Joist spacing question

[Richard]

One of three pictures.

this picture is facing an overhang we're going to "roof". Post is 6x6 set about 12" (perhaps 18, I forget) and in concrete.

The rafters/joists are going to be going from left to right. I'm going to tie them into the log on the right (using hangers) and tie them into the 2x12 you see on the left.

The angle you are viewing is a 13 foot span. We are NOT going to have them on the same plane as this part, they are going to be higher on the right and be flush with the 2x12 on the left. Wife wants a small slant so (in this pic or the following) you will see we are going to move up a single 4x4 and then mount them to the next higher LOG. I'll have to cut both ends so they will be flush with the log and come down to the existing 2X12 you see on the left (which is 12' long)

I'm going to then put some plywood on top and shingle it to match our roof.

Questions:

1. I am planning on using 3/4" marine grade plywood, sufficient/overkill??

2. What kind of spacing might I need/want to use on the spanners so I have enough support strength? I'm going to space them evenly, but my thinking is roughly 16/18" OC. If it takes 14" to make them look "balanced" so be it. I'd rather have 2 extra up there than 1 too few (since I'll be walking on this to clear out the gutters above) /forums/images/graemlins/crazy.gif

3. Will the 2x12 on the LEFT (12' long) be strong enough to support all this attached stuff?

I don't know if I posted on this project a year ago or not, but this is the post I dug for, carried up the hill, set into concrete and the VERY next day the wife says in a VERY small voice...
"will you be mad if we move it 6 inches further out"

/forums/images/graemlins/tongue.gif

I commenced to rip it down and move it out six more inches. That necessitated removing the stringers (right name?) and the post. resetting the post (after digging out new hole and partially filling in old one. And then I had to get a new 2x12 because I'd already cut the original to length /forums/images/graemlins/tongue.gif

Alas, the things we do for our women

 

[Richard]

This is the head on view of the 2x12x12. You can perhaps better see the higher log I'm going to tie into. how she plans on hiding the transition of the sloped 2x12 to the horizontal one ....ya got me /forums/images/graemlins/confused.gif

 

[Richard]

This is from the inside looking out. The right side will be the receiver for the joist hangers and the left side will essentially be just an inner structure for some kind of skirt, depending on how we finish it out.

come to think of it, I've never seen a skirt hiding 10' 6x6's

/forums/images/graemlins/blush.gif

 

[EddieWalker]

First thing you need to do is find out what "Code" is in your area. Does it snow? High winds? Heavy rain? etc ...

Just my opinion here, but the first thing you need to address is the 2x12 joist you will be useing to attach your rafters to. A single 2x12 spanning 13 feet will sag in time with the extra weight.

I'd suggest you rip some half inch plywood the width of the 2x12 and sandwich it between another 2X12. Use liquid nails for extra strength and either screw or nail it together. Repace the single joist hanger with a double.

Be sure to use the finished edge of the plywood on the bottom side, then seal it with caulking.

As for the rafters.

If you want to use 3/4 plywoood, then 24 inch centers are plenty. Lots of homes are on 24 inche centers with half inch CDX plywood or OSB. No need for marine grade wood. That's just throwing money away.

Again, depending on your loads, I'd suggest 2x8's for your rafters.

Now if it was me, I'd go about it a littel different then what you described.

I'd run a ridgeboard diagnally from your outside corner to the inside corner on the home. A pair of 2x8's with the plywood would work perfectly.

Depending on the angle of slope you want, is how high I'd set it. Remember to measure your pitch with a framing square to know your measurements.

Minimum pitch should be 2 in 12.

When you know the pitch, then it's easy to figure out the rest of your cuts.

Then I'd cut the rafters from the ridgeboard to your joists every two feet. It's called a hip roof, but your only doing one corner. You can use 2x6's for this.

Install half inch plywood, tar paper and shinglels.

Good luck,
Eddie

 

[Richard]

Thanks for the comments.

Went to the store last night & seems the guy there had some ideas... the wife totally went for them soooooooo most of what I said above is now for naught. /forums/images/graemlins/tongue.gif

First, he pointed out what you did about the single 2x12 holding all that weight. I'm to double it just as you said.

