Calculating an opening size

When detailing a glass block wall, calculating the opening size correctly is the first and most important step as glass blocks cannot be cut. An opening can be calculated using a formula:

The dimension of the block plus the width of the joint multiplied by the number of glass blocks, plus one more joint width, equals minimum opening size.

**Example 1** *- 4 blocks wide (5 joints) x 3 blocks high (4 joints)*

● Take the dimension of the block, e.g: width = 190mm.

● Add the width of the vertical joint (10mm).

● Multiply by the number of blocks in the horizontal/vertical course.

● Add one more joint width (10mm).

Width | Height | |||||

190mm glass block and 10mm joint | 200mm | 190mm glass block and 10mm joint | 200mm | |||

Number of blocks a) | x4 | 800mm | Number of blocks b) | x3 | 600mm | |

Plus additional perimetre joint | 10mm | Plus additional perimetre joint | 10mm | |||

a) Minimun Opening Width: | 810mm | b) Minimun Opening Width: | 610mm |

If incorporating framing (such as U-channel or box section) the dimensions and tolerances need to be added to the formula measurement. If slip joints or support steel are required then this may also affect the opening size dimensions.

**Example 1** *- 3 blocks wide (4 joints) x 7 blocks high (8 joints)*

● Take the dimension of the block, e.g: width = 190mm.

● Add the width of the vertical joint (10mm).

● Multiply by the number of blocks in the horizontal/vertical course.

● Add one more joint width (10mm).

Width | Height | |||||

190mm glass block and 10mm joint | 200mm | 190mm glass block and 10mm joint | 200mm | |||

Number of blocks a) | x3 | 600mm | Number of blocks b) | x7 | 1400mm | |

Plus additional perimetre joint | 10mm | Plus additional perimetre joint | 10mm | |||

a) Minimun Opening Width: | 610mm | b) Minimun Opening Width: | 1410mm |

Curved openings

For curved walls the same formula is used to calculate the opening width but only applies to the inside face of the curve (shorter radius) (e.g., 10 blocks and 11 joints is 2010mm, the same as a straight panel). The outside width dimension of the curve (longest radius) will be increased dependent on the radii as the blocks are faceted and external joint width will become wider.

The calculation for the height of straight or curved is the same.

The minimum radius required for various block sizes is covered in detail in ‘Curved Panels’.