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how far can I cantilever?

Gumshoe's picture

guy wants a roof over his 2nd floor patio, 9' out from the house. Problem is, the structural support is 5'8" out from the house. So can I cantilever 3'4"? I'm thinking 2x8 @ 16" o.c., with tile roof (per his request), 4:12 pitch. And can I put tile on a 4:12 roof?

"Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid...He must be, to use a rather weathered phrase, a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it." - Raymond Chandler

(post #64844, reply #1 of 26)

1) find a structural engineer
2) ask the tile manufacturer (though on this one my gut says sure, why not)

(post #64844, reply #2 of 26)

it's late ... but I ain't gonna let that stop me.


anways ... the usual 3rd's rule of thumb ... one out/two in ... is for nonloadbearing.


for load bearing ... the rule of thumb is only "out" the depth of the joist.


so ... I'm picturing the roof line landing some load out there ...


now ya gotta figure out how much.


 


I know nothing about foor tiles ... now sure how that'd play into it.


 


another vote here for something engineered. Not your basic cantilever.


my guess is .. yeah .. just support the roof load somehow. let the "deck" take care of itself.


Jeff


  Buck Construction 


   Artistry in Carpentry


        Pgh, PA

    Buck Construction

 Artistry In Carpentry

     Pittsburgh Pa

(post #64844, reply #3 of 26)

no, friend, you can't use floor tiles for roofing....Ha Ha

(post #64844, reply #4 of 26)

Yeah, I could recommend the structural eng. route, but its just a patio cover. You guys really think it merits a structural engineer? I could just end the patio roof back a little to minimize the overhang. Using the thirds rule, I guess it would be OK to cantilever 2'10", and crown them all down?


Edited 2/23/2005 3:01 am ET by Huck

"Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid...He must be, to use a rather weathered phrase, a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it." - Raymond Chandler

(post #64844, reply #5 of 26)

Huck, it don't look right to me.


Looks like it would make a nice diving board, and you're going to put a tile roof on it? I'd rethink it a little.


Vince Carbone

Riverside Builders Franklin NY ICQ #47917652

   Vince Carbone

Riverside Builders

Franklin,NY

(post #64844, reply #6 of 26)

 


   " I guess it would be OK "   "but its just a patio cover"


No Huck,  guessing will not be ok and its an overhead structure that could fail if not contructed properly. You either have an expert figure what is "OK" and have the customer pay for that expert or walk.  It's not your problem that the customer's project requires certain fees for professional services to incorporate his " (per his request)"   It's not your job to figure this out.  Besides, in my local I need to pull a permit for what you are doing (regardless of how simple this project may appear) and that permit requires professional drawings with specs. 


Now, to answer your question:  As far as the engineer/architech says you can. 


Edited 2/23/2005 5:46 am ET by GaryJR

(post #64844, reply #9 of 26)

Add some supports under the cantilever if you are going to do it this way.  Get a waiver from the HO.

(post #64844, reply #10 of 26)

Thanks all for some great insights and thought-provoking replies. (Diving board - that was a good one!) Obviously I feel uncomfortable with the situation, otherwise I wouldn't have posted here. The homeowner wants it 9' out, but he isn't inflexible. I'm sure he would pay for an engineer, if we needed it, and I'm sure he'll accept a shorter overhang, ending at maybe 8' out. In fact, I'm pretty sure I can talk him out of the tile roof if it is a critical factor. He likes the tile because it matches the house, and the other patio.

The structure below has a supporting beam at 5'8" out from the house. I want to keep the load transfer in line with the supporting structure. It's a relatively small roof, and I wanted to keep the design hassles to a minimum. I can tweak the variables to make it work. My question was: How far can I cantilever, given the conditions mentioned. I also feel 3'4" is too far, but wanted to see how close to it would still be viable. 2'10"? 2'4"? Or would the 3'4" overhang work if I doubled the rafters? Went 12" o.c.?

As far as permits, he's outside the city limits, and the county here is much more lax than the city. I'll have to check and see if a permit is required. If it is, then we'll submit a drawing once I've pinned the design down, and see what they recommmend. Sometimes on a little project like this, they'll engineer it themselves and make any corrective notes on the drawings that concern them. I'm pretty fanatic about everything I build being safe strong and "over-engineered", and I lose a lot of bids because of it. But I sleep better at night.

