deck framing advice - Contractor Talk - Professional Construction and Remodeling Forum

builditright · 05-05-2008, 01:16 PM

Thanks men for all the good advice from my original post. I decided to re-post this since i still am not sure how to fix my screw up. Photos are now attached.

So to recap:

-The deck is 25'x 15' total area
-The joists are 2"x8" (span 11' -6") in two bays
-The Beams are 2"x10" bolted to 6"x6" posts (span 14'-6")
-There are 4 posts going down to the sill plate below of the one story extension. The goal was to have the four posts and the ledger support the deck without anything coming in contact with the roof. Problem is I built the extension too high so now i had to use some lesser beams and joists than i would have if i had the height. I can not raise the lintel of the window.
-The ledger board is only 2"x6". Its bolted with 12- 5/8" dia. bolts

So as you can see from the photos. The beams are independent on either side of the posts. I did this so each bay of joists would not be tied together. This now leaves me room to double up the beams or maybe even add a piece of steel in that gap to minimize the sag.

Any info would be greatly appreciated. I know i screwed up but now i have to make it work.

Thanks again

nick

Patrick · 05-05-2008, 01:29 PM

builditright · 05-05-2008, 01:29 PM

here are two more.

Patrick · 05-05-2008, 01:32 PM

How are those 4x4's attached to the house, and do you have a picture of the flashing detail you used? also worried about the ventilation under this thing not too mention the current condition of the roof. You are going to have 20 year products over something that is going to need maintenance.

rbsremodeling · 05-05-2008, 01:32 PM

beside the obvious. What are/were your problems?? What do you need help with?

builditright · 05-05-2008, 01:51 PM

Quote:

Originally Posted by Patrick

How are those 4x4's attached to the house, and do you have a picture of the flashing detail you used? also worried about the ventilation under this thing not too mention the current condition of the roof. You are going to have 20 year products over something that is going to need maintenance.

The ledger is a 2"x6" attached to the brick with Hilti's chemical anchor system. Its very strong for sure. As for the ventilation.. I understand its not ideal but the bottom of the joists are only about 1 inch above the roof deck at the high end. More than three inches at the far end because of the roof pitch. That with an over sized spacing (1/4") of the deck boards at i should be ok with ventilation.

I am worried about the deflection of the beams. i want to stiffen them but with what. Another 2'x10" be enough. Or a piece of steel?

John Hyatt · 05-05-2008, 02:41 PM

If your joists are on 2' centers your going to have to use at least 5/4 ipe, 16'' on center would have added more weight. If you go 5/4 your frame is going to be sitting on the roof not to mention the trampoline effect. A few rows of blocking would help but there again your adding weight.

When we do a roof top deck we support it with acq .40 blocks landing on the roof,or just 2/ stringers laying flat on the roof. I have the Roofer leave some torch down material so each framing member is sitting on a strip of it.

You might be able to do a variation of this by cuting slots in your framing for the little bocks. These added to what you already have would probley do it.

Be Very Very Very carefull walking on that roof and do not drop even one screw on it anyplace near where your walking, also combine this advice with garded use of the saws if you do install those blocks retro. Dont ask how I know this

Who designed that thing anyway ghessssssssss now is a Hell of a time to figure the span. John

cmansmith · 05-05-2008, 03:34 PM

I am not sure what your question is but I can tell you this. I use steel plates sandwiched between lvl beams often. The only thing I would throw caution to is putting them in between green plate might cause them to rust like crazy so some type of flashing would be a good idea. I am confused though. are you wanting to incorporate steel with your ledger board? I don't see how that would help anything.

deckman22 · 05-05-2008, 03:38 PM

I'm in agreement with John, no reason you can't put blocks under your joist & or beams for extra support. One of those torch down strips layed on the roof then a block, no problem. Do not screw or nail it, use glue.

