Another deck question

[basslkjohn]

Build my cedar deck in 1983. It parallels the house and is 40 feet long and about 12 feet above the ground level. I've started to replace the decking boards and will be replacing individual stringers over the course of the summer. Recently saw an add for composite tongue and groove decking that looked interesting...and expensive. But I could mount the t/g decking perpendicular to the long axis of the deck rather than the traditional method, and grade the deck to fall a couple of inches toward the outside rail. Then several good things could happen: the area under the deck would stay dry, the deck stringers would not rot due to moisture and debris accumulating between the deck boards, and I might be able to place the t/g over the existing deck boards and eliminate the need for blocking between the existing stringers.

Does this make any sense? Thanks for your comments.

[solbes]

What is your joist spacing? I installed a Trex deck (non T&G) and spaced 10" joists at 12" on center rather than th 16" min code. Makes it much more solid and less springy.

Also although the composite material should never rot, the one concern you do have is mildew/mold. There is a certain gap that is recommended for Trex. Also plenty of ventilation below the deck helps keep it mold free. Not sure if the T&G material you are talking about would have this problem or not, but it's something to think about. Does it have some weep holes in the tongue so the water can at least drain out?

[LightningBG]

I'd be worried about weight if you put the new decking over the old.

[jentz]

Build my cedar deck in 1983. It parallels the house and is 40 feet long and about 12 feet above the ground level. I've started to replace the decking boards and will be replacing individual stringers over the course of the summer. Recently saw an add for composite tongue and groove decking that looked interesting...and expensive. But I could mount the t/g decking perpendicular to the long axis of the deck rather than the traditional method, and grade the deck to fall a couple of inches toward the outside rail. Then several good things could happen: the area under the deck would stay dry, the deck stringers would not rot due to moisture and debris accumulating between the deck boards, and I might be able to place the t/g over the existing deck boards and eliminate the need for blocking between the existing stringers.

Does this make any sense? Thanks for your comments.

Excellent idea!! The drop from house to outside edge only needs 1/4 inch per 4ft. would be 3/4 inch drop the extra you write of would work better 1 & 1/2 inch would double it and provide more than sufficient drain.T&G Composite I was wondering when it would come out for decking? Leaving the space below water tight.I dont think weight problems will arise,But what are the joists 2X what and the span they cover? from house to beam? With cedar under the composite no worries of much and the T&G shouldnt leak with the 1 & 1/2 pitch.

[Tom7227]

Two thoughts - clearance for the doorway leading out to the deck and scumbosis getting going if the older material gets wet at all.

[basslkjohn]

Jentz: thanks for the comment. The joists are 2x6s on a 16 inch center and the sill to outside edge distance varies from 6 feet to 12 feet.

[basslkjohn]

Hadn't thought about the mold issue. But I'm assuming that the tongue and groove fitting would be water tight...or could be caulked to keep the runoff moving toward the outside rail...with sufficient grade.

[jentz]

A bead of caulk at each edge would stop moisture penetration,Even without it the pitch would limit it,The 12 ft span for a x6 is maxing its structural value out,either bridging or a row of solid blocking will distribute that weight load out,You stated cedar on it now,cedar is light and depending on the weight per sq ft of the new T&G it should be a go.

Again great idea.

T&G is water tight when applied horizontal with the tongue up,in your case water could seep in,A pliable caulk like butyl rubber will seal that for years.and can be reapplied on the deck side should any leaks appear.

A Z flashing should be applied at the point where the deck meets the house to stop water penetration but with the deck existing it should be there.

[soldoncass]

If your joists are only 2 x 6's and the deck width is 12 feet, it is way underbuilt for composite decking. That stuff is way heavier than cedar (maybe 3x). I wouldn't recommend ADDING that much weight to it, on less than 2 x 10's. What are the joists made out of, cedar or green treated pine? Forty year old decks were built lighter than anyone recommends today. In this area, you can use 2 x 8's up to 12 feet @ 16" centers....but composite is soooooo heavy, that is stretching it.

