Building an overhanging deck?

[BackAgain]

Out in behind my shop I have a storage area that is about 4' wide and 30' long that I would like to make better use of. There is a 4' strip of land, and then it drops off about 35 feet to a creek below, really steep, maybe a 60 degree? angle.

I want to make it wider. I was thinking I could pour concrete on this 4' strip of land quite thick, maybe 8 or more inches. In the concrete there would be metal beams that overhang the cliff an extra 3-4' maybe. I could then build a deck out on this overhanging area.

My issue is that I don't want any posts holding up the overhanging end. Only a big concrete slab and beams. Can I do something like this? What size metal beams would I use, and how thick of a concrete slab would you pour? Basically it would be the weight of the concrete holding up the overhanging deck. The deck area would be for lighter weight storage.

What do you think?

 

[Mike in Ohio]

This is really a question for an engineer, but my unprofessional guess is no you can't do it without support posts. I think it is more a question of balance than weight. Think of a teeter-totter. Your beams would have to go back pretty far under your building to support the overhang.

 

[blkhonda1991]

just build a concrete frost wall under where you want the slab

 

[X1 Mike]

A cantilever is a legitimate construction technique.

 

[toxicz28]

Can I do something like this? What size metal beams would I use, and how thick of a concrete slab would you pour?

Can it be done, sure it can. But, would it be cost effective? I don't think that you could just put a floating slab with some beams sticking out and be done with it. What about a retaining wall to give that extra 4'?

p.s. Consult a structural engineer.

 

[sdb3023]

my roommate who is a civil engineer says get one lol...yes a cantilever is a nice idea...in fact its been done out over the grand canyon

concrete will be used to provide the foundation but the design of it with respect to footers and such will need to be done by an engineer

 

[Fiberglass Fred]

+1 on the engineer. Different soil types and things specific to your location will made a big difference on what needs to be done.

If your soil is big protrusion of granite, like Manhattan, then you'd design the slab differently, compared to if you were building up on the edge of a bayou in Louisiana.

Remember, it's not just about making sure it's strong enough to hold up the cantilevered part of the deck. It's also about making sure the whole slab doesn't slide down that 60 degree embankment. Depending on your location, that's a possibility if the slab isn't designed correctly.

 

[Kevin54]

Way too many people standing out on that for me!!! I think I'd have to crawl out and the first person that came up behind me, I'd have claws dug in like a wildcat. I'm not afraid of heights but I want something under me that is solid in color and not clear.

 

[CraigFL]

A cantilever is a legitimate construction technique.

One of my favorite Wright designs....

(But you do know that recently it has been redesigned and strengthened because of the cracking problems...)

But back to the original question: I suspect the answer will be to put support pilings in the 4ft area and run beams attached to the shop wall passing(over) the pilings to the desired overhang. This will be an architectual wonder and not a cost effective storage space because of the engineering involved.

 

[rocketman]

One of my favorite Wright designs....

(But you do know that recently it has been redesigned and strengthened because of the cracking problems...)

I was going to bring that up. However, The reason it needed reinforcement was because the builders did not use the cement and build it according the Wright's specifications. His original plans and specs would still be flawless!!

Sorry for the hijack, but when you're into architecture and live so close to Oak Park and so many Wright homes you tend to study up a bit!!

 

[jmack]

Anything is possible given enough money and time.

What you want to do will cost some serious $. The nature of your question leads me to believe that you are just looking to build a place to hang out that makes better use of a useless space. To me, that implies low-budget. I could be wrong, but I am guessing this will cost 10x what you were probably looking to spend.

 

[Fudge]

I'm new to this site and have not done my proper into so please don't flame me to hard. That being said, I have had some experience with catalievering wood decks. The rule I have always followed, which I picked up from an old time builder, For every foot of cataliever you need 2 feet of anchor. So if your deck floats out in the air for 6 feet you need it to go 12 feet back the other way. This is also how I have done bay windows, lumber goes out 3feet from the house it must go 6 feet back under the house. I hope that makes sense. Now I just need to do an intro. lol

 

[CraigFL]

I was going to bring that up. However, The reason it needed reinforcement was because the builders did not use the cement and build it according the Wright's specifications. His original plans and specs would still be flawless!!

