decking issues

[grease monkey]

Great site, very useful but I have some questions that maybe some one could help with.

I am building a 1.4m raised decking (well, replacing an old, rotten one).
I plan to use F7 H3 Primed radiata with a Aus. mixed hardwood deck.

1. Are 88 x 88 posts adequate? Is 113x113 (next size avail. in primed) an over kill? (bearer span is 1.6m, bearer 185 x 42, Joist 138 x 42) I have seen a recent project next door where the person used 88 x 88 @ 3.6m to support a deck 1.5M and pergola roof.

2. The posts are to continue past the deck level to become the handrail supports. I plan to use s/s cabling under the handrail (@125mm or less spacing). Is my post size adequate for the force that these generate if I am using the 88 x 88?

3. Are joist hangers as strong as laying the joists on the bearers?
I have only found either 45 X 90 or 120 X 50 hangers in the local hardware. Can I use 45 x 90 for the 138 x 42 joists?

That will do for now.....

Thanks for your advice, grease monkey. Us mechanics will have a go at anything!!!!!

[OBBob]

Hi There

1. I think AS requires that you have to provide diagonal bracing over 1000mm in height??
2. I would have thought you would have a lot of trouble falling against a 90 x 90 handrail and breaking it. I'm not sure ... but you may be able to incorporate the diagonal bracing as part of your handrail above the deck instead of below ... if it suited better?
3. Not sure why you would use joist hangers when you have 1.4 clearance? Definately not as strong and there are a lot of nails to bang in ... about 15 per hanger from memory ... plus you have to curt down all your joists to fit between the bearers. Sure you'd get away with the 45 x 90 but I wouldn't go that way unless you had to. Check the pryda site for hanger sizes, a timber yard probably has more.

Good luck.

[pharmaboy2]

Great site, very useful but I have some questions that maybe some one could help with.

I am building a 1.4m raised decking (well, replacing an old, rotten one).
I plan to use F7 H3 Primed radiata with a Aus. mixed hardwood deck.

1. Are 88 x 88 posts adequate? Is 113x113 (next size avail. in primed) an over kill? (bearer span is 1.6m, bearer 185 x 42, Joist 138 x 42) I have seen a recent project next door where the person used 88 x 88 @ 3.6m to support a deck 1.5M and pergola roof.

2. The posts are to continue past the deck level to become the handrail supports. I plan to use s/s cabling under the handrail (@125mm or less spacing). Is my post size adequate for the force that these generate if I am using the 88 x 88?

3. Are joist hangers as strong as laying the joists on the bearers?
I have only found either 45 X 90 or 120 X 50 hangers in the local hardware. Can I use 45 x 90 for the 138 x 42 joists?

That will do for now.....

Thanks for your advice, grease monkey. Us mechanics will have a go at anything!!!!!

1. yes, mnore than adequate.
2. stronger in tie down effect and lateral forces, not as strong in vertical weight. Having said that, never seen a hanger fail personally (nor a standard joist on bearer).
3. lots of sizes for hangers, widths available include 35 and 45 for H3 treated pi9ne standard sizes - see decent timber supply company for trades - will stock at least 6 sizes of hangers, even bunnies stocks all the 45mmm wide hangers, although not usually the 35 wide numbers.

have fun!

[grease monkey]

Thanks OBBob, It is just as I thought... Yes, I will use bracing ( Have copy of the Staines Bible!)

I originally wanted to stack the joists and use trip-l-grips but my only problem was the asthetic look of the front, having the joists finished by a fascia but still have a visible bearer (deck is in a corner and for the decking boards to run away from the main window, same direction of the bearers [as the mother in law wants it], viewed from front of house). If the joists were hung, it would look better with a single fascia. But with the under bracing, might just talk her into putting battens or lattice to hide it anyway... then the visible bearers wouldn't be a problem.


Thanks. back 2 work

[grease monkey]

Thanks Pharmaboy2.

but I still have on question. WIll the 88 x 88 uprights take the stress of cabling for the mid section? (there will be a 90 x 35 hardwood handrail positioned in between the posts and not on top.)

cheers

[Pulse]

Hey Grease monkey,

The uprights should be plenty strong enough. The BCA has revised the spacing between wires and includes a table. My local inspector just said they prefer 100mm spacings with uprights close together (about 1.5m) If the posts are further apart then the tensions need to increased or the spacings reduced.

Cheers
Pulse

[UteMad]

88x 88 posts are good to about 2.4 m height subject to the m2 each post supports.....

