Porch deck — install Trex over PT????
Okay…here’s a new one for me:
A retired couple has a gently aging pressure-treated deck. Their complaints are mainly that the cupped boards hold moisture, that it grows algae, and that it’s dangerously slippery. They want to replace it with a variation of Trex. The complications, of course, are that ripping up the really large wrap-around deck and walkway, upgrading the structure with additional joists, and also buying the decking is very labor and material -intensive.
They asked me today if it would be possible to install the Trex right over the PT. Although I’ve never heard of it, I can’t think of a good reason not to. We could even overlay the pieces exactly so that the drainage is the same. It would save a great deal of time and money. The additional height is not a problem at the doorway, and of course the step heights would all remain the same.
Am I missing anything?
Thanks!
Sue
Replies
Would the trex by able to slid ie expand and contract ehrn it warms in the sun.
Or is the too much friction as it is in continious contact with the old deck.
Hmmm....good question. I guess that depends how it's attached. How WOULD I attach it, anyway? Trex is usually just screwed down, isn't it (as opposed to some that recommend hidden fasteners)? I get them confused. How would screwing it to solid wood be any different from screwing it to joists as far as expansion is concerned? I'd be willing to use a hidden fastener system, but can't imagine how I could do that and line up the gaps between boards for drainage.Sue
For hidden fasteners, screw through the PT into the trex.
I can't get under it; it's only about a foot above grade, if that. Sue
My bad, looks like hidden fasteners is out.
They don't care about hidden fasteners -- just want to know if the idea itself will fly. Any reason not to do this? Sue
Three thoughts (without any actual first-hand experience)...
I would be concerned about moisture getting trapped between the 2 layers and accelerating the decay of either one/possibly both. I'll bet the composite decking warranty would be void.
I would also be concerned about any warping that might occur in the PT layer. It would affect the composite layer which otherwise would lay flat.
The owners should be concerned about resale value. I know if I was looking to buy a house and saw 2 layers of decking, I would be wary.
DonCanDo -- All good concerns. Still, given the huge amount of money they'd save, I'm not sure I'd be convinced not to try it. Keep the posts coming! Sue
I agree with Don.Water will get between the two layers and the owners will not be happy when they have to rip up their new deck to replace the structure. Another reason to tear up the deck is to inspect the sub structure.
I have never come across a deck that didn't need some work on the substructure when the surface was ripped up.I might be tempted to walk away if they didn't want to do the job right, cause you know who the client will come back to if there is a problem down the road.Harryholtzheritage.com
Edited 8/10/2007 10:53 pm ET by harryhandsaw
I'm with DCD - the trapped moisture would be a perfect environment for mold to grow. (Think potential liability here)
My understanding is that wood to wood contact should be minimized outdoors - this plan would test the preservative function of the old PT to the utmost , even though only one side is wood.
BTW, PT does rot after enough time.
May your whole life become a response to the truth that you've always been loved, you are loved and you always will be loved" Rob Bell, Nooma, "Bullhorn"
"We Live" http://www.youtube.com/watch?v=7kuBgh0VCqI&mode=related&search
And Annie Ross's "Twisted" http://www.youtube.com/watch?v=8lqivrCIRGo&mode=related&search=
", given the huge amount of money they'd save...."This has to be a pretty large deck or very unique style for the amt of money to be huge
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Yeah, I know you/they are not particular about the fasteners. Personally I can't come up with any strong objections to placing the trex substitute over the pt, maybe someone with more trex experience will chime in.
Sorry not to be of more help.
Random thoughts:
Moisture between the layers would be a significant concern, and no way to be cheaply addressed later
The bottom riser will be taller than the others by the layer of trex on the first tread. This may/may not make any difference, depending on current stair arrangement
If the project looks like a go, I would try and sell them on picture framing the deck with ripped lengths of Trex on edge to hide the multi-layer look that would result.
"I am the master of my fate, I am the captain of my soul." Invictus, by Henley.
