Seattle Home Inspector's Blog


Loving our decks to death!

We love our decksWith all the recent deck collapses around the country it may be time once again to re-visit deck construction methods and materials.

Actually we have pretty much figured out the “methods.”  It is getting builders to follow the proper method that is the problem with newer decks now. Many of the failures of older decks were the result of poor practices at the time of construction but may not have “technically” been against the codes of the time. Sorting all that out could be a nightmare in itself.

We clearly know HOW to build decks safe now–there is simply no excuse for catastrophic deck failures like we have been seeing in the news.

So if we have figured out the “methods,” what about the “materials” the decks are made of?

Modern decks are generally required to be constructed of rot resistant materials. Around here, that generally means “ground contact” pressure treated lumber.

I started thinking about the adequacy of this type of lumber when inspecting a deck recently. As near as I could tell the deck appeared to be about 20 years old. One of the support beams had a crack in the side of it. This is not unusual for wood beams–they often check without being a structural issue. Since many of these cracks will only show up after installation, we cannot simply say no checked wood can be used in deck construction.

What was frightening about this beam was that the crack had fungus growing all along it.

Pressure treated wood beam with fungal growth
                                                  Pressure treated wood beam with fungal growth

Those of you that have experience with ground contact pressure treated lumber and for those that do not, it is typically only the outer ½” or so of the beam that will be saturated with the preservative, leaving the center vulnerable to wood decay/rot and wood destroying insects. A check that goes deeper than the preservative will lead to rot of the interior core of the beam if a supply of water is provided to it. This is not hard to do in the Northwest.
Decay of beam
            This is how much of the center of a ground contact pressure treated 6 x 10 can “disappear”

That is what was happening to this beam. It was hard to tell how much of the strength of the beam was still present but it could be anywhere from a lot to very little. For example the untreated part of a 5-1/2” x 11-1/4” beam is approximately a 4×10. Clearly if the entire center portion of the beam turns to mush, the beam has lost virtually all of its strength.

So what is the solution?

The solution would be to require that all structural members of decks exposed to weather be constructed of “foundation grade” pressure treated lumber.

    (I can argue that all flat surface deck and roof structures should be constructed of pressure treated lumber. It is not a matter of if they will leak but when they will leak, especially if they are walking surfaces.)

This type of pressure treatment is certified to be treated all the way through the lumber.

This may be an idea that’s time has come.


Charles Buell, Real Estate Inspections in Seattle

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Comment balloon 28 commentsCharles Buell • July 12 2015 07:21AM


Interesting information and I always like how you incorporate great photos too to illustrate your points!

Posted by Kristin Johnston - REALTOR®, Giving Back With Each Home Sold! (RE/MAX Realty Center ) over 4 years ago

Great "Call to Arms" on decking! I just had one the other day that liteally shook when you walked on it... how can you relax on something like that?

Posted by Fred Hernden, CMI, Albuquerque area Master Inspector (Superior Home Inspections - Greater Albuquerque Area) over 4 years ago

Thanks Kristin

Fred, decks eat up a lot of inspection time---and often create problems with purchase and sale

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 4 years ago

Charles- how many decks will have to fall before we use the right materials!  I'm very cautious when I'm on a deck, especially the ones we have here that go out over the water. 

Posted by Kathy Streib, Home Stager - Palm Beach County,FL -561-914-6224 (Room Service Home Staging) over 4 years ago

Kathy, yes, and the point of this post is that most people consider this ground contact type pressure treated lumber to be sufficient---I think it is not.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 4 years ago

I actually didn't know there was any other kind than treated all the way through. 

Posted by Tammy Lankford,, Broker GA Lake Sinclair/Eatonton/Milledgeville (Lane Realty Eatonton, GA Lake Sinclair, Milledgeville, 706-485-9668) over 4 years ago

Well.  It doesn't take a Rhodes Scholar to know that, when the support beams for a deck are loose from the house or the beam in the footer is a termite infested rotten mess for me to



Posted by Lenn Harley, Real Estate Broker - Virginia & Maryland (Lenn Harley,, MD & VA Homes and Real Estate) over 4 years ago

Charles with all the media attention on fallen decks it's good for all of us to be more aware of decking.   We don't have decks like most of the country in the Phoenix Metro area but there are some of which I'll be more aware of - great post.

Posted by Anna Banana Kruchten CRB, CRS, GRI, WLS, 602-380-4886 (HomeSmart Elite Group) over 4 years ago

Ive never seen the rotted inside of a post quite like that. great article


Posted by Mike Rock, Granite Bay Luxury New Construction...For Less (Complete Design) over 4 years ago

I wondered where I left my swiss army knife.