If you want to get the joist to run into the front bearer bolt a 4x2 on the inside of the bearer set down enough for the joists to sit on top flush

Do your bracing under the floor joists its a lot neater and we reckon works better than post bracing which always flexes

cheers Ute Mad

www.dialadeck.com.au (http://www.dialadeck.com.au)

[UteMad]

Forgot to add your better using rougher header treated for joists than the primed ones we find them stronger and better to nail the boards to

cheers utemad

[grease monkey]

Thanks utemad. I don't think I understand what you mean between post bracing and joist bracing. Do you mean putting either horizontal or diaganol bracing in between the joists? How does that effect the post stability as I thought I needed to brace in between the posts to give it rigidity. Also, It has become apparrent that I might have to make the deck free standing and not attached to the wall as the previous deck supports sunk and moved, there fore damaging the wall when it pulled away. I already have to re-mortar 6 bessa blocks back in but I am dubious as to whether I can re-attach to them again.

How is undressed wood better than the dressed primed? Why are they stronger or is it a cost issue?

Thanks, grease monkey out.

[grease monkey]

I wish the budget allowed for all duragal. I could have just welded the whole thing together and it would have been as strong as buggery. ....and rather permanent!!!!

[UteMad]

Thanks utemad. I don't think I understand what you mean between post bracing and joist bracing. Do you mean putting either horizontal or diaganol bracing in between the joists? How does that effect the post stability as I thought I needed to brace in between the posts to give it rigidity. Also, It has become apparrent that I might have to make the deck free standing and not attached to the wall as the previous deck supports sunk and moved, there fore damaging the wall when it pulled away. I already have to re-mortar 6 bessa blocks back in but I am dubious as to whether I can re-attach to them again.

How is undressed wood better than the dressed primed? Why are they stronger or is it a cost issue?

Thanks, grease monkey out.

Can't comment on attachment to the house cause i haven't seen it.... It is always advisable to attach the the house cause it provides a rigid place to brace off

The prime 6x2 are laminated blocks so we prefer to use the solid single piece jobs..... Its funny cause we use the lami primed in large sizes for beams just not the smaller sizes for structural

Joist bracing is simple you solid block the joists if required then put a 90 x 35 under the joists on the angle like a gate brace and attrach it to the bottom of the joists with either nails ...coach screws ... bugel screws etc
We brace our structures under the floor cause if the floor is attached to the dwelling and braced rigid all the posts are doing is holding up the weight.... Obviously if its super high we would brace the posts but it would be more to eliminate deflection in the post than to brace the deck


How bout a photo of where its going

Cheers Ute Mad

[grease monkey]

I see, Iv'e seen that type of bracing in the Staines book. Iv'e Got a new problem.......

on the front wall, the previous deck had sunk and the bearer that was bolted to the wall damaged the wall, pulling away bricks (access opening to underside of house is directly below door) on both sides of the gap between the under access. As it is, I have to re mortar the besa blocks back in but do not trust them again to support a bearer. Therefore, I will still attach the beare to the wall ( not in the same places) but am unable to give the dyna bolts 'decent' spacing so I must use support posts. But the foundation comes out from the wall, under the g/l. How can I attach a post to it? I've come up with an idea.... see attached pictures... but I don't know if it is legal or practical. I can bolt to the other wall so thats not a problem but maybe it may be prudent to include supports as well being that it spans 5.8+M?

Any ideas would be greatly appreciated..

Oh, yea... have a look at the plans. Do I need to brace the whole deck or just the largest area?

Thanks,

Grease monkey

[grease monkey]

sorry, attachments didn't work. I'll try again in zipped format:doh:

[UteMad]

Hi grease monkey ....if you want to post photo's easier go onto photobucket put your image there then just paste the img code straight into your post......

If the wall where the bearer attaches is shot another way is to put a post up the wall against the houst and dyna bolt it to the house with some 125 x 12 galv dyna bolts then house your bearer( wall plate ) into the posts this way the attachment is stil to the house but spread over the whole way down....you can even put a styrup under the post and pour a foooting aswell if you wanted


cheers utemad

[UteMad]

Hi Grease monkey

Here are a few photos that might help

finished job i know lattice is daggy but they are (customers) sometimes the ones with the money!!!!

http://i91.photobucket.com/albums/k287/utemad/Deckstructure-3.jpg


Wall attachment method
http://i91.photobucket.com/albums/k287/utemad/Deckstructure-8.jpg


Another wall attachment method
http://i91.photobucket.com/albums/k287/utemad/Deckstructure-7.jpg



