Determining nail sizes and pattern

Lew Frye · 09-21-2009, 06:29 PM

Need advice on determining nail sizes and nailing pattern for existing plywood attached to trusses.
Thanks,
Lew

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**Brandon Whitmore** · 09-21-2009, 08:03 PM

Is the roof already on? You say existing, but.......
If roofing is in place, checking the spacing is gonna be impossible as far as I know. Your code book will show the required spacing. What building code does your area fall under?

Checking for proper nails or staples should be easier. Just look next to the top chords and find the fasteners that missed.

If you need to know what sizes are allowed, the building code your state works off of will have fastener tables, etc.

Your question is either kind of vague, or I may be a little off tonight.

Mitchell Toelle · 09-21-2009, 08:43 PM

Originally Posted by Lew Frye

Need advice on determining nail sizes and nailing pattern for existing plywood attached to trusses.
Thanks,
Lew

I assume you are referring to the roof sheathing? If so I believe that 6"OC on edges and 8" or 10" in the fields...but I want you to double check me on this, and it may vary depending on what area you are in. Engineers in areas with higher wind upthrust may have a differing nailing schedule.

Please, if anyone else can add to or change what I said please do.

**Jerry Peck** · 09-21-2009, 08:53 PM

I am also having problems figuring out how he is going to check nail sizes and spacing on existing (in place) sheathing without tearing the roofing off down to the sheathing and actually looking, and that is for spacing.

For nail sizes you would then need to pull a few nails to measure their diameter, head size, and length to check if they are box nails, common nails, ring shank nails, etc.

**Brandon Whitmore** · 09-21-2009, 09:57 PM

For nail sizes you would then need to pull a few nails to measure their diameter, head size, and length to check if they are box nails, common nails, ring shank nails, etc.

Checking the nail head is the only tough one. If I really needed to, I could get that one figured out as I just so happen to carry tools with me. Not that I've done it, but you could pop the nail (pick one of several that missed the framing) back up through the sheathing enough to locate the bump, loosen up shingles, assuming shingles were used, and slide the nail out from the top side.

A.D. Miller · 09-22-2009, 04:29 AM

Originally Posted by Lew Frye

Need advice on determining nail sizes and nailing pattern for existing plywood attached to trusses.
Thanks,
Lew

LF: This may help.

Lew Frye · 09-22-2009, 06:55 AM

Originally Posted by Brandon Whitmore

Is the roof already on? You say existing, but.......
If roofing is in place, checking the spacing is gonna be impossible as far as I know. Your code book will show the required spacing. What building code does your area fall under?

Checking for proper nails or staples should be easier. Just look next to the top chords and find the fasteners that missed.

If you need to know what sizes are allowed, the building code your state works off of will have fastener tables, etc.

Your question is either kind of vague, or I may be a little off tonight.

Sorry, I was too vague. The finished roof is on, the house is 10 years old. For wind mitigation inspections in Florida, this is one of the questions that require an answer. I can determine the nail size since some did miss the truss but the spacing is more difficult. I just wondered if there is some sort of hand held sensor that could actually located each nail location through the truss. I really don't want to tear the underlayment or disturb the integrity of the roof covering. thanks for your help.
Lew

**Wayne Carlisle** · 09-22-2009, 07:50 AM

Use a stud locater and run it along the inside of the rafter. It will be a PIA but it will work.

Mitchell Toelle · 09-22-2009, 08:03 AM

Originally Posted by Lew Frye

Sorry, I was too vague. The finished roof is on, the house is 10 years old. For wind mitigation inspections in Florida, this is one of the questions that require an answer. I can determine the nail size since some did miss the truss but the spacing is more difficult. I just wondered if there is some sort of hand held sensor that could actually located each nail location through the truss. I really don't want to tear the underlayment or disturb the integrity of the roof covering. thanks for your help.
Lew

Just as Wayne said (use a stud finder), but you would be wise to visit the attic as well to look for missed nailings and view a sample of areas. Look for an edge area where missed nailing will give you a sampling and a field area to get a sampling. This is only a sampling and you would need to note that the consistency of missed nailing would affect the integrity of the panel securing as well.

Michael McCann · 09-22-2009, 09:25 PM

Roofs normally have 1/2" or 5/8" ply with 8d or, maybe, 10d nails at 6" on center at the plywood panel edges, and 12" on center in the field. This would be normal for residences. Commercial and retail projects will have closer and different nailing patterns, particlularly at drag struts and the edges of the roof diaphragm.

For floors, the field spacing is 10" on center.

**Jerry Peck** · 09-23-2009, 06:15 AM

Originally Posted by Michael McCann

Roofs normally have 1/2" or 5/8" ply with 8d or, maybe, 10d nails at 6" on center at the plywood panel edges, and 12" on center in the field. This would be normal for residences.

Depends on what part of the country you are in.

Some areas will have nail spacing at 4" on center at the edges and 6" on center in the field.

**brian schmitt** · 09-23-2009, 08:22 AM

Originally Posted by Jerry Peck

Depends on what part of the country you are in.

Some areas will have nail spacing at 4" on center at the edges and 6" on center in the field.

jerry,
are those spacings codified or peckified?

Ron Bibler · 09-23-2009, 09:22 AM

You can get some information for the attic.

Best

Ron

**Jerry Peck** · 09-23-2009, 10:12 AM

Originally Posted by brian schmitt

are those spacings codified or peckified?

"codified" as those are the requirements in the high wind event areas here in Florida.

After Hurricane Andrew back in 1992 testing was done and it was determined that the 6" / 12" fastener spacing resulted in 33 fasteners, and that 33 fasteners properly spaced, properly installed, with no errors, would hold the roof sheathing on in a 120 mph wind (I think that was the wind speed), BUT *31* fasteners WOULD NOT. That meant there was a fudge factor of *1* fastener - and how many fasteners are actually installed "properly"?

Then they found that Hurricane Andrew had wind speeds of 140 mph, so all that changed, not only for a safety factor over 33 fasteners, but to accommodate the higher 140 mph wind speed uplift. Now there are 53 fasteners. Now there are also different "zones" around the roof which require different fastener spacing, with the eaves, rakes, and ridges being higher rated and requiring more fasteners.