Cracked deck joist fix

[bpscores]

My deck is only framed currently (no deck boards) and I have been placing 2x10 joist blocking every 3.5 ft of joist span (max 17ft joist span). There is very tight space between the joists currently (8.5 inch O.C) so all blocking is being done with right angle attachment to an impact driver and predrilling every screw before fastening.

I noticed a crack/split in one of the joists. The crack is about 3 ft long and is through the thickness and is approximately at the center of the 2x10 height along the grain only.

• Is it sufficient to fix the crack by sistering with 2x10 boards on both sides of the crack with some glue and structural screws?
• There is a joist block in between the length of the crack. Can the sistering be done on either sides of the block (so 4 pieces) without removing the blocking?

This deck framing was done over the winter with the plan to lay the deck boards in spring and finish with railings. But come spring time, we had to replace several joists that had sagged/warped over the season change (my mistake in not locking the joists for winter). After replacing the sagging joists we placed temporary 4x4 on top of all the joists and screwed them down to keep all joists level until it was time for deck boards.

 

[FredWanaker]

just replace it since no deck boards are on it or it will forever bug you that you didn't.

 

[Zeke]

Am I reading this correctly? 8 1/2" O.C."?? So 7" blocking? @x 10 blocking so I assume 2x 10 joists?
That needs to be seen. Pics please.

 

[firebirdparts]

If you are talking about a 17 foot unsupported span, then that crack is probably respectably important, but obviously you could ignore it and it wouldn't really ever matter. if it's at the center height-wise, then it's not terribly affecting the board. It may run, and then of course it may run to the top or the bottom, which would more or less give you a total failure of that one joist.

I contend you should not sister anything short. That's just nonsense.

 

[619DioFan]

If you are going to sister in a new 2x10 I would do it as one piece only , otherwise just replace the one bad joist,

 

[BombShelter]

I'm not an expert but I do work under decks all the time and have built my own. Your description does not seem like the 100's of residential decks I've worked around but local conditions and a non-standard design might require your extreme build.

Are you using a deck build-guide? There's several on the internet that give common spacing and sizes. Like Zeke said, it sounds more like an 120 year-old basement ceiling. I think my deck is something like 24" O/C but only 12' span and there is no blocking, it looks like every other regular style deck around here.

I don't know how much room you have but I think I would put the 4 x 4 under the joists, get some Harbor Freight Bottle Jacks and lift the sagging joists that way instead of pulling them up with screws.

I feel like there might be more to this, I'd pull out the split board but height, weight or some other factors might make that difficult. If you do have 8.5" of spacing it might be severly overbuilt and not a big issue.

 

[Hank11]

Replace do not sister. Unless you live in the desert a sistered deck joist creates a rot pocket when it gets wet and can’t dry. You’ll be fixin’ it again.

Obviously, you will need to remove and then replace all the blocking around that joist.

 

[bpscores]

Thanks for the many replies. I took a pic from both sides of the joist and added labels to show the multiple cracks color coded. Only one crack appears to be visible on the other side. I also flushed some blue wood preservative (coppercoat) into the cracks to help visibility.

Yes these are 2x10 joists with 17ft total joist span. Code table allows max 16ft at 12inch O.C. hence the reduced joist spacing.
Deck boards are Timbertech PVC who recommends 12 inch O.C for perpendicular decking and reducing the spacing for angular decking. Planning to run boards at +/- 45 degrees like a herringbone/chevron hence the 8.5inch O.C leading to 7inch gap between joists.

The sagging joists have all been replaced earlier in summer but since I am working on it gradually I did not want any more sag until I got the deck boards so, hence the choice of locking everything from the top to keep level.

I am using the deck guides but the angular decking and 17ft joist span made us reduce the spacing.

 

[rancherbill]

Thanks for the many replies. I took a pic from both sides of the joist and added labels to show the multiple cracks color coded. Only one crack appears to be visible on the other side. I also flushed some blue wood preservative (coppercoat) into the cracks to help visibility.

