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STRUCTURAL WOOD ASSESSMENT
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WOOD STRUCTURE ASSESSMENT
How to measure the level & plumb position of a deck, floor, post, wall or other structure. This article summarizes methods to check that a deck or other structure is level and plumb - important measures to assure that a structure and its connections are safe and properly made.
This article series describes critical safe-construction details for decks and porches, including avoiding deck or porch collapse and unsafe deck stairs and railings.
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The cardinal rule of carpentry can be summarized as follows: build it plumb, level, and square.
The best materials, finest tools, and greatest design cannot overcome a structure that has been put together contrary to this principle, since errors in any one of these attributes can quickly multiply as the project progresses.
[Click to enlarge any image]
“Plumb” means true to a vertical plane. A plumb object takes maximum advantage of gravity, transferring loads directly to the earth. “Level” means true to a horizontal plane (that is, to the horizon).
And when a plumb object meets a level object, they form a 90-degree angle, which is the basis of “square.”
Fortunately, each of these properties can be checked easily with the techniques described here. By monitoring your deck building for plumb, level, and square at each step, you can ensure that succeeding steps start off on the right foot.
How to Establish Plumb - Perfectly Vertical Posts, Walls, Other Structures
When you start installing the posts for your deck, you will need to make sure that each one is plumb. To do so, hold a carpenter’s level securely against the post, then move the post until the bubbles are centered in the two end vials. Check and plumb two adjacent sides.
Another tool that can be used is a plumb bob. On a still day, a plumb bob will hang perfectly straight up and down from a piece of string.
How to Find Out if a Framing Member or Structure Level
When you are using a level to check a long board or post, place the level at several spots along the entire length. If the bubble changes resting spots from one location to another, the lumber is probably bowed and may need to be replaced.
Squaring up an irregularly-shaped deck (left) still requires that its surface be properly leveled and its posts properly plumb.
Levels are some-what delicate tools. To see if yours is accurate, place it on a flat, solid surface that is nearly plumb or level. With the level in position, take a close look at the location of the bubble. Then, without lifting the level, rotate it on its axis 180 degrees, and let it come to rest in the same position on the surface. If the bubble 4s in the same position as before, the level is accurate.
Sometimes you need to establish a level between a reference point on one surface, such as a ledger, and a point on another, such as a post, without having an installed board between them on which to set a level.
There are several methods to accomplish this chore easily and reliably.
How to Check the Deck Floor Frame or any Wall or Floor Framing Installation for Squareness
Most decks are rectangular or made up of several adjoining rectangles. If the corners of the frame are not square, the decking will be harder to install and the results may look odd or worse. There are two methods used by carpenters to check for square, depending on the situation.
Measure Diagonals to Determine if a Frame is Square
To quickly determine if a rectangle is square, measure both diagonals. If they are identical, the corners are square. Be sure in using this method to confirm you are working with a true rectangle; check that parallel sides are exactly the same length.
Use the 6-8-10 rule to Determine square or right angles in deck, porch, floor, wall, or roof framing or any other buildng framing or construction task
To check a single corner for square, use the “3-4-5” technique. Measure along one side 3 feet, along a perpendicular side 4 feet, then measure the diagonal formed between these two spots.
If it equals 5 feet, the corner is square.
This approach can be even more accurate if you use a set of larger numbers that have the same ratio, such as 6-8-10 or 9-12-15.
Everything you ever wanted to know about the 6-8-10 rule for squaring up anything you're building can be read and the mathematical underpinnings of angles, slopes, and tangents can be read at FRAMING TRIANGLES & CALCULATIONS.
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