Re-decking with Trex

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Forum topic by jasoncarpentry posted 11-18-2016 05:12 PM 1576 views 0 times favorited 19 replies Add to Favorites Watch
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147 posts in 2801 days

11-18-2016 05:12 PM

Topic tags/keywords: trex deck joist spacing

I’ve got a large wooden deck which I’ve let go to pot. As a result, I need to replace all of the decking. I’d like to use Trex (or some other “engineered lumber”). Here’s my question: The existing support joists are on 16” centers, and I’ve been reading that Trex (at least the 1” thick type) requires that the joists be on 12” centers to avoid sagging. Is this true? And if so, should I use 1.5” thick material?

Another idea would be to scab some 1.5” 2×4’s onto each side of the joists. This would decrease the joist spacing from 16” to 13”.

I could always go back to wooden decking, but I’ve learned the hard way that the oak trees above my deck are bad news for wood. Maybe it’s the tannic acid, I dunno. Wood is cheaper than Trex, but it requires a REALLY thorough pressure-wash every year.

Any input would be appreciated!


-- Jim in Tennessee

19 replies so far

View jasoncarpentry's profile


147 posts in 2801 days

#1 posted 11-18-2016 06:17 PM

I’m just now hearing about Ipe wood. Any thoughts? I know that there are other wood options available, such as red cedar and redwood. Does anybody have price info. on these non-PT wood types?

-- Jim in Tennessee

View jmartel's profile


8155 posts in 2296 days

#2 posted 11-18-2016 06:19 PM

Ipe is very pricey. Cedar is going to be the least expensive of the non-pressure treated stuff.

Trex is pricey, and at least a few years ago I was looking at houses that had some installed. They can get moldy. Not sure if they’ve fixed it yet or not, or if it’s specific to the soggy Seattle area. But something to look out for.

-- The quality of one's woodworking is directly related to the amount of flannel worn.

View bondogaposis's profile


4993 posts in 2498 days

#3 posted 11-18-2016 07:52 PM

Were the original joists assembled with screws? If so you could disassemble them add a few more at 12” spacing then go w/ the trex.

-- Bondo Gaposis

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126 posts in 1165 days

#4 posted 11-18-2016 08:22 PM

the other thing with trex is you cannot walk on it barefoot in the summer if it sits in the sun.

View OnhillWW's profile


137 posts in 1379 days

#5 posted 11-18-2016 10:31 PM

Jason I resurfaced my deck with Trex 21 years ago and could not be happier. Adding joists between existing joists is a good Idea. When I did my deck over the deck boards were very weathered with deep cracks / checks and cupping, but when I cut into the actual decking boards ( PT 2×4s) the cores were still very strong so what I did was to pull three deck boards and leave the fourth giving me a 11” gap with a 3.5” board to screw the new decking into. The result was a VERY solid deck people are amazed at how solid the deck is. Trex may be pricy but remember that 100% of the material is useable vs. wood where you need to purchase 10% more wood for the task than is needed because you will cull out twisted, cupped other less desirable material. I also layed my decking at an angle so that I only had to remove a very short angled piece from each end of the board maximizing usage. My deck is 3.5’ off the ground so I was able to get under the deck and attached the decking from the underside – doing so leaves the decking unmolested from the top side, very nice to look at.

-- Cheap is expensive! - my Dad

View xeddog's profile


205 posts in 3154 days

#6 posted 11-19-2016 12:00 AM

I replaced a small redwood deck with a 14×16 Trex deck. It is mostly a light grey colored material with a darker picture frame 2 boards wide around the outside. I read about the joist spacing too, so I just made them 12” centers. While it seems to be stable, it also sorta kinda feels like 12” centers was more than just a good idea. Another choice I made was to use the invisible anchors. To that I can say DON’T USE THE TREX product. Find something better.

Someone else mentioned not being able to walk on it in the summer. For my deck, if I go out on it barefoot on a 100 degree day, it will be pretty warm, but since I go barefoot as much as I can I have a good crust built up. Some tender foot would be screaming. But if I step onto the darker colored border, even I will start screaming. I would guess that the temperature difference between the light and dark materials is probably 30 degrees.

All-in-all, I am satisfied with my choices with the exception of the invisible anchors. Good solid concrete anchors, pressure treated Douglas Fir joists and posts, and Trex for everything visible including railings and balusters, stairs, etc.

Someone else mentioned mold. As I understand it, this is possible with decks built close to the ground without adequate ventilation underneath. Since my deck is 3 feet above ground this isn’t an issue for me. But all-wood decks are also subject to mold. The old redwood deck I replaced frequently had mold on some of the surfaces. There is nothing like that even starting so show and it has been 6-8 years.