Thanks again.

"Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid...He must be, to use a rather weathered phrase, a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it." - Raymond Chandler

(post #64844, reply #11 of 26)

Not sure what the cost would be in Bakersfield, but I could probably get an engineer's stamp on my drawings for less that $2-hundo on something like this (assuming that it is just a "review").  Well worth the investment IMO.


What you have to consider is the ramifications if it fails.  Best case, the tile roof is shot and has to be replaced prematurely (more expensive than the engineer's cost).  Worst case, it has a catastrophic failure with 6 people under it.


Obviously your gut is telling you something.  I learned a long time ago to listen to my gut (along with listening to the little voices in my head)... it is rarely wrong.

(post #64844, reply #12 of 26)

There's a lot of factors to consider beyond just will the roof hold. For example, someone is gonna get up there to do maintenance someday, so there will be live loading. And maybe they'll stack materials on the edge, causing more load than anyone planned. Picture the maintenance process--someone will carry materials up the ladder and set them on the edge be/c they can't reach in far enough, and then they'll climb on the roof's edge, too. That's a potentially big and dangerous load. There's wind loads too, be/c wind uplift will be different on the cantilevered section than on the other part. I wouldn't even take an educated guess...my first call would be to my engineer.

(post #64844, reply #13 of 26)

The structural engineer is the right call, but here's another solution to ponder.  An artistic type could probably make it look pretty good too.  Be sure to tie the two uprights together

"Listen, strange women lying in ponds distributing swords is no basis for a system of government."

Jon

"Listen, strange women lying in ponds distributing swords is no basis for a system of government."

Jon

(post #64844, reply #15 of 26)

My gut feeling is not to be that concerned with such a small structure. Rather than wasting time and money on an engineer, bring your rafter spacing to 12" on center and consider doubling some of them. I think your connection to the original roof is more important than a 3 foot something cantilever.

I like the idea of a waiver

2c

(post #64844, reply #16 of 26)

At first, I thought this had the whole deck candylevered out that far and that would sure be bad, but for just a roof, I don't see any red flags, just the yellow flag you waved at the house end connection. maybe the beam connection for wind uplift too.

Definitely do the engineer/ permit as needed, but this one doesn't scare me.

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #64844, reply #17 of 26)

I was picturing a porch deck with the roof over it too ..


both cantilevered ... with the porch roof posts landing out there too ...


 


just a roof ... just hang it. Build it stiff enough so it don't sag.


Jeff


  Buck Construction 


   Artistry in Carpentry


        Pgh, PA

    Buck Construction

 Artistry In Carpentry

     Pittsburgh Pa

(post #64844, reply #19 of 26)

Its like this

"Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid...He must be, to use a rather weathered phrase, a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it." - Raymond Chandler

(post #64844, reply #20 of 26)

Yeah, that's always a concern. I really hate attaching to the fascia, and normally don't. I much prefer attaching a ledger to the house with lag bolts into the studs or headers. But here I have no choice. So I'll probably pre-drill and run some 3&1/2" deck screws from the fascia into the rafter tails (stucco'd eaves, otherwise I'd pressure block between existing tails, and screw the fascia into the pressure blocks also).

Then I'll toenail my new rafters into the fascia, pressure block between my new rafters, with deck screws from the pressure blocks into the fascia, and my new rafters nailed into the pressure blocks. I generally like to overkill this connection, because I've seen the usual back-nail from the fascia into the new patio rafters pull away over time, leaving a dangerously weak connection, and a water problem. Plus, I don't consider the fascia structurally sound enough to attach anything to, when its just nailed into the tails with a couple of 16's.

"Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid...He must be, to use a rather weathered phrase, a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it." - Raymond Chandler

(post #64844, reply #22 of 26)

Unless you have a good solid sub-fascia you are only attaching to a pie3ce of trim. Now that scaresme.
I see no reason why you can't get into the soffit to attach at the wall with a ledger, but if you have to surface mount to the fascia, and there is no subfascia, you better lag a superfascia on top, through the fascia and into the rafter tails so you are solidly tying framing to framing. then add you new rafters. That intersecting joint will be subject to up loads from the cantilever and down loads from snow drifting and stacking on itself there.

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #64844, reply #23 of 26)

I agree w/ you Piffin. He should cut the overhang back to 2'-10" (1/2 of 5'-8") and secure the inside end of the rafters against the exist fascia for both uplifts & down loads.