[jentz]

If your joists are only 2 x 6's and the deck width is 12 feet, it is way underbuilt for composite decking. That stuff is way heavier than cedar (maybe 3x). I wouldn't recommend ADDING that much weight to it, on less than 2 x 10's. What are the joists made out of, cedar or green treated pine? Forty year old decks were built lighter than anyone recommends today. In this area, you can use 2 x 8's up to 12 feet @ 16" centers....but composite is soooooo heavy, that is stretching it.

Maybe you could tell me the live load of a 2x6 spanning 12 ft.? how about the dead load? with those numbers it could be verified.

[soldoncass]

IF we knew what the joists were made out of, I'm sure you could find a chart with the live/dead loads, if it is important to you. I was never interested in that....all I had to do was follow codes and a chart, showing sizes required for which spans. In this area a 12' span required 2x8's or larger, and double decking WAS NOT on the list. I did a composite deck last year....it was unbelieveably heavy. I would check codes....don't want it to collapse under your friends.

[jentz]

I figured you could help the original asker better than I.I have seen prints and built many decks with 2x6 spanning 12 ft.Now if it were a interior floor yes 2x8s would be minimum required.

You know the codes? A building official?

[Surface Tension]

Its not a good idea to cover up wood like you suggest. For one, what your putting on top of it is not going to be any better then what is underneath. With the cedar being covered, if it gets wet it;ll stay wet. That is more weight and perfect conditions for rot.

[LightningBG]

Maybe you could tell me the live load of a 2x6 spanning 12 ft.? how about the dead load? with those numbers it could be verified.

Doesn't look like a 2x6 will do the trick for a 12ft span per:

[soldoncass]

Nice chart. Every location has different codes to follow. Here they pretty much follow interier floor spans/sizes. Sometimes it seems like overkill, but it only takes a couple collapsed decks (with injuries) to make you realize they make sense. I heard of 1 a few years ago that collapsed with 30 people on it...... I'm NOT a building official.....just someone with 38 years experience in the construction industry. If said deck is made with cedar joists, the spans on your table go DOWN not up. In this local area, 1/360 is minimum required for floors.....we built heavier to take most of the bounce out of the floors.

What several guys have mentioned about mold/rot concerns are real, and poster already mentioned replacing boards because of rotting. I just mentioned the span/weight/support issues, because that is the safety aspect of the whole thing, and shouldn't be ignored.

[CAMAN]

Its not a good idea to cover up wood like you suggest. For one, what your putting on top of it is not going to be any better then what is underneath. With the cedar being covered, if it gets wet it;ll stay wet. That is more weight and perfect conditions for rot.

I agree.

One thing that came to mind though if he did do an overlay would be to put a layer of the adhesive rubber water and ice shield between the two decking materials. And wrap it down the sides and up under the siding a couple inches. This should prevent any water penetration into the existing wood decking.

But I would definitely strengthen up the 2x6 joists, I'd suggest 2x10's simply because if your going to do it you may as well do it right and go a little overboard with something as heavy as composite decking.

[Tom7227]

Looks to me as if the original poster is SOL on his plan. But could someone teach me something - what is live load vs dead load? I don't think I'm going to be any lighter after I die, and I would hope the missus got me off the deck in a fairly short time if I croaked out there. Especially in the summer.

[CFRay]

Dead loads are weights of materials, equipment, and components that are constant throughout a structures life. The weights of steel beams, wood framing, rooftop air conditioners, roof shingles, walls, etc.

Live loads are people, furniture, plants, snow, wind, rainwater, things that are somewhat variable through the structures life.

[Surface Tension]

A picture of your deck would help.

So your deck is 12' is some spots. 2x6 is not enough unless you have it cantilevered over a girder or a second girder. You said your replacing stringers, I think you mean joists. In that case replace with 2x8's. If your using a girder this will raise you deck. If your clearance under the door works out then raise the ledger. If not drop the girder. I'm getting ahead here as I don't know what your using.

