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Old 09-08-2018, 09:03 AM   #1
Mini-Skoolie
 
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Roof Deck Install - Question about Span for Trex

Hello!

I saw a crazy deal on Trex composite decking at Lowe's the other day and picked up 34 12-ft planks for around $300. Not bad, considering that almost half the cost was shipping.

I wanted to use composite vs 2x4s to reduce the need for maintenance and because I have an impression they are lighter. To be honest, I can't prove the latter, but if somebody could verify that then it would be appreciated!

My question is regarding span length. I read the Trex installation manual and it states that for pedestrian use (100 lbs per square ft) that there is a max span of 24". If I calculated correctly, the span between roof ribs is about 28-30".

I didn't think twice to pick up this material because I had seen so many others using it for their own roof decks. I want to ask the community, should I be concerned about surpassing the max span length? I dont mind a little sag, but a safety issue is another thing.

Thanks in advance for your advice!

Chris
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Old 09-08-2018, 09:12 AM   #2
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I am going with Trex on roof as well as my rear deck and will stick with their recommended support as a minimum. Only their engineers can really tell you how it will perform, but... I suspect there is at least a little buffer built into their numbers just as a CYA/liability factor.



The other way to check is to buy a strip, lay it across whatever span...then jump on it.
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Old 09-08-2018, 10:56 AM   #3
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In my experience building decks, Trex was always way heavier than real wood at time of purchase. Real wood will dry out and get lighter, Trex never loses weight.
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Old 09-08-2018, 01:17 PM   #4
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The other way to check is to buy a strip, lay it across whatever span...then jump on it.
I would also recommend doing this. Lay a whole bunch of your trex pieces across a span that is equivalent to the space between your roof ribs. Walk around on them and see what you think. I would imagine it'll feel fine.
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Old 09-08-2018, 01:35 PM   #5
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Depending on how you are running your boards?
Long ways with the roof would be quickest.
But if you
Make your attachments to the roof ribs and run sub base stringers like is done for metal roofing and cut the boards for the width of the bus.
You will have a stronger and no worries finished product.
And as already stated lumber over time will dry out,get lighter and ROT if not sealed/maintained as needed and composite material will not lose weight and last longer with minimal maintenance.
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Old 09-08-2018, 02:18 PM   #6
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I would do significantly less than the maximum span. That trex stuff is prone to sagging. Do a quick google search and you'll see what I mean. There are many disappointed deck owners out there. I would expect UV exposure to be a contributing factor.
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Old 09-08-2018, 02:37 PM   #7
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I've sold decking and used to design decks in my old job (as well as built a few). Composite decking is definitely heavier than wood.....especially cedar. Also, depending on what version Trex that you have is dependent on the joist centering. Most is 16" MAX. I usually would recommend 12-16" to my customers. The other thing to remember about composites is that while they require less maintenance than wood but still need annual cleanings (it was always hard convincing my customers that this was the case).
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Old 09-08-2018, 09:11 PM   #8
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Good advice there.
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Old 09-10-2018, 10:12 AM   #9
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Originally Posted by Whisard View Post
I've sold decking and used to design decks in my old job (as well as built a few). Composite decking is definitely heavier than wood.....especially cedar. Also, depending on what version Trex that you have is dependent on the joist centering. Most is 16" MAX. I usually would recommend 12-16" to my customers. The other thing to remember about composites is that while they require less maintenance than wood but still need annual cleanings (it was always hard convincing my customers that this was the case).
Yep, it's heavy. In humid environments some people end up unhappy I think and in other areas they love it. Read some reviews to see the negatives.
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Old 09-10-2018, 09:04 PM   #10
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myself i wouldn't use it i've been building for 35 yrs i've tried it every way and it moves so much in the heat and cold it's crazy and it sags there isn't a replacement for wood i've put just plain spruce decking on 5/4" x 6" and its lasted 20 years now with nothing on it but if you want it to really last mix used base oil and kerosine half and half before you deck it put 30 lb felt paper on your stringers and on any joints with curl down so sheds water it will last for as long as you need it to and spruce decking is cheap and you could get away with 24" on center id go 16o/c but its up to you but i wouldn't put the crap on anything but the dump! sorry im honest can't help it have a good one stop by if your in maine!
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Old 09-11-2018, 05:14 PM   #11
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Awesome feedback from everyone!

So I got the call from the freight company this past Saturday, stating that it would be delivered on Sunday between 11-3p. Nothing on Sunday. I'm thinking this will give me a good opportunity to cancel the order and have a good excuse for it.
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Old 09-15-2018, 06:31 PM   #12
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Tree

Trex is heavy- it requires more support than regular lilumber and it absorbs heat and can go rubbery. Id stick with a metal frame with expanded wire.
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Old 09-15-2018, 07:04 PM   #13
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I absolutely considered this as well. If anybody has experience with this, I would love a good resource. I don't know much about the guidelines for this or where to purchase it!
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Old 09-15-2018, 08:29 PM   #14
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Expanded metal could be a good option. Since it sounds like you haven't worked with it much I'll mention the one thing that drives me crazy about that material: sharp edges. When I see expanded metal in a fence, on a playground, as a guard around moving parts on machinery, etc it always looks and feels nice. I wouldn't worry at all about my kids getting close to it knowing that they're going to touch it, stick their fingers through the holes, etc.

But the few times I've bought expanded metal, the product I receive has razor-sharp flash half way around every diamond-shape opening in the entire sheet. It has to be handled with gloves and is totally unsuitable for anything where people might touch it.

I never have been able to figure out whether it's a matter of the weight of the sheet, the manufacturing technique, the manufacturer, or whether there's an optional processing step that dulls the sharp edges. In any case, if you're going to work with expanded metal, I suggest inspecting the actual material you'll use before buying or building anything.
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Old 09-15-2018, 09:57 PM   #15
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I would not use Trex for a roof deck. It weights a lot more then wood of the same dimensions, and it tends to flex more (which is why you'll often see it require closer/tighter joist spacing then regular wood.)

We looked at doing our house deck in trex - we'd have to spend so much time adding joists that its not worth it.
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Old 09-15-2018, 10:11 PM   #16
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I'm very glad that I was able to cancel the order and refund the money before it arrived! Either wood or screen now.
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Old 09-15-2018, 10:51 PM   #17
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Go for a marine look...TEAK!
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Old 09-15-2018, 10:56 PM   #18
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Lol watch my deck cost more than my bus...sounds like something my dad has done with the house...
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Old 09-16-2018, 01:24 AM   #19
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If I were to add a roof deck I'd use an frp decking or grating. Not cheap, though.
With insurers now redlining buses with decks I've shelved any plans I had for a roof deck.
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Old 09-16-2018, 09:19 AM   #20
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Deck on bus roof

I'm thinking sheet metal that's perforated and then Rhino coating both sides
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