Building deck on side of Gambrel style roof - questions

sheslostcontrol

I have a two-story detached garage/office with the office area tucked inside the gambrel roof. The south side of the building runs parallel to the ridge vent and this side faces a garden and some woods - great view. I'd like to install a deck to enjoy it more.

The thought is to remove a 24' wide section (32' total width), add a 10' x 24' deck, build a roof over the deck, and tie the deck roof into the existing gambrel roof.

Before I rush into anything, do any of you foresee potential pitfalls with cutting out a section of the side of a gambrel roof to make room for a deck?

Here is a very rough sketch of the west side of the garage (measurements are not exact).


Here are photos of the inside of the attic area:








Here are some ideas of how this new deck might look:






Look forward to any comments or suggestions.

Ron6519

Is the roof of this deck a traditional joist sysyem with sheathing and fiberglass roofing?
What are planned for the walls of the deck?
Ron

sheslostcontrol

The roof will be made of 2x6 rafters over 2x10 joists. Plan on laying down the same shingles I have now, wiht felt paper over radiant barrier. I will put some R-30 in the joist pockets.

The walls (which are 36" high knee walls, with screen above that. Walls will be 2x4.

The deck posts will be 6x6 set in 12x12x24 footers. According to the inspector I have to float the deck, so I'll have 4 posts on each side (8 total).

sixeightten

Not sure why the inspector would tell you that. I think if you hooked up with a decent engineer, this could end up exactly like you want.

sheslostcontrol

GIven this is a DIY forum, am I going to wind up paying as much to an engineer for plans as I would for the labor or materials? What is wrong with floating the deck? If it is the same height, and buts up to the building and has a roof over it?

sixeightten

Many building departments will want you to have some approved plans for a project like this anyway. I don't think there is anything wrong with a floating deck. I prefer the deck that you proposed however. Fewer posts will look better in my opinion.

sheslostcontrol

Am I wrong to freak out about the prospects of having to pay 500-1000 to an engineer to draw plans? This kills the project. They did not require plans like you described when the garage was built last year -- I drew them up on my computer, and submitted to the city inspector.. no problem.

Robo_geek

I'm no structural engineer, but the combined mass of the deck and the roof above it is quite a lot. Unless the side wall of the structure is framed really well, it's loading that side of the structure a lot. Therefore the most conservative approach is to add more structure, e.g. floating the deck.

While your structure looks very solidly built, often you see wimpy 2x4 framed walls and undersized footers on this type of structure. Adding a deck to such a structure could at best, cause it to rack,and typically cause it to sag.

sheslostcontrol

The lower walls are 2x6, 16 on center. The floor/ceiling joists are engineered OSB I-beams. I first thought I could just lay down deck floor joists on top of the existing 2x6 exterior wall. Inspector nixed that via phone. I thought the 2x6 wall would have been plenty strong enough, but I assume he knows his business better than I.

Ron6519

The ceiling joists in the picture look like dimensional lumber. If the floor joists are the I beams, the rim joists would be what material? I don't think the typical engineered rim joist wouldn't support a ledger for the deck.
Work up a plan like you did for the garage. If it's not approved, modify it until it is.
Ron

sheslostcontrol

Right -- the pictures are of the garage attic, over the upstairs. I guess I called them the wrong thing.. the floor joists between the shop & upstairs are the engineered I beams. The ends of the i-beams look like OSB. I thought I could cut out sections and rest the deck joists on the 2x6 wall, but considering the weight of the deck and roof -- it makes sense to fully support the deck with posts set in footers.

Ron6519

What sort of footing do you have under the garage that the building inspector wouldn't allow the deck joists to rest on the top plate of the wall?
Most of the weight would seem to be on the posted edge of the deck, not the wall.
Ron

sheslostcontrol

Poured slab with rebar reinforcement. I think the edges of the building are at least 12" deep (live in Georgia low frost line).

Gary in WA

As said, you will be changing the shear and loading of the structures side/roof with that big a hole removed. I would expect to shear wall (add inside sheathing) of the last 4' at each side of the opening. A header would need to be spec'ed out and bearing point loads on to the ceiling (strengthened)/floor engineered joists below to carry the new load. Possibly a new ridge beam, not existing board, may be needed for the low-slope new rafters unless the B.D. approves of whatever you draw. With the deck floating, I doubt the roof will be attached and structural. The ridge/ceiling joist would probably need engineering. Keep us informed…..
One of our pro Engineers should be along shortly, or a house designer.......


Gary

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sheslostcontrol

Ok, can I get this out of the way? How much should I expect to pay to have someone (an engineer) draw up plans for this project?