# Forum Home Renovation Decking  Deck wobble- Bracing? 4 mtres off the ground

## famreeks

Hi, 
I had a deck built years ago and it has always wobbled when you walk across it - so much so that a coffee cup on the table in the middle may splash. It does not appear to be ready to collapse or anything but it would be nice to reassure friends by removing the wobble!! 
It is about 4 metres off the ground and has a V shape stell strap under the deck.  
I have recently added a single wooden diagonal timber length from one corner to the other. 
There is no Post brace. 
Any thing to suggest? 
Mike

----------


## john0

I'd try knee braces on all corners first, lattice between posts also works really well but may not be suitable in your situation. You basically have to stop lateral movement of the posts with what works and looks good in each situation

----------


## UteMad

Wobbly decks dont cut the mustard and i dont blame your friends i wouldn't walk on it either or have paid the monkey who built it....... 
The steel brace underneath is this the strapping with all the holes in it for the nails???
If so its useless as it stretches 
The timber you stuck under as a brace what size was it???
Did you run it from the house wall plate out to the front beam from the middle of the deck at the house side and towards the outer corners at the front... the angle you want to achieve is approx 45 degrees..
the end result should be a V with one brace going either way and butting into each other at the house so there pressure apposes each other 
The timber would be like 90x35 pine or similar and fixed with 86mm nails or 75 mm bugel screws into every joist.. a run off solid blocks through the middle of the deck will also help the brace tighten up the deck if they arent there.. if the floor is braced properly the posts dont have any work to do other than support the down load.. by all means brace the posts but not as the only way to cover up a loose floor structure 
Safety first if it aint good dont put your friends and family on it as you'll be liable if it falls down and this i have seen with a customer we rebuilt a deck for in the past after someone fell off it.. 
Get a proffessional contractor to quote the repairs for you if unsure or get an engineer to do a site inspection and offer his opinion first hand off what he sees on you deck as like anyone who gives any opinion its not based on your deck just decks in general 
cheers utemad

----------


## intertd6

It *needs* timber post braces as per the Standard or you can have a engineer design steel rod "X" bracing
Regards inter

----------


## chuth77

What size is the deck? 
Something else that will help is to half block the joists... i.e. halfway along the joists, put blocks cut neat to be tight between, and nail them between all joists... Makes a huge difference to deck bounce....

----------


## namtrak

A deck 4m above ground wobbling?  That's a pretty basic failure of construction 101a I would suggest. 
Maybe some pics of the underside and topside of the deck would help with some of the analysis

----------


## Ronaldo451

What are the dimensions, how many support posts are there and does it wobble/shake side to side, or bounce up and down, or both? This info will help scope the issue to be solved and possible solutions

----------


## autogenous

Is the deck attached to the house? 
Speed bracing
Cross bracing 
You seriously need to address that before you have your christmas party vanish before your eyes. 
Do you have a picture?

----------


## famreeks

Thanks to all for your replies. I did not know I had replies until checking today.  
As a newbie to the forum I will work out how to do photos and also provide dimenisons at that time as well. 
Stay tuned and I appreciate your input. 
Mike

----------


## famreeks

I am trying to attach the photos to assist you all. Appreciate all the advice to date. 
The deck is approx 6.3 x 4.3. It has 3 posts across the front each around033 apart. The posts are 90x90mm.  
I have added a diagonal timber brace that extends from the front outer ? joist to the back of the decks outer joist. It is 70 x 45 mm Pine. 
I added blocks to assist bounce but the joists were so not square that I had a hard time cutting blocks to fit. But gave it a go and most a very tight even though part of the block has gap with the joist.  
Should I add anything else ??  
Small diagonal post brace to the joist on each post and 2 on the middle post? How long a diagonal? Timber brace size? 
Is there a metal strap that can be put on the underside of the deck now? and tightened? 
Thanks a heap for the advice. 
Mike

----------


## famreeks

Forgot to mention. The joists attach to the old joists which go inside the house floor. The 2 joists attach by way of 1 bolt. I figure there should be at least 2 bolts?! Yes?So I will add another bolt holding the individual joists together. 
Mike

----------


## Vernonv

Hi Mike,
That bracing you have won't do a great deal (but even so, don't remove it). You need to brace from the top of a post to the bottom of the next post and vice versa (preferably for every post). You will end up with an "X" pattern of bracing between the posts. This will aid in stopping the deck swaying from side to side.

