-Joe Lstiburek

A. FLASHING DIMENSIONS

D. Drip Edges
Flashing with a hemmed drip-edge breaks water surface tension and prevents water from running along the underside of the flashing and back into the wall.

Important Note: Flashing penetrations: Penetrations (pipes, cables, refrigerant lines, vents, etc.) must be flashed before the cladding is installed. It is nearly impossible to properly flash a penetration without removing the cladding around the penetration. Be sure to have a plan for all flashings through the building enclosure prior to cladding the building.

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About Head Flashing:
In high exposure locations, head flashing should incorporate an end dam to prevent water from running off the end of the flashing. At this location the cladding may need to be cut to fit around the projection of the end dam.

• Clip flashing back to window casing at bends to create flaps for bending.
• Trim hemmed edge so it ends at the edge of the window casing and does not extend with the other tabs.

• Fold front tab back against side of casing.

(Arrow) Back leg of flashing should extend past head casing.

• Fold down the horizontal part of flashing over the side of the window casing.
• Solder head flashing at the ends to make watertight.

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Note: Because sealants are just as good at keeping moisture in as they are in keeping it out, placing a bead of caulk in the wrong location can result in moisture accumulation, mold and rot, envelope failure, and hundreds of thousands of dollars in repair and remediation. If we know anything, we know that building envelopes will get wet – the question is, “where will the water go?” Make sure you know the answer throughout construction, especially as you seal joints.

• Joint Rule of Thumb: Sealant should be hourglass-shaped and width should be twice depth (shown in diagram).
• Backer rod diameter should be 25% larger than the joint to be filled.
• Joint size should be 4x the expected amount of movement (usually about 1/2” of space on all sides of the window casement).
• Ideal joints are within a range of 1/4” at minimum and 1/2” at maximum. Joints outside this range require special design and installation.
• Always use the right tool: sealant is not caulk and should never be tooled with a finger (saliva interferes with bond).
• Substrates need to be clean, dry, and properly prepared (primer if necessary).
• When dealing with thermally sensitive materials, apply sealant under average temperature conditions because joints expand and contract with changes in temperature (see below).

Joint Expression and Compression

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Rough openings are inherently dangerous spots on a building, like big holes in the hull of a ship. So it is vital to flash them well and install windows and doors in an airtight manner that also manages moisture and thermal transfer. Our preferred method outlined here – fluid applied flashing – is guided by three truths:

1. Windows will leak. Not all of them, but over a whole building, it’s a matter of when, not if. We therefore need to detail our rough openings so that when a window leaks, the water can drain out harmlessly. (Note: this is why we place the air seal at the inside edge of the window, or door, assembly, to allow water to drain outboard of that seal.)

2. Origami is hard. The conventional way of flashing a window with papers and tapes depends on dozens of steps being performed perfectly every time: careful folds and precise manipulation of less-than-forgiving materials in the field. Simple mistakes, like reverse lapping, can be catastrophic to the assembly but can be covered up by subsequent layers of material, so checking work thoroughly can be impossible. Now multiply these risks by the number of windows on a building and you will understand why window installations can be anxiety inducing.

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• Slope the sill using beveled siding or a wedge.
• Apply Joint & Seam Filler to all joints and voids larger than 1/4” that are to be covered in FastFlash.
• Ensure that all nails are set, apply pink Joint & Seam Filler and tool into place.

• Apply FastFlash to sill, extending 9” out from the RO to either side.
• Take care not to FastFlash too far below the RO because the transition strip will become embedded on contact and the water-resistive barrier (WRB) will not be able to slip underneath.
• Recommended: spread FastFlash 2” down from the bottom of the RO.

SureFlash Installation:

• Install transition sheet.
• Must extend down from sill at least 4” farther than FastFlash to adequately lap over WRB to be installed later.

• FastFlash around the rest of the RO and tool over top edges of transition strip to avoid reverse lapping.

• Provide complete, level support for windows, where framing allows, by installing plastic or decay-resistant wood shims.
• Use horseshoe shims to hold window flange off of the sheathing so water can drain if the window fails.
• RECOMMENDED: 1/16 or 1/8” horseshoe shims.

• Insert window in RO and fasten according to manufacturer’s specifications.

• Apply Joint & Seam Filler to head and side flanges and tool. For special cases where flanges must be taped for warranty purposes seek additional guidance for suitable alternative.
• NEVER seal the sill.

