How to extend existing deck to add aluminium pergola?

[deecay]

Hello! I'm putting together a plan to extend our deck and then install a DIY kit-pergola (aluminium).  Im wondering if the below design/plan looks reasonable to the experts here?

In summary: 

- existing low-level deck sitting next to a slab of concrete that was previously holding a rainwater tank

- I want to anchor a new joist to the joist on the edge of the existing deck, then build out the frame on concrete deck feet

- new frame will have additional joist on the edge with some blocking/reinforcement for the aluminium posts

- new frame needs to navigate around some plumbing against the house wall

- I will be reinforcing the opposite existing corners of the deck with some additional joists/blocking for the other two posts

- deck will sit on top, followed by the pergola posts which will anchor into the deck and underlying joists/blocks

Some dimensions/tech specs:

- area of new deck: 2500mm x 780mm

- area of entire deck (including new): 2500mm x 4500mm

- weight of pergola: 210kg (point load of ~52.5kg per post)

Figure 1: existing deck showing edge joist and beams opposite an empty concrete slab

Existing deck showing edge joist and beams

Figure 2: anchor new joist to existing, then extend out frame along adjustable deck feet, reinforcing corners and wrapping around unmovable plumbing.

Anchor new joist to existing, build out frame on adjustable deck feet, reinforce corners

Figure 3: lay decking

Lay deck

Figure 4: add pergola, anchoring to deck + underlying joists or reinforced blocking.

Add posts and anchor into deck + joists/reinforced blocking

[MitchellMc]

Welcome to the Bunnings Workshop community @deecay. It's brilliant to have you join us, and many thanks for your question about extending a deck.

That appears to be a solid plan and I can't see any issues with it.

I would emphasise the importance of following the manufacturer's instructions for the installation of the pergola, whether you’re attaching to the timber joist frame or the concrete slab. It’s important to avoid connecting to the decking itself since it isn't considered structural timber.

Additionally, ensure that any fasteners and anchors used are appropriate for the materials involved, and check local building codes to guarantee compliance. This will not only enhance safety but also ensure the longevity of both the deck and the pergola. Always a good idea to consult with a professional if you're unsure about any part of the installation.

Please let me know if you have any questions.

Mitchell
 

[deecay]

thanks @MitchellMc !

One follow-up question - the existing joist I wish to attach to is at a slightly off angle to the straight frame extension I need - if I followed it, the framing would veer away from the house wall slightly.  I essentially need to close the gap between the old joist and new joist that starts at 0mm at the house and increases to 23mm at the furthest point away from the house.

What would be the most effective method here? Would I place some shims in between the joists? Or would I attach the new joist at the off angle, then cut the connecting joists at an angle to straighten up the frame? Or perhaps something else?

[EricL]

Hello @deecay 

I technically understand your description, but it would help if we could see the joist assembly you are attaching to. Can I please request for a photo of the existing joist assembly. This will give our members a better idea of what you're joining onto. We can then give recommendations on how to proceed. 

If you need further assistance, please let us know.

Eric

[deecay]

Thanks @EricL, here are two images showing: a) the existing deck and edge joist I was planning to anchor to and b) the same view in my design tool illustrating that the angle of the joist is not perpendicular to the house.  

Figure 1: edge joist of existing deck siting on two cross beams and a waling board attached to house slab

Figure 2: illustration showing the edge joist is not perpendicular to house

[EricL]

Hello @deecay 

Thank you for posting those extra pictures of your deck extension. I'm going with your first idea of using shims as it would be the most convenient. This will save you a lot of cutting and guessing, once the joist is in the correct angle everything should line up properly.

Let me call on our experienced members @Dave-1 and @Jewelleryrescue for their recommendations.

If you need further assistance, please let us know.

Eric

[Dave-1]

Good Morning @deecay 

@MitchellMc and @EricL have covered all the points I would make as well.

I would like to reafirm that the posts themselves should be attached to the concrete themselves not through the deck. Otherwise that would be a very weak point.

If you end up with a too straight looking join line between old deck and new deck, maybe you could feather the boards in by removing a few and swicthing them around so they cover the new and old one end and teh short bit on the old deck instead?

It would be an interesting project to post up here once you have done The issues that you descibe a lot of people have something similar so it would be a good reference point. Please take photos, there are never too many photos!

Dave