deck roof addition

[CEmonkee]

Hi - I'm working on a project that involves adding a roof to a 2nd story deck (this is an existing house that was built about 15 years ago). I've attached a .jpg file that shows a cross-section.

As shown, the roof will be added over the upper deck. The slope will be 1:12 and extended from the existing house roof. On the right side of the image file, I have shown a detail of a possible way to connect the new roof at the existing roof line.

At the end of the new roof (circled in green) I'm not sure what the best way would be to support it. Here's a couple of options I'm considering:

(1) Frame the header supporting the roof rafters into a post which would then extend down to the lower deck, where it would be supported by a beam between the two 6x6 posts.

(2) Extend a beam out from the upper floor and support everything on the upper deck (basically a cantilever beam that would support the roof header post). At this point I'm not really sure what the upper deck framing is like beyond the wall (area circled with ???'s). The original drawing showed the deck joists framing back into the upper story floor, but there's a change indicating that the joists stop at a continuous rim joist under the wall. I'm trying to verify what was actually built.

Some preliminary loads:
Wind uplift at each end of the new roof header = 600 lbs/post

Snow + Dead = 420 lbs/post

I would appreciate any comments on the two options I outlined above, or if anyone could suggest a better option.

Thanks!

 

[msquared48]

Why wouldn't you knock out the existing blocking over the wall, install the new rafter to bear on the double top plate of the wall, and install new blocking?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[CEmonkee]

Hi Mike - thanks for pointing that out. That sounds like a better way to do it.

Any thoughts about the best way to support the other end of the rafter? Do either of the two options I outlined sound like they might work?

 

[msquared48]

As to your two options, I prefer #1 by a longshot as it is far less impact to the existing structure.

The cantilever of #2 would be deep and very disruptive to the existing structure, therefore costly.

#`1 may have architectural and view implications however. It should be the owners perogative which to use here. It's his money...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[CEmonkee]

Option #1 would be my preference as well...

I have attached another .jpg file - it shows a 15' post supporting the new roof and going through the upper deck down to the beam below. On the right is an image from the Simpson catalog of a PC post cap - I thought this might be an easy way to connect up the post and beam, it would be installed flipped upside down from what is shown in the catalog. Offhand, do you see any problems with using something like that?

 

[msquared48]

Nope...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[CEmonkee]

Thanks Mike, I appreciate your input. This gives me a good starting point to start discussing options with the owner.

 

[CEmonkee]

Hi - I've run into an issue on the deck roof I posted about a couple of weeks ago. Please see the attached image file, specifically the area I have encircled in the magenta cloud.

Originally I thought the posts labeled as POST #1 and POST#2 (between the upper and lower deck floors) were one continuous post. However, it turns out that it's actually two 6x6 posts (#1 is on top of #2). I'm won't be sure how the existing posts and headers are connected until they start ripping up what's there (it's currently covered with siding).

At the top of POST #1 the load is about 900 lbs, at the top of POST #2 the load is about 1800 lbs.

With the new upper deck roof, we'll need a new header framing into the top of POST #2, as shown in the plan view at the right. The load from this header will be about 700 lbs.

I'm thinking these two posts should be replaced with one continuous post and the lower deck level headers could be framed into the post with hangers.

Or does anyone have suggestions on how to use what is currently there and make it a strong connection point?

 

[Ron]

One thing I've noticed that you haven't seemed to note is that you are changing from a 6/12 pitch to a 1/12 pitch....that typically requires two different roof systems...have you considered this?

 

[CEmonkee]

Hi Ron,

The existing rafters on the main structure (at the 6:12 roof pitch) will be cut off at the wall line, then the rafters over the deck (at the 1:12 pitch) will tie in at the wall. Both roof systems consist of rafters (see the attached image).

Wind controls over seismic in this area - I've analyzed the new roof in a couple of ways (1) As a large "eave" of the existing house; (2) As a monoslope roof.

 

[hokie66]

I think Ron is cautioning you about the roofing rather than the structural system. The break in slope is a great place for leakage, and the roofing system on the steep part is not likely good enough for the flatter section.

 

[CEmonkee]

Hi Hokie66 - thanks for your reply.

I'm not exactly sure what you mean by "the roofing system on the steep part is not likely good enough for the flatter section" - could you elaborate a bit?

My thought was that roof pitch change would be similar to a change in pitch that you would have at a shed dormer. Please see the attached image file (it has a couple of figures from Rob Thallon's Graphic Guide Frame Construction).

As shown in the figure on the right, the deck (low-pitch rafters) and the house (high-pitch rafters) will lap and both bear on the wall for support.

Is there something that I'm overlooking?

 

[hokie66]

Roofing, roofing. The stuff that prevents the roof from leaking. Not your framing. Maybe that's not your responsibility, but you should know about it.

 

[CEmonkee]

I agree - it's important to keep everything underneath the roof dry. I believe that the contractor was going to use a detail similar to the attached image at the roof slope transition (if I haven't mentioned it previously, this is a metal roof).

These details are important and I'm not going to neglect them, but my main concern at this stage in the project is the support framing for the new roof, e.g the issue I asked about earlier this evening regarding the post.