Yes these are 2x10 joists with 17ft total joist span. Code table allows max 16ft at 12inch O.C. hence the reduced joist spacing.
Deck boards are Timbertech PVC who recommends 12 inch O.C for perpendicular decking and reducing the spacing for angular decking. Planning to run boards at +/- 45 degrees like a herringbone/chevron hence the 8.5inch O.C leading to 7inch gap between joists.

The sagging joists have all been replaced earlier in summer but since I am working on it gradually I did not want any more sag until I got the deck boards so, hence the choice of locking everything from the top to keep level.

I am using the deck guides but the angular decking and 17ft joist span made us reduce the spacing.

Replace it. It slipped through grading, but you should not have that kind of knot.

On a previous comment you mentioned glue. GLUE is never to be used for repairs like this. Glue fails. Only use architecturally approved fasteners like nails or lag screws.

 

[bwringer]

I'm on team "yikes, replace".

I'm also on team "holy **** I'd be very angry if someone sent me lumber that looked that crappy and probably never would have used it".

 

[bpscores]

Good points! I had not noticed that knot earlier until I looked at the crack. I will have it replaced. Thanks everyone!

@rancherbill
I meant glue earlier in the context of sistering a joist with construction glue between the sandwich and structural screws.

@BombShelter
Yes, I realize that this is probably overbuilt with the blocking and reduced joist span. But I didn't want to take any chances based on the guildelines from Timbertech for keeping things absolutely level and firmly blocked for PVC decking to avoid a springy deck or hills and valleys in the finished deck floor appearance.

 

[MoonRise]

Multiple issues.

re: the cracked joist Replace it. But see the end of this write up for some more info ...

re: PVC (composite) Timbertech deck boards Deck boards rarely have enough strength or stiffness to pull the joists back into place, composite/plastic deck boards even less so. The joists are the structure of the deck, you make the joists level first. The deck boards are the 'skin' and they just sit on top of the joist structure.

I understand the closer joist spacing that is required when using composite/plastic deck boards, and good for you for checking and following the deck board manufacturer's instructions. But I think you misread the required joist spacing. Timbertech says that for deck boards on a 45 deg angle (aka your chevron layout) the joists should be a max of spaced 12" OC.

https://www.timbertech.com/wp-content/uploads/2023/01/TimberTech-PRO-TimberTech-EDGE-Speciality-Decking-Intallation-Guide-ENG-12.16.2022.pdf

But using a closer joist spacing does NOT magically enable you to exceed the span table REQUIREMENTS.

A 17 ft span at a 12" OC joist spacing REQUIRES 2x12 joists. You are NOT meeting the span requirements for your 17 ft span.

You have a big beefy engineered lumber end beam there, and joist hangers, and blocking. All good stuff.

BUT YOUR JOIST SIZE IS UNDERSIZED FOR YOUR SPAN!

Deck Joist Sizing & Spacing | Decks.com

We've provided step-by-step instructions and tips for framing a deck. Learn how to install treated wood joists and beams at Decks.com!

www.decks.com

Which now makes me ask what and how you are holding up your deck? What are your posts that support that end beam? 4x4 posts? That size post hasn't met code for years. Minimum (except in very limited circumstances) is deck posts must be 6x6 or even 8x8 depending on deck height and some other conditions.

Where are you located? Some locales have more stringent building code requirements then others (such as seismic requirements, etc).

 

[bpscores]

Multiple issues.

re: the cracked joist Replace it. But see the end of this write up for some more info ...

re: PVC (composite) Timbertech deck boards Deck boards rarely have enough strength or stiffness to pull the joists back into place, composite/plastic deck boards even less so. The joists are the structure of the deck, you make the joists level first. The deck boards are the 'skin' and they just sit on top of the joist structure.

I understand the closer joist spacing that is required when using composite/plastic deck boards, and good for you for checking and following the deck board manufacturer's instructions. But I think you misread the required joist spacing. Timbertech says that for deck boards on a 45 deg angle (aka your chevron layout) the joists should be a max of spaced 12" OC.

https://www.timbertech.com/wp-content/uploads/2023/01/TimberTech-PRO-TimberTech-EDGE-Speciality-Decking-Intallation-Guide-ENG-12.16.2022.pdf

But using a closer joist spacing does NOT magically enable you to exceed the span table REQUIREMENTS.

