Photo of a residential deck construction(C) Daniel Friedman Porch & Deck Ledger Connections to buildings
Best Practices for Deck Ledger Boards
     


InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

This article explains critical safe-construction details for decks and porches, including avoiding deck or porch collapse and unsafe deck stairs and railings.

Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.

Photos & Construction Details of Unsafe Compared with Safe Deck & Porch Connections to the Building

Deck Ledger Board Connection to Building Band Joist

Photograph of   a collapsing deck (C) Daniel FriedmanMost residential decks are supported on one side by a ledger that is bolted or lagged to the home’s band joist. This connection is critical, since a failure here can cause a deck to collapse.

[Click to enlarge any image]

Deck Collapse Case Study (link given below) describes several improper connections between a residential deck and the building that led to the catastrophic deck collapse shown here.

As noted in Best Practices Guide to Residential Construction, Chapter Four, Best Construction Guide for Building Decks and Porches:

Most residential decks are supported on one side by a ledger that is bolted or lagged to the home’s band joist.

This connection is critical, since a failure here can cause a deck to collapse. Failure of the ledger can be caused by too few or undersized fasteners, or by decay in the ledger or band joist. Lags or bolts provide little support when fastened to rotted wood. So proper flashing of the ledger and band joist area is critical.

It is also important that the band joist be nailed adequately to the surrounding structure, since the ledger is only as strong as the structural members it is attached to. Also see
our BOOK REVIEW: Best Construction Practices.

Deck ledger nails exposed (C) Daniel Friedman

Though deck failures are rare, ledger connections are typically at fault when they occur.

Through-bolts make the strongest connection, but adequately sized lag screws can also work.

With either, it is critical to flash the ledger area and to only use metal components that are compatible with pressure-treated wood.

Our photo (left) shows what can happen if the deck ledger board is simply nailed to the structure.

Deck Collapse Case Study includes additional photos of improper connections between a residential deck and the building that led to a catastrophic deck collapse.

Band Joist-to-House Connection.

Strengthening the band joist (C) J Wiley & Sons, S  BlissContinuing from from Best Practices Guide to Residential Construction:

In new construction, if a deck is planned, make sure the band joist is pressure treated and adequately nailed to the sole plate above and the sill or top plate below, using stainless-steel or double-hot-dipped galvanized nails.

In new construction, if a deck is planned, make sure the band joist is pressure treated and adequately nailed to the sole plate above and the sill or top plate below, using stainless-steel or double-hot-dipped galvanized nails.

Fastening with 16d common nails at 8 inches on-center is recommended.

If the nailing cannot be confirmed in a retrofit, extra toenails driven through the exterior can help to reinforce this connection (see Figure 4-6 at above-left).

 

Ledger-to-Band Joist Connection & Bolt Spacing Requirements

The table immediately below gives the bolt spacing requirements for connecting a deck ledger to the building when the ledger board is bolted directly to the structure.

Table of spacing for bolts or screws connecting deck to house (C) J Wiley & Sons, Steven Bliss Table of spacing for bolts or screws connecting deck to house (C) J Wiley & Sons, Steven Bliss

Table of Bolt Spacing for Deck Ledger Spaced Away from the Building

Table of bolt spacing for a spaced deck ledger (C) J Wiley, Steve Bliss

Spacing for bolts and lags used to connect the deck ledger to the building are shown in the table at above-right (ledger bolted directly to the building), and at in the figure at left for deck ledgers that are spaced away from the building.

Through-bolts are the most reliable connection, but lag bolts are adequate (photo, above left) as long as they are long enough to fully penetrate the band joist.

For through-bolts, drill holes 1/16 inch larger than the bolt. For lags, drill a full-diameter hole for the unthreaded portion and a smaller hole (65 to 75% of the lag’s diameter) for the threaded portion.

Use washers under the head of the lag bolt or at both ends of through-bolts to keep the head from crushing the wood. Soak the holes with a preservative before inserting the bolts.

Soak the holes with a preservative before inserting the bolts. Spacing for bolts and lags are shown in Table 4-5 below.

Table 4-6: (C) J Wiley, S Bliss

In humid climates, some deck builders prefer to leave a 1/2-inch air space between the ledger and house to assist with drying in the event that the ledger area gets wet. Because this weakens the connection, through-bolts should be used, as shown in Table 4-6 below.

[Click any table or image to see an enlarged, detailed version.]

Table 4-6: (C) J Wiley, S Bliss

To prevent splitting, lag screws or bolts should be held back two inches from edges and staggered as shown in Figure 4-7 just below.

Table 4-6: (C) J Wiley, S Bliss

Alternative to Deck Ledgers: Self-Supporting Decks & Porches

Table 4-6: (C) J Wiley, S Bliss

 

Given all the problems inherent in supporting a deck with a ledger, one approach is to forgo the ledger altogether and support the deck on posts on all sides, keeping it structurally independent of the house.

In the no-deck-ledger approach, the self-supporting deck still may be braced to the house to help it resist racking, but all vertical loads are carried to the ground by posts (Figure 4-10 at left).

A conservative rule-of-thumb for cantilevered structures states that joists can cantilever one-fourth of their total length, assuming that the cantilevered end is not carrying any loads other than the normal uniform floor loading.

-- Adapted with permission from Best Practices Guide to Residential Construction.

Details about selecting the proper fasteners for constructing decks and porches and how they are installed can be read at Deck Nails, Screws, Hidden Fasteners.

Also see critical deck flashing details for the ledger board, found at Deck Flashing at Building.

Also see DECK COLLAPSE Case Study (collapse of a new code-approved deck)

and see DECK FLASHING LEAKS, ROT Case Study for an example of an older deck with rot and collapse due to improper construction and missing building flashing.

 

Continue reading at DECK PIERS & POSTS or select a topic from the More Reading links shown below.

Or see DECK LAYOUT if you nee to know how to lay out and square up the deck plan to set exact pier & post locations.

If you have not read it see see DECK LEDGER BOARD INSTALL - for the basics of locating & installing the deck ledger in our online deck design-build guide.

Suggested citation for this web page

DECK LEDGER BOARDS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

More Reading

Green link shows where you are in this article series.

...




Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Publisher's Google+ Page by Daniel Friedman

Click to Show or Hide Citations & References