Bearers
The sizes for these structural timbers is the most obvious requirement from NZS3604, however it takes a bit of interpreting from NZS3604. Firstly the size of the bearer is dependant on the grade, the maximum span of the bearer (continuous over two more spans), and the loaded dimension of bearer (please see the diagram). Also the "Wet in Service" table needs to be followed, this comes with a 2Kpa load.
SG8 grade bearers for wet in service use with a 2KPa load from table 6.4b from NZS 3604
| Maximum span of the bearers (continuous over two more spans) (m) | Loaded Dimension of Bearer (m) | Bearer Size (Width x Thickness in mm) |
| 1.3 | 1.2 | 90x90 |
| 2.3 | 140x70 |
| 3.0 | 140x90 |
| 4.3 | 190x70 |
| 1.65 | 0.7 | 90x90 |
| 1.4 | 140x70 |
| 1.8 | 140x90 |
| 2.7 | 190x70 |
| 2.0 | 1.2 | 140x90 |
| 1.8 | 190x70 |
As an alternative to SG8 grade bearers SG6 or SG10 grade bearers may be used as per the tables below: SG6 grade bearers for wet in service use with a 2KPa load from table 6.4b from NZS 3604
| Maximum span of the bearers (continuous over two more spans) (m) | Loaded Dimension of Bearer (m) | Bearer Size (Width x Thickness in mm) |
| 1.30 | 0.8 | 90x90 |
| 1.5 | 140x70 |
| 1.9 | 140x90 |
| 2.7 | 190x70 |
| 1.65 | 0.5 | 90x90 |
| 0.9 | 140x70 |
| 1.2 | 140x90 |
| 1.7 | 190x70 |
| 2.0 | 0.8 | 140x90 |
| 1.1 | 190x70 |
SG10 grade bearers for wet in service use with a 2KPa load from table 6.4b from NZS 3604
| Maximum span of the bearers (continuous over two more spans) (m) | Loaded Dimension of Bearer (m) | Bearer Size (Width x Thickness in mm) |
| 1.30 | 1.2 | 90x90 |
| 2.3 | 140x70 |
| 3.0 | 140x90 |
| 4.3 | 190x70 |
| 1.65 | 0.7 | 90x90 |
| 1.4 | 140x70 |
| 1.8 | 140x90 |
| 2.7 | 190x70 |
| 2.0 | 1.2 | 140x90 |
| 1.8 | 190x70 |
Cantilevered Bearers
With bearers it is possible to have the bearer cantilevered at each end. The maximum distance is set out as below:
- Bearers at spacings not exceeding 2m: 300mm
- Bearers at spacings exceeding 2m: 200mm
Bearers used in ROBO Deck Designer
For the low and pergola decks, a SG8 bearer size of 100x100 is used, though a 90x90mm size could be used due to the differences in rough sawn timber sizes.
For the medium height decks, a SG8 double bearer of 150x50 is used, though a double bearer of 140x45mm size could be used due to the differences in rough sawn timber sizes.
Also the bearers are cantilevered by 175mm
Connections of bearers to posts
There's two types of connections to posts:
- A standard join
- A butt join between two lengths of bearers, please see the webpage on posts for more details.
For more information on bearers for a deck, please refer to NZS3604.
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Disclaimer: Whilst this website contains a lot of information on the design of decks which has been produced with the highest level
of professional care, ROBO Deck Designer, ROBO Design Solutions or Paul Roberts (the developer of this website) does not accept any responsibility for
the accuracy of the information on this website. This website is intended as a guide only, please refer to the New Zealand building code for the
appropriate regulations. | 