A 17 ft span at a 12" OC joist spacing REQUIRES 2x12 joists. You are NOT meeting the span requirements for your 17 ft span.

You have a big beefy engineered lumber end beam there, and joist hangers, and blocking. All good stuff.

BUT YOUR JOIST SIZE IS UNDERSIZED FOR YOUR SPAN!

Deck Joist Sizing & Spacing | Decks.com

We've provided step-by-step instructions and tips for framing a deck. Learn how to install treated wood joists and beams at Decks.com!

www.decks.com

Which now makes me ask what and how you are holding up your deck? What are your posts that support that end beam? 4x4 posts? That size post hasn't met code for years. Minimum (except in very limited circumstances) is deck posts must be 6x6 or even 8x8 depending on deck height and some other conditions.

Where are you located? Some locales have more stringent building code requirements then others (such as seismic requirements, etc).

Good observations and I agree, MoonRise! Sorry for the confusion but some clarifications here-

The angle decking came as an afterthought. For 17ft joist span we explored 3 options-

1. Switch to 2x12 joists
2. Doubling up 2x10 joists
3. Using 2x10 joists at reduced joist spacing

An engineer approved option #3 for us with minimum 10 inch O.C (which was more economical) along with the beefy glulam beam and 6x6 posts so that's what we went with. Our posts are 6x6 using Simpson LPC6Z. Since we needed a reduced joist spacing to meet code, we decided to use that opportunity to go with an angular deck. I used the 12 inch on diagonal to arrive at 8.5 inch O.C. for angular decking.

The biggest challenge we had was to figure out angled beams (we had 45 degree corner clips on the deck front) connection for a flush beam install.

The confusion was from my mentioning 4x4 on top of the deck for leveling. Those were only temporary for leveling.

We are in MN. All lumber is KDAT #1 SYP but we seem to have received plenty of bad boards despite the premium costs. The labor we hired for primary framing didn't do a good job in culling out bad lumber.

 

[Youngandfree]

How does reducing the OC spacing enable the overlength beam not sag, like yours are doing? The smaller OC spacing is for the composite deck boards not to sag.

Cutting corners to save money will cost more in the end.

 

[rancherbill]

@rancherbill
I meant glue earlier in the context of sistering a joist with construction glue between the sandwich and structural screws.

There is NO ENGINEERING TABLE FOR GLUING. For repairs such as yours, the only engineering table that are relevant are for nails and lag screws, both along with an approved fastener pattern. It is a waste of time and money for glue. There are so many ways glue can fail.

 

[jkuro]

For 17ft joist span we explored 3 options-

A 2x10 12" 0C, you can use DF#2 18'-5", YP#2 18'-0" or HF#2 17'-3". This is for a 40lb live load. SPF#2 will only span 16'-10".

 

[Hank11]

There is NO ENGINEERING TABLE FOR GLUING. For repairs such as yours, the only engineering table that are relevant are for nails and lag screws, both along with an approved fastener pattern. It is a waste of time and money for glue. There are so many ways glue can fail.

This is correct but field repairs can use more methods than just screws or bolts. Some will use adhesives. What will be called for is a proper repair done with good workmanship. Which does not apply here anyway.


If you are not dead set on Timbertech, I suggest you use something with some structure to it —- like good ol’ wood. Appearance KDAT 5/4 would be a good choice, IMO. Your deck will “walk“ lots better and last. I think your current framing will be a little flexy with plastic decking.

 

[rancherbill]

This is correct but field repairs can use more methods than just screws or bolts. Some will use adhesives. What will be called for is a proper repair done with good workmanship. Which does not apply here anyway.

I broke a roof truss. A real Professional Engineer told me glues or adhesives cannot be used in any structural repair. For example, if the wood gets wet as deck do and there is freezing temperatures will the glue adhere?

I am sure lots of people would slop some glue on and call it good - including me.

 

[bpscores]

@rancherbill
I know what you mean. I was not referring to using glue by itself. My initial thought was sistering with structural screws in some pattern. The glue was just to go between the two boards but not relying on ONLY-glue for fixing the issue.

