New deck project have some questions

Thanks for all your responses woodchip, it was very helpful

Originally Posted by woodchip

Don't bother trying to source a 140x70, it would be cheaper to use 2/140x35 handling is easier too.

I haven't gone to the point of working out what was readily available and adjusting my bill of materials (BOM), but I will do that soon

On the deck im doing at the moment I got a 60x60 HDG (hot dipped galvanised) bracket to put under the bearer, you could also put one on the vertical face also to prevent rolling)

Not sure what these things your are referring to are. Do you have a picture or a link?

butt them over the 2/140x35 bearers & add a 140x35 cleat to one side.

I think I know what you mean here. Instead of the cleat can I use a nail plate on both sides? I was going to use triple grips to secure the joists to the bearers. If I was to use a nailplate is it OK to nail the triple grip over the nailplate?

Should be ok if you pre-drill & are careful, I prefer 45mm joists for this reason.

I may well change my BOM as well

Because the 140 are a fairly high joist I'd also block them with a 140x35 block between either side of a joist every couple of metres or so

I'm not sure what you mean by these. Ordinarily I thought you were talking about noggins, but I have them in the plan so I am unclear what you are referring to. Can you elaborate?

Regards,
Z

Originally Posted by Godzilla73

G'day,

With your joists i'd go 140x45mm, on a deck the size of yours you'd be looking at about $200 more. Gives you more timber to fix the boards too, and also helps stiffen the structure up and take the bounce out of the deck.

I think you and woodchip have pretty much convinced me to go that way now.

Z

Originally Posted by zforum69

Hi,

I’m about to embark on my first deck project, which is an L-shaped 45m2 low deck. I’ve been trawling through this forum gathering all sorts of information and have now drawn up a plan but I still have some questions:



Referring to AS 1684 for the span tables, for the bearers it says I need 2/140x35. I really don’t want the extra work of attaching two bearers together. When looking at other tables it seems they have been substituted with 140x70, which is what I plan to do. Is this OK? If so where do you derive these equivalents from, as I could not find it in the standard?

I wanted to use some sort of bearer hanger (like joist hangers) to secure ends of the beans to the wall. I could not find any reference that this was an OK thing to so I plan to use posts. However, I would like to use some sort of bearer hanger as it is less work that putting in a post, so is it possible and if so where do I find the details?

On two walls (brick veneer) I am installing ledger boards (same 140x35 as the joists) which will have joist hangers. These ledger boards need to be set away from the wall as they are going over weep holes. I was planning to use anchor screws to bolt them to the wall. Is that OK and if so how often should it be anchored into the wall is that OK. What should I use to maintain the gap between the wall and ledger boards without compromising the anchor screws.

In my plan to get the 7.9m joist I assumed that I sit two joists side by side on the middle beam. I’m not so sure this is correct as the decking screws would not line up at that point. How should you connect two joists?

With regard to decking boards I assume when joining to deck boards together they should join over a joist. I also assume that each board needs two deck screws to secure it to the joist. On a join as there will be two deck bards, there will be four screws securing the deck boards to the joist. My concern is the width of the joist being 35mm. That will give is each screw 17.5mm of the board to secure it and assuming it screws in the middle that means the centre of the screw hole ill be 8.75mm from the edge of the decking board. Is 35mm enough room to have two screws side by side over two boards, even with pre drilling?

My last question is regarding the steps. I haven’t really thought about it other than the will be 180mm wide and high (2 decking boards). I assume there are many ways to do this but can some body point to some places where I can get some information.

Any advice appreciated.

Z

Mate you need to check your timbers being specified as they are a under rated for the job, from your plans I read the following specifications, corrrect me if i'm wrong.
Bearer span between supports 2075
Joist span 2050 spacing 450 ?

You want to use 2x140x35 F7 ? as bearers, 140x35 F7 as joists

Working on the above spans your bearers are under rated for the three intermmediate bearers (remember these are taking two loads one from each side)
And truthfully a 140x45 is also not suitable for an end bearer, your spans are too big.
End bearer using your specs a 190x45 will be rated to 94% capacity which is WAY to high, you need to drop your bearer spans to around 1800 to get a 190x45 to perform at the 71% capacity.

