Under Deck System to catch water

annemarie29September 22, 2010

I imagine there is a post here about this, but can't find it. Can someone direct me to a post, or can I hear from anyone that installed a system under their deck to catch the rainwater so they could use the space under the deck more like a room. Hope to screen it in down there. My concern is water being trapped and causing mold, etc...

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If your looking for a water tight no maintance roof to fit under your deck and fasten to the joists.

There is none. No matter what the info says. All the marketed systems leak,require a lot of cleaning and are really spendy.

But if you dont mind a few drips here and there and cleaning out the total gunk...Go for it. J.

    Bookmark   September 22, 2010 at 9:12PM
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There has to be something that you can use on top of the joists instead of conventional materials that is waterproof. Has anyone figured this out or seen it done?

    Bookmark   September 28, 2010 at 7:57PM
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Plywood over the joists with provided fall,torchdown roof with all needed flashing, pt 2x4 stringers laying in the direction of the fall,decking screwed to the stringers not thru to the roof.

Bang Bang Done. J.

    Bookmark   September 28, 2010 at 8:58PM
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Why wouldn`t cheap plastic corrugated roofing or used tin roofing attached to the bottom of the deck at a slight angle to drain work?

    Bookmark   October 5, 2010 at 10:35PM
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When I built my second story deck for our new house, I made my own rainwater catching system using TPU roofing, a heat gun, and vycor deck protector. Total cost was less than $200 for 11x12 deck. So far, so good. Two winters, no leaks. Even if it does leak someday, it's not the end of the world because I mainly wanted to keep the area under the deck dry because the patio door is directly under our deck. After I waterproofed it, I put a ceiling under the deck for a clean, finished look.

Here is a link that might be useful: deck magazine

    Bookmark   October 8, 2010 at 2:39AM
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That was an intersting approach and article.

The system will colect fall thru and become a muck of rot inbetween the joists.

The fasteners going through the material are a problem.

The protection factor needs time to tell,its very possible water is traped by the fabric and will cause the framing to fail faster not extend its life.

Its ok to do one of these for your self. However it is defentley the end of the world if one fails for a Customer.

The material bill might be short but the labor involved is not.


    Bookmark   October 8, 2010 at 8:51AM
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John is definitely right about this being something that to do for yourself is one thing, but to do it for a customer is something else. After reading the article, I went searching for a product that I felt was significantly more reliable than the poly sheeting that the article recommended. The roll roofing that I used is heat welded at all joints and I used the vycor over every joist because my research told me that the vycor would form a "seal" around the fastener penetrations. I don't know how true that is, but I am planning on keeping an eye on the condition of the framing as time goes by. John is also definitely correct about the labor involved. It was definitely not something that I would recommend to someone who is not very "handy".

That being said, I would like to add that I have read quite a few posts on this forum over the past two years or so, and I would recommend to people that when the pros like John Hyatt and the others that frequent this site give you advice, you would be well advised to to follow their advice. They have far more knowledge and experience than us do-it-yourselfers will ever have.

    Bookmark   October 9, 2010 at 2:11AM
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I have a 20 year old deck 8' above a cement patio. I plan to renovate the deck because the 4x4 posts I originally used aren't "code", and the deck floor/rails are failing. I would like to make the patio rainproof as I rebuild the deck.

I was debating whether to put roof paper and PT plywood over the joists and outdoor carpet over that, or building a sloped frame topped with corrugated plastic panels underneath the deck.

I can't build a roof over the deck itself because of smoke from the BBQ.

If I understand the posts above, trying to make the deck itself a roof for the patio is not the best idea. So has anyone done the under-deck/plastic panel idea? It doesn't have to look pretty; it's just me and 2 cats...

It seems simple enough, but it will be just me building it. Any advice? Anyone know of a site showing how to do it best?