Interior View:

• Insert backer rod.

• Apply sealant on top of the backer rod and tool into place (see Sealant Joints section).

• Slide WRB under transition strip.

• Apply WRB around window.

• Complete WRB face, lapped.
• Make sure WRB is lapped over the built-in flashing at the top of the window and taped.

• Install trim.

• Cut a slit in the WRB, fold up, and use tape to hold the flap out of the way while the head flashing is installed.
• Attach head flashing.

• Apply Joint & Seam Filler to the top of the back leg of the head flashing.
• Tool Join & Seam Filler into place.

• Fold WRB flap back down and tape the slit to prevent water intrusion.

• Attach siding.
• There should be a 1/4” gap between the bottom of the sill trim and the siding underneath for expansion and contraction.

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• Existing conditions to be retrofitted.

• Carefully remove existing trim and try to salvage for use after new window is installed.

• Remove existing window.
• Adjust framing as necessary to make opening square and allow for 1/2” of space around window frame.
• If adding a sloped sill, be sure to account for the height of the sloped sill in addition to the 1/2” of space on each side of the window casing.

• Apply Joint & Seam Filler to corners, intersections, and edges of opening.
• Tool into place.

• Apply FastFlash around inside of opening and extend out as far as possible from opening on face of sheathing.

• Lift up any existing building paper and continue FastFlash out as far as possible.

• When possible, bring FastFlash out over the top of siding for continuous lapping (shown with window installed).

• Use shims to leave a space between the bottom flange and building frame to allow drainage in case of window failure.
• 1/16” to 1/8” horseshoe shims are recommended.

• Install window in RO and fasten per manufacturer specifications.

• Bead and tool Joint & Seam Filler along top window flange to prevent water intrusion.
• Optional (pictured): Apply Joint & Seam Filler to jambs as well, but NEVER to sill.

• Install head flashing to protect the trim.

• Complete the window retrofit by fitting trim and caulking around edges where the trim meets the siding on the sides, but NEVER the bottom.
• Kerf bottom of sill trim with a 3/16” drip edge.

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• Apply Joint & Seam Filler to the opening where the buck will be installed.

• Screw window buck into masonry opening.

• Use Joint & Seam Filler to seal around the installed window buck.
• Also apply to corners and seams where the pieces of the buck come together.

• FastFlash the buck from the inside edge of the sill to the building face.
• Extend FastFlash out from opening as wide as the trim to be installed.

• Install Window in FastFlashed RO.

Interior View:

• Insert properly sized backer rod, taking care not to puncture or damage it.

• AirDam over the backer rod and tool the joint.

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• Tool Joint & Seam Filler.

L-Metal Installation

• Set L-Metal into bed of Joint & Seam Filler.

• Apply another bed of Joint & Seam Filler over L-Metal to form a continuous barrier.

Applying FastFlash

• Apply FastFlash to sill, extending 9” out from the RO to either side.

• When installing a wood door threshold, coat the bottom of the threshold  with FastFlash. Alternatively, the height of the rough opening can be sized slightly larger and composite shims can be used to elevate the wood threshold off of the sill.

• Install door threshold and sill.
• Fasten accordingly to manufacturer’s specifications.

Interior View

• Insert properly sized backer rod, taking care not to puncture or damage it.
• Make continuous around door frame.

• AirDam over the backer rod and tool the joint.

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Built right, rain screens are vital to modern construction in our Pacific NW climate. They are also poorly named with multiple definitions. At Hammer & Hand, when we say “rain screen” we are referring to the ventilated rain screen, with that all-important ventilated cavity between cladding and the rest of the wall assembly. That cavity serves two functions for the exterior wall assembly:

1. The cavity helps protect the wall from water intrusion. By separating the cladding from the face of the wall assembly, the rain screen cavity interrupts capillary action into the assembly and provides a drainage plane for bulk water to drain away harmlessly.

Note: we also include a WRB (water-resistive barrier) inboard of the cavity to provide a final line of defense against bulk water intrusion.

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• When the WRB is complete and lapped correctly, the rain screen installation begins.

• Install vertical furring to correspond with the framing method (aligned with vertical framing members).
• Use untreated 1×4 furring.

• Attach Cor-A-Vent SV-5 insect blocker strip between furring.

• Attach siding.

• Install blocking to attach the rabbeted trim to.

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