How to extend deck and add new bearer?

Question

Hi, I'm looking to extend my current deck. It's been suggested to me that i add a new bearer to my existing last bearer (laminate) to both the bearer and joist and then do inline joist hangers of the new joists out to new stumps/bearers. I've got my head around the new 190 x 45mm bearer connecting to the existing 90 x 45mm joist and 90 x 45mm x 2 bearer (which sits across three stumps and a brick pier) but have concerns that the new 190 x 45mm bearer is 'floating' and not sitting on anything. The existing deck is 4.8m wide and the extension would only be 3.9m and would extend out 2.66m to the near stumps (or slightly less if i cantilever the end 300mm).

The new joists would be 190 x 45mm as well.

The chippy i'm talking with says that the laminating of the new bearer to the existing joist and bearer should be enough, but i'm still unsure. Any advice would be great. I don't have the space to add new stumps and the connecting point.

Pods · Answer

Thanks Jacob. I'll suss out those two options further.

Forgot to add, if we have any engineers/chippy's lurking happy for any feedback/input/thoughts.

Cheers

JacobZ · Answer

Hi @Pods,

Thank you for the additional details and photos, they certainly help.

It really is quite tough to advise on this as when you are laminating a new bearer to the old bearer, the whole load that your new bearer is supporting is actually being taken by the bolts that attach these bearers together. In standard decks, bearers always sit directly over the posts, so the weight is sent directly down into the post, then into the foundation below. In this situation, that is not the case, it is transferred laterally, through those bolts.

It could well be fine, and the calibre and quantity of bolts certainly sounds good, but as it is outside the norm when it comes to deck building, it is not something we can really advise on.

In this situation, I'd either ask your chippy to point you towards the specific part of the relevant Australian or New Zealand standard for deck framing that states this is an acceptable solution or speak with a structural engineer for their guidance.

Let me know what you think.

Jacob

Pods · Answer

Thanks Eric. See image below which i hope explains it a bit better (note: the existing dwelling wall spans the entire existing deck; AI error).

The extension will be connected to the last existing bearer which is approx. 300mm from the edge of the existing deck. The Plan is to remove the cantilever and then affix the new 190 x 45mm bearer to the existing bearer and joist- sketch also below for proposed attachment. Existing bearer is a laminated 90 x 45mm x 2 and joist is a 90 x 45mm.

The attachment to the last bearer would be via m12 hex gal 180mm bolts and 50 x 50 square washers through the new and existing bearer and then using Simpson SDWS TIMBER structural screws into the joists (2 per joist). The bolts would be spaced at one bolt between each of the joists, so probably 10-11 total (noting the bolts are through the bearers). I’d also add extra blocking between the two joists closest to each end of the new 3.9m bearer.

The extension will be approx. 2.66m in depth (2.36m of new deck and .3 of replaced cantilever) and 3.9m in width. The new joists would be 190 x 45mm (approx. 12 of them) and i would use joist hangers at the new/existing deck connection point and then a laminated 190 x 45mm bearer over three new concrete stumps at the other side of the new deck.

The existing deck is supported by three bearers on concrete stumps (3) and a brick pier and one bearer bolted to the house. Existing spacing is approx. 1500mm across the bearer.

The existing deck has a roof structure (thus the left and right posts notes) but they are not tied into the deck and are free standing.

Hope that's helpful. Would greatly appreciate any feedback.

Thank you