If you want the area below to stay dry you could put in soffit. Drop the outside edge down 3" and use a gutter to collect the water and divert it with downspouts.

[basslkjohn]

Thanks for all the responses to my decking question. I have saved many hours by following the advice I've received to other dyi questions that I and others have asked on this forum.

So, to summarize:

1. I will not place the tongue and groove composite over the existing cedar decking. The old decking will be removed.

2. Those portions of the existing deck that are 12 feet wide do have a set of steel support legs that rest on the concrete walkout apron under the deck at the halfway point...so I think I have the loading question resolved.

3. The joists running perpendicular to the house include 32 8 foot joists and 15 12 foot joists (the deck is actually about 60 feet long, not the 40 feet I originally posted...have another beer.) The joists are 7x2 inches.

Sooo, I will replace the joists with nominal 2x8s and place blocking between the joists to support the t/g running perpendicular to the long dimension of the deck.

4. I'll check the local codes, if any, to double check joist sizing and for composite and dynamic loading at the 8 and 12 foot widths.

One other advantage of the t/g decking: you won't catch chair legs in the deck cracks... Thanks again for all the advice.

[MuleShack]

I didn't see anybody mention this, and I'm not sure myself but if you are "remodeling" your deck, wouldn't that need a "permit" for that to make sure it is rebuilt to specs?

It seems that the city or the county has their fingers in everything these days, so just thougth i'd throw it out there. I guess i'm curious to the answer myself. When you "remodel" the siding or the roof on your house you have to pull a permit, right?

[Tom7227]

A friend used some sort of material maybe 10 years ago and put it on 16 inch centers. The specs were for 12 inch centers and he had to redo the entire thing. I don't know what material he used other than it was a plastic or composite material. Point is to check into the specs on the material you use so you don't have to backtrack a lot.

[LightningBG]

Honestly I have a tough time believing that tongue and groove is going to be water tight, unless it's siliconed in between each board, which would be very time consuming and could get expensive. Add in the cost and time of blocking in between each joist. Yuck.

IF it were me.... I would ditch the center support poles (to make the space under more usable). cut down the outside poles. use 2x10 or 2x8 joists. lay the decking parallel to the house. put soffits underneath to drain away water.

[soldoncass]

You are coming to the right place for advice/ideas...there are very experienced, knowledgeable guys on here to get good advice from. As with anything, though, there are likely to be more than one idea suggested. No one way is "right" and the rest are "wrong" thing.

I'll suggest a couple more ideas for you: I agree, I'd lose the 2 support poles underneath, by beefing up that portion of framing. At least you have 2x8 joists to work with, so it isn't terriblely underbuilt (like 2x6 would be). That 12 by 20 portion may need to be 2x10's...or add another beam (center)with end posts to clear up an area underneath. With your 12 foot heighth you have room for a roof under there for a future screen sitting area. An angled soffit would work also, but the water that gets through the decking(count on it) ,would NOT dry out fast if enclosed....now the mold/rotting issue can be a problem again. My thinking is keep the decking level, because water will get through somehow eventually...then control it underneath with a roof....I personally like level surfaces to sit on. Outdoor surfaces are usually done with 1/4 inch drop per FOOT(or more), so water runs off decently...otherwise it puddles in spots.

We don't know the supports/ beam sizes, spacing etc.,but make sure you check that out, before adding all that weight.

Good luck to you, and I'm sure we were ALL glad we could help.

[Tom7227]

lay the decking parallel to the house. put soffits underneath to drain away water.

I'm far from an expert but laying it parallel to the house seems like a bad idea to me, expecially for something this wide. You'd have to slant it an awful lot to get the water all the way off and you'd be dumping an awful lot of water into that area. If you slanted it 'against the grain' to the short dimension the water would have to 'jump' the cracks and I think that would be a hassle. On a version of This Old House Tommy had it going the shortest distance and away from the house.