View RH913's profile


52 posts in 3131 days

#7 posted 11-19-2016 12:10 AM

I just redecked a 400sf deck with Trex Transcend
Joist 16” on center

Instructions said no problem
If you run at a 45 degree angle then 12” on center was recommended So far so good it’s been up all summer


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147 posts in 2801 days

#8 posted 11-19-2016 02:00 AM

xeddog: You said: “Another choice I made was to use the invisible anchors. To that I can say DON’T USE THE TREX product. Find something better.” But the rest of your post seems to be positive about the use of Trex. I’m confused!

Please clarify.

-- Jim in Tennessee

View xeddog's profile


205 posts in 3154 days

#9 posted 11-19-2016 05:01 PM

jasoncarpentry – The Trex decking materials (deck boards, trim boards, railing and baluster materials, etc.) were all just fine. The deck boards I got are t&g along both sides and Trex sells an anchor that fits into the two adjoining slots in the boards and screws into the joists. The anchors sold by Trex were awful. Little plastic things with a small sized stainless steel screw that snapped the heads off if you looked at them wrong. I used my little Hitachi driver for some of them, but the rate at which the screws snapped was just too much. Using one of the torque adjustable drills reduced the failure a lot, but there was still quite a few that snapped. There are also quite a few of them that seem to be loosening. I think the screws are sinking into the plastic clip.

Bottom line, the Trex material was/is fine, just the awful anchors.

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147 posts in 2801 days

#10 posted 11-19-2016 05:13 PM

xeddog – Thanks for the clarification. And the video makes it look so easy to use those anchors!

So, what kind of hardware did you end up using?

-- Jim in Tennessee

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205 posts in 3154 days

#11 posted 11-20-2016 05:38 PM

My biggest mistake was finishing the deck using them. I had them and there was no option locally. Most of them are still holding, but there are a few of them that have let the deck boards “lift” a little. Not much, no more than maybe the thickness of a sheet of paper or two, but it is just enough so that when you step on them you can hear a slight tap as the boards contact the joists.


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944 posts in 1588 days

#12 posted 11-20-2016 07:46 PM

Jim—If you go the Trex rout I suggest that instead of scabbing on a 2×4 to each side of the existing joists, that you block between the joists about every 4 feet and hang a 2×4 centered between the joists (per the attached pic).

Scabbing on a 2×4 will trap water between the old joist and new 2×4 and promote rot.
Hanging a 2×4 between the joists will reduce the decking span to 8” with less material.

-- Jerry, making sawdust professionally since 1976

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147 posts in 2801 days

#13 posted 11-20-2016 11:23 PM

Jerryminer- Good suggestion! But I’m also hearing that 16” O.C. might be OK. As far as my “scabbing on” idea goes, I could go ahead with that and put butyl tape (whatever that is) on top of the joists (or double joists) to protect them from moisture. I read this here:

Has anybody used butyl tape?

-- Jim in Tennessee

View Stewbot's profile


199 posts in 1230 days

#14 posted 11-21-2016 02:42 AM

I’ve used that window butyl tape before on a balcony ledger where it attached to the house. It seems to be holding up well, however it is attached to a pressure treated board (I saw that tip in one of those yellow carpentry books, Taunton press maby…).

A word on Ipe if you decide to go that route. As mentioned it is pricey but looks really good (IMO). The boards however can be hard to work with and take some persuasion to get the lines parallel, sometimes two people are neccesary. If your lumber yard doesn’t stock your desired material with a pre-cut groove, I’ve used these along with a biscuit joiner. I cannot speak on behalf of how well those clips hold over time because they were installed at a job with my previous employer and I haven’t seen them since. The Ipe will also probably need more maintenance.

Another wood similiar to Ipe is called tiger wood, I think it’s more affordable but from what I saw didn’t seem to hold it color as well as Ipe.

-- Hoopty scoop?

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Roy Turbett

168 posts in 3726 days

#15 posted 11-21-2016 06:21 AM

You shouldn’t have a problem installing Trex on 16” centers unless you are planning to do so on a diagonal. I ran into this problem at my mother’s condo because they require the decking to be run on a diagonal. I was able to reposition every second and third joist and ad a new one to change the 16” centers to 12”. I used the Bear Claw fasteners and found them easy to install. Since then I’ve learned that the lumber yard is recommending the Camo fastener system. Its basically a jig that positions the board with the recommended gap and installs two screws on an angle similar to how a Kreg jig works. It can also be used on treated lumber. Another advantage is that you can remove a single deck board in the middle of the deck without disturbing the others. Here’s a link to the website.

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