Also, changing the rafter spacing, or doubling them up, does nothing for a cantilever. 2" X 6" @ 16" oc will carry approx 60 lbs/sf at a 7' span. No need to beef up framing beyond what is necessary. A cantilever acts like a "see-saw", so the weight of the roof tiles on the overhanging side is cancelled out by the weight of the tiles on the other side of the beam. Of more concern is the total load of the entire new roof, with tiles, being transfered down to the existing beam. Can that beam below carry the total new load?


That is the question to worry about, and have an engineer review.

(post #64844, reply #24 of 26)

What Piffin said, plus if you do put on a new ledger board of 2x material, and are concerned about the original fascia connection but feel good about the integrity of the rafter tails then you might consider shooting some lag screws on an angle to catch the side of the tails in addition to whatever you put into the endgrain. Not much shear value there but it will help hold the ledger really tight against the old fascia.

Previous poster said that changing the spacing and doubling up rafters would not help a cantilever but I can't believe that distributing the load over more structural support (i.e. each rafter carries proportionately less weight) would not help the long term ability of this not to sag. Maybe he wasn't thinking so much of sag but of absolute failure. I have not a doubt that you can make this work and carry the roof load but I was concerned with getting some droop over time and that's why I suggested changing the spacing and maybe adding some meat to the whole plan. He's right about the beams underneath, I took it as a given that you'd figured the underlying structure would adequately handle this, otherwise why ask about it?

Again though, I'd remind everyone about the small scale of this project. Engineers? Wasted money here.

(post #64844, reply #25 of 26)

The simplicity of how this project may appear is irrelevant of the fact that there is a very real safety factor here.  I know, and understand construction, and know enough not to spec something out.  It’s not my job or my field of training.  Sure, many of you have years and years of field experience and many good points and concerns have been brought out in the open, but not to stress the importance of a professional to inspect this project on site and draw up proper specs is down right foolish.    It’s my job and responsibility as a contractor to follow the drawings and specs made by and engineer or architect paid for by the client. 


  It boils down to poor business practices.  Afraid that the project cost will be too high and the client won’t go for it.  Professional fees are part of the process and if you don’t include this important element then you are jeopardizing public safety.  I care because I don’t want my daughter playing on a deck with an overhead that was not properly designed! 


 

(post #64844, reply #26 of 26)

Engineers? Wasted money here.


 


after seeing what it really is ... 100% agreed.


Jeff


  Buck Construction 


   Artistry in Carpentry


        Pgh, PA

    Buck Construction

 Artistry In Carpentry

     Pittsburgh Pa

(post #64844, reply #14 of 26)

That's funny!


 


told ya it was late ....


 


I even misspelled "floor" ...


Jeff


  Buck Construction 


   Artistry in Carpentry


        Pgh, PA

    Buck Construction

 Artistry In Carpentry

     Pittsburgh Pa

(post #64844, reply #7 of 26)

  the codes as i understand them require joist stock no smalleer than 1/4 the distance


to be cantilevered at 40" out that means true 10" joists .  i  would ' flitch' the outside


joists and the rim under the outside wall . 9" by 3/8" steel  sandwiched into 9.25"


stock the corners will need special consideration,  maybe 18" of the same steel bent


to 90 degrees and bolted.    draw it then run it by an engineer .


 

(post #64844, reply #8 of 26)

why can't you add decorative posts up to the roof under some lam beams and keep it safe and even a bit more detailed and interesting?????


Be well


a...


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  I honor the place in you where the entire universe resides,





I honor the place in you of love, of light, of truth, of peace.



I honor the place within you where if you are in that place in you



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(post #64844, reply #18 of 26)

How are you going to tie your 2x8 rafters (16 or 12 o.c.) to the existing roof? Consider adding ties to prevent the cantilevered load from uplifting the existing rafters/fascia. Oftentimes rafters are not particularly well fastened to their wall plates...

 

(post #64844, reply #21 of 26)

That's a good point. Unfortunately, the eaves are stucco'd, so I have no access. The expanded metal lath nailed at this juncture should help, and the framing seems to be top quality from what I've seen in the attic, so I feel comfortable with it. Thanks.

"Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid...He must be, to use a rather weathered phrase, a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it." - Raymond Chandler