Specs you should be working from are 62kg/m2 Dead Load, 3kPa Live Load, 1.8kN Live Point load

Intermediate bearers 140x35 x 2 F7 not suitable seriously overloaded capacity, you would need 140x35 x 4 to give you a rating of 83% loaded capacity
140x45 x 2 F7 not suitable still seriously overloaded capacity
190x45 x 2 F7 somewhat suited but nearing its capacity at 85%
190x45 x 2 MGP10 86% capacity

The above figures of 85% and 86% are still too high for what we will build, we try to aim for a figure in the 70% range and your 140x35 or 140x45 are NOT SUITABLE AT ALL
You will need to decrease your bearer and or joist spans, or up the timber sizes to make it suitable

Also your joist of 140x35 are a little light, I would up these to 140x45 for a 51% load rating capacity.

I assume that this deck is not going through council approval, as they would not pass it with the specifications you have presented for good reason
You never build to the maximum capacity of any timber elements.

Figures I am quoting you are not made up, these are generated from the simulation software we use when designing structures for our clients, which are based on the latest AU Standards.

Originally Posted by METRIX

Mate you need to check your timbers being specified as they are a under rated for the job, from your plans I read the following specifications, corrrect me if i'm wrong.
Bearer span between supports 2075
Joist span 2050 spacing 450 ?

You want to use 2x140x35 F7 ? as bearers, 140x35 F7 as joists

Thanks for taking the time to check the timber I chose, I want to be sure. The specifications you derived are correct. My choice of timber was straight out of AS 1684.2-210 Residential timber-framed construction - Non-cyclonic areas. The tables were in the supplement.

Under the N1/N2 - F7 seasoned softwood chapter, there is a section for Verandahs, posts and decks. In there is a table (49) for bearers more than 1m off the ground. Mine is under 1m and there a note under the table to use table (5) for decks up to 1000mm high. Table (5) is for floor bearers - supporting floor load only. So the first question to ask is whether I am using the right table?

Assuming it is the right table, I assume with my deck I need to use the continuous span tables. From the table, a 2400mm floor load width, span (ie not cantilever), 2/140x35 gives a span for 2000. That is almost exactly what I need. So close that if I use posts instead of brackets then the span I need is under 2000. Or if I measure of the middle of the bracket it is exactly 2000. I could use 2/140x45 then the tables say I can have a span of 2300mm. I may well do this considering the joists are going to be that size and i just need to buy one size. But I cannot work out why you say it is way overloaded, unless I am reading the tables incorrectly which is entirely possible so please tell me if that is the case. Your comments make sense if I use the tables referring to decks above 1mm, which is not applicable to my deck.

Also your joist of 140x35 are a little light, I would up these to 140x45 for a 51% load rating capacity.

I've decided to use 140x45 anyway. The joist table (50) says 140x35 can have a 2000mm span for 450mm spacing, continuous span, span (not cantilever). 140x45 will give me 2300.

I assume that this deck is not going through council approval

That's correct. In the ACT you don't need to if it is under 1m.

Again thanks for checking my plan out, I really do appreciate it.

Z

On the supplement 2 span tables see the Notes at the bottom i) Maximum bearer span is based on supporting a maximum decking mass of 20kg/m^2, this is bugger all.

If you really want to base your timber choice on the rating of 20kg/m^2 then that's your choice.

Our program does not even go down to 20 kg/m^2 rating, the minimum it will go to is 30, and the very minimum I would rate any low deck at is 40kg/m^2, at this rating your bearers of 140x35 are at 96% capacity, if you choose 140x45 x2 the beareres will be rated to 75% of their capacity which is fine but you will still have that springy feeling when it is loaded up as the deflection is 3mm.

The rating we design all our decks for is 62Kg/m^2 as a deck will be expected to handle larger loads than an interior floor which is normally rated at 40kg/m^2, the reason why a deck is expected to handle more load is these are usually used in parties etc, and you tend to have a lot of people in close proxiity to each other than you would normally get inside the house.

Whenever you design a structure to be near it maximum, this means you will also be getting maximum movement at all the joints, example for your scenario the following will be the expected deflection.