@Youngandfree @jkuro
The joist span code table itself lists values for 12,16 and 24 inch O.C. You can see the trend that as the joist spacing is reduced, the allowable joist span increases. For the same reason, reducing the joist spacing to values lower than 12inch OC will allow longer spans. The code table only lists common joist spacing. Another way to think of it is that for a given load (say 40psf), when you reduce the joist spacing you are putting in more joists in total; the equivalent load on a joist is reduced because the total load has been distributed among more joists so the deflection is lower. Notice that the code table lists max span for the same allowable maximum deflection (L/360). So you can increase the joist span and reduce the joist spacing to match the same deflection.

BTW the sag was due to the joists being subject to the weather (MN winter and western sun) without any deck boards or blocking to prevent movement.

 

[CoronadoBruin]

Recently retired carpenter of 45 years who built an absolute shitload of decks:

1) Believe it or not, the split due to the edge knot and heart cut doesn't matter that much but could/will deteriorate with time. The waaaay overdone span blocking actually helps a bit here.

2) Replace it or, as one poster said, it will bother you if you don't and he's right. Never scissors anything less than full length. Doubling it up will be as much work with all your span blocks as a replacement would be. And, yes, moisture is an issue with doubled joists (many people use PT wood). If you don't use PT wood, consider a moisture barrier along the top edge of the deck joists. There are some products made specifically for this or you can make your own. If you want some ideas, just post an ask.

3) Joist sizing (Never mind, I just saw the remark that you dealt with an engineer on joist sizes; good choice)

4) 4x4 posts are fine and are more of an issue of height than load. 4x6 posts don't come into play until something like ten feet in height. Properly installed braces will help here. 6x6 posts are for show only and to match a beefy 6x deck girder above, and in 45 years I have never seen 8x8 posts for structural reasons, only aesthetics. I've twice been corrected, once by an engineer and once by plan check in a major city notorious for being tough, that 4x4 posts were acceptable. I went ahead and used 4x6 at one deck, anyway. On my last deck (for my late mother), I corrected the engineer re joist sizing. He was not amused.

5) WTF is up with all the span blocking? Did the engineer spec it? Some of the joists seem to be a really crappy #3s so the span blocking will help.

As you just learned, it's not a good idea to let wood sit through a winter between start and finish. Also must be sealed, either paint, stain, sealer, etc., by code. Edit: I see the lumber has been sealed; good stuff.

 

[Old tool guy]

An engineer approved option #3 for us with minimum 10 inch O.C

I hope you got that in writing, with his stamp. As others have pointed out that spacing is not in the code so a city inspector can fail it. Common sense is not part of code.

 

[CoronadoBruin]

I hope you got that in writing, with his stamp. As others have pointed out that spacing is not in the code so a city inspector can fail it. Common sense is not part of code.

If a licensed and qualified engineer shows the calcs and stamps the calcs (and plans) and stands behind it, AHJs will defer to that engineer unless it is obviously improper. Not everything can be "in the code." Happens all the time. Essentially, the engineer is god on the project as long as s/he doesn't disagree with basic physics, and some will never let you forget they are god.

Changing the span and adding more joists is arguably the simplest change possible in Type V construction, and no AHJ would disagree if there is a current stamp on the calcs/plans with an o.c. layout of 10" instead of 12" or 16" or 19.2" or 24".

 

[Toolfool]

My biggest issue with your design is that you are depending on brackets as your load bearing point, where you should have a BEAM UNDER the ends of your joists. In 35 years of constructing custom homes I have never done, or seen approved engineered plans of, a deck spanning more than 8' without a supporting beam UNDER the joists.
Edit : I'd like to add that when I was first starting out in construction I took a lot of 'repair' jobs. One was a deck built like yours, no beam, pushing the span limits, that had collapsed during an engagement party. Lots of people and furniture on the deck. Several people injured, none life-threatening. Taught me early on to always build a beam to support both ends of the joist system. Never rely on rim joists and brackets to support the load.