The walkway is not a traditional set of stairs, but a series of platforms about 3' x 3' (or maybe 4' x 4') that are each a step higher than the other. It would be easy to raise the grade at the bottom to accomodate the added height of the Trex at the driveway. The biggest portion of deck is between a retaining wall and the house, so the structure of the deck doesn't show at all, eliminating the necessity of hiding the edges. On the walkway and a small portion of stairs, I would add a bandboard to disguise the layering. I do, however, hear the issues about moisture and possible deterioration of the substructure, and that will have to addressed with the owners. Sue
Not only will you trap and hold moisture in the PT layer you will reverse the PT's moisture condition and that will cause a new set of warps, cups, racks, checks and splits that will telescope to the expensive new composit decking.
Currently the PT is dried from the top and the bottom remains "wetter" as it is on the groundside. Cover with composite decking and now the PT's normally dried surface is now continously moist and the bottom side is the drier!
You have no idea of how the boards are going to react and where thay will move and shift. It is probably treated yellow pine which is "swarmy" even before treating and worse afterward!
PT is rot resistent...BUT when continually moist in an areobic environment PT will rot at an accelerated rate. Secondly the trapped water will ensure the growth of organisms that have already infected the existing deck.
No way would I consider overlaying and put my name and reputaion next to it!
..............Iron Helix
Edited 8/11/2007 7:16 am by IronHelix
Trex has designed and built decks that are basically trex decking over treated "decking" (actually purlins with 100% coverage at the leaf tips and edges and on 12" centers in the field).This deck was built by Trex as a gift to the state of Minnesota.
Thanks for the additional info...learn a little something each day!
I don't mind the details as shown for the 12"O.C., as there is plenty of ventilation.
The solid decking overlaid with trex is looking good where the deck is elevated and will dry readily.
Those pictures indicate all new construction rather than existing with an overlay.
The considerations for the OP was that the deck is set to the ground and already exhibits moss and algae as a result of poor drying circumstance. The condition of the existing decking is not the same as a new install.
If my memory serves me correctly ,Trex does not like to see installations at ground contact level or in continually wet environments.
So I would still stick with my "No Way" under the current circumstance as explained..
..........Iron Helix
Your caution sounds well placed in OP's application...I just like being contrarian. ;o)
A robust discussion always hones one verbal and mental skills and yields alternate points of view which broadens our horizons. Only an open mind can access these benefits.
Nice exchange......Iron Helix
On the other hand...if you are too open-minded your brain might fall out. <g>
If it were my job, i'd be pulling a deck board or three to see how the sub structure is and how the ledger board was attached and flashed before proceding with the project.
CMA..............Iron helix
PS.....So that is why my short term memory isn't there anymore!
Good ideas.Speaking of memory, I saw that there is a movie with Denzel Washington called Deja Vu at the rental place, but I don't even remember it ever being at the box office.Maybe it didn't do well because people thought they had already seen it. ;o)
I agree with those who were concerned with trapped moisture, so, is there room to add something like 2x2 PT sleepers every 16" across the existing PT deck boards and then screw the Trex to those?
I don't think there's enough height at the doorway for that to work -- would be higher than the threshold. I'd need them at 12", wouldn't I? Can Trex have a 16" span? Not a bad idea, though. Maybe if they were 3/4" instead of 1 1/2".....keep thinking. It doesn't resolve questions about the structure underneath.....Sue
My opinion is with everyone else here. I wouldn't feel right doing it. Maybe if sleepers were installed... maybe. If the decking is at at 45 degree angle to the joist/sleeper, then yes every 12 inches o.c. the sleepers should be. If the decking is perpendicular, then the typical 16 inch o.c. applies. You said you're putting down a variation of trex. Do you know what brand. We use trex on the houses we do and I hate it. Scratches too easily, fades too much, gets very hot, and the widths have varied to 1/8 inch. I know this isn't a big deal. But we make our framing length a certain dimension so we'll end up with a full piece when we come to the end of the house. I lay decking from the end of the deck to the house. On my last deck I realized eight boards to the end I'd have to change my spacing to 3/8 or rip a 1 1/2 filler at the end. I ripped a filler. Again not really a big issue, only for me maybe. I've been looking into procell decking and hearing great things about it. I'm thinking about putting it on my deck when I build soon. http://www.procelldeck.com/
i just installed procell , about 25 % more expensive than trex, but seems lighter, installed on 16" span ,it would flex when i stood on an individual board, seems to soft to me, felt like a floating floor
The way I see it, Trex is heavy,VERY heavy, would need to calculate the extra weight And then look at existing framing to see if it would carry the load. I look at the situation the same as a roofover ,which is generally a bad idea. As for furring, by the time you add materials & labor, i think it would be about the same to just tear it out & do it right.
