4 foot Beams for deck / 2x10s versus Two 2x8s

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Old 05-17-18, 06:25 PM
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4 foot Beams for deck / 2x10s versus Two 2x8s

Hi,

I've looked through all the span tables, beams, etc and I cannot find anything at all that speak to this.

I am building a small deck off my patio door, it's going to be 4' x 8' (8' along the house, and 4' out).

It's a free standing deck (with deck blocks), I am using 4 posts (4"x4") and was planning on using 2x10s for the beams (beams will span 4' (so perpendicular to the house). I was planning on notching the 4"x4"s and then connecting the 2x10s with structural screws.

Then I have 4 joists (parallel to the patio door) sitting on top of the two beams at 16" apart.

Anyway, this is the info I submitted to the city, they gave me a permit.

However, would it be better (more solid - less bounce) to replace the 2x10 beams with sistered 2x8s, sitting on top of the 4"x4" posts? for the 4' span, would this make any difference, or would it be negligible?

I can't find any table to give me this sort of information, most beam calculators and tables have sistered beams.

Any help would be appreciated.

Thanks!
 
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Old 05-17-18, 08:22 PM
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Always difficult to follow without an attached schematic. Deck blocks are usually not approved as footers for a deck and are more likely used for a free standing shed. Deck post usually need to be anchored to footers sunk in to the ground depending on your location and frost line.
 
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Old 05-17-18, 09:52 PM
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I guess I overcomplicated it with all the info, I'm just asking what is the difference between a 2x10 and two 2x8s sistered, when using either option as a beam that will span 4 feet? Is there any calculation or chart that will show me this?
 
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Old 05-18-18, 02:57 PM
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See if this code book for decks will answer your question.

http://www.awc.org/pdf/codes-standar...Guide-1405.pdf
 
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Old 05-18-18, 05:26 PM
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Thanks, I have this document and it's pretty great, I found this in my search for documents that address rules and best practices for decks and framing.

However it doesn't cover my situation where I would like to use 1-2x10 as a beam. All tables always shows 2-2xWood; ie, based on the table and my span of 4' for the beams, I can even use 2-2x6s but nothing showing me a single 1-2x10 would be ok.

I would think a single 2x10 would be stronger than 2-2x6 as beams
 
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Old 05-18-18, 07:35 PM
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It sounds like you are overbuilding it for a 4' span, however, this is not a bad thing. I always never strive to build to the bare minimum to pass code. Build it strong and you will never have a problem. The cost difference between 2x10 and 2x8 is not enough for you to not go to the max. I've had customers comment that I am not the fastest contractor, but I overbuild and make sure it is a strong as possible.
 
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Old 05-19-18, 11:51 AM
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I prefer to do it right the first time, even slightly overbuilt. I'd rather it be rock solid than have a little bounce, even if the latter is within requirement/code and would be fine strength wise.

This is why I chose to also go with mostly screws (simpson strong tie has suggested screw replacement for pretty much everything that needs nails, as well as now there are engineered structural screws one can use instead of lag bolts); if anything need to be changed, modified it's much easier to deal with.

I will go with 2x10 beams and notch the 4x4 posts, then use structural screws to connect them to the posts.

>>Do people usually use that flashing/waterproof tape on top of joists/beams? Seems that if you are using pressure treated wood it's overkill yet I see it on videos and such. I know some things are pure marketing, but also doing things right the first time, I'm wondering about that.

Cheers!
 
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Old 05-20-18, 11:49 AM
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Use simple metal flashing against the house, but I've never use flashing on the joists.
 
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Old 05-20-18, 01:35 PM
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For your situation, I’d think the two 2x8s on top of the posts would be much stronger than a single 2x10 in a notched 4x4. Notched 4x4s don’t keep
much strength at the notch. I’m pretty sure the reason for sistered beams is because the joist hanger hardware has to go through both plys of a two ply beam, and they’re usually 2-1/2” long. But, if you’re worried about bounce, run your joists on 12“ centers and use blocking between the joists. That will remove any twist or flex. For the price of a single 2x8, about $10, you’d be much happier with the rigidity. Out of curiosity though, why are you running your joists parallel to the house? You’ll be left cutting 16 deck boards to 4’ instead of trimming the ends off 8. Also, do you need handrails? That would play a part in your framing plans too and would determine the need for 2x8s or bigger.
 

