Decks, Diving Boards and Cannon Balls

By
Home Inspector with JRV Home Inspection Services, LLC HOI 394
https://activerain.com/droplet/4t9J

Diving boardI would suspect anyone over the age of five is familiar with a diving board. A springy plank meant to propel the swimmer high into the air for a splash landing in the pool. Looking at a diving board, it's a simple and ancient design, essentially a lever and fulcrum.

A lever is arguably one of the oldest tools known to humankind. By setting a sturdy tree limb atop a rock, placing one end of the branch under the object to be moved and then applying force to the opposite end of the limb, the force exerted can be multiplied. In this way, large, heavy objects can be moved.

Deck with a long cantileverRevisiting the diving board, the forces applied at the opposite end of the board are then huge. A 200 pound man bouncing on the board would be creating several times that force on the opposite end of the board past the fulcrum. The very same multiplication of force can be found in structures. A great example is a deck.

Many decks are built using posts and beam to support the outer part of the structure. Typically the deck is cantilevered over the beam.

Can you see a similarity to the lever and fulcrum and the diving board?

With decks and any structure that is cantilevered, there is a major structural strength parameter that has to be considered;

The distance the structure can be built past the beam. The wood joists are only so strong, so depending on the species, grade and dimensions of the board, a specific amount of overhang is allowed.

In the picture above, the joists are 2" x 8" milled of southern yellow pine, the common species used in pressure treated wood found in Connecticut. Span charts for this species state that a 2' 8" cantilever is the maximum allowable distance. Most deck building specialists and internet sites do not recommend exceeding two feet no matter the size and species of wood. The main reason for this advice is the amount of stress that can potentially be exerted on the opposite end of the board at the house connection. Remember the deck is a lever.

While the cantilever is the short end of the lever, the force at the house connection is redirected as weight is applied past the beam onto the overhang. Instead of a downward force from good old gravity, the stress at the ledger board is altered becoming upward. As such this magnified up and down action can weaken the connection, especially when, as is so often the case, the fasteners are inadequate.

Decks most often fail at the ledger board.

Long cantilever or is this a diving board?Inspecting a newly built deck recently with an already horribly constructed stairway, the diving board like distance of the cantilever grabbed my attention. It was immediately quite apparent the length was well in excess of any framing and deck building parameters.

Look at the decking boards atop the joist. There are seven board plus from the where the beam is placed. The width of these boards is 5-1/2". That would equate to about 40". That's over three feet! Further look at the beam end. It does not support the outer joists. Instead the DIYer used his nail gun to pop about 10 nails into the post that supports the beam. The opposite end was "supported" exactly the same.

More nails does not make the connection stronger, it weakens the wood.

Unlike the stairway, the deck will not need to be entirely rebuilt. A new post and beam system properly placed will solve the issue.

That should prevent a bunch of dancing party goers from unexpectedly cannon balling off the edge of the diving board, deck.

 

Posted by

James Quarello
Connecticut Home Inspector
Former SNEC-ASHI President
JRV Home Inspection Services, LLC

 ASHI Certified Inspector

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Serving the Connecticut Counties of Fairfield, Hartford, Middlesex, New Haven, Southern Litchfield and Western New London.

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Re-Blogged 1 time:

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  1. Lenn Harley 10/10/2013 10:40 PM
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Rainmaker
690,134
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

Ed, Yes, thankfully it is repairable. 

Oct 10, 2013 11:27 PM #9
Rainmaker
690,134
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

Jerry, Have not heard of that happening. There is always something new to consider.

Oct 10, 2013 11:28 PM #10
Rainmaker
1,767,182
Tom Arstingstall, General Contractor, Dry Rot, Water Damage Sacramento, El Dorado County - (916) 765-5366
Dry Rot and Water Damage www.tromlerconstruction.com Mobile - 916-765-5366 - Placerville, CA
General Contractor, Dry Rot and Water Damage

Great post James, I liked the way you explained the reasons for concern.

Congrats on the Feature!

Oct 10, 2013 11:52 PM #11
Rainmaker
694,665
Clint Mckie
Desert Sun Home, commercial Inspections - Carlsbad, NM
Desert Sun Home, Comm. Inspection 1-575-706-5586

Hi James,

What a crappy deck. At least your deck had steps. On a recent post of mine. the balcony on the roof didn't even have any steps for egress.

Have a great day in Connecticut.

Best, Clint McKie

Oct 11, 2013 12:02 AM #12
Rainmaker
651,497
Bill Reddington
Re/max Southern Realty - Destin, FL
Destin Florida Real Estate

Not a contractor but a pretty easy fix I think. Just something else to deal with. First question, was it permitted?