30kg/m^2 = 3mm deflection of the bearers 71% capacity
40kg/m^2 = 3mm deflection of the bearers 75% capacity
62kg/m^2 = 4mm deflection of the bearers 85% capacity

Alternatively 190x45 x 2
62kg/m^2 - 1mm deflection of the bearers 52% capacity

What this means is the deck will always feel "springy" and will feel worse when you load it up, and over time this springyness can cause connections to start working loose, with eventual failure a real possibility, but for your situation if this does happen thankfully there is not a lot of distance to fall.

I know the Standards show the span tables can do a certain distance but you need to take note of the Notes at the bottom to see where these figures are being derived from, and if they suit your situation.

Any good builder will never build a structure to be near it's maximum limits, you need to leave a good leeway to ensure the structure can withstand whatever the client may do in the future (to a point), this ensures you have a non springy structure that will last the lifetime it should with no problems.

And the difference in materials price to ugrade to the next sized timber is negligable, compared to the cost if it fails.

Thanks for your comments. It is very informative. I have another question:

Originally Posted by METRIX

On the supplement 2 span tables see the Notes at the bottom i) Maximum bearer span is based on supporting a maximum decking mass of 20kg/m^2, this is bugger all.

That table (39) refers to decks above 1m. The table I'm using is for decks under 1m which is table (5). The notes under there say 40kg/m2 but you are recommending 62kg/m2. Does that change things when you say 2/190x45 achieves 62kg/m2 as I have no idea how the tables are derived, for example does 2/170x45 achieve 62kg/m2 for a deck under 1m?

I know the Standards show the span tables can do a certain distance but you need to take note of the Notes at the bottom to see where these figures are being derived from, and if they suit your situation.

Until your posts I had no idea what a suitable decking mass would be. In fact I can't understand why the standard would point me to a table that achieves 40kg/m2 when you are saying 62kg/m2 is more suitable for a deck for the reasons you mentioned which make sense to me, and for that matter why a higher deck (over 1m high) the standard implies that the lower decking mass of 20kg/m2 is suitable .

And the difference in materials price to ugrade to the next sized timber is negligable, compared to the cost if it fails.

Totally agree.

Z

Originally Posted by zforum69

Thanks for your comments. It is very informative. I have another question:



That table (39) refers to decks above 1m. The table I'm using is for decks under 1m which is table (5). The notes under there say 40kg/m2 but you are recommending 62kg/m2. Does that change things when you say 2/190x45 achieves 62kg/m2 as I have no idea how the tables are derived, for example does 2/170x45 achieve 62kg/m2 for a deck under 1m?


Until your posts I had no idea what a suitable decking mass would be. In fact I can't understand why the standard would point me to a table that achieves 40kg/m2 when you are saying 62kg/m2 is more suitable for a deck for the reasons you mentioned which make sense to me, and for that matter why a higher deck (over 1m high) the standard implies that the lower decking mass of 20kg/m2 is suitable .


Totally agree.

Z

Ok will try to clarify.

Table 5 Point i) Maximum Bearer spans supporting roof loads are based on flooring mass of 40kg/m^2

This means that if you are calculating bearer spans with a roof load attached then the figures are based on flooring calculations using 40kg as the base measurement.

Now here is the problem, Table 5 is a "Supporting floor load only" but you will notice on Table 5 they have "Roof Load Width", but they don't give you figures for either sheet or tiled roof ??.
I think this is a typo and it should say Floor Load Width and NOT Roof Load Width, and the point i) should say Maximum bearer spans are based on supporting floor loads of 40kg, I think this point is also a typo for that particular table.

This would make sence, and the figures provided are for loads of 40kg for up to 1000mm which would be the minimum load I would use for a low deck as stated earlier.

Referring to Table 49 for Decks over 1m, the figures provided are based on 20kg/m^2 as stated in point i), this does not mean what they are saying is automatically suited for your situation, it just means this is the base measuremnt they used to derive the tables from, for consistancy perhaps they should have used 40kg as their base measurement rather than 20kg, especially when it is stateing for a deck OVER 1m.

The figures could mislead you to think if you build a deck under 1m it needs to be stronger that one over 1m which make no sense, and the opposite is in fact true.

