THREE B's

THREE B’s

(No, not those three Lutheran guys Beethoven, Brahms, and Bach. They weren’t famous for their carpentry.)

Blocking is installed in stud walls for several reasons. Blocks are placed to prevent “chimneys” for fire protection, and to provide a nailing surface for sheet rock, etc. Blocks add to wall strength by reducing the “L/d” ratio.

For sheet rock and other cladding, accurately spaced, parallel studs are necessary. Studs can easily be shoved out of parallel by careless blocking, with either too long or too short blocks. Because studs themselves may be warped, the block will often not fit snuggly. Measure the actual space between the stud pairs at the nearest plate to the block, and subtract 1/16 inch for the cut length. This will help maintain the studs parallel or nearly so after the whole wall section is blocked.

When possible, stagger the blocks around the line, with a 1/3 to ½ overlap. This permits direct end-nailing of blocks, in lieu of toe nailing.



Bridging enables neighbor beams to “share the load” under a floor or roof, and provides lateral stability. Bridging used to be made from two pieces and placed in an X pattern; this has given way to using solid sawn wood. As in blocking, achieving parallelism in the beams is important.

Bracing can be temporary or permanent. Remember that forces act in a straight line. Determine the direction of the force you are bracing against, and place the brace in direct linear opposition to it. Brace from “flimsy” to “stout”, not from “flimsy to flimsy”! Efficient bracing makes triangles, (sometimes imaginary) with two points of the triangle at the ends of the brace, and the third point at the intersection of a line along a solid base in the plane of the triangle.

Visualize how the force in a brace will resolve into horizontal and vertical components at the end points. A steeply sloping wall brace will have a smaller horizontal component than a flatter brace, but larger vertical component, and vice versa. A steep brace will have less resistance to the wall over-turning, but a flatter brace will be longer and heavier (assuming it’s attached to the wall at the same point). The best slope of the brace is about 45 degrees. Paradoxically, compression braces to a free-standing wall will actually introduce overturning forces into the wall, the same forces the brace is to resist, so be careful not to apply excessive lateral bending forces with the brace. Braces in compression are less effective than braces in tension. Because a brace in compression acts as a column, its strength and stability is diminished unless it is stiffened along its side. Since temporary braces will be removed, avoid over nailing and remember to leave the nail head proud about 1/8 inch for ease in withdrawing.

Double cross (X) braces not connected at the crossing point will be unstable, unless the brace makes a complete triangle with all three end points fixed.

A final word on the Bs: Do not block the bottom chords of light trusses until they are fully loaded, or nearly so. Remember these chords are in tension and will straighten on their own. Premature blocking may inhibit this, and in extreme cases introduce unwanted tension or lateral stress in the chord.

Also, temporarily brace the top chords of TJIs, etc. against overturn, but it is foolish to waste time bracing their bottom chords.