    Bookmark   October 24, 2010 at 6:37PM
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I ran into this issue many years ago, there was no solution so I invented one and got a patent on it (see: http://www.freepatentsonline.com/5195281.html). There are no pictures provided, but basically what I did was to insert longintudinally V-folded aluminum flashing to hang on and fit in between the joists. I then put 2x4 "runner boards" atop the joists with minimal screw penetrations (and a rubber washers to prevent leaking). I then attached the decking boards atop the these runner boards (no plywood!). You have to cantelever the deck a bit over the deck support beams so as to allow the open ends of troughs to dump water out. It's relatively easy at that point to catch the water in a spout under the deck cantelever. Further, like I also did, you can fabricate the troughs so that they're pitched to create a high closed end and lower open end. If your using say 2x8 joists you can implement a 7-inch drop. It works, been working at my house for almost 20-years now with no failures.

Here is a link that might be useful: Deck Trough Patent (expired)

    Bookmark   November 3, 2010 at 1:59PM
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How much money did you make with that invention? After 20 years you must be really wealthy! Where do they sell the product?

(Call a patent lawyer because the person using the black landscaping plastic stole your idea)

    Bookmark   November 3, 2010 at 2:30PM
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I guess I should have gotten a patent on my under deck drainage system using metal roofing, I could be rich now, ha. It's so easy I can't see why others haven't figured it out too. Myself & a couple of buddies have been doing it here in Austin for at least 20 years without problems.

I've made 2 car garages under an existing deck on a lake a house a few years ago, workshops & many storage rooms under decks like this. It's not something you want if it's going to be inside the house living area, you'd have to add a ceiling under it for that so extra cost there. However, for anything else by far the less expensive way. I can sell it for less than half what a torch down system would cost & still make decent $ as a contractor & customers get something that's going to last 20 years plus for half the $. No competition can touch you.

All it takes is a good roofing supply house that will make you custom flashing & some roofing skills along with the ability to think upside down.


    Bookmark   November 3, 2010 at 4:02PM
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Barry20, why did you use TPU and where did you get it? I was going to do a similar setup but with epdm.

    Bookmark   November 22, 2010 at 10:50PM
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I may have been mistaken on the correct name of the product. It may have been tpo roofing? I used it because after looking at many plastic and rubber options, it seemed way more durable and fairly cost effective. It's white on the top side and grey on the bottom. You use a heat gun and a roller to make heat welds at the seams. I also think the vycor is a must. I got my supplies from a local roofing supply house. It comes in different width rolls. I'm not familiar with the charactistics of epdm. By the way, for anyone who's interested, so far, so good. No leaks on my system. No problems with any debris falling through and mucking up the troughs. If a person wanted to, you could remove the deck board closest to the house and flush out each trough if necessary. I havn't found it necessary, but then, mine is a second story deck with no tall trees near it to drop debris onto the deck.

    Bookmark   December 5, 2010 at 1:14AM
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Thanks for the response. I'm going to use the black epdm. I don't wanna stare at the white material between the deck boards. I don't think I can use the Vycor stuff with epdm. I think Vycor is asphalt based and I don't think epdm likes asphalt. I'll probably find a butyl product if anything. Glad to hear your's is holding up!

    Bookmark   December 5, 2010 at 4:57PM
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You don't see the white between deck boards. I used Azek decking and spaced it 1/8th between boards. Fastened with cortex screws and matching plugs. The vycor was to help seal the penetrations where the screws are. With that and the plugs on the surface, I feel pretty good about water not getting to the joists. Time will tell.

    Bookmark   December 10, 2010 at 5:05PM
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I know it's been a few years.. I want to see if BARRY's system is holding up well, as I plan to do the same project.

    Bookmark   March 11, 2013 at 12:30AM
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Been looking for an idea to use deck when it rains. This was a suggestion and just had it installed. It hasn't rained or had snow melt but it looks like it will meet the goal. This is just metal roofing attached on the underside with a slight grade to allow for run-off.

    Bookmark   November 17, 2013 at 1:28PM
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To portlanddenise: I'm not an expert but it looks like your corrugations are perpendicular to your joists. May not be! If this is the case, would that not just trap water instead of letting it run off? Great pic but can't see the end of the deck. Thanks for sharing!

    Bookmark   December 4, 2013 at 5:17PM
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