----------


## Bloss

> Hi Mike,
> That bracing you have won't do a great deal (but even so, don't remove it). You need to brace from the top of a post to the bottom of the next post and vice versa (preferably for every post). You will end up with an "X" pattern of bracing between the posts. This will aid in stopping the deck swaying from side to side.

   :What he said:  But if you want the area underneath to remain clear then 45 degree bracing at each post on each side as far down as you can will do a good job too. The movement you describe is in the posts not the substructure of the deck so the timber you have put there is unnecessary (but can be left alone if you are happy with the unsightly look). One bolt is never sufficient on any structure so yes get some more fixings in place to.  :2thumbsup:  
Simple rule for all structures - triangles are strong and stable  - squares and rectangles (and their variations) are not (circles are stable too, because they embed triangles, but that's another story). So the idea is is to ensure triangles of some sort strengthen every plane - your deck has bracing in the horizontal plane but still has none in the vertical planes - and with posts that high the forces that create the wobble are against the vertical planes. A bit hard to tell from photos, but bracing is the go. Dunno who built that deck, but if they are licensed - they shouldn't be . . . :Frown:  
Btw the pics are pretty, but it is the posts that need attention so pics of them would be good. As it is fixed to the house at one end bracing on two sides of each post at the outer end would probably be enough.

----------


## Bloss

> What size is the deck? 
> Something else that will help is to half block the joists... i.e. halfway along the joists, put blocks cut neat to be tight between, and nail them between all joists... Makes a huge difference to deck bounce....

  Nah, blocking the joists is not an answer for this problem and it would be odd if this helped any bouncy deck. Blocking is simply to resist twisting of deeper timbers. Bounce is usually due to undersize timber for the spans and loads involved or occasionally poor or failed fixings (or rotting timber). This deck has sway due to insufficient bracing - potentially much more dangerous as it can cause catastrophic collapse. Anyone on it when that occurs is in big trouble - a women was killed in Qld recently when she and 27 others were on a 3-4m high deck that collapsed. It had poor fixing as well as insufficient bracing.

----------


## famreeks

Bloss, 
Thanks for the reply. 
Sounds good. 
I have added 2 more picks hoping this will assist you with what to suggest to me. 
If I understand correctly, - I do not want to place X supports between the posts for visual reasons so I should use a diagonal - 45 degree on each end post to the cross beam and the middle post should have a diagonal on either side of the posts to the cross beam?  
What size timber should I use? 
A builder said he would use a metal strapping that could be installed and then tightened under the deck as it stands. Should I go with this at a cost of $450 or will my diagonal brace efforts suffice? 
Cheers 
Mike

----------


## namtrak

Bloss has got it right, but maybe if you stood back and took a pic from a wider view.  With all these close in pics you cant see the wood for the trees - so to speak. 
I would be using the metal straps and doing it myself.  I think the timber stuff may look a bit cumbersome. 
Cheers

----------


## famreeks

Do you know what the straps would be called?

----------


## namtrak

Its galvanised metal bracing straps.  Comes in rolls of 50m/100m. 
Get a wider pic in here first and some of the bods may give you some ideas on the least obtrusive places to put it.

----------


## barney118

Fam, 
I would say this deck doesnt cut the mustard as it is. Not sure of the joists that have been used it looks like a hardwood/ oregon timbers? For starters I'd give them a thorough check over for rot etc. 
I believe off memory the standard states you have to cross brace the posts, which will be ugly if you want the area open. There are 2 references in A/S 1684 for decks below 1m and decks above 1m for correct sizing of timbers by grade.  
Thats why on building mine I used brick piers to eliminate the cross brace within the posts. 
Alan Stains book gives you the basics (Bunnings). 
Knee bracing is onlt good upto 1800mm high decks, its worth the $30, just looking my 3rd ed, only covers upto 3600mm high decks.