Sorry for the hijack, but when you're into architecture and live so close to Oak Park and so many Wright homes you tend to study up a bit!!

I lived in Wisconsin and spent quite a few days visiting at Taliesin in Spring Green and T-West in Phoenix... As far as I know though, the restoration in 2002 was required because Wright designed the beams too flimsy.

 

[X1 Mike]

One of my favorite Wright designs....

(But you do know that recently it has been redesigned and strengthened because of the cracking problems...)

I am sure if he gets 75 years out of the deck to match the time Fallingwater has stood he will be happy.

Neat fact, it has been said that today no one would give him permits for that house.

Since you are in Florida have you ever been to Florida Southern College? I make it a point to go a couple of times a year. It is probably the most accessable of all his works.

 

[Stuart in MN]

Is this creek subject to any local department of natural resources regulations? Generally there are limits on how close you can build to waterways, and at least around here you don't want to get in trouble with the DNR.

Even if that isn't a problem, since there's a creek at the bottom of a fairly steep dropoff I'm guessing that you occasionally get fast water running through there. Over time it's probably going to erode the bank...if there's a 4 foot strip of land at the top now, there may only be a 3 foot strip of land in the future. All the rest will be washed downstream.

 

[Stuart in MN]

I was going to bring that up. However, The reason it needed reinforcement was because the builders did not use the cement and build it according the Wright's specifications. His original plans and specs would still be flawless!!

Sorry for the hijack, but when you're into architecture and live so close to Oak Park and so many Wright homes you tend to study up a bit!!

Like many of his designs, Fallingwater had structural problems from the day it was finished due to Wright's specifications.

http://www.plinia.net/browser/browser-fallwater.html

It is every homeowner's nightmare. Years ago, the architect, one of those visionary types, got into a fight with the engineer over whether the design skimped on structural materials. The engineer wanted to make the floors stronger, but the architect said extra steel would make them unsupportably heavy.

Now, both are long dead, and it turns out that the engineer was right. The beams in the house are cracking so badly that the floors are sagging and the house is in danger of falling down. The estimated cost of repairs is so high that the work has been put off for years.

What to do?

If the architect was Frank Lloyd Wright, the owner installs a glass porthole in the floor so paying visitors can see how badly the beams are cracking, and raises the admission price for the privilege of watching the repairs.

 

[jamesemery728]

Are you trying to get rid of someone?

 

[Zeke]

Will someone mention the forms that need to be built to pour this thing?

It's not a very practical idea IMHO.

However, you might be able to put in a vertical foundation stem wall and cantilever out over that with a wood structure. I'd sure tie the land end down well!

PS, I've been a general contractor since '81 and I've done some things. The 2:1 ratio is fine for a cantilever when built into a larger structure. All by itself the engineering would surely be a comfort factor.

 

[BackAgain]

Well, some interesting ideas....maybe just using wood would be easier/cheaper. I've seen a million wooden decks in places that seem rather dangerous with not a whole lot of lumber supporting them. Posts below the overhang would be nearly impossible, the ground over the edge is mush quite deep, I don't even know what kind of equipment you could use to do that job. I still haven't managed to find a way to get down there myself to get the flashlight I dropped!

That said, the land in front of the drop off is quite sturdy. My old Jeep is currently parked there as close to the edge as possible (well, as much as it fits) and I was kinda hoping it would end up in the creek...but it's still there. There are some older trees growing along the side of the hill that keep things held together pretty well. The creek is runoff from all the parking lot drains in the industrial area, looks like brown paint, and dumps into the river next to the sewage treatment plant. I don't think there are many environmental regulations to worry about.

Now, the building in front of the 4' strip of land currently only has a gravel floor, I could theoretically extend beams all the way inside, I want concrete in there someday too. If I only want a 3-4' overhang, and I used a 12-14' peice of timber thick enough, that could work. I would definately talk to an engineer, but would be designing and building myself.

