The days of staggering bolts every 16 inches or so are over—especially if you want to step down to the deck
Poorly attached ledgers are often the cause of deck collapses, which we read about every year. Accordingly, the International Code Council (ICC) has addressed bolt patterns for deck ledgers in the International Residential Code (IRC). The hope is to reduce those fatal deck collapses.
More attention by the ICC usually means more difficult codes. But you won't have to worry about a deck full of people crashing to the ground on a deck you built.
So there's that.
Before the 2009 IRC, builders usually staggered lag bolts high and low every sixteen inches or so. The bolts were usually about two inches below the top and above the bottom of the ledger.
When the 2009 code passed, a table was added to the book which specified a few things (1:33):
- A 2 inch no-bolt zone at the end of a board: either at the end of the deck, or where two boards meet in the middle to form a long ledger.
- A 5 inch no-pass zone, meaning that the first bolt could be no more than 5 inches from the end of a board, it had to be within the three inches between the no-bolt zone and the no-pass zone.
- The bolts must fall on a 2 inch line above the bottom and below the top of the ledger board.
The 2012 version of the code added a couple more wrinkles to the mix (3:40):
- The two inch bolt lines were eliminated and replaced with no-bolt zones. The bolts don’t have to land on the lines, they just have to avoid the no-bolt zones.
- The bottom no-bolt zone was shrunk from 2 inches to 3/4 inch. This is due to internal stresses in the ledger. The ledger basically hangs on the top bolts, but sits atop the bottom bolts, so more space is allowwed.
The bolt pattern must be clearly thought out (5:06)
Considering a 2x10 ledger and a 2x10 band joist as an example, let's start at the beginning.
The first bolt goes in from the end at least 2 inches and not more than five. It must also be down from the top at least 2 inches and at least 3/4 in above the bottom.
The second bolt has some extra regulation associated with it. The second bolt must be at least 1-5/8 inches below the first bolt, but no more than 5 inches below the first bolt. This means that the second bolt lands well above the no-bolt zone along the bottom.
So far, so good.
The second bolt also has another vertical control: minimum distance from the top of the joist to the lower bolt; the numbers depend on the size of the joist:
- 2x8: min 5.5 inches below the top of the joist (Exception: if there are 2x8 joists and a 2x8 ledger, this distance can be reduced to 4.5 inches)
- 2x10: min 6.5 inches below the top of the joist
- 2x12: min 7.5 inches below the top of the joist
For a 2x10 ledger this is pretty consistent with the 2009 code: 2 inches from the top and about 2 inches from the bottom.
If needed, the bolts can be lowered significantly (the lower bolt can go all the way down to 3/4 in above the bottom), but the upper bolt needs to drop down corespondingly.
There is a dual relationship in the bolting pattern:
- Relationship of the bolts to the ledger
- Relationship of the bolts to each other.
The 2012 codes makes you look at the band joist—literally (7:55)
In order to meet the bolting requirements for the band joist, you need to know how big it is, where the ends of it are, what its made from, etc … You need to actually be able to visually inspect the band joist.
As with the ledger, there is a 2 inch no-bolt zone at ends of band joist boards. The upper and lower limits are the same as the ledger's (2 inches and 3/4 inch) only opposite because the forces are reversed (band joist is fully supported along its bottom).
Overlaying the drill/no drill zones of the band joist and ledger indicates where the ledger can be bolted to the band joist: almost no where (only kidding). There is plenty of space for bolting unless yopu live in snow country.
In snow country, builders drop decks down a step. Adding these bolting requirements to a step-down deck makes lower the bolt impossible to locate legally. In fact, the maximum step down for a 2x10 ledger bolted to a 2x10 band joist is 3/4 inch if the bolting requirements are followed.
Back doors to bigger step-downs—within the code(10:45)
Clearly, some head-scratching is in order. To solve the puzzle, begin with what you can’t change: the size of the band joist that is already part of the house that you're building on to. Next, look at the ledger options for opportunities.
For a 2x8 band joist:
- 2x8 Ledger = 1.25 inch step down
- 2x10 ledger = (-1.25 inch) — IMPOSSIBLE
For a 2x10 band joist:
- 2x8 Ledger = 1.75 inch step down
- 2x10 Ledger = 1.25 inch step down
- 2x12 ledger = (-.25 inch) — IMPOSSIBLE
For a 2x12 band joist:
- 2x8 ledger = 3.75 inch step down
- 2x10 ledger = 2.75 inch step down
- 2x12 ledger = 1.75 inch step down
Not very encouraging.
Let’s look at it graphically (11:19):
Bolting a 2x12 ledger to a 2x12 rim joist according to code is a surprising exercize: at first glance, it seems impossible to bolt because the minimum distance seems lower than the maximum distance.
To solve this, the upper bolt needs to be lowered. To step down, bring the lower bolt to its lower limit and attach.
For a 2x12 ledger and band, this only yields a 3/4 in step down.
To get a bigger step down, decrease the size of the joist. A 2x8 joist can yield up to a 5.75 inch step down. This is the greatest step you can get that still complies with the IRC.
Updating the previous bullet lists to include smaller joists, gives the maximum step you can get for the various ledger/band joist combinations (13:12):
For a 2x8 band:
- 2x8 ledger and 2x6 Joist = 3.25 inch step down
- 2x10 ledger and 2x8 joist = 3/4 inch step down
For a 2x10 band:
- 2x8 Ledger and 2x6 joist = 3.75 inch step down
- 2x10 Ledger and 2x8 joist = 2.25 inch step down
- 2x12 ledger and 2x8 joist = 3.75 inch step down
For a 2x12 band:
- 2x8 ledger and 2x6 Joist = 5.75 inch step down
- 2x10 ledger and 2x8 joist = 4.75 inch step down
- 2x12 ledger and 2x8 joist = 5.75 in step down
Special Feature: code guy counsels code violations?
Lowering that bottom bolt is illegal, but most likely perfectly safe because the bottom of the band joist bears solidly on the mudsill, which bears on the foundation. Glenn suggests talking with your engineer and local building inspector about this option as it may be a safe way to get you out of a mathmatic and bureaucratic jam.
- SECTION R317 PROTECTION OF WOOD AND WOOD BASED PRODUCTS AGAINST DECAY
- SECTION R502 WOOD FLOOR FRAMING
- SECTION R507 DECKS
- R703.8 WALL COVERINGS / FLASHING
—Glenn Mathewson is an inspector/plans examiner in Westminster, CO. This video is excerpted from his Building Code College, a free ICC-approved online school for building codes.