As I stated when we design a deck we base out figures on 62kg loading because we want the deck to be strong, have no movement to ensure the longevity of the deck, because it is exposed to a harsh environment being rain, dirt, UV, moisture etc, that an interior floor will never be exposed to.

We also don't bother with the span tables but use design software to give us accurate and fast results, we can change the timber members and loads to see what the effect is straight away, the span tables only give you one figure which is MAX span, that is not saying the span tables are not correct, because they are correct, but as they only provide the MAX span this can be a bit limiting for information, we never have and never will build to maximum of any timber member.

The software will give you the span, % loaded up to, deflection, plus we can adjust Dead Load, Live Load, Point loads etc to suit any circumstance, this way we know exaclty the outcome, you cannot get this information from the span tables, we can also calculate end or intermediate bearers, and using any timber from HW, to F Rated Pine, MGP, LVL, Cypress, Tecbeam etc, you would need a lot of span tables to get the information the program can provide, and it can all get quite confusing and mistakes can be made easily, it is just easier to use a tool which generates result in real time.

I have seen a number of people under design their deck, and this is due to two reasons, 1) Genuinely not understanding how the span tables work, II) Trying to skimp out on materials as they don't really understand the difference between one sized timbers performance vs another (and their is big differences), or they think a M8 bolt will do in place for a M12 etc etc.

When you have complying developments allowed, and in places such as ACT the complying development is very open to interpretation regarding decks in comparison to Sydney, things don't need to be signed off by anyone, or checked for safety, and basically Joe Citizen can build a deck thinking he knows how it all goes together from reading up a little and doing a bit of Internet work.

This is where the forums are good because you can come here ask a few questions, get some advice, go away and do further investigations and then decide what you want to do, the most important thing is that when you get advice, you actually listen to the advice, take it all in and try to decipher what's right and what's not right, this is the same for any situation, at the end of the day you want to build something that is safe for your family and friends to enjoy and not put others safety at risk.

I am all for the handyman to give it a go, sometimes they do a better job than the tradies as they take their time, but not always, and sometime critical things can be missed that only comes with experience.

The areas we service Sydney, the councils are very strict on complyng developments in relation to decks, and usually anything over 10-20sqm and any higher than 300mm off natural ground requires DA.
This can be a bit of a pain, but at least you know someone is checking the specifications to ensure it's all correct.

Saying that this does not guarantee a safe deck, as seen recenlty in Sydney another deck which fell down, this situation appears to be due to private certifiers not doing their job correctly, and the builder not building to code so nothing is infaliable, another reason why Private certifiers days are numbered.

Hope this makes sense.

Originally Posted by METRIX

Hope this makes sense.

Yes it does and thankyou for taking the time to explain things.

I am going to take your advice and use 2/190x45 bearers, and use 145x45 joists. I was hesitant with using 190 bearers (which was why I asked whether if 170 was going to be ok) as I was concerned about ground clearance. This is because on the ground I intend to spray with glysophate, lay down weed mat can cover it with some sort of gravel to keep it down. When the deck is down the ground is effectively unserviceable so I don't want anything growing there at all. When looking at it again the ground clearance issue is only at house side but there I am using a ledger board with joist hangers so it will be OK. Everywhere else the bearer height + joist height is OK.

I'm sure I've got more questions to ask, but first need to redo my BOM and then mentally walk through it all to see if I've got all the things covered.

Thanks again,
Z

Ok, I have finalised the plan and written up some construction notes. I aim to start building this weekend so I would appreciate your comments particularly with the questions:

Below is the new plan:



Below are my construction notes:

Timbers

• Bearers 2/190x45 MGP10 H3 treated pine
• Joists and ledgers 140x45 MGP10 H3 treated pine
• Decking boards 90x19mm merbau

Ledger board

• Back (4150mm) ledger board had to be split due to down pipe 560mm from end of wall
• Ledger boards packed out with 20mm decking off cut, to prevent covering weep hole.
• Ledger boards secured with 150mm anka screws, 4 for the back ledger board left of down pipe, 2 for the one to right of down pipe, 4 for front (3080mm) ledger board

