Building a deck : questions

[radhak]

This for a friend, who has not done much of woodworking, but has been bitten by the home-improve bug, and recently laid a decent area of pavers around his swimming pool all by himself. So, inexperienced, but willing to learn, and bend his back.

Behind his swimming pool is a sloping grassy area around 20 feet wide, a fence at that point separating his property from the lake behind it.

He wants to build a smallish deck there all by himself, of an area around 15 x 15 ft, approx. I would help as much as I can, but I have never built a deck before.



I visited him yesterday, and he has already installed most of the posts in the ground: at around 5 feet apart. He was wanting to use plastic/composite lumber, but found them 'very flexible, not stiff like wood', and asked for advice.

At this point I realized that he was planning to build the decking right on top of the beams, without joists!?! He says he's willing to consider stronger wood, like ipe, if that would be good enough. He's also willing to add more posts in between, with beams running across, if that could help him avoid joists.

Why does he want to avoid joists? Dunno - probably because he had not planned for it, and thinks it adds work without adding value, this being a rather small deck.

Just in case I am not being very clear, this pic shows what I mean :



I told him I'll ask around, but most probably he will have to pause a bit and do it the right way : joists on top of the beams, decking on top of the joists.

So here I am, asking: does anybody here think this is a shortcut anybody should be taking: decking right on top of beams? Is ipe (or any other material) strong enough to go right on top of the frame provided by the beams without the support of joists?

And while you are at it, has anybody used ipe? Is it really that strong and durable as claimed? And if he does add joists, at say 16" apart, would ipe be still better than composite lumber (looks, strength, longevity)?

I created a sample design on Lowes.com, for a rough idea of the shape and build:

[Stytooner]

No. There are no short cuts if you want an approved structure. It has to be an approved structure to be safe. You cannot rely on thin decking material to tie the post and beams together. You must have framing members (joists and bands) to do that. This is what makes it all structurally sound. How deep and what type posts has he used? That is another place that under engineering will bite you quickly. No frost line to worry about, but the are other issues that are of big concern.

[pelligrini]

I doubt he could use composite decking without doing joists. It just doesn't do large spans. Trex recommends 16" max spacing for residential. Ipe would span farther, but I think the 5' spacing would still be too much.

[jking]

What Lee said above. No, you cannot omit the structural framing and end up with an adequate final project.

When you say composite lumber, I assume you mean decking such as Trex. This is not used as structural framing. It is used for the decking layer.

I would suggest he buy a copy of a book on decks. Taunton publishes a good series of books, they have one on decks. If he thinks adding posts is less labor than installing proper joists, I wonder whether his posts a properly installed.

[radhak]

Thanks guys, for the affirmation.

I don't think he worried about code, and probably his posts need a closer look too.

Good thing is, he's not bull headed, and will listen to reason. And 'code' is good reason .

Btw, anybody want to hazard a guess on where the code for decks will be? This page has all the codes, but I can't seem to find anything for Decks in the 'Building' or 'Residential'.

[RAFlorida]

For load bearing, you NEED joists. As mentioned by 'jking', buy a book on decking. They have such books at Lowes, or at least here in Florida they do. To build the deck without joists is pure folly...
In time the floor decking would be spongy and weak.
BTW, check with your local code enforcement office concerning the code for the decking.

[capncarl]

The decks that I have seen that use composite decking materials were all re-decks where they pulled the old wood off and replaced with new composite, all were built with joists on 16" centers and they all showed their joists by slightly sagging between joists! The info I have on composit says a minimum of 16" centers for conventional framing and 12" centers for decking on a 45"degree. I believe the sun has a lot to do with the composite sagging so I would consider framing it on 12" centers for the hotter Fla. sun.
capncarl

[Stytooner]

And if you use 12" centers, you may get by using 2x6's. Depends on the span. If they are only 5' spans, then I would say that would work fine. For a low deck like this one basically is, I would go with double banded joists and use hangers instead of the joists sitting on a double beam like shown above. Double 2x8's for the bands. That saves height and makes it stronger in higher winds like Florida (and us) sees on occasion. Don't use a nail anywhere. Proper screws will outlast all of us.

[JimD]

With lots of posts you can get by with only joists and no beam but you can't go from posts to flooring - unless your posts are on no more than 16 inch spacing. You might stretch that to 24 inches with much thicker flooring, maybe. But that would be a huge amount of posts. It costs a lot less to do things the "normal" way. There are simple tables you can google up that will tell you what you need for different spacings. 2x10s could span the whole distance but you would either need a post for each end of each joist or you would need peripheral beams. I didn't check but I think 2x6s would work with a mid span support (post or beam).

[radhak]

Makes sense, guys. Joists would be simpler, stronger, and code compliant. I will be sharing this with him the next time I see him, probably Monday.

I think ipe might still be the better wood, instead of composite. Lemme see if he agrees.

I am now interested in looking closely at his posts - I'm worried he might have taken shortcuts there too.

[woodturner]

I don't think he worried about code, and probably his posts need a closer look too.

He will likely need a permit - and if he does the work without a permit, he will have trouble selling the house, may be subject to steep fines, and may be ordered to tear it out. Can't imagine any code official would sign off on those plans, and if they saw them, would probably insist on plans stamped by a PE.

anybody want to hazard a guess on where the code for decks will be? This page has all the codes, but I can't seem to find anything for Decks in the 'Building' or 'Residential'.

In theory, IBC is adopted throughout the US. If you comply with IBC deck standards, you should be OK.

Another issue - the pool. The pool relies on the presence of solid ground some distance (10'?) out from the edge of the pool to support the walls and foundation. If you start digging holes for posts in the support field of the pool, you may cause the pool walls to crack or the pool foundation to fail. This really needs to be reviewed by a PE with structural background.

[radhak]

Thanks everybody. All your advice was useful, timely and educative, both to me and to my friend!

All those points, and that last part from woodturner about support for the pool has made him pause and think. Since the sole reason he wanted a deck here was to be able to put a couple of ease-chairs and sip a cold one with spouse or friends, he says he does not really need a deck.

He has decided to instead level the farthest area of the slope by adding some soil and maybe stone, and plant some nice grass on top and make it an extended bit of lawn adjoining the pool. Since this would not need any new construction, he would not need to worry about any building codes. The amount of soil he'd add is also not very substantial, just enough to alleviate the steeper part into a more even area so that a chair or two there does not topple over.

He had installed only the posts furthest away from the house/pool, so taking them out would be easy and not much effort wasted.

I am happy I (we) did our part and warned him from going too far down a risky path, before it became irretrievable, so that he was able to course-correct. Thanks all!

[capncarl]

It's probably a good thing he changed his mind. It seems that most newbys at deck building seem to run into some kind of bad luck on their first outing. Accidentally "finding " a buried water pipe to the pool with a post hole digger is a real possibility and provides years of story telling .

[Pappy]

Even the small 6x8 deck I built by the pool needed joints. The steps are only 2' wide and required a center stringer to support the Trex on the steps.