And Here's the First Pitch!

Roof pitches are expressed in several ways depending on where you are building.  Common in the United States is to use a number over 12.  That is, for every 12 inches you go horizontally, a certain pitch will go up a certain number of inches.  A 4/12 pitch roof goes up 4" for every foot it goes out.  It's a rather shallow roof, easy to walk on but still sheds rain in all but the most of monsoons.  It's not highly aesthetically pleasing though unless it utilizes 3' overhangs for a prairie style look.  An 8/12 pitch roof CAN be walked on with the right shoes but also looks much better and can have livable attic space.  This convention can be used for any number.  A 16/12 roof is not unheard of.  A 21/12 pitch roof will give you a nice equilateral triangle.  Though most designers won't even think about it, it is perfectly acceptable to call out a 5.71/12 pitch roof if that would help make the roof plane 20' even instead of 20'-7.5".

In other countries where the X over 12 makes less sense due to the metric system, degrees of pitch can be used.  This is almost simpler on one hand.  But building it in the field requires a different skill set or tool.  A high schooler might immediately understand a 30° pitch roof better than 7/12.

For your convenience here is a simple chart showing the comparison of roof pitches to angles:

1/12	4.76°
2/12	9.46°
3/12	14.04°
4/12	18.42°
5/12	22.62°
6/12	26.57°
7/12	30.26°
8/12	33.69°
9/12	36.87°
10/12	39.81°
11/12	42.51°
12/12	45°
14/12	49.40°
16/12	53.13°
18/12	56.31°
21/12	60.26°
24/12	63.43°
27/12	66.04°
30/12	68.20°
45/12	75.07°

Or you can use this handy calculator.

Istockhouseplans strives to make the best use of your materials.  If you would like us to analyze your plan and convert roof pitches to the most economical use of your lumber, please contact us.

Lumber Sizes

Ever notice that a 2x4 isn't really 2"x4"?  What's with that?   Fact is that the piece of wood started at 2"x4" but is called "rough sawn", that is it has unfinished faces.  The stick is then sent through a planer to smooth the faces and reduce serious splinter casualties.  About 1/4" is shaved off of each of the four faces resulting in a lesser dimension than you would expect.  Besides, who would want to say "one-and-a-half by three-and-a-half"?  Mind the twist at 2x8 and beyond...

Now pay attention as we mention dimension convention:

1x:

• 1x2 = .75" x 1.5"
• 1x3 = .75" x 2.5"
• 1x4 = .75" x 3.5"
• 1x6 = .75" x 5.5"
• 1x8 = .75" x 7.5"
• 1x10 = .75" x 9.5"
• 1x12 = .75" x 11.5"

(5/4 material is similar but is 1" thick)

2x:

• 2x2 = 1.5" x 1.5"
• 2x3 = 1.5" x 2.5"
• 2x4 = 1.5" x 3.5"
• 2x6 = 1.5" x 5.5"
• 2x8 = 1.5" x 7.25"
• 2x10 = 1.5" x 9.25"
• 2x12 = 1.5" x 11.25"
• 2x14 = 1.5" x 13.25" 

3x: (for those odd structural plates that engineers like to call out)

• 3x4 = 2.5" x 3.5"
• 3x6 = 2.5" x 5.5"

4x:

• 4x4 = 3.5" x 3.5"
• 4x6 = 3.5" x 5.5"
• 4x8 = 3.5" x 7.25"
• 4x10 = 3.5" x 9.25"
• 4x12 = 3.5" x 11.25"
• 4x14 = 3.5" x 13.25"

6x and beyond follows typical pattern as above.

And while we're at it, how about some typical engineered wood sizes.

I-joists are created by standing a piece of OSB or plywood upright and capping it with a 2x flange.  The result looks like a capital serif 'I' hence the name.

I-joist flange widths (varies by manufacturer):

• 1-3/4"
• 2"
• 2-5/16"
• 3-1/2"

I-joist heights (total height):

• 9-1/2"
• 11-7/8"
• 14"
• 16"
• 18"
• 20"
• 22"
• 24"

Laminated Veneer Lumber (LVL) beams are created by gluing several sheets of 7/8" thick plywood together.  Installation is by standing them on edge so that the profile looks similar to |||

LVL widths:

• 1-3/4" (2 layers)
• 2-5/8" (3 layers)
• 3-1/2" (4 layers)
• 5-1/4" (6 layers)
• 7" (8 layers)

LVL heights:

• Any height possible though generally intended to match I-joist material.  Can match dimensional as well.

Glu-lam beams are created by gluing and compressing several layers of post milled dimensional lumber together.  The whole beam is then planed again to create an even surface.  For this reason, glu-lam beams are slightly narrower than dimensional lumber.  *The industry has recently changed to also offer Gle-lams in full 5-1/2" widths as well.  Heights are always in multiples of 1-1/2" due to the size of the plies.  *The industry has recently changed to offer heights that are consistent with solid sawn and engineered lumber as well.  Due to general engineering practice the height should always exceed the width though rare exceptions always exist.

Glu-lam widths:

• 3-1/8"
• 3-1/2"
• 5-1/8"
• 5-1/2"
• 6-3/4"
• 7-1/4"
• 8-3/4"
• 9-1/4"
• 10-3/4"

Glu-lam heights:

• 6"
• 7.5"
• 9"
• 9.5"
• 10.5"
• 11.875"
• 12"
• 13.5"
• 14"
• 15"
• 16.5"
• 18"
• 19.5"
• 21"
• 22.5"
• 24"

Glu-lams can be used as posts as well.  A 3-1/8"x6" glu-lam post is sturdier than a 4"x6".