Bearers

• Bearers attached to wall with 100x100x75x4mm brackets. Brackets secured to wall with M10x100mm dynabolts, and to bearers with 2 x M10x50mm coach underneath bracket. Additional bracket installed vertically to prevent bearer from rolling, also secured with M10x100mm dynabolts M10x50mm coach screws.
• Question: Is 75mm bracket should be OK with 90mm (2x45mm) bearers?
• Bearers resting on full stirrup posts (of various heights) embedded in concrete footing directly attached to bearers with M10x50mm coach screws.
• On the 2 front long bearer stretches I staggered the joins, one join is carried on the 4th stirrup post from the wall, the one is carried on the 3rd stirrup post from the wall.
• Question: When the stirrup post is carrying a bearer join, do I have to do anything else other than attaching the 4 coach screws

Joists

• I was aiming for a joist spacing of 450mm. What I ended up is with 464mm and 456mm apart. If I add another joist on the shorter spans it will be 387mm apart and on the longer one it will be 410mm. Question: Is the way I have it on the plan close enough to 450mm, or do I have shorten the joist spacing?
• Joists are attached to ledger boards with joist hangers and attached with 35x3.15 timber connector nails. Two joists are 50mm away from wall to allow room for attachment of joist hangers. Question: Will the resulting 50mm overhang on the decking boards be an issue?
• The longer joists spans of 7900mm will be joined end-on-end so that the deck screws stay inline. I staggered the joins, so that they do not all sit on the second bearer. Question: Do I need to use a steel connector plate on these joins, or will the skew nailing into the bearers be good enough?
• Due to down pipe the joists had to be cantilevered by 110mm.
• Blocking for joists as per plan. I putg blocking either side of the bearers on the long joist spans as that is where the joins for the joists will be. Question: I did not put any near the ledger boards as the joists are secured with joist hangars, is that correct?
• At the end of the joists I will put a header joist. Question: Is securing just by nailing through to the end of the other joists OK?
• Header joist will need to be split in two. Question: Do I just use a steel connector plate to join the two header joists, as I’m not sure if there is enough room to join the width of a 45mm joist end? Can I assume I don’t need any blocking here as the header joist will to the job?

Steps

• For the perimeter steps I intend to install box steps as per plan, ranging form one to three steps. Question: Is my proposed tread size of 3 decking boards (270mm) wide with a riser of 2 decking boards (180mm) high OK?

Regards,
Z

No comments?

I'd appreciate any feedback before I start this weekend.

Z

What software did you use for the deck plan ?

Cheers,

Raging

Originally Posted by raging

What software did you use for the deck plan ?

Cheers,

Raging

Sorry for the late reply, just saw your post. I used visio, not for any other reason other than I know how to drive it due to me using it a lot in drawing network and IT diagrams.

Regards,
Z

Originally Posted by Bloss

Make sure that all your timbers are spaced not at the minimum spans - Metrix's advice is spot on. You might already be across this, but in case your are not you should note also that the ACT is not a simple 'under 1m' is exempt.

The ACT has two approvals that might be required - 'development approval' (DA) and 'building approval' (BA). See Section 1.48 at pp 147 here for decks http://www.legislation.act.gov.au/sl...pdf/2008-2.pdf. The need for approvals hinges on a number of caveats relating to the boundaries of the block and in some cases a deck between 400mm and 1m might need one or both approvals. Most won't as will be under BCA 10a rules - but you should confirm anyway - or take the punt as it is your risk and your consequences.

Main thing is to construct it safely and well - this forum can help with that.

Thanks Bloss

First up, I'm in Melbourne. Sorry for the confusion.

I guess what I was wondering is when Matrix says:

"Specs you should be working from are 62kg/m2 Dead Load, 3kPa Live Load, 1.8kN Live Point load"

and:

"The above figures of 85% and 86% are still too high for what we will build, we try to aim for a figure in the 70% range "

Does he mean to shoot for 70% of their conservative tables or the Australian Standard ones?

Whilst i have your attention, if I chose to use joist hangers to help gain more clearance, assuming the correct ones are used properly , will they affect the rigidity and longevity of the structure by much? ie will I notice a difference in feel?

Hi,
What program did you use to draw your plans?
Cheers
Trev

Originally Posted by treble

Hi,
What program did you use to draw your plans?
Cheers
Trev

Check post #20

Cheers
thanks