----------


## namtrak

I think we need to place a caveat here as well.  The advice here is all care and no responsibility.  You probably need, as a minimum, to get a qualified expert to at least view the deck.  4 metres is a large and potentially fatal fall for a person, and if there were a few people on the deck it could be quite horrendous.  Take on board, the advice here - but don't use that as your only form of restitution for the quality of the deck.

----------


## Bloss

Steel strapping works only in tension so to be effective here would need to go top to bottom in an X shape on the front and sides. Ugly as can be and dangerous too with sharp edges etc - unsuited to this problem. Timber works in both tension and compression and in this application compression resistance is mainly what you are after. 
As others would know I am a great supporter of Allan Staines books which will give good pointers on this as well as span table etc. Save yourself some pain and trouble - go to Bunnies or others and pay $30 or so for _Deck & Pergola Construction_ or a title similar to that anyway. 
Easiest is to use timber the same size as the joists - say 90 x45 and a minimum of 600mm long - but at 4m up they could be 900-1200 and not get in the way when you bolt them on at 45 degrees. Depends how pretty you want the m to look and what the alignment is, but if the fit in the same plane as the back of the post and the back of the bearers they can just be clamped in place, drilled (two bolts in each - min M8 (5/16") better M10 (3/8"). If there is no aligned planes then they will need to be housed or blocked out (sometime both - at either end, depending on how things line up) then drilled & bolted. 
If all this sounds new the you need to get a pro or some help from someone who has done this before. 
As I think some one else mentioned you could try ready steel bracing angles - of a decent size at least 45mm wide x 6mm and around 500mm x 500mm with a welded diagonal. There are also patterned cast iron brackets that just might be sufficient if fixed well enough in each top corner between post & bearer and between post & joist.

----------


## famreeks

Thaks Namtrak on the caveat. I understand the position of the members and that of the forum and appreciate the advice from the skilled, not so skilled and the smucks like me.  
I am trying to learn and improve as I go and along the way seem to be fixing up others more qualified, supposedly, mistakes they have made at my home in the past. 
The wider shot is now attached which may assist. 
Hi Boss and again appreciate the advice. I will look at the book. 
The deck is exactly 3.7 m off the ground. 
The joists or is it ?  bearers ? are hardwood as well as the posts. 
alignment is, but if the fit in the same plane as the back of the post and the back of the bearers they can just be clamped in place,So the underside of the bearer is the 'back'? the narrow edge that runs back to the house which I have been calling joists!  Or is the bearer the bt that runs left to right across the face of the house and the joists are the ones that run back to front - back to the house!! I think I have it now. 
All the best for Xmas all. 
Cheers
Mike

----------


## famreeks

File attached - OOPs

----------


## president_ltd

crickey, based on this new pic you posted, i am wondering if you're fine with the span tables and code at all ... 
from my laymans observations... 
bit concerned about the overhang at the front - i.e. that the posts aren't on the corners.
as a guess looks to be an overhang of about a metre between the bearer/posts at the front and the ballustrading? 
particularly concerning as it looks like you have a pergola posts from the front corners, now you have wind force to deal with too. 
those posts sure look spindly too when viewed in the context of the height 
the ends of the joists exposed to weather is also not a good thing.  i'd say its not to code.

----------


## Vernonv

Hi Mike,
It's always hard to tell from a pic, but it does look a little "off" (spans, etc). In your original post you said that you had the deck built - who designed the deck and did you go through council to get it approved? 
I reckon you should go for solid (timber or [even better] steel) knee bracing on all posts ... that is if you are totally against X bracing. Did the original plans show any bracing?

