters, and even the side cut compound angles for the upper ends of the jack rafters that rise from the wall to the hip rafters. After you understand these tables you will find they are also stamped on the side of the framing square, but are probably useless there without the explanation that the book provides. An electronic builder's calculator should calculate the same tables as a rafter manual but it's more expensive and just as difficult to learn.

After college I made a stake to pay for grad school by joining the Carpenter's Union and worked as a framer for a few years. Believe me, carpenter's math is a precise science where rafter tables are essential and trigonometry is irrelevant. A rafter table book is a lot cheaper than the wasted material caused by cut-and-try.

 

[johnday]

Willy; I ran your numbers for you. The length of your rafter is 10' 6 1/2", minus half the thickness of the ridge board. This measurement is from the outside edge of the top plate, or in the case of a polebuilding, the top girt, along the topside of the rafter.
Since your going to need a framing square to lay this out, do what California suggested and get one. They aren't that much, and there is a lot of info on them that you can use instead of dazzling your buds with math. Also a rafter table is easy too. Good Luck. /forums/images/graemlins/laugh.gif

 

[Theowegian]

What does 15" pipe cost per foot in your area?
dwight

 

[tc35dforme]

<font color="blue"> A rafter table book will be needed for more complex roofs </font> That's why we love AutoCad....build it in the computer and then ask it for the dims..... /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

But seriously...good info in your post...

 

[TWINKLE_TOES]

The rafter length is not equal to the distance from the peak to the wall (10' 6 1/2 inches). The 10' 6 1/.2" is what you would measure standing inside the roof from the outside wall to the inside peak. The rafter sits on the plate (wall) and butts to the ridge pole. The uncut length of the rafter must accomodate the overhang the angle to the facia board, The width of the ridge pole(the error using 1/2 the ridge pole thickness is quite small ~1/32) and the ridge pole angle. For 2x6 rafters add 1 and 13/16 for each angle.

Or get a rafter table and spend your time working instead of running numbers.

 

[johnday]

If you measure along the top, then use your framing square to to mark the birdsmouth plumbcut, guess what, you'll have the same measurement as you would on the method you describe. I always use a 2X for the ridge which comes out to 3/4". at any rate, the rafter will wind up being the same length from plumbcut to plumbcut. Give it a try. Or, you can just step it off with the framing square.
or, even better, use trusses, I find it hard to believe there will be any disagreement there. /forums/images/graemlins/smile.gif