I am building a 20x20 deck and need to know what type of fastner would be best to attach the ledger board to concrete blocks

Large bolts all the way through the foundation walls. Also beware of of missing ledger or improper leger flashings. water that drains behind the ledger can rust these bolts very fast. The ledger board should also be treated lumber but the bolts used must be properly selected not to conflict with the chemicals used in the treated wood. Otherwise the bolts will rust away rather quickly and fail. Do not forget about using the proper fasteners for the metal hangers if you are using them. Wrong fastener types will rust away very fast and end up failing as well.

Also be sure to use a flashing material that is compatible with the treated lumber. Aluminum flashing will corrode away in the same fashion as the fasteners

1/2" carrage bolt long enough to go thru the foundation for nuts and washers.
Make sure the top of the deck boards is at least 4" (7" is better)below any door threshols. If any higher water will leak in under the door and take out the sub floor.
I strongly suggest not attaching the ledger to the side of the house at all but make it free standing instead to eliminate any chance of water getting into the wall.
If you do attach it to the wall use copper or vinyl flashing and use 1" X 6" X 10" spacers made from vinyl limber where ever you install the carrage bolts. I attach the spaces to the ledger with finish nails and predrill the ledger and the vinyl togethaer then hold it up and drill for the bolts thru the concrete.
At least three times a year I have to go and replace the band boards on someones house and sometimes even the foundation plate because someone installed the ledger tight to the house and then to make it worst they install the deck board tight up againt the house. It will take out the sheathing and any wood lower the the ledger. It's also a great place to start looking for looking for termites.

http://www.vadeck.com/attach-free-standing-deck.htm

The fastners there talking about are called joist hanger nails.
For the decking use ceramic coated or stainless steel screws. Nails will just pull out over time.
Any nails have to be marked ACQ approved.

This message has been edited. Last edited by: joecaption,

Having evaluted several deck failures in the past They all had one thing in common. They were bolted to the house, Some through completly with bolts and some with lag bolts into the house ledger. The only way this will not fail is to be using a ledger board at least five or six inches wider then the floor joist they will support. Then the majority of the bolting must take place below the bottom of the Joist hanger. What folks do not realize is when they use bolts through a ledger of the same size as the joists is that the support for the joist hanger is below where they bolt to the house. The end result is the ledger board splits in half as the deck is hanging below the bolt not laying on top of it.
Also it is important and even critical if you live near salt water that you have the correct Z flashing properly installed. Also proper bolts with the new treated lumber is critical as the chemicals are eating away the steel bolts you would normaly purchase for such a job.
I like Joecaption method of installing a Free Standing Deck. You still need a flashing as some support would still be required against the home, but it becomes a much safer and stronger deck building it free standing.

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Originally posted by joecaption:

If you do attach it to the wall use copper or vinyl flashing and use 1" X 6" X 10" spacers made from vinyl limber where ever you install the carrage bolts. I attach the spaces to the ledger with finish nails and predrill the ledger and the vinyl togethaer then hold it up and drill for the bolts thru the concrete.

Can you clarify your usage of the the vinyl spacers? Are you placing the vinyl spacers between the carige bolts and ledger or between the ledger and house? A picture may be worth a thousand words here. thanks

Any time you have two pieces of wood in direct contact with each other and water comes in from above. water is going to get between them and rot out the wood.
The spacers or shims are to keep the two baord apart far enough so water can run down between the two pieces and not just lay there.
There tacked in place to the ledger to be installed so your not trying to line them up and the ledger at the same time. There predrill through the two piece so your not trying to line hold up the board and spacers while drilling throught the foundation. The carrage bolts are tapped in throught the ledger, throught the vinly shim and then go all the way throught the foundation and then a flat washer and nut go on inside the foundation to hold the whole thing tight to the foundation.

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Make sure the top of the deck boards is at least 4" (7" is better)below any door threshols. If any higher water will leak in under the door and take out the sub floor.

Read your building code carefully before you take this advice. There are code requirements which deal with the level of the surface just outside a door.

Builder get to build what designers draw up.
Us remodlers get to go back and fix things all day that just do not work out in the long run.
Improperly installed deck ledgers installed wrong with no flashing or to high, rank way up there on my money maker list.
The one we just finished last month had the deck level with the door way and it had taken out the door, kitchen floor and tile, the bottom plates in the wall, foundation plate, rim joist and wall sheathing.
The one before that had the deck 1" below the threshold and it had taken out the whole kitchen floor siding and rim joist.
Last year it was a 100 year old house with 3" thick heart pine thresholds and it had taken it out as well as the 4" X 6" beam holding the wall up. All becaue the stoops or decks were to close to the doorway.

I repeat: read the building code. Kinda ties my hands, and yours.

Another vote here for a free standing deck. Ledger boards aren't worth the potential trouble they can cause. I always do my darndest to talk my customers out of them.