Posted by Alan May, Helping you find your way home. (Jameson Sotheby's International Realty) over 4 years ago

Decks... ah yes... aren't they great? And some are more scary than a roller coaster ride. 

Posted by Andrea Swiedler, Realtor, Southern Litchfield County CT (Berkshire Hathaway HomeServices New England Properties) over 4 years ago

Weighing 230 pounds I have a tendancy to stay away from decks. Especially if a home has signs of lack of maintenance.

Posted by Bill Reddington, Destin Florida Real Estate (Re/max By The Sea) over 4 years ago

Hi Charles - Topics like this make me appreciate our semi-arid climate. We see very little rotting here - I wish the same was true of construction defects.

Posted by Dick Greenberg, Northern Colorado Residential Real Estate (New Paradigm Partners LLC) over 4 years ago

Tammy, I suspect there are a lot of people that would be surprised to learn this

Lenn, I freaked out an agent the other day when I demonstrated the deck was actually a swing :)

Anna, thanks, decks are nothing to mess with and the ones built in the 70's and 80's are poised for failure

Mike, it happens more than we like to think

Alan, yup---I find it sticking out of things all the time.  Here is another one in ground contact pressure treated wood used as landscaping timbers---and they were all like this---hollow/rotted on the inside.

Andrea, I love the ones three stories off the ground :)

Bill, and you probably don't push hard on railings either :)

Dick, your area and my area are sort of polar opposites in this respect.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 4 years ago

What about them Trex-brand decks, Charles Buell ? There still will be the wood support structure, correct?

Posted by Gerhard Ade, What sets me apart, will set you apart. (RSVP Real Estate) over 4 years ago

Gerhard, yes---still the wood structures supporting all the Trex---no different there.  Now we have these deck structures carrying a ton of IPE type deck materials too.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 4 years ago

Great post Charlie on an extremely important topic. While on vacation recently in MO  I looked at a 17 year old deck for a family member. It wasn't an inspection per se, just a quick look. Random spaced rusted nails held the the ledger board in place (Ugh!). There was no evidence of footings for the posts which were buckled a bit. Some decking was cupped, had checks and more than just a few popped nails. Also, there was no diagonal bracing. Sadly, this deck was at least 16 ft. above grade.  Looked to me like there was an attempt to minimize the amount of materials used. After I relayed my concerns and recommended a full inspection and a code check, the reaction was, "Looks strong."  I replied, "Looks can be deceiving, better have it looked at."     

Posted by James (Jim) Lawson, DBA, Broker Associate, RSPS, BPOR, HI & PE ( LLC) over 4 years ago

James, did you take any pictures?  Love to see this structure.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 4 years ago

Thanks for this informative post.  I had no idea about foundation grade lumber, but I do now!  Thanks!

Posted by Jan Green, HomeSmart Elite Group, REALTOR®, EcoBroker, GREEN (Value Added Service, 602-620-2699) over 4 years ago

Didn't take any pictures Charlie. I was caught by surprise to look at it. Seemed a bit flimsy. Don't know if it was built by a DIYer or a contractor with a low-end budget.  

Posted by James (Jim) Lawson, DBA, Broker Associate, RSPS, BPOR, HI & PE ( LLC) over 4 years ago

Jan, most people do not know the difference---so you are not alone.

Jim, it sounds pretty bad based on what you said.  Hopefully they will get it looked at.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 4 years ago

Great photo of a post rotting only on the inside!  I have needed that photo many times - people don't believe me.

And that "fungal growth" on the deck beam looks suspiciously like a Swiss army knife.  But I could be wrong.  I'm kind of far away.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 4 years ago

Jay, well Swiss Cheese is fungal

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 4 years ago

Gives a new meaning to the phrase...hit the deck! Maybe not, it may collapse!

Posted by Richie Alan Naggar, agent & author (people first...then business Ran Right Realty ) over 4 years ago

Charles Buell I never knew pressure treated lumber could rot from the inside out. Good information!

Posted by Michael Setunsky, Your Commercial Real Estate Link to Northern VA over 4 years ago

Charles Buell - lot to learn from your post (as always). 

Do we have all decks made from pressure treated material now? I have seen some real bad ones....

Posted by Praful Thakkar, Andover, MA: Andover Luxury Homes For Sale (LAER Realty Partners) over 4 years ago

Charles Buell, that is great information and the pictures are worth more than one thousand words.

Posted by Sybil Campbell, REALTOR® ABR, SFR, SRES Williamsburg, Virginia (Long and Foster REALTORS® 5234 Monticello Ave Williamsburg, Virginia) over 4 years ago

Richie, too true :)

Michael, it sure can---happens all the time

Praful, yes, if they are done professionally.  But even so, it is typically going to be the type pictured---that can decay on the inside without our knowing it.

Sybil, thanks

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 4 years ago