Oddly Shaped hip roofing

[Said the Sky]

hello,

I have an existing house that the owner wants to extend (it is the area with the red rafters). Another thing is due to truss manufacterers sipply chain issues the owner doesn't want to wait for months out for trusses. So he requested to do "A" framing using rafters and ceiling joist as ties. I have no problems doing a regular home with the hip-roof framing however this one is oddly shaped and am inclined to add posts to support the area where the ridge/valley rafters meet, but not sure if I am being overly conservatives. I do know that if there is equilibrium in thrust force in each direction at the ridge and also at the base of the truss where it meets top of the walls, then theoretically we do not need a post at the ridge.

let me know how you guys would frame this,

thanks!

 

[Said the Sky]

more pics

 

[SteelPE]

To me, all of the rafters on your plan look red. Are you talking about both sides of the house (The lazy L on the far left and the roof framing on the upper right).

What's the ceiling situation in the house? Are there cathedral ceilings everywhere or do you have flat ceilings. Usually, the ceiling type will dictate whether or not you have to use ridge beams and posts.

 

[DoubleStud]

No way. That roofline is screaming for a truss system. The main house is so wide, you wont even be able to do a flat beam and a king post plus ridge beam because the span is just too much. It is even complicated as is for truss system.

 

[Said the Sky]

its a ceiling system, not vaulted (thank god). diagonal side (left) im not too worried about span is about 17ft wall to wall, its the right side where the ridge kind of zig zags and bigger spans.

its originally a truss system, but they want the new addition to be A framed.

I checked the A frame system and it works, rafter sizes and ceiling joists are not overly stressed at all, its more so the rafter and ceiling joint where the number of nails required can get high to resolve the tension.

I am just not sure how the zig zag in the ridge line on the right side affects the need for a post. or does the horizontal thrust still get resolved, not requiring a post at all (like normal hip roof framing where no posts are required.)also another thing that complicates things is that at hip valley rafters where you have rafters framing from both sides into it, I am not too sure how the matching ceiling joist below would be framed to take out the thrust force at the wall level. (example picture attached)

Im going to site tomorrow to meet the architect to discuss this.

 

[SteelPE]

I think what you are looking at is a bunch of "lay over" roofs.... that is, you frame the main lower roof as you normally would, sheath the system and then put sleepers down to frame out the "layover" areas above. No sense in putting traditional valley rafters here as they are really only for show (use sleepers). How will the thrust be resolved???? Through the diaphragm action of the lower roof.... you just need to work with the architect/owner/contractor to make sure they sheath this covered area.

Now, if the architect was trying to have a bunch of cathedral ceilings and such, that would be a much bigger headache as you would be forced to have structural ridges, post and transfer beams as you try to get these loads down to the foundation.

 

[Said the Sky]

thanks SteelPE I suspect that you are correct. will see on site tmr.

 

[BAretired]

I'm having trouble getting my head around the framing shown below. The yellow lines represent existing framing. Is the intention to retain the existing framing and just build on top? Or will some of the existing framing be removed to make room for the new? I would have to study the layout a bit longer, perhaps marking elevations on critical points to get a better feel for the project. There seems to be a problem with the yellow lines, and I'm not sure the red lines are all oriented correctly. (but I may be wrong)

BA

 

[DoubleStud]

I think the yellow will be removed and most of the existing exterior wall on that yellow part will be removed and all new roof.

 

[Said the Sky]

Im going to see it tomorrow to wrap my head around it some more, it seems we cannot keep the old trusses because the slopes don't match up with the new. (ridge lines are at different locations. If we build on top of old trusses then we have to check old trusses, which I don't think I have the capabilities to check the metal joint connections, if I do go this route I may sub it out to a truss supplier to check for me.

but I am thinking new roof entirely for that area. beams/posts if needed but I think it may not be needed.

I didnt draw in the rafters in the area near the bottom where it meets the garage yet, not sure how it works there.

 

[DoubleStud]

What we dont see are the interior walls. I hope the architect is really thinking about how the trusses will be supported. I highly doubt it though.

 

[SteelPE]

I'm thinking that a good portion of the existing roof needs to come off to make this work. I can't say that I have ever approached a similar addition by adding on bits and pieces to the existing roof. I would more than likely remove and replace.