6. Roofs Archives - Hammer & Hand

6.1 KICK-OUT FLASHING

sproutbox — Sun, 22 Sep 2024 15:41:17 +0000

Whenever a roof surface abuts a vertical wall surface, moisture intrusion and rot become a risk at the connection between the two planes.

Kick-out flashing, a somewhat forgotten practice except by the best roofers, addresses this risk at the most vulnerable intersection between sloped roofs and walls: the drip edge.

Be sure to leave space between the end of the fascia and the wall where FastFlash, WRB, and siding can slide up.

Install FastFlash along the wall at the roof edge.

Stick top edge of transition strip membrane to FastFlash.
Bead and tool FastFlash to the top edge of transition strip.

Peel and Stick along the edge of the roof and lap over top of fascia.

Attach drip edge.

Install Peel and Stick the entire length of the roof-to-wall intersection.

Attach roofing felt. Extend 4” up the wall.

Nail on starter strip of roofing material.

Kick Flashing Guide
Note: All Kick-Out Flashing fabricated on site must have welded seams.

Fasten kick flashing in upper right corner.

Install first course of shingles.

Step Flashing Guide
Note: Align with top edge of shingle course.

Fasten stepped flashing.
2” minimum overlap with preceding piece of flashing. Top of flashing piece should align with top of shingle course.

Continue alternating shingle course and stepped flashing until the roof is complete.

Install Peel and Stick over the stepped flashing.

Slip WRB as high and tight as possible under the transition strip membrane.

Continue layering WRB up to the top of the wall.
4” minimum overlap between sheets.

Install siding.
Allow for a 2” clearance between bottom of siding and roofing material to avoid water damage.

Install gutter under drip edge.

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6.2 VENTED AND UNVENTED ROOF ASSEMBLIES

sproutbox — Mon, 23 Sep 2024 20:54:18 +0000

Vented Roofs (For Pitches of 3:12 or Above)

When detailed correctly, vented roofs have a long, successful track record in the Pacific Northwest. Vented roofs provide the capacity for moisture to be removed from the underside of roof sheathing via convection currents in the vent cavity.

Because today we as an industry are insulating below the vented cavity as standard practice, the building itself is no longer heating the cavity. So, convection currents need to be carefully designed.

To establish sufficient stack effect for these convection currents:

Install exterior air inlets at a location lower than outlets. Opposing vents with no or minimal elevation change will not generally provide sufficient airflow.
Maintain a free-flowing channel between vents the full width of the rafter bay and with a minimum of 1” depth.

Note that the drying capacity of vented roofs can easily be short-circuited by bad workmanship or flawed design.
Be sure to avoid these four pitfalls:

Bulk water intrusion via water leaks from outside (poor workmanship).
Air-borne vapor intrusion via air leaks from inside (poor workmanship).
Constricted airflow due to insulation baffles not fully spanning from rafter to rafter (poor workmanship).
Vapor drive from inside (poor design).

Net Free Area (NFA) of exterior venting is to be a minimum of 1/300ths of the horizontal plane below the roof with equal parts at top and bottom. When in doubt, follow local code.

Unvented Roofs

Unvented roofs are increasingly common due to design priorities. An understanding of heat, air, and moisture as well as the causes of condensation is critical in detailing unvented roof assemblies. Potential pitfalls to avoid include:

Incorrect ratio of vapor impermeable insulation (directly under the roofing and substrate, if present) to the vapor open insulation beneath it. If the vapor impermeable insulation is too thin then its bottom surface can be cold enough to allow condensation where it meets the vapor open insulation.
Poor air sealing. If the assembly is not airtight then air movement through the assembly can carry moisture concentrations into the assembly, with significant risk of condensation.
Careless detailing of partial penetrations. If not properly detailed, partial penetrations into the unvented roof assembly (for things like can lights or ceiling fans) can undermine the insulation and/or air tightness strategies alluded to above.
Insufficient fill below the impermeable insulation layer. If air gaps are present between insulation layers, convection currents can significantly reduce the performance of the assembly and compromise durability.

Two potential unvented roof assemblies:
1. Preferred: Monolithic continuous exterior insulation (CI) above structural sheathing.

40% of insulation R-value to be above sheathing. If not feasible, additional analysis required.
Roof sheathing to be air-sealed.
CI to be installed in multiple layers to limit insulation by-pass from gapping of insulation.

2. Acceptable if above is not feasible: Closed-Cell Spray-Polyurethane Foam (ccSPF) at bottom of roof sheathing.

R-value of ccSPF to be 40% of total assembly. If less, analysis is required.
NO mechanical systems (electrical, plumbing, HVAC, fire suppression, etc.) can intrude into ccSPF layer.
Insulation below ccSPF is to be blown-in fiberglass, blown-in cellulose, or open-cell Spray-Polyurethane Foam (ocSPF). No batt materials.

Because the drying capacity of unvented roof assemblies is inherently lower than vented ones, it is especially critical to control built-in moisture during construction. Control construction moisture content with tenting or temporary roofing when necessary. Moisture content in roof structure must be less than 18% prior to covering. Rigid insulation (if present) must be kept dry.

Roof assemblies must control for exterior moisture in a monolithic and complete fashion. Test roofing membranes for integrity prior to covering from below. In unvented ‘flat’ or low-slope roofs with parapets, perform a full ‘flood’ test to ensure leak-free installation of roofing membrane.