That sounds like a wonderful place for vermin - mice, rats, bees, hornets, to nest.
Did you join PETA?
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Good point--didn't even think about the vermin. But don't they get into the space under the deck anyway? I was also wondering if she could remove two deck boards, keep one, remove two, etc. and then put the Trex down cross ways? Still would have lots of places for moisture to collect I suppose.
One way to approach this decision is as a risk assesment. List the risks if they remove what they have and replace, then list the risks if they overlay the materials.For the former, it is almost a negative list. They have a known cost plus the advantage of being able to acess and inspect all existing framing conditions and easily repair and upgrade.On the other side of the list, there are 4-5 probable and potential negatives, any of which will be very expensive to fix later. Looked at from that POV, I would not even try this.from another POV, if they cannot afford to do it right, they should just refasten what they have, sand it, paint it with anti micro paint, and be done with it.Sounds like maybe the customer has a neighbor or friend who has gone to trex and wants to keep up with them but do it on the cheap. Even though this schlock idea is their own, the contactor will be the one who gets the complaints.Were there ever a cause for lawsuit if these folks are bent that way, there is legal theory that would lay the blame on the contractor because being a pro, they are expected to know better and to say so.
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There are composite decking materials specifically made for this duty. They are profiled with ribs on the bottom, to avoid trapping (quite as much) moisture.
Are the ribs crosswise? I think I've seen some with lengthwise ribs, which wouldn't really help in this situation. Sue
Lengthwise, but that would still help when you overlay the lumber 1-for-1. If you were anal you could drill holes throught the sides of the new pieces every foot or so, or drill holes through the existing PT, to let in air.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
I can think of LOTS of problems with that idea.
The Trex will trap moisture in those cups .... making a fungus factory and mosquito breeding ground.
Trex is a different material than wood. It expands / contracts nearly twice as much as wood, so it needs to be designed with that in mind.
Trex also is only half as stiff as regular lumber, so it needs additional supports.
If you do decide to lay the Trex over the existing deck, I would look first for a competing product that has channels on the backside. Without something like that to help with air flow under the deck, you would need to somehow space it above the old deck.
Then, no matter the material, I would sand the deck to remove that cupping. You might even, before sanding, drill 1/8" weep holes in the places water pools, to allow for future drainage.
several problems I see. Maybe this has all been mentioended already....
Trex will shape itself under heat and load to some degree. Si I would expect that after a while, it would have the same cupping telegraphing through and the same problems repeated that you are trying to get rid of.
Second, Trex and it competitors all REQUIRE that it be allowed "adequate ventilation" under it. I talked with one company rep from one of them once, and they generally consider 18" to be a good guideline, so direct contact with the PT under it would not qualify and probably void the warrantee.
Thirdly, I would be concerned with squeaks from one board rubbing on the other. I know some of these products are a plastic slippery feeling stuff that would probably self-lubricate. But there would also be the problem of thermal expansion. The Trex will grow in length and the PT substrate will not. I don't know what problems that might cause.
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If I HAD to do it I would....
- Add furring/spacer strips on top of the PT. Maybe 1-1/2 wide x 1" thick. This would keep the trex off the PT. Make sure the screws penetrate the PT and go into the joists. Consider using an adhesive.
- Install the Trex perpendicular to the PT/strips. That way the Trex and PT aren't trying to move as one long board since they have different expansion/contraction. I would consider screwing only into the strips but not the decking.
