Masonry Column connection to Wood Decks

[Bruce Ramsey]

I see a lot of exterior decks and porches. Most are constructed of all wood. A trend seems to be creeping into new construction where masonry posts are constructed and the deck is built on top. Gravity seems to be the fastener of choice to connect the deck to the masonry posts.

It would seem that there should be some mechanical fastening system similar to where the house is bolted to the foundation to prevent the deck from sliding off the masonry post.

Can anyone suggest a specific reference that defines how a wood deck should be connected to a brick masonry column?

[Jerry Peck - Codeman]

Hi Bruce,

First, there are two things to consider with decks supported on masonry piers: 1) are they attached to the house in any way; 2) are they free standing and not attached to the house in any way.

If attached to the house in any way, then the pier footings are required to be below frost level just like the footings for the structure. With the deck attached to the structure, the structure will provide some lateral support and bracing.

If not attach to the house in any way, then the pier footing are not required to be below frost level. However, with the deck now completely free standing and receiving absolutely no lateral stability from the house, the deck itself will need to be designed to provide its own lateral support to resist leaning, twisting and other affects of loads trying to move the deck. Those other loads include occupants moving across the deck and moving about on the deck.

The masonry piers will need to be constructed in accordance with, including limitations on their height:
- From the 2006 IRC. (underlining and bold are mine)
- - R606.6 Piers. The unsupported height of masonry piers shall not exceed ten times their least dimension. When structural clay tile or hollow concrete masonry units are used for isolated piers to support beams and girders, the cellular spaces shall be filled solidly with concrete or Type M or S mortar, except that unfilled hollow piers may be used if their unsupported height is not more than four times their least dimension. Where hollow masonry units are solidly filled with concrete or Type M, S or N mortar, the allowable compressive stress shall be permitted to be increased as provided in Table R606.5.
- - R606.6.1 Pier cap. Hollow piers shall be capped with 4 inches (102 mm) of solid masonry or concrete or shall have cavities of the top course filled with concrete or grout or other approved methods.

The piers which are tall enough to support a deck would exceed 10 times their least dimension and require being filled. Additionally, for a deck with an height below it of 8 feet (96 inches) the minimum masonry unit size would be a 10 x 10 inch unit, a 12 x 12 inch unit is a more common size. The piers would also have to address any and all loads, including uplift, overturning, sliding, lateral stability, etc., just to name a few. It is most likely that the pier would need reinforcing steel in it, and quite likely that it would need multiple reinforcing steel bars vertically to attain the stability required, most likely 4 vertical bars with hoops to hold the bars in place, making it into a free standing column with the masonry units acting simply as a form for the concrete/grout used to fill them.

There would also be required to be an embedded anchor bolt or other attachment as is required by the code as related to your specific area, likely a minimum 1/2 inch embedded anchor bolt.

Can anyone suggest a specific reference that defines how a wood deck should be connected to a brick masonry column?

Short of being able to link an ACI 318 or ACI 530 reference on the internet, go here (note: place cursor over link, right click, select "Open in New Window" - http://www.awc.org/Publications/DCA/DCA6/DCA6.pdf ), scroll down to page 9, scroll down to Figure 12: Typical Footing Options, the right footing with the embedded anchor, and make that footing taller vertically into an 8 foot high column, with the embedded anchor bolt being used to anchor the directly to the deck instead of through an intermediary post.

Does this provide sufficient information for you are should I try to find something more specific if possible?

[Jerry Peck - Codeman]

Hi Bruce,

Here are a few things I want to add to my response above.

I did not know if you were asking about a free-standing deck or a deck attached to the structure, there are different in their construction, with free-standing decks requiring more design and construction to attain the required stability.

I did not know if you were asking about a deck high enough to be walked under, such as a deck at second floor height, or a lower deck just a foot or two off the ground.

The higher the deck is, the taller the masonry piers are, the more problems which will be encountered, the more likely there will not be a prescriptive design for its construction, meaning that the deck would need to be engineered.

In the Prescriptive Residential Wood Deck Construction Guide referenced in my response above, on page 14, Figures 21 and 22, addresses free-standing decks and has additional requirements for footings, beams, posts, and stability.

Again, once the design and construction varies from this prescriptive guide, engineering would be required. Where wood posts can be braced against, masonry piers would not be braced against, not unless reinforced.

This is a plan showing masonry piers (note: place cursor over link, right click, select "Open in New Window" - http://www.chesterfield.gov/CommunityDe ... etails.pdf - page 11 of 14 at bottom), however, it shows no details for the construction of those piers. The construction of those piers would then require engineering and which would specify the anchoring of the pier to the footing, the reinforcement within the pier, and the anchoring of the pier to the deck above.

Do you have any more specific information, such as height above grade, free standing or attached, etc.?

[Bruce Ramsey]

Thank you for the explanation.

As a home inspector, it is often dififcult to see if the brick column is filled with grout since the deck is resting on top limiting access. Certainly the construction of the brick/masonrry column is important, along with a proper footing and connection of the column to the footing. Again, as a home inspector, it is often difficult to confirm that steel reinforcement, grout and other specific construction details were included.

With all the ballyhoo about wood decks collapsing, it seemed that the connection point between a masonry column and the wood deck band joist should be some type of mechanical fastener and not just rely on gravity. I have reported the lack of a fastening system several times in reports and so far no one has pushed back. I am just gathering data in preparation for the call from the builder who states there is no requirement or prescriptive method to join the two.

Most often the deck is attached to the house on one side and masonry columns approximately 12 -16 inchs square support the outer edge of the deck. The deck rests flush with the outer edge of the brick column so only the outer 2 inches are supporting the deck. Correlating to centering beams and girders over columns and piers, this techinque is flawed. The slightest horizontal movement and the deck would be pushed off the edge of the masonry column. If the column is not anchored as you described above, it is likely the column would tilt over and fail.

It seems to me a metal L bracket bolted to the band joist and secured to a bolt embedded in the masonry column would be a valid connection point if they must have the column flush with the outer edge of the deck.

Thank you for the reference to the AWC document. I heard about that a few months ago while attending a Doug Hansen ICC prep class.

[Jerry Peck - Codeman]

Hi Bruce,

Here is a link to the Simpson Strong-Tie online catalog ( http://www.strongtie.com/ftp/catalogs/c-2009/C-2009.pdf ), or you can get the separate sections here ( http://www.strongtie.com/literature/c-2 ... urce=hpnav ).

If you click the second link, you can scroll down and see what pages are applicable to what type of connection, i.e., connections to concrete, holdowns and ties, caps and bases, lateral restraints, then several types of wood to wood connections. You would want to review the anchors in the concrete anchor section - pages 21 to 36.

Using the full catalog from the first link, you can look those up and find multiple options, all based on what the engineer specifies.

With any column, centering the load is best, however, with engineering the load can be placed at the edge of the column and anchored in place.

However, with a brick column, a column of laid up brick all interlocking around the column, there is less room for reinforcement in the column and may not have any. With brick columns, anchoring becomes very important, for the reasons you have given. With a CMU column, the center is open for grout and reinforcing, not that they are in there, but should be.

Given the heights of some of the columns in your photos, the columns should have reinforcement in them, be anchored to the footings, and have something more than a gravity holding the deck in place (that offers no lateral restraint or restraint from any movement). The only restraint is provided by attachment to the building and through the deck structure itself.

I believe you are on solid ground writing those up, and the correct answer to "how is it corrected" would be "in accordance with the engineering design" for the correction. Just going out there and installing some type of anchor without any supporting engineering may, or may not, accomplish any goals at all. An added connection, added improperly and to the wrong location, may actually be detrimental.