Building Deck and Need Advise

[The Dougster]

While I have never used the plastic decking, I have several friends that have, and to the man, have complained about it... I'm sorry I don't have specifics but in a couple of cases, they have had the plastic removed and gone to a wooden deck.
Your's seems especially pricey... have you priced other wooded material? (E-pay)... sorry, I don't know how to spell it.. lol

 

[dfeck]

Yea, I've been spending way too much time thinking about this. At this point I might be over thinking it. The deck will be 30" off the ground and mostly in the sun. The house is new construction so it's not under shade. I've viewed the Trex website and see some PICs in their gallery that shows decks that are skirted with their product. Similar to what I was going to do. I see no vents in the PICs but don't really know if there was something else that was done. At this point, I think I'm going to do the skirting and gap it 1/4"-1/2", keep it a couple inches off the ground and add the vents. I'll keep an eye on it and see how things are working out over time.


As for plastic, In my area most people are going with Composite or PVC (plastic). Real wood isn't being used much. Yes the price is very high but the benefits outweigh the price. Mainly due to longevity and maintenance. My parents are 67 and I don't want to be staining the deck for them every few years. I've also tried to convince them to use composite material so they could lower their cost. The difference is ~500 between the two.

Doug

 

[dfeck]

I found this on the Trex website.

Gapping

Trex® decking must be gapped, both end-to-end and
width-to-width. Gapping is necessary to facilitate
proper drainage and for the slight thermal expansion and
contraction of the Trex decking boards. Another reason
for gapping is to account for shrinkage of the wood joist
system. Following the proper gapping requirements will
ensure that your deck will look great year after year.

- Always follow Trex recommended gapping guidelines.

- Maximum allowable overhang for Trex is 4"
perpendicular.

- All decks require air circulation to keep them dry and
looking good. Leave openings under the decking or
increase gapping to 3/8" to improve air flow.

Fascia

- Trex used as vertical siding or fascia around the base of
a deck must be gapped the same as decking to allow for
air flow.

- Fascia should be attached every 12" with three Trex approved
screws. The top screw should be placed 1" from
the top of the rim joist, the second screw in the center of
the rim joist and the third screw 1” from the bottom of
the rim joist.


So, it seems that if I leave a gap of 3/8" I'd be ok. Agree?

Doug

 

[tanglefoot]

Doug,
It sounds like they are saying the ventilation should be adequate by increasing the gap to 3/8". I've read that Choicedek settled a lawsuit a few years ago that involved mold growth in their material. Now, they have a chemical in Choicedek (and Trex, I assume) that will combat mold formation.
I'm considering removing the old deck surface boards(2X6 cedar) and filling the joist spaces with gravel up to within an inch of the top of the joists. I realize this will hold moisture against the joists, but they are treated pine, so they should last 30 more years. This would leave no spaces for wasps to build nests or skunks to dig into. Then I'll resurface the deck with a composite material, leaving the necessary gap. See any obvious problem, anyone?
Butch

 

[CurlyDave]

So, it seems that if I leave a gap of 3/8" I'd be ok. Agree?

I disagree completely.

The problem you are going to have is that water gets under the deck in liquid form but has to get out as vapor, with thousands of times more volume. Throw in the fact that air is a most a few percent water vapor and you have to move maybe a million times more air out from under the deck as water went in. This is not going to happen with 3/8" gaps between fascia boards.

Unless you are in the desert, it is going to be dark & damp under the deck.

Even worse, if the ground is at all damp from ground water, you will get water vapor from the ground, which will also make it damp under the deck. Think about how many damp basements you have heard of. This is the same thing.

I would use a light-colored lattice backed by about 1/4" mesh hardware cloth to close off the area under the deck and keep animals out.

Under the deck will always be dark, and the light colored lattice will draw the eye and prevent seeing under the deck. If you ever do get mold under there you will have to remove it all before increasing the ventilation. Spraying some sort of nasty chemical in a space 30" high (minus the joist height) is going to be a hard job. Prevent the problem rather than abate the problem after it happens.

 

[MossRoad]

CurleyDave,
I think they were saying if you don't vent the sides you should gap the decking at 3/8".

 

[CurlyDave]

CurleyDave,
I think they were saying if you don't vent the sides you should gap the decking at 3/8".

I still don't think that is enough, and my experience has been that once mold becomes established in any area, it is very difficult to get it to just go away. Even if you change conditions by increasing vent area, the mold will not usually die off on its own.

The space under the deck is cramped and confined, remediating mold is not going to be a fun job. Do it right the first time & provide more than enough venting.

If the issue is not being able to see under the deck, fixed louvers will block any visual path while providing lots of air flow.

 

[dfeck]

I thought long and hard about this. I even called the manufacture of the product I'm using and they said it shouldn't be an issue without using vents. I also got feedback from a variety of sources while most were ok with the idea there were a few that had reservations. I'm going to use the product as vertical skirting. In addition to gaping I'll still place vents along the skirting and leave a 2" gap from the ground.

Doug

BTW - I checked some of the manufactures website photo galleries and you can see in some of the photos others had done this.