- Think about adding vycor on top of the PT first.
This is just a guess as I've never done this before.
Kevin
Maybe I'm missing something. Unless this is a monster deck, it sees like it would only take a couple of hours with a circular saw and pry bars to remove and discard the old decking. A couple more hours with a recripricating saw and you could slice through the nails in the joists. Use some joist hangers and you could re-space the old joists if necessary and simply fill in the blanks with new material. In half a day, problem solved.
Why run the risk? Just junk the old boards and put down the Trex. That close to the ground, and you are just asking for trouble. Water is our biggest enemy don't give it any unnecessary advantages.
Also, I have never used Trex, but I understand it can be quite slippery when wet, eliminating one of your potential advantages for this whole endeavor. Ipe is a great alternative. Although less environemntally friendly, it is more attractive and less expensive than Trex. You can also use the existing spacing on the joists. Ipe is unbelievably strong and is all but impervious to rot. It burns at a rate just above concrete. I have used Ipe several times very successfully; both standard decking and tounge & grove. It is a bit tougher to work with, but the results are worth it.
Good Luck,
Doug M.
Another one to ask you to consider VERRRRRRY carefully.
All the issues here have been mentioned: mould, weight, water trapping, poor load bearing issues.
Just for the heck of it, I called my insurance agent to see what he said (I may have a similar issue arising in the near future), and he told me that if the Trex (or whatever company) would not verify in writing that the install would be to their standards, and there was an issue later on, they would come after me after the pay-out.Quality repairs for your home.
AaronR ConstructionVancouver, Canada
I appreciate all of the feedback I've gotten on this question. I understand and share the concerns, and will most likely not do the overlay. A couple of people have questioned the cost savings. I don't know that I'd call it a "monster" deck, but, within my frame of reference, it's a large one. It wraps around two sides of the farmhouse and includes a series of platform steps extending to the driveway, perhaps another 30-40'. I'm working from visual memory here, but would say maybe 30' on one side of the house, varying in width from 12' - 6' wide, another 20' of walkway along the front of the house, maybe 4' wide, plus the step platforms. Here's the way I see the comparison: A -- do the overlay. Costs: Buy the composite, cut it, fasten it on, put new band-boards on. Sweep up, go home. B -- Take the cautious approach and do NOT overlay. Remove all of the old 2 x 6 deck boards, which were installed 15-20 years ago with galvanized spiral deck nails. Hundreds of them. Take 2-3 trips to the landfill to dispose of the old PT boards (40 mile round trip, gas, labor, landfill fees). Buy new additional PT structural members and install them. Oh -- another biggie: The PT bandboards that exist are at the height of the top of the 2 x 6 flooring, so they will be too tall for the composite. In most cases, these boards are also the framing members to which the joists are nailed. This means that, for all practical purposes, I'll be starting over with the framing for all of the platform steps and more than half of the decks. Where were we? Install the additional pressure treated, either between the existing, or by sawing out the existing and spacing them all closer together. All of the work so far has been in addition to what "approach A" would have involved. Then install the composite. Imagine doing this on retirement income, solely to eliminate a dangerously slippery floor. They're not gaining anything else (except, perhaps, resale value). This is why I thought it was worth looking at. Thanks again for all of the input! Sue
Maybe just buy some truck bedliner in a can, and brush it on?Would take care of the slippery part.
:-)this is an anti-tagline
I think it would trap moisture between the underside of the trex and the top of the already rotting treated boards. I'd get in there and chop the existing decking up into 8" pieces and rip them out and lay new trex on the existing treated joists. Otherwise it will get all spongy as the underlying deck boards rot out. Also the level of the deck will stay the same which will be an asset.
M
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"You cannot work hard enough to make up for a sloppy estimate."
INSTALL NEW DECKING OVER PT DECKING
IF YOU ATTACH 1X2 PT STRIPS TO EXISTING DECK AND THEN FASTEN NEW DECKING TO STRIPS. I ALSO DRILL HOLES IN EXISTING DECKING TO ASSURE DRAINAGE.