Step One: Install your underlayment completely and your shingles up to where the wall begins, so that the first piece of flashing, or the corner flashing, will rest on a shingle.
Install flashing at bottom of all exterior walls and properly integrate the flashing with other wall water management details to direct water down and out of the wall. Install flashing under the bottom edge of the house wrap or other weather-resistant barrier shingle fashion to direct water out of the wall.
The drip edge shall extend back on the roof a minimum of 2 inches (51 mm). Underlayment shall be installed over drip edges along eaves. Drip edges shall be installed over underlayment along rake edges. Drip edges shall be mechanically fastened a maximum of 12 inches (305 mm) on center.
Headwall flashing should extend up behind the exterior wall covering and down over the roof-covering material, as you see here. This is true no matter what type of roof-covering material is installed.
On drip edge flashing, the shingles and underlayment go over the flashing. On rake edge flashing, the shingles go over the flashing, and the underlayment goes under the flashing. On roof penetrations, the shingles go over the flashing on the upslope side, and under the flashing, downslope.
○ The new underlayment should extend at least 4” (102 mm) to 6” (152 mm) to fold over the ridge and be inserted between the shingles and existing underlayment.
Roll roofing does not require underlayment, but it's well worth the added effort and cost to install.
Step Two: Install drip edges on the eaves first. Place the drip edge down, aligning it so water will drip into the gutters.
Step One: Install your underlayment completely and your shingles up to where the wall begins, so that the first piece of flashing, or the corner flashing, will rest on a shingle.
This kind of underlayment is commonly called tar or felt paper and can either be made with natural materials, such as wood cellulose, or synthetic materials, like polyester or fiberglass. The base materials are then soaked in a protective coating made of bitumen (asphalt) or something similar.
(The drip edge will be installed over the ice and water protector and other underlayments at roof rake edges.) You should install ice and water protector before other underlayments, including roof felt. Around roof features like dormers and chimneys, you should place ice and water protector below flashing.
Wrap the entire wall surface including unconditioned spaces. Lap Tyvek® WRB over all flashing (e.g. step flashing, wall to roof intersections and through wall flashings). Weep screeds and expansion joints need to be integrated with flashings and the Tyvek® WRB.
The upper leg of Z flashing must be tall enough to slip under the building's water-resistive barrier (house wrap or felt) and the siding, while the middle section must be pitched slightly to shed water. The lower leg acts as a drip edge and may have a slight bend at its tip to “kick” water away.
The housewrap is used to flash the framing before the window is installed. After installation, it gets counterflashed. Both are critical.
When a lap seam is used, the overlap should be a minimum of 2 inches for vertical faces, and a minimum of 6 inches for conditions where water must be shed such as valley flashing.
Flashings must be designed to provide weather-resistance for the roof or wall cladding, independent of the use of sealants or other materials to provide such weather-resistance. Unpainted galvanised steel is incompatible with most inert materials and is subject to inert catchment corrosion.
Step 1: Start at the eaves: Begin by placing the drip edge along the eaves of the roof, aligning it with the roof's edge. Make sure the drip edge extends slightly over the edge to direct water away. Step 2: Secure the drip edge: Use roofing nails or screws to secure the drip edge in place.
Remember, roof underlayment protects your decking if water ever gets underneath your roofing material. Without underlayment, this water eventually rots your roof decking leading to leaks, mold/mildew forming, and even structural damage.
Tip: Make sure the two white sides are as close as they can be and lay one over the other and tack it down. That is how you will know if it's on upside down -- if the tape strip is down, it is backwards. It is very important that the underlayment run the same direction as the flooring.
So, underlayment on low-slope roofs should overlap 19 inches. Remember that underlayment on steep-slope roofs should overlap 2 inches. Also, remember that asphalt shingles should never be installed on roofs having a slope of less that 2:12. The difference is easy to see, once the underlayment is installed.
To start laying the underlayment, position yourself at the bottom edge of the roof. Carefully lay the first strip horizontally across the roof, ensuring that it is straight and even. Allow the underlayment to overhang the eaves by about an inch; this will help direct water away from the roof and into the gutters.
Many roofers will tell you that staples are fine for installing the synthetic underlayment. Others will tell you that cap nails are more effective. Both options often depend on the slope of the roof itself. Cap nails are typically made of steel and feature a plastic cap to prevent roof leaks, hence their name.
When the underlayment is wet, it can prevent the shingles from adhering correctly, leading to poor sealing. This can make your roof more susceptible to wind uplift, leaks, and other issues.