Floor bracing method
http://i91.photobucket.com/albums/k287/utemad/Deckstructure-6.jpg


Another project if you look close you can see floor bracing disregard the piece on the posts its not left there
http://i91.photobucket.com/albums/k287/utemad/Deckstructure-2.jpg


This is with the joists sitting on the front bearer ...far sfer this method for you as a novice
http://i91.photobucket.com/albums/k287/utemad/Deckstructure-1.jpg


Not to discourage you but if your not confident mabye its better that you hire someone to do the deck or hire a chippy if you can find one that will help you do it ..... that way if you have questions you know you'll have the answers at hand as well as someone to help lift and hold things....

Sorry its not an offer though as working with customers would be my biggest nightmare!!!!!


cheers ute mad

[grease monkey]

Thanks for your reply, utemad. This deck has sent me around the bend. It's not like the area is perfect, level with no obtructions. There are heaps of remanents from previous work. Old stairs that have been removed, cracked bricks, uneven wall areas not true nor square, two decks built in the same place and a plethora of old stumps that I keep finding... exactly where I need to place a new foundations. Fortunately, they are only 300x300 and 300 deep!

The pics really helped, that's what I thought under joist bracing was. You have just attached it with bolts on to some nogging in between the joists? I will use that as it is more attractive than post bracing. And yes, I will use joist over bearer method... Just because it is easier with less cuts! (and will take more weight so the mother in law can have big parties on it!!! Hah Hah.)


As for the front wall, I only have a few spots that are secure enough to bolt to. Every brick were the ledger would run are far to corrupt to expect any type of structural bearing. How ever, there are three spots lower down that are integral... exactly where the posts are going to be! I have already decided that I was going to put in three support posts to take the weight of the bearer and then dynabolt the posts to the wall. The only problem is the placement of the stirrup against the wall (as the foudation edge is 150mm under the ground line). The only option seems to be as I laid out in the attached drawing. To build a concrete pier, 600mm down the side of the house foundation ledge and have it overlap the edge to a height of 300mm, thus giving me at least 200mm above the ground line. Then I can bolt a stirrup on top, placing the post along the wall so it can be dynabolted. Is this method reaoneable? Otherwise, the stirrup can only be placed 75mm away from wall. tricky, huh?

cheers, grease monkey.

[strangerep]

I plan to use [...] with a Aus. mixed hardwood deck.

Beware of "mixed" hardwood! It tends to mean a mix of
class-2 and class-3 timbers (e.g: blackbutt and stringybark).
Blackbutt is ok outside, but stringybark is not. Go for a
specific timber species and research its properties carefully.
E.g: tallowwood and ironbark are both class-1.


2. The posts are to continue past the deck level to become the handrail supports. I plan to use s/s cabling under the handrail (@125mm or less spacing). Is my post size adequate for the force that these generate if I am using the 88 x 88?

Beware again. The required tension on such s/s cabling is quite enormous,
if you want to meet regulations. If I recall correctly, for a 1.5m post
spacing, and 80mm cable spacing, 3mm (1x19) cable, you have to be able
to hang a 2kg weight at the middle of a cable span, and it must not deflect by more than 5mm! Larger spacings require even higher tension.

I haven't done the experiment with pine posts, but I can tell you 65x65
blackbutt is not even close (and blackbutt is far more rigid than pine).
Most people use 100x100 blackbutt (or other hardwood), but
when I walk up and press my hand against a cable, I seriously doubt
whether it's tight enough. There's a reason why people use 50mm diam
stainless steel posts for this. And even those can bow inwards by 1-2mm
at the centre if spaced too wide apart.

Try doing an experiment: make up one section of the ballustrade as a
stand-alone frame. Then put in your s/s cabling and tighten it up to
spec (using something which is measured to weigh 2kg). How much
does the wire deflect at the middle? Do the posts start to bow inwards
under the tension.

[UteMad]

To meet current standards the way i get it ...

you can't use horizontal cable with floor heights greater than 4m
for a 1500mm post spacing using 3mm 1 x 19 stainless cable you must be able to tension 1330 N with a 5mm allowable deflection.......
There are ways of minimising the timber post flex that most guys get but thats a secret LOL if you want to put your posts wider or are unable to get the required tension you can buy 40mm x 6mm fat stainless bar with a bend at either end to attach the the floor and under side of top rail (they come predrilled)this will break the span without visually adding another post and cuts down the cable flex.....

cheers Ute Mad