The exact number of noggins required in floor joists is not a fixed universal quantity; rather, it depends directly on the span of the joists and the number of joist bays in the floor structure. The primary purpose of noggins, also known as blocking or dwangs, is to provide lateral support and prevent the joists from twisting, thereby enhancing the stability and load distribution of the floor.
Noggin Requirements Based on Joist Span
According to building guidelines, the necessity and quantity of noggins are determined by the joist span:
- Short Spans (Less than 2.5m): For joists with a span shorter than 2.5 meters, noggins are generally not required. The inherent stiffness over such a short distance is considered sufficient without additional bracing.
- Medium Spans (Up to 4.5m): If your joists span up to 4.5 meters, a single row of noggins is needed. This row should be placed at the mid-span of the joists.
- Long Spans (Above 4.5m): For joists spanning above 4.5 meters, two rows of noggins are necessary. These rows should be strategically placed at the third points along the joist span, effectively dividing the span into three equal segments.
The following table summarizes these requirements:
| Joist Span | Number of Noggin Rows | Placement of Noggins |
|---|---|---|
| Less than 2.5m | 0 | Not required |
| Up to 4.5m | 1 | At mid-span |
| Above 4.5m | 2 | At third points |
Understanding Noggin Placement and Quantity
A "row" of noggins refers to a series of individual noggins installed in a straight line between each adjacent pair of joists across the width of the floor area. Therefore, to determine the total number of individual noggins required, you multiply the number of required rows by the number of joist bays (the spaces between individual joists).
Practical Examples:
- Scenario 1: Medium Span
- If you have a floor with 12 joist bays and the joist span is 3.5 meters (requiring one row of noggins at mid-span), you would need 12 individual noggins for that single row.
- Scenario 2: Long Span
- If you have a floor with 12 joist bays and the joist span is 5 meters (requiring two rows of noggins at third points), you would need 24 individual noggins in total (12 noggins per row x 2 rows).
It's also important to note the dimensional requirements for noggins: they need to be at least 38mm wide, and their depth should be at least 0.75 times the depth of the joists. These dimensions ensure the noggins provide adequate support and stability.
