Deck Bracing and Mushrooms

Okay back to see if NACHI still has guys who help or if it is over run by sarcastic goofballs.

Looking at this Deck today and think it needs bracing diagonal between posts ] .A permit was obtained in 2014 to add lagbolts and fasteners.The posts appear to be aprox 18 feet tall however looking at the official NACHI illustration see a max of 14’ pertaining to the illustration .What does that mean and any way this deck is good for sway protection ? The Contractor that obtained the upgrade permit is known by me and one of my referrals…


May get Mushrooms …:slight_smile:

You’re right again Bob.

Back to our gun debate.

Yep, nothing changed.

Nice forum…where can I read the obituary ?


The X-bracing under the deck is the work horse providing the bulk of the anti-sway prevention on this deck. The 18’ posts are capable of supporting the vertical deck loads without 45° bracing. Did you try shifting your weight side-to-side while on the deck? Most published guidelines are generic and ultra-conservative and I wouldn’t make any statements the deck was inadequate just because it did not meet NACHI or some other guidelines. Chicago has a Porch Design & Construction Guideline book located here

Like most prescriptive guidelines, it has a disclaimer. The following paragraph is in the introduction of this guide.

The design information included in these Guidelines is not, however, intended to provide the sole method of porch and deck design and construction necessary to meet the requirements of the Chicago Building Code. As there are innumerable porch configurations in the City of Chicago, the load tables, details and examples cannot be expected to address every possible condition. The applicability of any detail or framing plan must be made with consideration of the actual porch configuration and required load transfer. For conditions that are beyond the applicability of the framing shown and load tables provided, designs must be created that conform to the requirements of the Chicago Building Code, referenced standards (such as the National Design Specification), and accepted structural engineering practice.

Randy no visible footers.Diagonals on center post should be at corners.X bracing is redundant.Should not the decking be serving same purpose ? Do not see how that stops post sway.

You would not call it out then ?

Ledger bolts were added retro 2 years ago.Saw permit online .Build date I am guessing at 1998 due to appliance ages and roof tiles.

Thanks have it but not an answer.

**Randy your PDF is secured but I actually have 4 PDF from the city and sure enough you are correct . Damn } **LATERAL BRACING – Is a system within the porch structure to
prevent lateral movement such as racking and possible collapse.
Many, if not most, porches rely on the buildings that they are attached
to for lateral stability. Therefore, the porch structures must be securely
attached to the main buildings through the ledger beams or other
means. However, even with attachment to the main building the
outstanding or free edge of the porch structure must be braced. This is
especially true of stair structures that are constructed at the edge of
the main porch platforms or decks. (See Drawing 1D for a plan of this
type of porch.)
The forces that can cause racking of a porch structure are wind loads,
vibration and impact from porch use and out of plumb framing.
Because these forces can occur or impinge on any porch structure,
every porch structure must be designed and constructed to include a
lateral bracing system. The lateral bracing system must be designed
to resist a lateral load equal to at least the wind load plus 2% of the
gravity dead and live loads. The minimum wind load is defined as 20
pounds per square foot (psf) in the Chicago Building Code.
Lateral bracing is therefore most commonly found on the face of the
porch structure that is parallel to the rear wall of the building. This is
also considered to be the free edge(s) of the porch platform(s). X, K or
inverted V bracing is commonly used for this purpose as are diagonal
braces at the corners of posts and beams. The X, K or inverted V
bracing carries the lateral load from the various levels of the porch to
the ground.
As the building is typically considered adequate to provide some lateral
support, no bracing is usually considered necessary to prevent
movement perpendicular to the rear wall of the building. It is also
possible, with some porch configurations, to brace the porch structure
with diagonal bracing in the plane of the decks. If the porch decks are
designed to act as horizontal diaphragms, then it is possible for the
entire structure to be adequately braced using the stability of the
building. Bracing of decks can be accomplished by the use of
dimension lumber attached diagonally under the joists and beams.
Furthermore, decks can be turned into diaphragms by installing the
deck boards on a 45 degree angle.
Because of the multitude of porch configurations in the City of Chicago
and many possible bracing configurations, specific methods of lateral
bracing are not considered, in detail, in these Design Guidelines.
page 10

404 - File or directory not found.
How about this…

Since your not doing code inspections or an engineering evaluation, I don’t see any issues from your picture. I typically don’t dig down to the bottom of the posts to verify what the posts are sitting on, but in a case like yours I may dig down a few inches below the soil to see if any wood rot exists. Most treated posts will eventually rot at or just below the ground surface.

It’s the best way to stop post sway. The front corner is effectively fastened to the structure, how is it then going to be able to move? No decking is not doing the same thing, its running adjacent to the joists, that will not resist sway in the least.

Need to go grab a Beer and ponder that .

Bob, I’m not trying to be a smart A but it might be a good time for you to brush up on a few courses, or take a few. Instead of relying on diagrams and basic codes or instructions.

Cross bracing to prevent swaying is Decks 101.

I’d like to see what that upper deck post are bearing on inside the railing of the lower deck.
Swaying is not an issue on this deck. Those two little knee braces are doing nothing.

He’s right.

Here Marcel



Well, it does look different from that angle.
How did they splice that column?:slight_smile:


According to Chicago’s deck requirements it should have a bolted lap splice. The attached picture comes from that manual.