On the other hand I'm trying to see if there's any way I can shove a 20' steel cargo container back there, that would REALLY be nice for storage!

 

[sdb3023]

any type of cantilever design like this needs serious design work by a professional engineer........think about it this way....ur storage container falls into creek....city or town shows up and wants to know why this happened....u end up in a small boat with a hole in it up ur creek without a paddle......since its a creek...where fish live...or ducks.....the dec will get involved....quickly....and then u will now be in an even bigger, stinkier creek.....still without a paddle.....please dont do this.....my basic understanding of engineering says this is bad.....my roommate who is an engineer says this is even worse

 

[BackAgain]

ur storage container falls into creek....city or town shows up and wants to know why this happened....

Not possible...if anything fell it would get caught half way in the trees, but my property line extends to the creek. So technically I could throw a container half way down there if I wanted too. There's already some garbage down there other people have thrown...I'd clean it up, if I could reach it...

since its a creek...where fish live...or ducks.....the dec will get involved....

I'm 99% sure there is no wildlife in the creek. Like I said it looks like brown paint. Fish would suffocate. Too small for birds. Water from all the local parking lots drain directly into this creek. It may or may not pass through the sewage plant, I'm not exactly sure...(it flows directly to it next to the river)

 

[sdb3023]

you quoted me but forgot to quote this part "my basic understanding of engineering says this is bad.....my roommate who is an engineer says this is even worse" notice the last part? AN ENGINEER....said this was a bad idea to attempt as a DIY

 

[regguy1]

I was going to bring that up. However, The reason it needed reinforcement was because the builders did not use the cement and build it according the Wright's specifications. His original plans and specs would still be flawless!!

Sorry for the hijack, but when you're into architecture and live so close to Oak Park and so many Wright homes you tend to study up a bit!!

I've read in more than one place that the builder in fact felt Wright's specs on the cantilever over the creek were not good enought and put in more renforcement than called for, but even that wasn't enough. ???

 

[sdb3023]

he added to much....that was the problem....he used a larger re-bar size then called for bc he thought it needed the extra strength....this increased the load on the beam causing it to fail.....not my explanation....that was my roommate again...who is the civil engineer

 

[Snap50]

You need a hard support as far out as you can, like a continuous wall. It would also serve to retain the soil at the edge of the slope, and because of that needs a different footing and reinforcing bars to make it a retaining wall.
If you have 4 feet of "anchor" slab width and 4 feet of cantilever, you are going to have to hold down the end near the building to counter the teeter effect. It can be done with enough dead weight (extra burried concrete), but having more anchor span than cantilever would make the whole thing better.

You need someone who who can run the numbers on all the components.

 

[BackAgain]

you quoted me but forgot to quote this part "my basic understanding of engineering says this is bad.....my roommate who is an engineer says this is even worse" notice the last part? AN ENGINEER....said this was a bad idea to attempt as a DIY

Oh, ok...one guy on the internet said he knows another guy that says this is a bad idea, so I'll completely forget I ever had that idea.

Think about it like this. Take an 8' long 4x8 peice of lumber. Lay it on the ground so 4' overhangs the cliff and 4' rests on the ground. Now put a 500lb rock on the end of the lumber.

Can you walk out to the overhanging end of that board? Sure you can. My idea is simply that with many many more beams.

Yes, I'll speak to an engineer about this, but it isn't rocket science. Just because I'm not a structural engineer doesn't mean I'm an idiot. I'm not trying to park a truck out there for christ sake. I can't stand "professionals" with a superiority complex that think nobody else can do what they do...

 

[sdb3023]

Sure the idea works for the mechanics of it. Its a simple force-moment diagram. But is the hill sturdy enough to hold the load? Or does a retaining wall need to be placed? how much load are you looking to place on the entire storage area; how much of it will be on the overhang? is there erosion control so stop erosion from underneath the slab due to it being on a hill? the problem with this situation is the hill falling of rapidly to 35ft, the simple cantilever is workable, the problem lies with the hill and its ability to hold to the load. just because it seems sturdy when you walk on it doesn't mean it will continue to support everything after a couple freeze cycles.

