Should you expect a little spring in a new deck?

[banjo]

Hi Team, just joined and first post but I'll admit that I have been browsing for a while and taken inspiration from other peoples projects.

I'm just finishing up a low level deck extension (Please ignore the tired older deck in the photos, I will be coming back to fix that up once the new part is done)

So in my mind everything is built to code and technically exceeds it I believe but I have a question regarding some spring/bounce in the deck now that I have laid the decking. Please note, I have yet to completely finish screwing the boards down. In most cases there is only a single screw per board per joist and in some cases, every second joist may have no screws just yet for that run of board. So I do wonder if completing the screwing will tighten it all up further, but thought I should ask at this point anyway.

Now I did purposely maximise my spans as much as possible. I chose to spend more on material than digging holes - my least favourite part lol. So there 3 bearers, one front, back and on the 45 degree.

The new part of the deck is completely independent to the old deck.

The specs are:

Overall size is just under 6000 x 4000 on the longest sides

Longest side has 4 posts at ~1950 centres
Back side has the same with a shorter spacing on the inside post closest to the centre of the old deck.
45 degree has a wider centre between posts (there are only two) but is still to code and is carrying a shorter joist span. (Note that the cantilever on this bearer is actually only a 3rd of what you see in the photo as it's now been trimmed to be square with the front bearer)

Bearers are 2/190x45

Joists are 240x45 at 450 centres

The whole subframe was nailed with a framing nailer. Deck is being screwed down.

So yeah, is a little spring/bounce completely normal and expected? The span for the joists is quite big, but less than the maximum span for 240x45 and when I stood on the centre of a single joist before putting a deck on, I didn't notice any flex at all. It's only now with the decking on that I am feeling it.

Thanks for reading and happy to answer any questions

[EricL]

Hello @banjo 

Welcome to the Bunnings Workshop community. It's wonderful to have you join us, and thanks for sharing your question about your deck.  

Wow! What an impressive decking framework. The material you've used really stands out, however, having maximised the span and not putting in extra bearers in the centre is possibly causing the joists to flex when weight is applied. Not a great deal mind you, but enough for it to be noticeable. 

I suggest using BuildTuff 300 x 300 x 90mm TuffBlock Instant Foundation System Deck Support under the joists. The other option of course is to install two more bearers in the centre, but footings will still need to be installed to support these.

If you have any other questions we can help with, please let us know.

Eric

[banjo]

Thanks Eric for that suggestion, I might look into the tough blocks as that seems like something I could do retrospectively and quite simply.

It's funny, I noticed that if I stand on it bare foot that actually when I notice the spring. With shoes on (or boots as I was laying it) you don't really notice at all. I'll finish fixing all the boards down and then decide if I think it's really necessary to put some extra support in because it's really just a small amount of reverberation that I'm feeling. I'm also wondering if with a bit of weight on the deck if that will actually dampen that little bit of spring out as well.

[Fatsquare]

Merbau price almost doubled compared to the last project I had done  in 2017.

[EricL]

Hi @banjo 

I don't recommend putting extra weight on the deck to reduce the flexing. This will technically have the effect of bowing the joist. It will not appear immediately, but if enough time passes it will become noticeable and repairing it will become a whole new issue. I propose adding the extra posts to eliminate any flexing in your joist assembly.

Eric

[banjo]

Thanks Eric, by weight I only meant some outdoor furniture. In the end though I had my son jump on the deck whilst I observed from underneath and could see that the joists were flexing midspan. Again, I’m a little surprised given I’m well inside the code but let that be a lesson for next time.

I ended up putting a midspan bearer in under the longest joists. I laminated 2 x 140x45’s and used the tough blocks as you suggested to put four posts underneath. Cost me $180 and a few hours crawling around under the deck.

The spring in the deck has now completely gone. But I’m not surprised considering I now have 240x45 joists spanning a max distances of 1860. It’s now massively over engineered but I’m pleased with the result.

I think if I ever build another deck again I would seriously consider using the tough blocks. Concreting the posts at least in the corners to lock it in then using the tough blocks everywhere else would be a really good combo and the cheapest and quickest option you could do. Thanks for the suggestion!