----------


## famreeks

It is getting a bit demoralising. The deck was done by a builder. Those you trust when your naive to such things and learn as you go that not all are as thinking as we would all want.  
The overhang from the bearer(the hardwood that runs across the deck) is 600cm. The posts are hardwood and are 95x90. 
X bracing would not look great so I will try the knee bracing- that is angle bracing on the post and bearer correct? 
Will I also put in a second post at each current post site? Sitting flush with existing , running up to the bearer to beef it up? 
It has been up for say 15 years and all has been fine except for the wobble which is to say not like a sway in the breeze but does shake a cup of tea. 
I would like to do enough to add a margin of safety around the deck not create a new deck and I hope that this does not sound ordinary. Just want to make better. 
Cheers  
Mike

----------


## president_ltd

600 overhang is probably ok - just looks like more in the pic - but more than likely code (& span tables) have been updated a few times in last 15 years - what was ok then perhaps isn't now. 
for the hardwood, clearly water can get onto it, so strongly suggest you want them primed/painted anyway.
if that hardwood goes into the ground or into a concrete pad, i'd have concerns on that 15 years later too.  not sure if they sit in stirrups, but even if they do, it needs protecting from the weather nontheless. 
you probably want a fascia board over the front of the joists too - if anything for aesthetic reasons. 
i would go with cross-bracing - at least, front posts to back wall - use wood - provides stability both for compression & expansion. 
may be able to get by with knee bracing on the front length-ways and keep the kids happy with a set of swings that still work. i guess you don't want to cross-brace the front because of view & the kids swings eh?  :Smilie:

----------


## Vernonv

> i would go with cross-bracing - at least, front posts to back wall - use wood - provides stability both for compression & expansion.

  I doubt you will even need bracing front to back wall, as most (all?) of the movement will be side to side (as I doubt the house is moving with the deck). You will certainly need it post to post (for X) or post to bearer (for knee).

----------


## famreeks

Gents! 
Down to tin tacks!!! 
The attached scan of my crude diagram. 
My questions /confirmation needed are: 
The Brace runs across the face of the post and the bearer.
The Brace should be 90 x 45 
Can be hardwood OR treated Pine
Will be 900 diagonal long which means down the post and across the brace approx 650. 
Also to be done on the middle post left and right brace angle.  
Should I beef up the posts by adding a second hard up against the existing posts in stirrups??  
Thanks again and hopefully I shall not take any more of your generous time! 
Cheers

----------


## Vernonv

Hi Mike,
You are now starting to get into specifics. What you are suggesting _should_ work, but to what extent I don't know. If you want a definitive answer you really need to consult an engineer. 
You could always try it and see what sort of difference it makes.

----------


## barney118

Crikey is correct. The overhang (cantilever) is allowed in the std and it will state the amount. The spring you are getting I would say would be from undersized joists or where connected to the house the timber has been recessed or knotched out which effectively reduces the span. 
Look I would say price up the total costs, given a bit of paint will go a long way, check for rot etc, but consider putting in concrete footings 450x450 x 600 or when you reach clay or stable ground and put in brick piers 350x350. Rough guess ~1.5-2K and a fair bit of your own time. You will be up for a couple of hundred to brace and still not achieve the result. 
I'd hate to see another QLD balcony tragedy. Was the council involved approving?  
The bearer is the timber that joins the posts, and the joists are ontop of this. Check the span tables in Alans book, He states quite clearly that Knee bracing is out of the question given your dimensions. The joist measurement is from the wall to the bearer and the overhang the cantilever section.  
the basics are continuous spans and single spans, your bearer is continuos and your joists are single.
there is nothing stopping you putting another bearer midway between the joists which will improve the bounce too.

----------


## kombiman

> File attached - OOPs

  from my initial look: 
The cross bearer looks way too thin 
You need cross bracing @ 4 mtrs, I dont see how it got approval without.  I tried all sorts of alternatives through the engineer on my pavillion structure. 
Get the calculations on spans and bracing for your area through an Engineer and rebuild it to that standard.  That would have blown to bits here in Brisbane in the recent blows.

