Building Deck and Need Advise

[dfeck]

I'm in the process of building a deck for my parents. The deck is about 30" from the ground, attached to the house and I've using PT lumber for framing and Aztec decking (PVC Plastic). I want to use decking to close in the under side of the deck (skirting) rather than using lattice or nothing at all. I know deck ventilation is important so my question is; the deck boards will be spaced ~1/8" plus I'm going to be placing additional 4" round vents around the skirting. Will this be enough venting to create adequate airflow?

Thanks,
Doug

 

[tanglefoot]

I built my deck 15 years ago, and it is in need of new deck boards. The treated pine framing is still strong, even though some of it is in full ground contact all the time. Instead of skirting the sides, I used Windsor landscaping blocks to fill in the openings which range in size from 4" up to 16". Mine has never shown any sign of lack of ventilation. I believe the spacing between boards is for drainage. With my next set of deck boards, I plan to decrease the spacing to 1/8". The 2X6 cedar boards have shrunk to the point where the 3/16" gap I allowed has increased to 1/2" in places.
If you don't mind, what is the decking material going to cost?
Butch

 

[20 20]

Dfeck; I don't see a problem with your idea.

Tanglefoot; why not butt the boards up together, they'll still shrink, probably enough for what your wanting.

 

[dfeck]

tanglefoot - The deck boards are rather expensive. It's about $3.50 per board foot! Yes, $42 per 12 foot board. I'll need around 55-60 boards.

The PVC plastic boards do look great and they are suppose to be better in respects to stability, less weight and scratch resistant. The downfall is the cost. I'll be using a screwing system called Cortex which have hole plugs to hide the heads. I'm sure it will be labor intensive but should look great in the end.

As for the gaping. I built a 16' x 35' deck on my house a few years ago and I did NOT gap the boards. Of course this was PT deck boards. They do shrink in the summer and I get gaping of 1/8" when they shrink. They will swell up when it rains to no gap. If I had to do over I would have used composite decking but at the time it was an additional 3K in price and that was a big pill to swallow.

Thanks,
Doug

 

[tanglefoot]

2020,
If I go back with cedar, I won't leave a gap. But I'm looking at composite, and they recommend a 1/8" gap. I don't know whether that stuff shrinks or not.

dfeck,
That is expensive material. If I can buy in-stock material at Lowe's it will be reasonable, but I will need several 20-foot lengths, and none of the Lowe's in this area keeps that length. When they special-order composite, it sure gets expensive.
Butch

 

[EddieWalker]

I'm not a fan of any of the plastic deck boards, but I don't know all of them either. From what I've read in Fine Home Building and the Journal of Light Construction, it's not an expense that lives up to it's reputation.

As for venting, you need allot of it. I was under a deck that was just a year old that had 2x6's for decking and solid sides except for a few 6x12 vents in places that you couldn't see, but also not the best locations. The wood underneith the decking was growing mold and the joists were very damp with mold growing on them too!!!

I don't know how much ventilation you need for a deck, but I was surpised how wet it was under there and how much mold there was. I'm guessing that allot of water gets through the gaps in the decking and then the soil remains wet long after the rains are done. I can say that it had been several weeks since the last rain on that deck, and temps were in the low to mid 80's. Nice weather, but not hot enough to dry out the soil under tht deck. Of all the decks that I've built, I've never sealed in the sides.

I've never see moisture and mold like that under deck either, so it makes me wonder how much of that moisture is from the sealed in sides. The homeowner told me she had it done to keep out snakes. She's terrified of snakes, which I can understand, but I think she's caused herself some problems with her desire to keep the snakes out with a wood barrier.

I'd leave it open, but that's just me.

Eddie

 

[tanglefoot]

Eddie,
I live northwest of you about 80 miles. I enclosed our deck because I didn't want skunks to make their home there. I imagine there is a moisture buildup at times, though. What would be wrong with making the deck shed water and keeping the underside dry all the time?
Butch

 

[EddieWalker]

Keeping wood dry is the secret to it's longevity. Letting it get wet, they drying out, then wet again is the cylce that causes all of the problems. Pressure Treated wood will last longer then untrested, but it will still rot out on you. I'm not sure what it would take to make the deck shed water, but from what I've read, it seems pretty expensive.

Eddie

 

[dfeck]

I'm only closing in the deck for looks not keeping critters out. So it won't be tight. The plastic (PVC) material is suppose to resist mold growth and decay caused my water. My plan was to gap the boards along with keeping a couple inches from the ground. In addition to that my plan was to use 4" round vents placed every 3-4 boards around the deck skirting. I could go with larger square vents (6" x 16", etc) and strategically place them to allow airflow. The problem is I'm fining ZERO data on how much airflow is necessary under decks. The only data I find is how much gap to use depending on how high off the ground the deck is.

Doug

 

[EddieWalker]

Doug,

I think the problem if trying to figure out how much air flow to have is because the ground holds moisture and figuring it out is really going to be a case by case basis. Your soil may hold allot of moisture, or it might drain quickly. Sand versus clay type of thing. Your plan sounds well thought out, but the only way to know if it's working is by waiting a year or so and then to start doing periodic inspections. The deck that I was under doesn't show any signs of moisture under it, but while under there, it was overwhelming. They have a real problem that I told them about, and he told me he knows about, but that's as far as we got. I think they are just going to ignore it and hope it goes away by itself. I see this allot, and it keeps me in business, but it's still frustrating to deal with. Plastic on the ground should help, but in the few cases that I've seen plastic on the ground, it's been a mess and not actually doing anything. Mobile Homes do this, so I'm not sure how effective it is. In theory, it should work if done right, but for whatever reason, I always see it unrolled in areas, shoved into other areas and missing in others. Under the plastic can be very wet, or very dry, it's always a suprise to me when I come across these things.

Northern Tool sells electric fans with moisture sensors that I've installed. I'm not sure how effective they are, but don't see any real negatives to using them if moisture is an isssue. The times I've installed them, they seem to help, but don't address the real problem of stopping the moisture from getting under the house. Some clients like to go through the steps of trying everything but addressing the real problem. I give them my advice and then do what they are paying me to do.

Eddie