Replies

1. 
   Sphere | Aug 19, 2004 12:26am | #1

   the little known phenomenon...

   sideways gravity.

   edit to include : often confused with centrifical force from the earths rotation, or G-force for the un-intiated. 

   Spheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations. 

   
   

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   Edited 8/18/2004 5:28 pm ET by SPHERE

2. 
   Shavey | Aug 19, 2004 12:42am | #2

   Richie,

   If it is properly lagged and nailed  to the house it  would take a great deal of weight to make it pull away,the lags and spikes stop the deck from being able to drop straight down. The ends of the joists are also nailed into the rim joist that is mounted into the house and the hangers are nailed into the rim joist which is lagged to the house so these 3 things are designed to keep your deck in the air.Now there is away that a deck could fail and thats if the lagbolts are only nailed into plywood because there is no exterior box present, just plywood alone(can happen on the second level) So in a case like that you have to find the ends of the floor joists at the second floor level then screw the lags into them. I hope this gives you a better understanding of the importance of a deck being properly supported at the wall.

3. 
   AKENGINEER | Aug 19, 2004 01:09am | #3

   That's actually a good question Richie.  As a municipal building inspector and engineer, I've actually seen deck collapses, with injuries, which occured due to improper deck connections.  In higher seismic risk areas, building codes typically specify that these connections cannot be made relying on only nails in withdrawal, however, these connections are too often overlooked.  Lag bolts can be used to resist these forces if properly installed through the ledger.  In addition to a standard joist hanger on the ledger, a metal strap tie or other metal connector can be used to connect the top flange or side of the joist directly to the ledger or structure behind to carry the tension forces and avoid joist hanger nail withdrawal.

   ADDED:

   As someone else correctly mentioned, the provision which prohibits lateral forces from being resisted by nails in withdrawal, whether for ledger nails or joist hanger nails, applies to all imposed lateral forces, not only seismic forces as I mentioned above.  As to how to properly attach the ledger to the main structure, there are many different framing situations that could occur depending on the location of the deck and 100 ways to skin a cat.  The bottom line is that this is an important connection to always consider.  Beware of anyone who tells you, ...but it is only a deck!"

   
   

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   Edited 8/19/2004 4:44 pm ET by AKENGINEER

1. 
   Sphere | Aug 19, 2004 01:14am | #4

   Tho' not seismic too often in NC we were using carriage bolts through the ledger and band...lags were a no-no.  But the question is, is the band to sill, and joist ends beefy enough? 

   Spheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations. 

1. 
   dIrishInMe | Aug 19, 2004 01:50am | #6

   I too live in NC and Sphere is right - we are required to use thru-bolts to attach the ledger to the house, so I don't worry about that coming loose.  Really the weak point is the joist to ledger board connection.  BTW - when I say ledger, I mean the 2x8 or 2x10 that is right up against the band joist of the house.  I was told by a building inspector that the first decking board should be nailed to both the ledger and the joists, helping to tie this connection together - although I know of no instance when someone has been sited for not doing this.  Really it's something I just do instinctively.  Also, the band joist should be tied to the home's joists via the floor sheathing and the 6" sege support nailing schedule.  On the other hand, the joist/ledger (beam) connection is very common in the standard platform framing of a house, especially since "open floor plans" are in vogue.   See attached pic.   Personally, I don't think there is any issue with the way I (we) do it ;-) Matt

1. 
   Sphere | Aug 19, 2004 02:30am | #7

   Matt, when I was hangin a deck off a house around Whiteside or Devil's Courthouse, anywhere near Cashiers area. I ALWAYS put a few hunks of 4x4x3/8th angle iron beside the floor joists. These were through bolted about a foot or less from the band, and had a 3/4'' hole in the flange to use a length of 5/8th galvy allthread to tie the deck ledger to the main house.

   Sometimes we'd run the all thread wild (after nutting it down on the ledger and add another angle to the deck joist and bolt that too.

   When the outside of the deck is over 40' drop to the ground (rocks) I didn't screw around..lol

   Had to use cable ties and turn buckles for diagonal bracing.

   And people ask why I moved to KY!  I tell em "we have mountains here too, we just don't BUILD on them"

   If ya ever can get past the guard house at Wade Hampton CC...you'd see what I mean..scary high stuff, all tools tetherd, ya don't bother going after the speed square, just buy a new one, I carried 6 in the truck at all times. 

   Spheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations. 

1. 
   dIrishInMe | Aug 19, 2004 03:56am | #9

   OK - ya got me!  I've never worked on any cliff dwelings.... :-)Matt

2. 
   Sphere | Aug 19, 2004 03:58am | #10

   you don't want to...LOL 

   Spheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations. 

