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Dangerous deck (C) Daniel FriedmanDodgy Deck Columns, Posts & Piers
Deck post construction & safety inspection

  • DECK POST MISTAKES - CONTENTS: how *not* to install supporting posts or piers for a deck or porch.
  • POST a QUESTION or READ FAQs about unsafe deck posts or deck post installation, size, spacing, construction & connections or connectors from post to pier or from post to supporting girder or deck framing.
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Dodgy deck posts & porch supports: this article describes questionable or downright dangerous deck posts, deck piers & poor connections (or missing connections) between the posts and piers and post tops and beams or girders that support a deck, porch, or wood-framed exterior stair.

This article series describes critical safe-construction details for decks and porches, including avoiding deck or porch collapse and unsafe deck stairs and railings. Our page top photo illustrates temporary bracing and support during replacement of unsafe deck posts. This deck was in danger of collapse.



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Unsafe, Collapsing Deck Piers & Deck Posts

Bad deck post (C) Daniel Friedman Bad deck post (C) Daniel Friedman Cracked concrete support column below a deck (C) Daniel Friedman

Above are some photographs of errors: unsafe short cuts taken to "get the deck up" when proper lengths of post were not available or where piers were re-cast on top of older poured concrete piers that were tipping or collapsing. It is surprising how often we see an extra block or scrap installed to make up for a deck post that is too short. This is an un-stable structure at risk of dangerous collapse (above left).

At above center the original concrete piers were probably not dug deeply enough nor properly constructed and were tipping and sliding down hill. A repair contractor placed a new pier on top of the tipping, sliding, collapsing pier - a dangerous repair. The cross bracing may slow the fall of this deck when it collapses.

At above right we see a concrete column or pier that has cracked and slid slightly sideways. It's possible that steel reinforcing rods were omitted in this pier.

Loose concrete block as a poor substitute for a masonry pier below a wood-framed structure (C) Daniel Friedman

Our photo at left shows a hollow core block set atop other concrete blocks and scraps supporting a wood framed structure. This is not a reliable building support for several reasons.

The wrong materials are used in the wrong position, with no connection between the masonry "pier" and the wood beam supporting the structure above.

The lower concrete blocks and block scraps indicated that there was no below-frost footing (this building is in a northern, freezing climate).

No doubt readers can point out other fantasies that the builder may have had in mind when using this construction method.

Reader question: concrete deck supporting column or pier with concrete voids

Large void in concrete deck column (C) InspectAPedia RHMy strata unit has a deck attached and is new. The concrete pillars supporting it where covered by the tube used to poor the concrete and when I removed it I found huge holes and air pockets all around the pillar with the rebar inside clearly visible. I will include a picture for you to see.

Is that a concern for the long time stability of the support? With this situation I would expect the rebar to rust out over time and the porous concrete to crumble under the weight of the deck.

Please give me an opinion on the issue as the builder insists that this is no concern at all.

Thanks for your advice on this. - R.H. 5 Oct 2014

Reply:

In my opinion, while I'm not worried about an imminent deck collapse blamed on a downwards bearing load from the deck, your photo shows a poorly-constructed supporting concrete column that should be repaired or replaced.

While it might not fail in compression (downwards load from the deck), the poor mix of concrete during the pour has left significant voids that could allow the support to fail by bending - not something that is likely but something that can occur during severe storms, impact, earth movement etc. In turn such a failure can cause a collapse.

If you check our article on CONCRETE COLD POUR JOINTS you will see examples of more harmless cold pour joints that are quite different from what you show in your photo. A harmless cold pour joint would not leave a significant void in the concrete column that in your place is apparently serving as a both a pier (or foundation) and a supporting column.

The contractor makes me nervous - failure to adequately pour one column suggests they all should be checked, as well as other structural supports and connections. If this column is the only such instance and if there are no other structural issues the matter should be a small one to correct.

To avoid wasting time arguing with your builder, ask your local building department to inspect the structure. In most jurisdictions a building permit and approvals are required to build a deck or porch. Those procedures help assure safety and code compliance.

Reader follow-up:

Thank you so much for getting back to me so fast.

The builders solution to this point has been to put some mixture in by hand (I assume it was quick mix concrete - he mixed it from a powder in a small bucket and then applied it to the holes and smoothed it along the column) and to tell me not to take the paper off the rest of the columns.

The one you saw the picture of was one of the shortest ones. Some of the others are somewhere between 4 to 5 feet tall. The unit is built on a hill and the deck surrounds most of the structure. From what you say in your email I should be quite concerned, right?

I do know that the occupancy permit was hinged on the deck being finished. As all the pillars are still covered by the tube used to pour the concrete I assume no one checked the quality of the pour.

I will let you know how it goes. - R.H.

Reply:

Don't panic but do pursue it. An engineer might explain it better, but a concrete column depends on the combination of concrete and reinforcing steel for its strength and performance. Leave one of them out over part of the column height and it is compromised.

Your building inspector may be satisfied with the repair you describe, provided the patch actually bonds with the original concrete of the column.

Watch out: Sometimes careless or sloppy work in one location is a clue that other shortcuts may have been taken, such as failure to take the deck pier to an adequate depth or failure to make proper structural connections.

I'd like to see a photo of the builder's repair. Also, have you pulled the cardboard sonnotubes off of all of the other columns? If so, how did they look?

Something else for you to check about this structure:

I see that what looks like a deck girder sits in a connector atop the column, and I can see the butted ends of two 2x members - (it's correct to place splices over a post).

If this is a built-up girder, that is if its thickness is more than a single 2x member (which I'd expect to be the case) then check the back side of the girder from the side shown in your photo. I want to see that the back side does *not* consist of a second pair of butt-jointed 2x members. In good framing practices, the splice we see should be covered by a solid member whose ends or splices are over other columns.

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