Oct 11, 2013 12:12 AM #13
Rainmaker
2,464,504
Richie Alan Naggar
people first...then business Ran Right Realty - Riverside, CA
agent & author

This post appealed to my common sense and is easy to support (pun) when read...thank you and sturdy post

Oct 11, 2013 12:51 AM #14
Rainmaker
471,447
Drick Ward Property Management / Broker Assoc
NEPTUNE REALTY - Virginia Beach, VA
"RealtorDrick" - Experienced Representation

Great post-thanks

Oct 11, 2013 03:50 AM #15
Rainer
284,418
Steven Cook
No Longer Processing Mortgages. - Tacoma, WA

James -- thanks for the very solid explanation of how the deck hs to be properly supported/constructed if it is to hold up to regular use.

Oct 11, 2013 04:57 AM #16
Ambassador
1,649,060
Alan May
Jameson Sotheby's International Realty - Evanston, IL
Helping you find your way home.

I love a good nail gun.  Hmm... seems to be jammed... let me take a closer look inside...!

Oct 11, 2013 06:03 AM #17
Rainer
102,393
Brian DeYoung
Howard Hanna Real Estate Services - Ithaca, NY
Brian DeYoung

What a great explanation of how a cantilever works. I will use this in the future. Thank you.

Oct 11, 2013 08:23 AM #18
Rainmaker
231,899
Helen and Larry Prier- Re-Max Gateway - Residential Real Estate
RE-MAX Gateway- Residential Real Estate Sales - Anacortes, WA
Anacortes & surrounding Skagit & Island Counties

James, Decks sometimes can be scary if they are at a great height. They are not for the DIY person for sure.

Oct 11, 2013 08:57 AM #19
Rainmaker
1,850,322
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

What?  More nails do not make it safer?  That can't be because so many deck builders use more nails in just the same place as you show.  So they must all know what they're doing.

Right?

 

;>)  Says he with a wink...

Oct 12, 2013 09:31 AM #20
Rainmaker
690,134
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

Thanks Tom.

Clint, No steps? Wow that can be a problem.

Bill, Second question if it was permitted, has it then been inspected. The permit is almost meaningless without the projected being inspected and the permit closed.

Richie, Thanks :)

Drick, Glad you enjoyed it. 

Steven, Thanks for your support :)

Alan, Cue sirens...

Brian, Thanks.

Helen & Harry, They generally are not. The information on doing it right is readily available, so I see no excuse for this type of construction. 

Jay, Absolutely! Everyone knows two wrongs don't make a right, but if everyone does it...

Oct 12, 2013 10:20 PM #21
Rainmaker
490,673
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

Jim. Those deck are always our friends :) I did one just Friday and was told it was just redone by a local contractor, wrong again. Jeepers this is not rocket science.

Oct 13, 2013 02:41 AM #22
Rainmaker
690,134
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

Don, I have come to dislike seeing a deck. Too often, I devote a good portion of the report to what is basically an addition to the house. 

Oct 13, 2013 09:25 PM #23
Rainer
74,745
John J. Woods
Big Dog Press, LLC - Winder, GA
Going where no man has gone before - wouldn't you?

 

   A "new post and beam system" could create other problems if the owner/contractor/builder wants to just move the existing post and beam system out to within 2'8" of the outer edge of the deck.  He could provide an additional system in the right place, if the span of the 2x8's going back to the deck is legal for the 2x8's used (in the picture, it appears to be right about 96"-98").  There are other ways to deal with this situation with additional material (that would have to be 'blessed' by an engineer), profiding the existing posts and their foundations, and any cross-bracing (can't see in the picture) are adequate.

   You noted how the "10 nails" were used in the rim joist, but not how the ledger was attached.  That might require some reengineering/rebuilding as well.  Details, details...

 

Oct 14, 2013 08:38 AM #24
Rainmaker
1,948,987
Andrew Mooers | 207.532.6573
MOOERS REALTY - Houlton, ME
Northern Maine Real Estate-Aroostook County Broker

Had a home getting insured for a cash sale with the same brokerage outfit that has had it covered for 34 years. The new couple were told bag the diving board. You can have a slide into the rear, deck surrounded in ground pool but no peter pans off the board if you want insurance coverage chummy.

Oct 14, 2013 09:25 PM #25
Rainer
375,681
Jerry Lucas
ABC Legal Docs LLC - Colorado Springs, CO
Mobile Notary Colorado Springs, CO Notary Training

Did you see this video on the news? Chinese invent group diving board 

Oct 15, 2013 03:31 AM #26
Rainmaker
690,134
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

John, Unfortunately details would convolute an already lengthy post. My purpose here was to discuss the cantilever. The ledger and its attachment are another topic.

I would disagree about hiring an engineer. It would be a whole lot simpler and more importantly cheaper to reconstruct the post and beam. Of course if the deck was properly permitted, the design would have been reviewed. Inspection would have followed (maybe). I'm quite certain none of that happened.  

Andrew, Good old insurance companies, they don't want us having fun :)

Jerry, I hadn't seen that. A little scary. 

Oct 15, 2013 09:27 AM #27
Anonymous
sophiawright

Great post on diving boards for swimming pools.Keep sharing such kind of information

Sep 21, 2014 03:20 PM #28
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