2. 
   DANL | Aug 19, 2004 04:10am | #16

   I said this once before in response to another discussion, but an architect on a project I worked on once had five stories of balconies designed just to sit like a bookcase--no ties to the structure. Fortunately, he caught the error before it was built.

3. 
   JohnSprung | Aug 20, 2004 10:46pm | #24

   >  As to how to properly attach the ledger to the main structure, there are many different framing situations that could occur depending on the location of the deck and 100 ways to skin a cat.  

   The two main different situations are that the ledger is either parallel or perpendicular to the joists of the main building.  Most decks are at or just slightly below the level of the inside floor.  The other big variable is whether this is new construction where you have easy access to the floor joists, or an added deck.  That gets us four possibilities, which could make this a fairly long thread. 

   I hope Pro-Deck takes a look at this, he's the specialist in high quality decks.

   -- J.S.

4. 
   DanH | Aug 19, 2004 01:33am | #5

   Keep in mind that the typical deck is very weak, side-to-side. It doesn't take much force to move it, so, similarly, it doesn't take much force to hold it steady (short off an earthquake).

1. 
   kclarson | Aug 19, 2004 04:01am | #12

   That statement makes no sense! If you were standing on a pencil, the situation would be very week side to side and someone would pay hell trying to keep you up on that pencil if you started to fall sideways. People walking on decks impose lateral loads...the more people the greater the load could be. Turn the music on to get them dancing and WATCH OUT!!!

1. 
   dIrishInMe | Aug 19, 2004 04:05am | #13

   That reminds me of something - our code's only spec for a railings strength is that is must be able to support 200# of lateral load.  My question always was, is that 200# of Matt or 200# of drunk and partin' Matt!!!

   Matt

1. 
   kclarson | Aug 19, 2004 04:08am | #15

   Well, You have to look deeper into the code...it states that a "Drunk Matt deck rail shall be designed for 400#"

2. 
   DanH | Aug 19, 2004 04:52am | #17

   Actually, the typical deck IS balanced on a pencil, or rather several of them. Granted, the pencil is stuck in the ground, but even with knee braces it doesn't offer much resistance to lateral motion. Get a deck ten feet up on a pair of 4x4s with no diagonal bracing of the deck surface and it will rock and roll like a 50s teen.

1. 
   kclarson | Aug 19, 2004 08:14pm | #18

   I agree, if it's not designed correctly. There are ways to create a deck that is rigid regardless how high up it is. I personally have a deck that is 16'-0' above ground at one end and it is rigid without the use of knee braces. The decking, which is typically 2x material, offers little stiffness in the lateral direction. Installing X straps on the bottom side of the deck joists will transfer lateral loads back to the structure. Also, a properly sized bracing system in one or more of the column bays will transfer lateral loads to the deck footings. Knee braces take lateral loads and place the columns into a bending situation which is fine as long as the columns are designed to resist this bending. As with the main building, decks are a structural element and should be designed correctly. Too many times I have seen people say "it's just a deck" and do a "half assed" job on them. Decks are typically gathering places and the risk to life is pretty big the higher the deck gets.

1. 
   DanH | Aug 19, 2004 08:22pm | #19

   Right.

   But my impression has been that probably at least 3/4 of all major deck failures (multiple people hurt/killed) are due to the ledger letting loose because it was only nailed. This is based on my reading of newspaper reports and the like. There's generally one or two every summer in our part of the country.

2. 
   kclarson | Aug 19, 2004 09:54pm | #20

   Yes, that has been my experience as well...a poor connection to the main structure. This is exactly why this issue has been specifically addressed in the Building Codes.

   The lateral stiffness issue is different but just as important. Each structural portion of a deck (or any structure) must be designed and constructed properly. It does no good to have a super strong connection to the house and have the joists, beams, columns or foundation undersized. The failure mechanism will be different than the ledger pulling away but it would be equally catastrophic.

   To give a good example, here in interior Alaska (outside the city limits and our jurisdiction) you can find hundreds of homes (1, 2 and 3 story residences) built with standard construction practices however, their foundation consists of unreinforced, ungrouted and unmortared concrete blocks resting on the ground in a pier fashion. These piers are commonly spaced at 10' to 12' intervals. We live in a high seismic zone and when the big one hits, there are going to be a lot of places turned into a pile of sticks. Last weekend I actually saw a small shop building sitting on (4) 55 gallon drums!!! The point is that the whole system needs to be designed correctly...it does no good to have a super strong house that resting on loose concrete blocks...likewise a deck must be properly designed as a complete system.

3. 
   rez | Aug 20, 2004 04:32pm | #22

   Last weekend I actually saw a small shop building sitting on (4) 55 gallon drums!!! 

