Trees Room Roof Slope

The highest priority open issue is the Trees Room roof. There are a limited number of possibilities:

• Flat (or nearly)
• Sloping toward the street
• Gable with a N/S ridge

Flat. A subtle slope is hard to achieve--does the plate slope? Maybe we're talking sloped insulation.

Sloping. Fine for a roof garden, but I'm not sure that's worthwhile--benefits seem elusive.

Gable. An E/W ridge wouldn't make sense: the south wall would be lower than the ridge, and we don't want rain running off to the S. We can do a high hip, but leave it as a gable on the S. The same slope can cover the dining room and entry, or not--we could do a hybrid with flat roofs at front and a gable or hip over the Trees Room only.

The Trees Room ceiling is a separate decision. We can expose the ridge beam and have a sloped cathedral ceiling, or we can have a flat ceiling with trusses above (vented attic).

One approach is a simple gable that runs long to cover the dining room. This results in a high roof over the entry/porch and a storage attic above the entry ceiling. Very 1970s. We need a pendant porch light tied in all directions for seismic.

We could have glass at both ends of the Trees Room, but we would forgo the storage attic, extend the large volume, lose the low entry ceiling, and make privacy a lot more difficult.

Process

The steps for deciding the roof slope:

1. Review the advantages of a roof garden and decide whether we want one. This would, generally, rule out a gable.
2. Create a basic interior envelope for an apples-to-apples comparison. 7' 9" ceiling at entry, 9' 0" at dining room, about 12' 9" in Trees Room. Assume a drag strut at the BR 3 shear wall.
3. Compare SIP and vented attic sections.
4. Create a few SketchUp roof designs. Compare cost, plusses and minuses. Curb appeal is huge, so this decision is critical to project success. That is, cost is not the final determinant.
5. Sketch a hip--how would that work over the dining room?
6. Decide, man.

Unfortunately, if we can't decide at a stroke, we need to develop alternatives enough to estimate costs. The Trees Room design isn't well understood--how high is the ceiling? Must there be clerestories on the N? Developing roof designs with this uncertainty is throw-away work.

Update 4/20/15: I expected process step #1 to rule out a roof garden. Instead, I was reminded why it is such a good idea. I got to step #3 and realized that a 14" deep vented but inaccessible attic over the Trees Room is dumb. Let's plan to use SIPs, at least there. Working on roof garden-over-SIP details, I decided that overhangs are dumb--we want a nominal parapet to attenuate wind erosion on the roof garden.

Once I got to step #6 and realized that I could really support a flat roof with no overhang, I extended it to the kitchen and mentally compared the complicated attic beams the structural engineer suggested for that tiny hip to a straightforward flat SIP or conventionally framed flat roof. That's gotta save us time and money. Also, as time went by, I found I really couldn't support That 70s Porch.