Michael,
From the IRC.
- SECTION R317
- - DWELLING UNIT SEPARATION
- - - R317.2 Townhouses.
Each townhouse shall be considered a separate building and shall be separated by fire-resistance-rated wall assemblies meeting the requirements of Section R302 for exterior walls.
- - - - Exception:A common 2-hour fire-resistance-rated wall is permitted for townhouses if such walls do not contain plumbing or mechanical equipment, ducts or vents in the cavity of the common wall. Electrical installations shall be installed in accordance with Chapters 33 through 42. Penetrations of electrical outlet boxes shall be in accordance with Section R317.3.
- - - R317.2.2 Parapets.
Parapets constructed in accordance with Section R317.2.3 shall be constructed for townhouses as an extension of exterior walls or common walls in accordance with the following:
- - - - 1. Where roof surfaces adjacent to the wall or walls are at the same elevation, the parapet shall extend not less than 30 inches (762 mm) above the roof surfaces.
- - - - 2. Where roof surfaces adjacent to the wall or walls are at different elevations and the higher roof is not more than 30 inches (762 mm) above the lower roof, the parapet shall extend not less than 30 inches (762 mm)above the lower roof surface.
- - - - Exception:
A parapet is not required in the two cases above when the roof is covered with a minimum class C roof covering, and the roof decking or sheathing is of noncombustible materials or approved fire-retardant-treated wood for a distance of 4 feet (1219 mm) on each side of the wall or walls, or one layer of 5/8-inch (15.9 mm) Type X gypsum board is installed directly beneath the roof decking or sheathing, supported by a minimum of nominal 2-inch (51 mm) ledgers attached to the sides of the roof framing members, for a minimum distance of 4 feet (1220 mm) on each side of the wall or walls. (Jerry's note: How can this extend to a minimum distance of 4 feet if there is an opening through it? See additional code sections below from the IBC for additional information.)
- - - - 3. A parapet is not required where roof surfaces adjacent to the wall or walls are at different elevations and the higher roof is more than 30 inches (762 mm) above the lower roof. The common wall construction from the lower roof to the underside of the higher roof deck shall have not less than a 1-hour fire-resistence rating. The wall shall be rated for exposure from both sides.
(The protection offered by the fire retardant treated roof sheathing or it protection of gypsum board is lost if there are openings through it.)
From the IBC.
- 705.6 Vertical continuity.
Fire walls shall extend from the foundation to a termination point at least 30 inches (762 mm) above both adjacent roofs.
- - Exceptions:
- - - 4. In buildings of Type III, IV and V construction, walls shall be permitted to terminate at the underside of combustible roof sheathing or decks provided:
- - - - 4.1. There are no openings in the roof within 4 feet (1220 mm) of the fire wall.
(There will be no "continuity" if there are openings through the protected area. At least not unless they are protected with an approved and rated fire stop system, which would cost too much for that (as compared to the no-cost-involved of just putting the opening a minimum of 4 feet from the side of the fire rated wall.)