   Do you mean to say 'empty' 55gal drums or filled with concrete? I would become self-employed except I'm too cheap to pay myself anything.

   sobriety is the root cause of dementia

4. 
   kclarson | Aug 20, 2004 07:06pm | #23

   Yes, they were empty and just resting on the ground...the guy had a wooden ramp built going up to the door.

5. 
   kclarson | Aug 19, 2004 03:53am | #8

   Hello,

   Very good question. As a licensed Structural Engineer and Building Inspector for the City of Fairbanks, I can quote a section out of our currently adoped building code (IRC 2000). Section R502.2.1 states that..."Where supported by attachment to an exterior wall, decks shall be positively anchored to the primary structure and designed for both vertical and lateral (Yes, horizontal gravity as a previous reader indicated) loads as applicable. Such attachment shall not be accomplished by the use of toe nails or nails subject to withdrawl." Lateral loads such as earthquake (and pedestrian) loads can be significant depending on the size of the deck and the weight of the stuff on it. To meet the code, the deck must be attached to the structure with screws, lags or bolts or nails in shear (not withdrawl). This question is timely as two weeks ago, a deck on the local military base (out of our jurisdiction) collapsed due to nails withdrawing from the structure. Seven people on the deck were injured and a young girl sitting below the deck nearly got killed.

1. 
   DougU | Aug 19, 2004 04:00am | #11

   Lurch

   Interesting read, I see your new and wondered where your from? Fairbank's, Alaska?

   Fill in the profile if you got time.

   On a  lighter note; if Lurch is your nickname that must be funny when the "inspector" shows up!

   Doug

1. 
   kclarson | Aug 19, 2004 04:06am | #14

   Yep, Fairbanks Alaska. Lurch was the nickname I had in Highschool. I couldn't use the names some of the contractors call me around here :)

6. 
   SteveInCleveland | Aug 20, 2004 12:24am | #21

   Drywall screws, silly!

   Signed,

     The crew from "Trading Spaces"

7. 
   hammer1 | Aug 21, 2004 12:25am | #25

   Back in the 70's I kept running into decks that were attached directly to the house. Water collects behind the ledger and rots out the rim joist of the house. In the Northeast carpenter ants love these places. Nails should not be used on the ledger or the railings. I've been standing my decks off the siding for quite awhile. I use 1/2" carriage bolts through the rim joist in a tight fit, lags where I can't bolt through. I have seen some manufactured metal chairs that serve the same purpose. I used heavy PVC connectors as spacers on the deck below. They could possibly bend if the party got out of hand but the rim joist would have to go with it before it collapsed. I keep the decking away from the siding. Some like to use flashing but I've seen that torn by the snow shovel. I just let the siding do it's job. TGIs or floor systems that do not have solid rim joists are another matter.

1. 
   Richie921 | Aug 21, 2004 01:54am | #26

   I'm glad there have been so many responses here and I thank everyone for taking the time.  Hammer, I was wondering, looking at your picture,  if you have experienced any problems usin the spacers?  I have seen where some have said that spacing like that in effect cantilevers the ledger on the lags/carriage bolts and weakens the connections.  Believe me I'm not doubting you, just looking for your opinion in regards to that claim.

1. 
   hammer1 | Aug 21, 2004 07:05am | #27

   I think it would take a cantilever that was at least 30% of the span coupled with tremendous weight and a shock or two. Probably would pop out of the joist hangers first. If water gets trapped between the ledger and rots out the lumber I feel this would be a worse scenario. I use 1/2"Ø minimum, the more the better. You have to be careful where you bolt so you don't break some siding. In the past I made wood standoffs by band sawing 2x4PT to fit the siding profile. The plastic fittings can be cut to keep the ledger plumb. I only have a five year history with the plastic, so far so good but the decks are also well supported and braced. After seeing the damage other methods have caused I think this is a step in the right direction. It's hard to fasten the deck boards without putting holes in the flashing. Homeowners get creeped out when you pull off an existing ledger and an army of ants blackens the lawn like a scifi movie.

2. 
   dIrishInMe | Aug 22, 2004 05:50am | #29

   Sorry, but there is no way that would pass an inspection in my state.  The deck to house connection either needs to be a structural attachment or a free standing and self supporting deck, not somewhere in between... 

   You say >>I used heavy PVC connectors as spacers on the deck below.<<  So what are those, PE approved plumbing fittings?

   I see what you are trying to do, and rot would obviously be significantly reduced or eliminated, but who care when the first time the parents go out of town and the teenage son has a keg party on the deck with 40 young people...  At least the one you pictured was not high off the ground... Matt

8. 
   Luka | Aug 21, 2004 04:05pm | #28

   "Deck Withdrawal"

   I thought Bob Simonson had retired...

   "Criticism without instruction is little more than abuse." D.Sweet