Handling rain runoff from deck

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Old 10-13-13, 08:26 AM
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Handling rain runoff from deck

We are replacing the pressure treated pine decking after 8 years of the sun beating up the original deck. There is the potential for good (dry) storage under the deck if I can figure out how to cause rain falling between the boards to run either toward the house, or better, away from the house. (One problem with this plan is that the deck, as it was originally installed, is level.)

Option one is to put corrugated sheets under the deck. Two big problems are loss of headroom and the difficulty in working overhead where one cannot stand fully upright.

My deck builder suggested to put Grace Tri-Flex roofing paper, which as I understood it would be tight enough to cause rain to run to the sides. One look at the attached photo puts that understanding to rest.

Clearly this is not a solution. The biggest issue is that water will remain in the pooled areas for many days keeping the underside of the deck damp, and surely mold will result, and there would be no way to treat it without removing the deck again.

Apparently the paper cannot be pulled tight enough to create a level surface. I am informed that if this is attempted, the paper will pull loose from the tacks holding it in place.

So my general question is how to solve this before we get any more decking down?

One possibility that occurs to me is a rigid underlay. Does anyone know of any kind of very thin, but rigid, plastic/fiberglass/whatever material that might underlay (or replace)) the paper. Ideally it would be 1/8" or less. It would not need to be strong as it would be sandwiched beneath the deck and the joists underneath. It's purpose would be to keep the sheeting flat. One caveat is that it must be capable of being penetrated by the deck fasteners without being excessively damaged.

Any and all ideas and suggestions gratefully received. The builder goes back to work tomorrow so I hope to find a solution today if possible. Thanks for your thoughts.
 
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Old 10-13-13, 08:39 AM
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Google "under deck drainage system".
Dozens of different company's will come up.
 
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Old 10-13-13, 08:41 AM
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The attached photo will not work, I have replaced entire decks that have attempted to do what you are doing. I will have to search in my files for the name of the system that will work. You waterproof from below using channels that take the water down to one side where you install a gutter to finish the water in your desired area. Hold tight while I find the info.


Here is the link to the product I have used successfully.

DrySpace Under Deck Drainage - TimberTech
 

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Old 10-13-13, 09:37 AM
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Thanks for these. However the replacement is underway and I am hoping to get an idea today that we might be able to implement starting tomorrow.

The idea is to create as much of a "dry area" as practical. Water can run off without guttering on either or both sides (i.e., next to house, and/or away from house.) The ground doesn't have to remain dry, I just want to keep water from falling on things like bikes, lawnmowers, etc.

In particular, I think that one possibility is a thin sheet of some sort, as mentioned. Does anyone know of a sheeting that might serve the purpose?
 
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Old 10-13-13, 10:52 AM
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However the replacement is underway and I am hoping to get an idea today that we might be able to implement starting tomorrow.
Do as you wish, but it will fail. Not fail to shelter those things underneath, but fail to shelter the wood and framing underneath from sitting in standing water with no way to dry out.

Let me know if these look familiar in anyway.... Total replacement 3 months after some so called contractor installed. They also installed the complosite decking too tight and it all buckled. But, notice the standing water. Plus you will drive hundreds of screws through the membrane. In this case, the yahoo used OSB as a base, but to illustrate my point, it is saturated in the picture and holding water against the framing members.

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Old 10-13-13, 02:29 PM
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Czizzi, Thanks for yours. Pretty convincing stuff.

Will work on an under deck solution for later implementation.
 
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Old 10-13-13, 03:39 PM
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Almost any form of decking material needs air flow under it for it to dry out. Even composite.
If you continue with doing it the way he's trying to do it now this it's going to end up being far more expensive when the framing also rot out.
 
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Old 10-13-13, 04:35 PM
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Would suggest pulling up what you have put down and building a traditional deck surface. Then, after research, install a dry space alternative of your choice. It is installed from below and does not need any adjustments from the space above other than make sure that you flash the area nearest the house so that the first 5" or so are channeled into the drain run off you install.
 
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Old 10-13-13, 08:26 PM
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Thanks for all the good guidance. You have made a believer out of me.
 
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Old 10-14-13, 06:43 PM
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One additional question. With fresh new pressure treated pine 2X8's, how close to each other should they be fixed now?

Should they be touching so that when they dry out, they will leave the right amount of gap, or should they be gapped now so that they gap will be greater when they dry out?

What is the ideal gap now (0-?"), and what after it drys out (in fractions of an inch)?

Thanks
 
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Old 10-15-13, 06:21 AM
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If you drive a nail into the wood and you can see moisture seep out, then it is pretty wet. In that case, you can butt them up against each other and they will create your gap as they dry out over the next few months.
 
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