Fire wall / multi-family

[Jerome W. Young]

Are there any additional requirements if you have a cbs wall all the way to the roof between units? No type x etc?

[John Arnold]

Jerome - See if this helps. I believe you'll find that the wall needs to go above the roof, not just "to" the roof. This is from a Jerry Peck post earlier this year.

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.)

[Rick Bunzel]

Does the IRC definition include Duplex's? I was in a Duplex recently that appeared to just have OSB panels between the units.

//Rick

[Jerry Peck]

Does the IRC definition include Duplex's? I was in a Duplex recently that appeared to just have OSB panels between the units.

From the 2006 IRC. (bold is mine)

DWELLING. Any building that contains one or two dwelling
units used, intended, or designed to be built, used, rented,
leased, let or hired out to be occupied, or that are occupied for
living purposes.

[Jerry McCarthy]

To add on to Jerry P's info:

[Jerry Peck]

The old way treated the two dwellings within the two-family dwelling as separate structures, i.e., similar to townhouses which are separate structures, in that the fire partition had to extend to the roof, etc., the new way treats them as two dwellings in a multi-dwelling single structure, i.e., similar to condos.

Condos are in one single structure and have 1 hour (or greater) separation between units, this includes not only the walls but the ceilings and floors, where the ceiling is fire rated with appropriate dampers.

Townhouses are considered as separate structures, which the fire separation extending from the foundation to the roof and 30" above (parapet wall) or protected out 4 feet from each side of that common wall, the ceilings are not fire rated (because each townhouse is one separate structure).

[phil kaznowski]

Jerry,

Do you know if seams need to be taped as in a garage firewall? It is common to come across an attic where the type X Firerock is installed, cut around framing, but the seams and gaps are not taped.

I have been unable to get a straight answer on this. Interesting to find out.

Thanks

Phil

[Jerry McCarthy]

Horizontal seams yes, vertical no, because theoretically the vertical edges land on a stud. However, most tapers tape every seam and often even the attachments. (nails/screws) BTW, its usually referred to as “fire taping.”

[phil kaznowski]

Thanks a million!

[Darren Miller]

Phil,

Technically, Jerry's (dare I say it) wrong.

A true firewall is either designed by the architect or chosen out of a book (USG, etc). The design has to be tested in order to obtain a rating.

Attached

http://www.usg.com/USG_Marketing_Content/usg.com/web_files/Documents/System_Catalogs/SA100.pdf

find all different types of 'rated' assemblies (with steel & wood framing). Note most state "joints finished" which means just that.

[Strong Arm of the Flaw]

Are there any additional requirements if you have a cbs wall all the way to the roof between units? No type x etc?

Typically you need a 1 inch gap between the common walls after they have been appropriately sheet rocked. Frame your walls laying down normally and square them up, then use what the architect calls for typically if he knows what hes doing, half inch sheet rock fastened vertically same as you would OSB. Because it is vertical and not horizontal fire tape is "not usually" needed in this particular application (because the gaps break on wood). Then stand the wall plumb and line. Do this for both common walls all the way up to the roof, as in to the OSB Roof sheathing making sure to keep each unit separate from the other. This will require some forethought in regards to second story sub floor, as well as continuing the common walls COMPLETELY up to the roof sheathing. This will typically satisfy most any common residential multi-dwelling building inspection.. It's important to keep the sheet rock tight, but it still isnt a piano. Best of luck to you guys.

When 2 units butt each other there is no need to "cut around" anything. make a fake gable sheet it laying down and stand it up. Very easy to do. Cutting off the tails of the fake gables can allow you to keep a continuous layout for your roof giving it a seamless appearance. Not only does this forethought make everything so much more simple, but aesthetically pleasing (and you keep your roof sheathing on lay out, remember production starts from the floor up, the more forethought you put into it the more money you make). Also no 2 inch bird block that splits in half when tommy derp nails it all to hell. Most importantly you meet all the code requirements. Just plumb and line and build the thing. It will turn out fine, no need to send wood through the wall to make it perfect. There is no such thing as perfect, but there is such a thing as close enough.

The only additional thing you may need for this is fire blocking between the firewall rafter and the next closest rafter on both sides of the firewall cut on a bevel to the pitch of the roof, shoved in tight standing up similar to a bird block. I had an inspector make me do this and he wanted 3 blocks butting each other on bevel gradually getting larger tight to plate and tight to OSB roof sheathing. Again best of luck.