Stone Mountain · 05-05-2008, 03:40 PM

Whenever we do a rooftop deck we always put an inch thick sheet of ridgid styrofoam under any part of the frame that touches the membrane.
The styrofoam is inert, so it won't rot. It keeps the wood off the membrane. It spreads the weight of the joist or beam (the foam should always be 3-4" wider than the wood)so that you don't get the wood sinking into the asphalt or tar.
Just don't run the foam continuously. Make sure you have cut slots for the water to run in the roof's natural direction.

Oh, and don't nail the sheets of foam down (ask me how I know)

John Hyatt · 05-05-2008, 06:07 PM

Hmmmmmmm thats a good idea Stone!!! Styro under the frame, mabey combined with the modified strip,,use that torch down mastic on both of them, styro would take the adhesive just fine.....

I like it!!!!!

John Mon

Charlie Roseman · 05-05-2008, 06:11 PM

You have a tuff situation wwish I could help out on this one but I dont know where to start.

builditright · 05-05-2008, 07:49 PM

Ok men thanks...

I will probably use the styro under the beam centers as you said.

So let me know if this does not sound right....

I am going to cut say a 10"x 36" piece of 1" rigid insulation and center it under both center and far beams. I am going to glue it down to the rubber roof with flashing cement.

Thats it??? I was about the have a custom steel box beam fabricated and bolted in between the posts (that cavity between the beams) and then bolt the deflecting beams into the the new steel. It would never deflect then but that was big $$ i would guess. This is a simple solution. I just hope the styro does not wear into the rubber over time and weight.

Thanks

John Hyatt · 05-05-2008, 08:04 PM

No Man your not going to do that,ghessssssss the foam board is a buffer between the acq block and cleat you install in the mid span or third span or what ever span.

How long have you been in the business,,, nevermind,,a bent elbow with the Joe Crow to you,and your project.

John Mon. www.deckmastersllc.com

redwood · 05-05-2008, 08:43 PM

I'm curious about the life of semi exposed rigid styrafoam. Also, how much weight can it absorb?

Thanks

Mark

buletbob · 05-05-2008, 09:16 PM

What is below the beams bolted to the 6x6's. Is there any type of girder or wall to carrey the existing roof rafters.or ceiling beams? You must at least have a triple girder to carrey the floor joists. and cut the span in half just my 2cnts. good luck Bob

builditright · 05-06-2008, 10:16 AM

Quote:

Originally Posted by buletbob

What is below the beams bolted to the 6x6's. Is there any type of girder or wall to carrey the existing roof rafters.or ceiling beams? You must at least have a triple girder to carrey the floor joists. and cut the span in half just my 2cnts. good luck Bob

There is a 5-1/2" power beam below the roof bearing on the 6"x6" posts. Those posts are then continued up through the roof for the future deck which i am building now. So in reality i just have to figure out a way to transfer the weight of the deflecting beams down into that power beam. If i had the height to run 2"x12" doubles as my beams. none of this would be being discussed. but since i did not have the height i ran 2"x10" which as someone said a while back is "over spanning'.

This is a mess actually. The goal was to have a roof deck that sat above the rubber roof completely so the roof would last close to the life of the deck. Now i just have to swallow the fact that in 10 to 15 years i will be removing the deck to re-roof.

I thought there would be a way to add steel in between the beams to keep it from deflecting. some of you guys have mentioned a flinch plate so i am looking into that now.

Thanks again for all the advice.

Iron Sheik · 05-06-2008, 12:56 PM

While you're beefing up the beam, you should double up the joists next to the skylights.

John Hyatt · 05-06-2008, 07:44 PM

Hang in there Bo..there is always a way to do anything.

The person who says it cannot be done should not interrupt the Person doing it.

Words to live by. John Mon

builditright · 05-08-2008, 05:06 PM

I just spoke to an engineer that looked at my problem. He looked at it for two seconds and said..."add another post in the center of the center beam"

I don't have a whole lot of room (one inch) under the beam but i have that cavity between the them so just like the other posts on the ends i will cut the roof and add one in the center.

Nice guy,, he didn't even charge me!!