 

[X1 Mike]

Way too many people standing out on that for me!!! I think I'd have to crawl out and the first person that came up behind me, I'd have claws dug in like a wildcat. I'm not afraid of heights but I want something under me that is solid in color and not clear.

About time I got to the end of that thing I would be wondering just where the engineer that designed it was ranked in his graduating class....

 

[bluesman2a]

Think about it like this. Take an 8' long 4x8 peice of lumber. Lay it on the ground so 4' overhangs the cliff and 4' rests on the ground. Now put a 500lb rock on the end of the lumber.

Can you walk out to the overhanging end of that board? Sure you can. My idea is simply that with many many more beams.

Yes, I'll speak to an engineer about this, but it isn't rocket science. Just because I'm not a structural engineer doesn't mean I'm an idiot. I'm not trying to park a truck out there for christ sake. I can't stand "professionals" with a superiority complex that think nobody else can do what they do...

THANK YOU!

Like so many things around here I think people make much ado about nothing. Yes, you must do it properly, but jeebus, you're not looking to build Falling-Frikken-Water here. It's a DECK.

Now I will add one more point here also...

You state that the bank itself is quite sturdy. If you can sink a post in that bank, then take a 45* beam out to support the edge, that's a much better design (think about a right triangle with the point DOWN and the 90* on top). It will require much less external support too.

 

[little d]

heres a coupla thoughts, if ya attach your joists that will make your deck to your cross joist with lag bolts, and then attach said joist with lag bolts to your garauge..... also, as far as the hill, im sure your going to use something for the joist to cantilever on, be it a footer, block on top of the ground or what ever, id think if ya drove a few t posts down as far as ya could under what ever your using, this would stabelize even the worst soil.
and the last one, really a saying my dad had, " dont get in my way doing it, while your telling me i cant", good luck with your project, and post some pics of it while your doing what cant be done, he, he, he, little d.

 

[kbs2244]

Think about the possibility of running diagonal supports from the ground level of the current wall out to the far end of the deck.

It may destroy your current Jeep parking area, but that is a trade off you may have to make.

 

[BackAgain]

Think about the possibility of running diagonal supports from the ground level of the current wall out to the far end of the deck.

I was just thinking about this late last night. I could possibly run a chain/cable from the top corner of the building to the far corner of the overhang. Of course then I'd have to reinforce the building, but....

id think if ya drove a few t posts down as far as ya could under what ever your using, this would stabelize even the worst soil.

I like that idea too. Maybe drill some holes along the edge with an auger and fill them with concrete?

I would take a picture for you guys but every time I go out there this time of year it's dark!

Also if I can get permisson from the absentee property owner next door, who I have no idea how to find, it would be a LOT easier to build something and get any kind of equipment in there from that side.

 

[austin308]

Just putting in my 2 cents worth on this subject. Without looking at the site it would be a huge guess for anyone to say what would be best at this location. Site conditions would be very important. Like exsitinting foundation conditions, PI of the soil, is this a FEMA flood plain, etc. I just don't see getting any real feedback that you would want to use to construct a structure from random comments without the person being able to see the current conditions. It is fine to get general ideals but they just may not apply to what you have to work with

 

[rikmeister]

you can cantelever. PSU stadium is all cantelevered stadium. largest all steel stadium in usa.

 

[BackAgain]

It is fine to get general ideals but they just may not apply to what you have to work with

And that's exactly what I'm looking for. I don't expect somebody here to draw me a set of architectural drawings...

I do, however, do my best work after I get a general idea and then just get the hell out there and start building. My brain doesn't interface well with paper drawings. If I spend too much time trying to design it I turn a $100 project into a $10,000 project...

This is probably not something I will do until summer so I have a little while to think about it.