----------


## Bloss

Wow - I have to agree with others - that is some dodgy deck!  :Eek:  
It looks recoverable, but I reckon you should pay for some advice - but not the $450 to the bloke who was suggesting some strapping. 
The problem you have is that this structure would not be legal in any jurisdiction in the country and to get it approved (not just fixed) you will need plans drawn up that meet BCA specs and get them submitted and approved by your local council (through whatever is the process where you are). Trouble is that might well be costly, but frankly with your limited knowledge and what I have now seen with that latest pic I wouldn't want you relying on a 'fix by website' - however well-intentioned and full of knowledge we all might be. I would have no confidence that the posts are in decent footings - and the council might not be either. 
So, not good news, but I wouldn't be holding too many parties on that deck until you get a certifier or builder to inspect and make recommendations based on that onsite visit and do the work they suggest.

----------


## raff

I agree with the above. Seems very 'under engineered'. From the pictures, I cant see how two posts can support all that weight including balustrading and a roof, irrespective of the joist size, especially with no additional cross bracing. 
Im no expert but from my own deck building experiences, to meet building regs I have used stronger weight bearing specs on my own deck which sits 250mm above the ground than yours which sits 3700mm above the ground. Scary stuff. 
It will definately need council approval and therefore engineering drawings. A costly exercise but better to be safe than sorry, im surprised its still standing.  
I would build as per engineering drawings which may involve running an extra set of posts halfway across the existing span with correct foundation specs with the extra bearer to support the joists. If the existing posts have any signs of rot, I would be running new sets of post/ bearers closer the the end of the deck. That would be my starting point and then add cross bracing from there. Its not hard stuff to do, guys on here can help with the DIY side of things, but the engineered specs and council aprrovals are paramount in a project such as this. 
Goodluck.

----------


## namtrak

Is there an update? 
I would be interested to see where we got upto with this deck!!

----------


## UteMad

Its contemplating what gravity wants to do to it.. Should i go left or should i go right ..or maybe a bit of each.. 
Nah seriously what was the outcome of the wobble 
cheers utemad

----------


## Bloss

> Its contemplating what gravity wants to do to it.. Should i go left or should i go right ..or maybe a bit of each.. 
> cheers utemad

  Stay off it .  .  .   :Biggrin:

----------


## UteMad

The deck or the topic seems to have been running for ages hehehee 
utemad

----------


## pharmaboy2

why not weigh in with an option...  :Wink:  
I had a somewhat similar deck at my last place.  the bracing was donw with visual effect in mind, so stainless steel cables were run at 45 degrees from the corner post back to the house ledger ( above a bolt through brickwork), the other opposing brace from the corner  - in this case the LHS looking at it -  to the centre post.  then fitted with turnbuckles and tightened equally. 
For the deck to woble side to side under those circumstances would require a cable to break, as when one cable loosens the other tightens with twist.  speedbrace wont get enough tension - especially in moisture exposed conditions imo. 
If bracing the underside properly stopped the side ways wobble, its done, if not then front std bracing would be required - in that case again stainless steel cabling could be used with through bolts (not just screwed to the post) which looks better than 90/45 imo.

----------


## Bloss

> why not weigh in with an option...

  Because most of us did in early December when the post was new - the poster has not returned (perhaps taken by the deck?) - that's why the queries.  :Confused:

----------


## pharmaboy2

Sorry Bloss, i was referring to myself - as in, even though it'll probably not be read, i'll weigh in with another opinion anyway, hence ...... and not ?

----------


## Bloss

> Sorry Bloss, i was referring to myself - as in, even though it'll probably not be read, i'll weigh in with another opinion anyway, hence ...... and not ?

  Ah nuthin to be sorry about - I took it a bit literally . . . and missed the self reference, thinking (as I do too often) you'd missed the date of the original post  :Biggrin:  Really would like to know what he did though - one dodgy deck!  :Rolleyes:

----------

