The nailing schedule will vary with the thickness of the underlayment, so refer to an underlayment nailing schedule chart to get the right schedule for your job. For example, ¼-inch underlayment calls for 3d ring-shank nails every 3 inches along the edge and every 6 inches within the field of the underlayment.
The underlayment shall be attached with corrosion-resistant fasteners in a grid pattern of 12 inches between side laps with a 6-inch spacing at side and end laps. Underlayment shall be attached using metal or plastic cap nails or cap staples with a nominal cap diameter of not less than 1 inch.
You can fasten your plywood underlayment using one of the following: galvanized, coated chisel-point staples with a 1/4" maximum crown; galvanized, coated ring shank underlayment nails with a 3/16" diameter head; or flathead wood screws treated with a moisture-resistant coating (such as galvanized or zinc).
Staggering the nails helps to prevent the felt from lifting or buckling, which can lead to leaks and other issues. The recommended staggering pattern is to place the top row of nails 6 inches from the top edge of the felt, the middle row 12 inches from the top edge, and the bottom row 6 inches from the bottom edge.
Fasten the underlayment with either staples or nails. Start on one corner of the panel and fasten the 8' edge first, spacing 2” along the entire edge.
The nailing schedule will vary with the thickness of the underlayment, so refer to an underlayment nailing schedule chart to get the right schedule for your job. For example, ¼-inch underlayment calls for 3d ring-shank nails every 3 inches along the edge and every 6 inches within the field of the underlayment.
Nail down squarely (90 degrees) into the deck to secure caps flush to the underlayment. In normal wind zones the nails should be driven at 6.0″ O.C. (on center) on both head and end laps. Fasten the field area in the middle of the roll a minimum of 24″ O.C. in normal wind zones.
Ring-shank and spiral-shank nails are the best fasteners for this application because they are grooved to increase friction and resist withdrawal. In fact, studies at Clemson University in South Carolina have shown that these nails have as much as twice the holding capacity of smooth-shank nails and staples.
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.
Underlayment screws are specifically designed for fastening wood underlayment to wood subflooring. These screws have an intricate thread pattern that tightly holds the two flooring layers together to prevent squeaking, which is one of their advantages over nails and staples.
Secure the Underlayment
Use roofing nails to fasten the underlayment, spacing them about 12 inches apart. Make sure to drive the nails in straight and at a slight angle to avoid damaging the material. Pay special attention to the edges and seams, as these areas are more prone to lifting.
(3) Fasteners for 5-ply plywood Underlayment panels, and for panels greater than 1/2 inch thick, may be spaced 6 inches on center at edges and 12 inches on center each way intermediate.
R905. 1.1Underlayment. Underlayment for asphalt shingles, clay and concrete tile, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles, wood shakes, metal roof panels and photovoltaic shingles shall conform to the applicable standards listed in this chapter.
Underlayment rolls that are 48-inch wide require 3 rows of cap nails to be installed between the laps at 12 inches o.c. and 6 inches o.c. at the laps. An additional row of button caps must be added for each 1-foot increase in roll width.
Rather than nails, screws are best to use for subfloors — these fasteners are convenient, easy to remove and capable of providing torque that nails lack. Because of their structure, screws can penetrate plywood more easily and improve the connection, whereas nails can weaken the plywood.
Other factors like type, sound ratings, and density matter just as much, if not more than the thickness. With that being said, most underlayments are 2-3mm thick, but are sometimes thicker for carpet or to smooth out an uneven subfloor.
There are three basic types of underlayment used beneath roofing materials: asphalt-saturated felt; rubberized asphalt; and. non-bitumen synthetic.
Grip-Rite 114ATUL1 1-1/4 in. x 12-1/2-Gauge Bright Steel Broad Head Ring Shank Underlayment Nails are designed for indoor use where corrosion isn't a concern. Thin, broad head ensures a smooth finished surface and strong grip when attaching plywood or subfloor materials.
Your roofing nails should penetrate at least 3/4 inch into the roof deck. This depth ensures a secure hold.
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.
More is not always better, and with underlayment, too much can compromise the integrity of your floor's locking system. Adding additional underlayment under vinyl with an attached pad can create too much cushioning, which causes the floor to come apart through use over time.
The top edge of the felt should be nailed no less than every eight inches. The middle and bottom edge should also be nailed no less than every eight inches. The next course of felt should also be aligned with the roof edge and should overlap the previous course two inches (sometimes referred to as head lap).