Can Composite Decking Rot?

Home Inspector with Jay Markanich Real Estate Inspections, LLC 3380-000723

Can composite decking rot?

If you go to the composite manufacturer websites will tell you their products do not rot.

If you search on line and find home repair websites, or forum websites, you will read that there are complaints all over the country.

Personally I had never seen composite decking rot in any way, until this inspection.  The listing information indicated that this was a Trex deck, but there are many imitators so we could not be certain.  Still, it was composite material.

Walking under the deck and looking up I found that every board had some form of rot or fungus growing on it.

One problem I noticed immediately was that there was little to no separation between the decking boards.

Again, if you go to any of the  websites, and to the installation guides, it says there must be space left between the boards so water can exit.

It also says that composite materials expand a lot with heat.  What I gather from that is that during the summer each board would squish against the one next to it.  Why wouldn't that crush the edges, and expose the insides to water intrusion?

The decking in the photo is a composite product - recycled plastic and various forms of cellulose.

It is said that the cellulose component approaches 50% of the composite material.

Cellulose has a high sugar content.

Fungus LOVES sugar!

There were many areas under this deck where a multiplicity of large, bulbous, fungal growths could be seen.

So the answer to the question in the title of this blog is YES.

The upper side of this deck had been recently painted.  Perhaps that was done to make it look nicer, or perhaps to cover up black stains which had migrated to the upper side.  There was visible damage up on that side as well.  And walking on the deck it bounced a lot between joist supports.

Until this inspection I had never seen composite decking painted before either!

The various websites say its decking can be painted IF it is cleaned properly first (not pressure washed), and then a primer/sealer layer is put on under the paint!

Was that done here?  I don't know.

My recommendation:  like everything, proper installation of any product is essential.  In this case it appeared that the installation at least had a role in the destruction of this material.  If water can't be eliminated from anything it will sit and find a way in.  When cellulose is included in any material - like composite decking or  fiber cement siding - it will absorb that water and the water will encourage the amplification of microbial growth.  Fungi is its own phylum!  Fungi exists for a reason.  Its purpose is to eat and destroy.  If not we would be surrounded by and under tons of old, old everything!  So don't let fungus eat your recycled deck!



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Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560


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Wayne Martin
Wayne M Martin - Chicago, IL
Real Estate Broker - Retired

Good morning Jay. All materials require proper installation and periodic inspection. Enjoy your day 

Mar 02, 2017 03:33 AM #1
Nina Hollander
Coldwell Banker Residential Brokerage - Charlotte, NC
Your Charlotte/Ballantyne/Waxhaw/Fort Mill Realtor

As with synthetic stucco and other materials... nothing wrong with them inherently... it's all about proper installation and maintenance.

Mar 02, 2017 04:57 AM #2
Sandy Padula and Norm Padula, JD, GRI
HomeSmart Realty West & Geneva Financial, Llc. - Carlsbad, CA
Presence, Persistence & Perseverance

I had no idea about this rot problem. I know many folks are building their docks here in Florida with Trex. Umm...time to re-think that use.

Mar 02, 2017 04:58 AM #3
Sheila Anderson
Referral Group Incorporated - East Brunswick, NJ
The Real Estate Whisperer Who Listens 732-715-1133

Good morning Jay. I always learn from you. Installation matters and doing it right can and does apparently make all the difference.

Mar 02, 2017 04:59 AM #4
Nathan Gesner
American West Realty and Management - Cody, WY
Broker / Property Manager

That's a good reminder to install properly! I've seen Trex warp and require replacement, but otherwise it has held up so far.

Mar 02, 2017 06:06 AM #5
Raymond E. Camp
Howard Hanna Real Estate Services - Ontario, NY
Licensed Real Estate Salesperson Greater Rochester

Good morning Jay,

Good thing the installer knew as I did not for our deck!

Make yourself an astonishing day.

Mar 02, 2017 08:42 AM #6
Fred Hernden, CMI
Superior Home Inspections - Greater Albuquerque Area - Albuquerque, NM
Albuquerque area Master Inspector

I have never seen that either... wow! But, like you said and we both know... installation is everything!

Mar 02, 2017 09:17 AM #7
Joe Pryor
The Virtual Real Estate Team - Oklahoma City, OK
REALTOR® - Oklahoma Investment Properties

I leanred years ago that you pay dearly for poor installation that youy thought was a bargain price.

Mar 02, 2017 04:29 PM #8
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Wayne - it's my history with Trex that it's a very good product and I wonder if the installation here is not the culprit.  It may also be a Trex-like material, but the seller's listing information said it was Trex.

Nina - nail hit on head.

S&N - you might want to contact the Trex people to find out how the product stacks up near water.  And be sure to install properly!

Sheila - and no matter the product!



Mar 02, 2017 05:10 PM #9
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Interesting Nathan.  I have never seen warping.  But then I have never seen rot either.  My typical line to clients is that it won't rot, warp, crack or split!

Raymond - my deck is old fashioned pressure-treated pine.  And I sealed the heck out  of it.

Fred - I'm still leaving open the possibility that it is a knock-off product, but so many sites and forums on line say that what I saw is not uncommon.

Joe - the old line is that if you think a professional is expensive then hire an amateur!

Mar 02, 2017 05:13 PM #10
Sally K. & David L. Hanson
EXP Realty 414-525-0563 - Brookfield, WI
WI Realtors - Luxury - Divorce

Every product has an upside and a down side...and it would seem that both installation and maintenance are issues not researched by these folks...our deck is great...years later ....paint it ? Really ?

Mar 06, 2017 03:22 AM #11
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

S&D - while apparently it can be painted, there are things that must be done first, according to the Trex website.  And it might be that this is not a Trex deck, even though it was so advertised by the seller.  But cellulose is subject to rot and Trex contains cellulose.

Mar 06, 2017 03:25 AM #12
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