extend roof over flat roof

nate1582 · 05-17-2012, 09:42 AM

Hi, i am trying to find out if it is possible to extend a roof pane over my flat roof. i would like to do away with flat roof. im thinking of taking 1x 10 and spanning them from the exsisting roof ridge down to where the edge of the flat roof is. i am planing on building up the inner wall where the eave is now to support the new roof plus install a knee wall inbetween the exaisting flat roof and where the new roof will be to give it support. i drew out a pic that kinda shows what i wanna do. the thicker lines are the exsisting framing and the thinner line is what the new roof will look like. also i included the two wall sections i plan to add for support.

OldNBroken · 05-17-2012, 11:58 AM

no pics but for starters I hope you meant 2x10 and not 1x10

nate1582 · 05-17-2012, 12:32 PM

yes sorry i meant 2x10s. picture will not upload. do u happen to have personal email that i could send the pic to.

Bob Mariani · 05-17-2012, 12:36 PM

yes this would work fine.

nate1582 · 05-17-2012, 12:55 PM

Should i leave original rafters in place and just add the new ones. if you would like i can email you thie pic and it will show you what exactly im gonna do

Bob Mariani · 05-17-2012, 12:58 PM

I would leave them and then fill the void with blown cellulose. If you want a cathedral ceiling use 2X12 to allow enough space for adequate insulation.

nate1582 · 05-17-2012, 01:01 PM

I was able to final download pic

OldNBroken · 05-17-2012, 01:48 PM

Oh, you are just doing it on one side. Well, that brings up another issue. The internet is not really the place you want to get final approval on that. Yes, it can be done and your idea is sound. Aside from the issues of tying into what I am assuming is going to be the wall on the far side as well as planning raising any penetrations or chimneys to the new proper height you have a more serious issue to verify. You are now creating an asymmetrical roof design that will throw all your load bearing calculations out the window. You may want to check with a structural engineer before proceeding. With that new roof deck the lateral forces are going to be tending to push that structure forward to the left of your drawing with any weight on it. I'm not saying it's going to do it but theoretically it will. Gravity getting in the way of a good plan again. Stupid gravity.

nate1582 · 05-17-2012, 02:14 PM

I had the same idea on what would happen. my concern was that it would push the roof to the left cuz of the new weight and the fact that we get alot of snow in our area dosent help. my uncle is telling me that it wont. the ridge to eave pane is now 12 ft and he wants to extend it to 36 feet to cover flat roof. the pic issnt to scale either.the slope isnt that dramatic

OldNBroken · 05-17-2012, 02:47 PM

Not saying it definitely will either. Just making sure you are aware of the potential. Like I said, not something to be determined over the internet. Looks like you have the correct thinking. Your lumberyard should be able to tell you what size rafters if you give them the spans.

nate1582 · 05-17-2012, 03:19 PM

thanks for the input. i called building inspector and hes comin over tonight to look at at it.

tinner666 · 05-19-2012, 07:53 AM

I'm not sure I understand where the knee wall is going.

Is it above a support wall?

Triangles are your friend. Not sure of rafter lenght, but if the knee wall is over a support wall, collar ties there create triangles and keep the load centered. ( Collar ties are the pieces that usually ties rafters together on each side of, and below the ridge to keep loads centered on bearing walls without pushing them outwards.)

nate1582 · 05-19-2012, 08:27 AM

the knee wall in center of slope is a mistake. i am not putting that in there. the knee wall at eave where previouse roof pane would be is at a support wall. the length of span from ridge to outter wall is 25 ft. flat roof length is 13 ft. the knee wall will be 2 1/2 ft. i also was told that i need to install collar ties in exsisting gable roof to provide support.

joecaption · 05-19-2012, 08:46 AM

I often see where a DIY built addition like this has some other issues that could be addresses at the same time as the new roof is installed.

Are both floors even, or is there a step down?
Is the outside wall 8' from floor to ceiling?
Are the ceilings at the same height in both rooms?

I'm thinking if you went with Glue Lams or LVLs you may be able to do without all the center supports.

tinner666 · 05-19-2012, 08:53 AM

Sounds right now. Don't just toenail the new rafters to the roof. Remove plaenty of roof area and install one or two 2x10 or 2x12 plates ontot the existing roof deck 'where' the new rafters will land, top and bottom, of course. These will be your nailers. Put plenty of thought into their placement! You have to notch the rafters ends of the rafters about 5" from their points and 1-1/2" deep. The tips of the rafters should land about 2" from the peak of the roof. The sheathing will then line up with the finish point.
Eave will need a different 'set'.