Second, though I showed her the diagonal idea as you had, she wants "flat" so to say. Since I have 2x12's, she wanted to keep a similar sized so we're using 2x10's. Picked up 10 2x10x14' (16" OC as I recall). Going to mount them "high" on the right wall (with the window) and going to "bird perch" or something called similar to that, them onto the doubled 2x12's (by cutting a notch in them & have them rest on TOP of the 2x12's rather than butted up to them)

Bought 5/8 BC plywood rather than CDX or marine grade. He said since it'll be protected by shingles we could get by with BC. Since I WILL be walking on it to clear gutters, I felt more comfortable with 3/4 but he said it was waste of money.

Now, you make mention of gluing some plywood BETWEEN the 2x12's. I have seen this done before and understand how it will strengthen.

his recommendation was just to screw two of them together.

My guess is, you might feel simple screwing them together might be insufficient?

Again, thanks for your thoughts.

/forums/images/graemlins/smile.gif

 

[Richard]

</font><font color="blue" class="small">( I'd suggest you rip some half inch plywood the width of the 2x12 and sandwich it between another 2X12. Use liquid nails for extra strength and either screw or nail it together. Repace the single joist hanger with a double )</font>

Already have the double joist hanger for the 2 2x12's. Hadn't thought about laminating though.

If I DO, and use 1/2", will that still fit inside a double joist hanger? I would have guessed not.

/forums/images/graemlins/confused.gif

 

[drm]

Richard,

It depends on the width of the joist hanger. Measure it and determine if you need the plywood sandwich or not. It is not required for strength. Glue and nail the 2x12's. Use 2 rows of 12d nails at 12" o.c. each side. The sizes you are using seem to be good but I do not know your local code and minimum design loadings. If you have any snow loads in your area you must design the framing (and post and foundation) to accommodate drifting snow from the higher roof on both sides. This gets to be a lot of load and the framing gets very heavy. May not be a problem there.

When you bolt the double 2x12 to the post use a minimum of two 5/8” through bolts. Also add an 18” long 2x6 or 4x6 (better) under the bottom of the 2 2x12’s. This brace can be cut at the bottom to provide some aesthetics to the end.

The minimum slope we like to put shingles around here is 3/12. A flatter slope may cause water infiltration problems but if you do not enclose the area this may be OK and not cause much problems.

…Derek

 

[EddieWalker]

Not using the plywood between your joists isn't going to be an issue for your application. I suggested it for consideration as the strongest way to go. You really don't need it for what you're doing.

Check the boards before installing them. there will be a slight bow in each one. Put the bow in the up position, so in time, it will settle flat. The bow up will aslo have more strength as oposed to bowing down, or sagging.

It doesn't matter, but for general information, they make joist hangers for doubled up joist, and for 4X material. There's a half inch difference between the two.

Eddie

 

[Richard]

Thanks!!

Update: Got 2 more 2x12x16's. Those are always so much fun to carry in a truck /forums/images/graemlins/crazy.gif

Opted to NOT put the plywood between them. Didn't think about the crown before glueing them /forums/images/graemlins/blush.gif

Took the one to be doubled down. Trimmed off the other one and trimmed down the very top of the post. Got the plywood painted (the visible side underneith...well the wife painted it)

All we got done today. Since we live in the county, they told me we can do what we want /forums/images/graemlins/crazy.gif

My personal disposition is to make it as good or better than they would otherwise make code...after all, I figure code is there to give guidance and to make sure everything works.

Don't want any surprises.

I'll try to remember to take more pictures as we go along.

/forums/images/graemlins/smile.gif

 

[JasonL]

I might suggest you use valley shield on the entire roof if it is 3/12 or less. If you're not familiar with it, it is a sticky backed product that comes in 3' rolls similar to tar paper (roofing felt). It seals down to the plywood and helps keep moisture away. If you have snow laying on the roof and then sun hits it , it can melt and work its way back under the shingles. This is especially true if you enclosed an area and heated it. Then the heat escaping up through the roof melts some of the snow and can create these "ice dams" which can then force water back up under the shingles. Just a thought. Jason