Last edited by Kjb87; 05-20-18 at 01:40 PM. Reason: Added info
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Old 05-21-18, 10:12 AM
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Use simple metal flashing against the house, but I've never use flashing on the joists.
Sorry, this is what I meant, joist tape like this: https://www.rona.ca/en/joist-guard-w...-x-75-74165162

It's free standing to no ledger board against the house.
 
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Old 05-21-18, 10:31 AM
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For your situation, I’d think the two 2x8s on top of the posts would be much stronger than a single 2x10 in a notched 4x4. Notched 4x4s don’t keep
much strength at the notch. I’m pretty sure the reason for sistered beams is because the joist hanger hardware has to go through both plys of a two ply beam, and they’re usually 2-1/2” long. But, if you’re worried about bounce, run your joists on 12“ centers and use blocking between the joists. That will remove any twist or flex. For the price of a single 2x8, about $10, you’d be much happier with the rigidity. Out of curiosity though, why are you running your joists parallel to the house? You’ll be left cutting 16 deck boards to 4’ instead of trimming the ends off 8. Also, do you need handrails? That would play a part in your framing plans too and would determine the need for 2x8s or bigger.
I would just use these hurricane ties to tie in the joists to the beam, either of the two below are ok if the joists sit on a single beam.

https://www.homedepot.ca/en/home/p.h...000152530.html
https://www.homedepot.ca/en/home/p.z...000170485.html

If 2x2x8' would sit on top, I could use either one of these:

https://www.homedepot.ca/en/home/p.z...000152342.html
https://www.homedepot.ca/en/home/p.2...000170474.html

I ran the joists parallel to the house as the decking will then be parallel to the stairs and figured if would look nicer. I get what you're saying, but I can't move 16' decking lengths, the most I can fit in my car is 8' lengths, but I can squeeze 10' decking (planning to use 5/4"); so I was planning on getting 5/4" x 10' and this would give me buffer for cutting etc as I just need ~4' planks.

Either way, I would still get the 5/4 x 10' decking even if going perpendicular to give me room for error when cutting. Yes, I do need railings as it's at 34" off the ground, anything over 24" will need railings but they only need to be 36" high.

I may do the 2x2x8' after all, notching is a slight pain although doable so sitting them on top would be easier.

I found this post elsewhere for sistering boards: "The nailing pattern is specified to be (for 2x8's) three 16d spikes (not sinkers) every 16 inches. For a 2x10, 4 per 16", and 2x12, 5 per 16"."

with 16d spike it looks like I would need to nail them in on an angle as they are 3.5" long, so I was planning on using using 3" deck screws (treated) to sister the 2x8s together.

Cheers
 
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Old 05-22-18, 07:15 AM
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I see now, I was picturing the step treads running parallel to the house, but I see and I agree, it would look just as nice to run all the deck boards the same direction. I'd think you could still use 8' deck boards as they normally come an extra half inch long so you can trim them and end up at 8' even. You wouldn't need anything that's 16' long. the 16 I was referring to was the quantity of 4' deck boards. Joist to beam connections are easy and those hurricane ties would be perfect. The beam to post connections are a little trickier and

