Stacking the Blocks...

All of the following issues are fully described in much greater detail in our new book which is titled DryStacked Construction Handbook. This website will alert you to many of the home construction considerations for using drystacking. The book will show easy step by step methods to work around these and other dry-stacked construction potential problems. While these explainations may seem difficult, the book offers simple solutions using spreadsheet tables or Freeware CAD programs to accomodate most of these block stacking issues. Our new videos also demonstrates the stacking procedures.

Half-block Madness
This detail concerns the fact that half blocks (half in length) are not really half at all. They are 7-5/8-inches long to allow room for 3/8-inch of mortar. So the installed block length of a half block is 7-5/8 + 1/16 = 7.6875-inches, which can be rounded up to 7.7-inches. The 1/16" allows for the fact that blocks can never be perfectly butted against each other. There will always be some slight gap between blocks. We have found this gap to be typically 1/16". Please note that two stacked half- blocks equals 15.4-inches of length instead of 15.7-inches which is the installed length of one full block. This means that two half-blocks in a wall makes that wall's row of blocks short by 0.3- inches. This by itself seems to be no big deal, but just try to stack the next row with all even blocks and that next row will be 0.3-inches longer, which will throw the ending corner or door opening out of alignment.

If another wall had two corner blocks (which are 8-inches wide + 1/16-inch) and full length blocks in between, then that row would be 8.0625 x 2 minus 15.7 which equals 0.425-inches longer than the row above or below. So there you have it, we have two different kinds of half blocks. We have corner half blocks which are whole blocks wrapped around the corner, which have an installed width of 8.0625 inches; and we have linear half-blocks which run with the wall length, and have an installed length of 7.7-inches.

Wall Growth Madness
Wall growth is what happens when the wall starts getting longer on its own. This happens when the previous rows of blocks become unleveled lengthwise. This forces a larger gap between the blocks as shown in the drawing. This slight increase accumulates along the wall and can make the wall end up an inch or more longer as the wall stacks. So here is another fudge factor. Experience has shown that wall growth seems to remain less than 1/16-inch per full block, when you re-level the blocks with mortar after stacking the sixth row. This standard of mortaring the blocks on the seventh row fixes block unevenness and controls wall growth that can accumulate within six rows of stacking.

Where to Measure From
Another dimensioning consideration is to remember where you do the measuring. Because block walls are quite thick (8" + insulation + sheetrock thickness), this thickness should be considered because it will reduce room size when a block wall is involved and measurements are from the outside of the wall. The floor plan must use outside wall dimensions because these set the foundation dimensions which must be large enough for block placement. Many stick floor plans measure from the wall center and this will not work for outside block walls and the associated foundation plan. DO NOT get caught by this middle wall measurement concept used in stick plans. Your Foundation Plan must be accurate!

Out of Plane Blocks
The next concern is about blocks where the top plane and the bottom plane are not parallel. Block lengthwise out of plane don't cause any significant problems, but block width out of plane will make the wall start to lean in or out as these errors accumulate in stacked rows. This problem occurs when the outside of a block is slightly higher than the inside of the block. We are talking about 1/128-inch or less, which is not noticeable with the naked eye. It is noticeable though when the wall starts to lean because of an accumulation of these out of plane blocks.

This problem has an easy solution for correction. Simply check the level (across the wall) as you place each block. When the block is causing the problem, rotation of the block will lessen the problem, or may in fact make the top of that block perfectly level again. The leaning block diagram demonstrates this effect. The left wall leans, but the right wall remains plumb using the same blocks with the same plane error. Simply rotating blocks 2 and 4 in the diagram solved the problem completely.

Stepped Blocks
If you notice that the blocks start jutting in or out relative to the row beneath, just to keep the wall plumb, then you are experiencing a leaning wall which must be stepped to remain plumb. This stepped action is correcting for blocks, which are not level or are out of plane. You should fix the leveling problem and not continue stepping these blocks. Very slight stepping can be tolerated due to the thickness of the SBC. Significant stepping should be corrected to keep your home construction project professional.

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