 

[bpscores]

@CoronadoBruin
Thanks for the comments! Yes, a humble lesson learned from seeing all the issues with letting the wood sit out from start to finish.
I will be putting G-tape to act as the moisture barrier.

The overkill span blocking was based on some conservancy w.r.t Timbertech PVC installation guidelines. They ask for blocking every 4-6ft. I went with blocking every 3.5ft because half of my deck is 14 ft joist span (3 rows of blocking at 3.5/7/10.5ft) and the other half is 17ft joist span (4 rows of blocking at 3.5/7/10.5/14ft). The blocking alone took me several weeks this summer working during free time.

One question on your comment about sealing the deck. Are you referring to sealing all surfaces of the joists and beam or just the top where moisture might settle? I am using G-tape on the top surfaces of everything. Do I need to apply a sealer on all vertical surfaces of the ledger+joist+beam+blocking as well?

@Old tool guy
Yes, I have the approval for 10inch O.C in writing and stamped.

@Toolfool
I respect your comment and the conservative approach with using beam support on both ends of joists. But I have to question the conclusion that that particular deck failed because of not having beam supports on both ends. Joist hangers when installed correctly should be more than capable of handling max rated deck loads.
I started with a drop beam concept and then switched to flush beam because of aesthetics and it gives me more vertical space at the end of the deck.

 

[rancherbill]

One question on your comment about sealing the deck. Are you referring to sealing all surfaces of the joists and beam or just the top where moisture might settle? I am using G-tape on the top surfaces of everything. Do I need to apply a sealer on all vertical surfaces of the ledger+joist+beam+blocking as well?

I did. I can't find a pic of exactly what I did, but this give you the idea. On old decks here the joists rot at the ends and the surface of the joist rots and the boards loosen.

First, I slathered contact cement on the joints where there were joist hangars and put a piece of 4" tape vertically covering the hangar and a little bit on to the wood. Then I put normal tape along the joist. Water shed off the rot areas. The other areas just air dry.

The picture (by Trex brand) would be quicker but I think my technique is at GJ level of OCD.

https://trexprotect.com/wp-content/uploads/2018/05/hanger-tape-300x300.jpg

 

[BombShelter]

I pretty sure here in the Midwest you can use 4x4's up to 5' which makes sense to me. Have you ever noticed that when the decks collapse on big old brownstones, they always are made with 4x4's? Anyway they scare me and I won't "party" on a high deck with them.

Visually 4x6's look goofy, 6x6 look good and strong and are very close in price. I think they require a beam here, I can't remember but all the new decks I see have them. I probably wouldn't care if they were close to the ground but once they get over 8' I'd put one in. The nice thing is you can cantilever something like 30% of the ends, for higher decks, a big beam and 6x6's look really nice (and strong!).

It makes sense that the manufacturer is calling for tight spacing and support with the composite, if anything moves, the boards will as well. I'm a wood guy, I've never used it but we did some studies of it years ago in college when it was bright and shiny.

 

[Joemctag]

Replace it. It slipped through grading, but you should not have that kind of knot.

On a previous comment you mentioned glue. GLUE is never to be used for repairs like this. Glue fails. Only use architecturally approved fasteners like nails or lag screws.

Yeah, a knot like that…..if I’d overlooked it when buying the lumber, I’d only use the board if the knot was very near an end and I’d put it on the bottom to not collect water.
You’re wise to do your joists like the deck-board people say to.
We’d like to see pics after it’s finished.

 

[jar944]

My biggest issue with your design is that you are depending on brackets as your load bearing point, where you should have a BEAM UNDER the ends of your joists. In 35 years of constructing custom homes I have never done, or seen approved engineered plans of, a deck spanning more than 8' without a supporting beam UNDER the joists.
Edit : I'd like to add that when I was first starting out in construction I took a lot of 'repair' jobs. One was a deck built like yours, no beam, pushing the span limits, that had collapsed during an engagement party. Lots of people and furniture on the deck. Several people injured, none life-threatening. Taught me early on to always build a beam to support both ends of the joist system. Never rely on rim joists and brackets to support the load.

Flush beams and joist hangers are standard enough on decks.