One concern, though, is that with your deck being 34" off the ground, you're going to need a building permit, which then opens up a whole new set of complications. Although you don't need to go down to frost depth (IRC 2015 403.1.4.1 Exception 3) , you'll still need to go to undisturbed earth in order to get your footing inspections to pass. Also, I think you will most certainly need to use a 2 ply beam sitting on top of the post, but you can use 10d nails which are only 3" long (IRC 2015 507.6) . Your handrail will need to be attached to posts that are attached to your rim joists with blocking surrounding it on three sides (not mandatory, but very cheap to add and really beefs it up). One thing to consider with your steps is the handrail. The handrail needs to extend to a point above the lowest riser, which in most cases, means the post has to be a the very end of your steps, not in the middle of the lowest tread. The work around is to attach a handrail to your guardrail, but those usually run an extra $100 or so and can be avoided by a little pre-planning. Basically you need to have an uninterrupted handrail from above your top riser, to beyond your bottom riser (IRC 2015 311.7.8.2). I'd recommend getting real familiar with the IRC 2015 chapters 3, 4, and 5 and working those exceptions to your benefit. Even though the building code is designed for safety, it really only limits you if your going the proper route and getting permits and inspections. If you choose to go without a permit and inspections then you can kinda do whatever you want at your own risk. I'm a firm believer that no one cares about the safety of your family and friends more than you so I won't try and sell you on the need for inspections, that's up to you. However, one good thing about getting inspections is that the inspectors (at least in my area) are available for questions from 7:30 to 8:30 every morning and they are more than willing to offer up advice or recommendations to help you out. From talking to a few guys in the building industry around here, the inspectors are much more willing to help out if you ask for help, but if you try and circumvent them or their processes, then they can be really anal about the code. If I were you, I'd give them a holler and get their take on footings and framing before you begin. Heck, you could even call them and pick their brain even if you don't get a permit. They won't know if you have a permit or not just by calling them. I'm all about DIY. I love to do things myself, and it's very rare that I'll hire a pro to do anything, but I also know my own limitations and lack of experience/knowledge in some areas so I have no problem asking for advice from the pros on how to proceed. Pausing to plan for an extra day is always better than rework.

Good luck and happy building
 
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Old 05-22-18, 12:34 PM
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Thanks for the feedback. I've been reading up on decks pretty much through the winter in order to decide what I want here, how and why, etc. Several great documents are the Decks.com planning guide, the Simpson Strong Deck Framing connection guide, Prescriptive Residential Wood Deck Construction Guide, Prescriptive Residential Exterior Wood Deck Span Guide, etc. All great publications.

Yes, I know about the guide rails and blocking, just screwing in the 4x4 is not enough.

>>For the record, I do have the permit already (mentioned in the original thread) and it was approved based on the design with two single 2x10 beams (perendicular to the house) on notched 4x4s. I will likely go with the 2x2x8s on top of the 4x4's though, I already have them purchased so why not.

The 4x4 will actually sit in these Pylex adjustable deck supports (https://www.renodepot.com/en/adjusta...black-80645129) which will be mounted into the deck blocks via tapcons. The deck blocks will be sitting on top of undistrubed ground, which is covered with hevier duty ground cloth (to prevent green from coming up) which has between 2"-4" of 3/4" gravel on top of it.

I'm including a couple of pictures, this is not the final deck, but just some sketches/options that I've done with free online design software.

Also these show the decking parallel to the house, which will not be the case.





I plan on making the last two steps extend out to the left (as you come down the stairs) at 90 degrees, so that you can come out before end of the steps. Not sure in this case to what point the rail needs to go, but I think it will need to go to the left along the last 2 steps (I imagine - I'll ask the inspector)

 
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Old 05-22-18, 02:06 PM
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Ok. You guys may have different permitting processes up there. When I got my permit, the deck was literally a 1" by 1" square drawn on my site plan that showed it was far enough away from the property lines. That was all they cared about. I had my detailed plans, but they didn't care. The inspectors were the ones that cared about the framing and footings. They are a different outfit.

For your handrail, I think you only need it on one side, so I'd run it on the easiest side, which is the straight side. But definitely ask the inspectors.
 
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Old 05-22-18, 07:12 PM
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Those drawings aren't exact as the deck is against the house side which is all brick, so I just need railings on the 3 sides, but not the brick side of the house. The inspector is alright, yes, will be working with him!
 
 

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