Drying of unvented roofing assemblies is, by definition, only provided to the interior. Therefore, moisture analysis of interior conditions and long-term management strategy is required at all wet locations or areas of high humidity generation such as steam showers, kitchens, baths, laundry, and pools. Special guidance and attention is required when selecting and installing roofing systems over these high humidity areas.

Note: For info about attics, see 5.3 Insulation – Attic Insulation

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6.3 PARAPET WALLS

sproutbox — Tue, 24 Sep 2024 13:54:34 +0000

Parapet walls are a difficult detail with a long history of failure. Unlike standard exterior walls, parapet walls are exposed to the elements on three sides. Furthermore, parapets are often inadvertently connected to interior space via balloon framing, gaps in structure, or penetrations for wiring and mechanicals, introducing warm, moist interior air into the assembly and potential condensation. To address these conditions, detailing must provide excellent bulk water management of roofing, parapet wall, and parapet cap, venting to promote drying, and careful attention to separating the parapet from interior spaces.

1. Height of roofing at wall: minimum of 12” to top of parapet.

Do not lap TPO over top of parapet unless required by unique construction conditions.

2. Top of parapet, below cap, to be sealed with fluid applied flashing.
3. Venting in wood framed parapets:

Provide venting to each wall cavity.
If cavity is greater than 12” above roof insulation, provide high/low venting in each wall cavity.
Can use round/louvered ‘soffit vents’ to limit bulk water intrusion if venting holes are in exposed locations.
For areas which do not need above, cover hole with bug screen.
Ensure ventilated siding cavity is correctly vented yet covered against bulk water intrusion at top.

4. Railing Attachments

Side wall: see Section 6.4: Flat Roof Assemblies.

5. Special Considerations

Strive to avoid penetrations through top of the parapet wall. If unavoidable, get further direction from design team before proceeding.
Likewise, strive to avoid balloon framing of the parapet wall. If unavoidable, get further direction from the design team before proceeding.

Venting and Roofing for Parapet Walls

Venting in wood framed parapets:

Provide venting to each wall cavity.
If cavity is greater than 12,” provide high/low venting in each wall cavity.
Can use round/louvered ‘soffit vents’ to limit bulk water intrusion if venting holes are in exposed location.
For areas which do not need above, cover hole with bug screen.
Insulate within parapet wall cavity to depth of roof insulation (if present).

Roof membrane must lap up wall to minimum of 12” above roof plane or per specifications, whichever is greater.
Terminate roofing on parapet wall with mechanically fastened termination bar.

A. ROOF MEMBRANE
B. TERMINATION BAR
C. INSULATION
D. VENTILATION HOLES

Counterflash termination bar with fluid applied flashing (FAF) to be encapsulated at both top and face, covering fasteners.

A. APPROPRIATE FAF

Top of parapet below cap to be sealed with vapor permeable FAF.
Install either fluid applied WRB from termination bar up and over parapet top or cover transition with transition strip.

Complete Parapet Wall

Interior

A. 24 GAUGE MINIMUM PARAPET CAP
B. WEDGE
C. C-CLIP
D. FLUID APPLIED FLASHING
E. VAPOR PERMEABLE TRANSITION STRIP
F. 1/2” SHEATHING
G. WRB
H. VENT HOLES
i. 1X4 FURRING
J. SIDING

Exterior

A. 24 GAUGE MINIMUM PARAPET CAP
B. WEDGE
C. C-CLIP
D. FLUID APPLIED FLASHING
E. VAPOR PERMEABLE TRANSITION STRIP
F. 1/2” SHEATHING
G. ROOFING
H. TERMINATION BAR
I. FURRING
J. SIDING/TRIM

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6.4 FLAT ROOF ASSEMBLIES

sproutbox — Wed, 25 Sep 2024 10:14:23 +0000

Before constructing a flat roof assembly, please refer to the unvented roof assembly comments under 6.2 Vented and Unvented Roof Assemblies and, if applicable, 6.3 Parapet Walls.

There is absolutely no room for error in the detailing and installation of roofing and air sealing in these assemblies. This step should be closely monitored and tested prior to acceptance of work. Do not rush this.

Continuous Insulation on Top of Sheathing (Exterior CI) with Fiber-Fill in Joist Cavity
This is how to detail an unvented roof assembly for flat and low slope roofs.

A. MINIMUM R-VALUE OF EXTERIOR CI DETERMINED BY TOTAL R-VALUE OF INSULATED ASSEMBLY (SEE ALSO: UNVENTED ROOF SECTION).
B. COVER BOARD IN HIGH IMPACT AREAS
C. ROOFING SUBSTRATE TO HAVE MINIMUM SLOPE OF 1/4”
D. FIBER FILL: BLOWN-IN ONLY, ENSURE COMPLETE CONTACT TO BOTTOM OF SHEATHING

E. RECOMMENDED ROOFING IS TPO
F. NEVER PENETRATE PARAPET ASSEMBLY THROUGH THE TOP
G. HOLD OFF WALL BY A 1/8” GALVANIZED OR STAINLESS STEEL WASHER FOR DRAINAGE GAP

Penetrating Post
Use this option when it’s necessary for the rail to penetrate a low slope roofing membrane.

Vented Post Detail with Low Slope Roof Penetration

a. TPO BOOT
b. TUBE STEEL OR EQUAL
c. SEAL TOP OF BOOT TO POST WITH COMPATIBLE SEALANTNote: If post (B) penetrates into thermal envelope, encapsulate with closed cell spray foam to mitigate condensation.

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