As each web opening is added it is checked against certain geometric and proximity recommendations taken from SCI Publication P068.

Guidance on size and positioning of openings

We advise you to comply with the following positional recommendations for web openings:

• Web openings are designed using the bending moment and vertical shear values at the side of the opening where the moment is lower,
• Openings should preferably be positioned at the mid-height of the section. If not, the depth of the upper and lower sections of web should differ by not more than a factor of two,
• Openings should not be located closer to the support than two times the beam depth or 10% of the span whichever is the greater,
• The best location for any opening is between 1/5 and 1/3 of the span from a support in uniformly loaded beams, or in lower shear zone of beams subject to point loads,
• Openings should be not less than the beam depth, D, apart,
• Unstiffened openings should not generally be deeper than 0.6D or longer than 1.5D,
• Stiffened openings should not generally be deeper than 0.7D or longer than 2D,
• Point loads should not be applied at less than D from the side of the adjacent opening.