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Old 01-11-2013, 11:15 PM   #1
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Nailing torch down underlayment


I am putting new underlayment & torch down over my old torch down. My question is do you still have to use the normal recommended cap nails? Or can you use regular roofing nails from an air nailer? Any recommendations would be greatly appreciated.

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Old 01-12-2013, 05:19 AM   #2
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Nailing torch down underlayment


Anytime you nail a base felt, cap nails should be used. Standard roofing nails with 3/8" heads don't provide adequate wind uplift resistance.

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Old 01-12-2013, 07:03 PM   #3
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Nailing torch down underlayment


If your going to nail a base down over existing modbit why not just tear off. Your putting so many nails into it anyway it isnt like your getting two roof protection. Also, if your redoing it you probably have issues already so why not t/o and go over a nice clean deck.

Additionally, if its flat and has ponding issues you will just be making them worse.

We voted, your tearing off, now get to it
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Old 01-17-2013, 08:39 AM   #4
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Nailing torch down underlayment


the nails are going to depend on the area you live. you can go with regular nails but i always nail around the eves, thats where the wind get under and tears it off. i do use cap nails because ive got the gun. but i wouldnt stay awake at night worry about it.
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Old 01-17-2013, 09:16 AM   #5
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Nailing torch down underlayment


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Originally Posted by hotrod351 View Post
the nails are going to depend on the area you live. you can go with regular nails but i always nail around the eves, thats where the wind get under and tears it off. i do use cap nails because ive got the gun. but i wouldnt stay awake at night worry about it.
Standard roofing nails should NEVER be used to secure a base sheet to the deck. The nails are the only thing holding the roof down, so you need a large surface area around the nail to prevent tear-through.

No roofing orginization or manufacturer allows the use of standard nails to secure base sheets.
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Old 01-17-2013, 09:47 AM   #6
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Nailing torch down underlayment


1. Dont use Nails.
2. Tear it off to the deck. Most people don't replace a dry roof. I assume you are most people.
3. Inspect and repair the deck. New decking must span three supports.
4. Assuming this roof drains to a drip edge, Install 1.5 inch Perlite up to 18 inches of the edge. Install 18 inch tapered edge at drip edges.
5. Install G2 ASTM 4601-Type II Base sheet. Fasten down all to deck with 3 inch roof deck screws and metal compression plates 1 per 2 sq. feet at the perimeter 4 feet in and 1 per 4 sq. feet in the field.
6. Install Two ply SBS modified bitumen roof system. Hot mop the first smooth ply, and torch the granular cap sheet, or cold process the first, torch the cap.

Detail per MFGR. Soprema Makes a good sheet, as does Siplast.
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Old 01-17-2013, 10:13 AM   #7
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Nailing torch down underlayment


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Originally Posted by jagans View Post
1. Dont use Nails.
2. Tear it off to the deck. Most people don't replace a dry roof. I assume you are most people.
3. Inspect and repair the deck. New decking must span three supports.
4. Assuming this roof drains to a drip edge, Install 1.5 inch Perlite up to 18 inches of the edge. Install 18 inch tapered edge at drip edges.
5. Install G2 ASTM 4601-Type II Base sheet. Fasten down all to deck with 3 inch roof deck screws and metal compression plates 1 per 2 sq. feet at the perimeter 4 feet in and 1 per 4 sq. feet in the field.
6. Install Two ply SBS modified bitumen roof system. Hot mop the first smooth ply, and torch the granular cap sheet, or cold process the first, torch the cap.

Detail per MFGR. Soprema Makes a good sheet, as does Siplast.
I agree with everything except torching a SBS sheet. SBS does not torch easily because it has a very narrow application temperature. Either apply cold process SBS or torch down APP modified bitumen.
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Old 01-17-2013, 12:23 PM   #8
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Nailing torch down underlayment


I have designed and installed thousands of squares of SBS Modified bitumen by mopping the first ply and torching the cap sheet. SBS takes much less heat than APP, Maybe thats what has given you trouble. There are definitely differences in the quality of sheets however, thats why I recommended the two that I did.

Cold process has come on strong in the last few years, however, and it is probably a good choice for a homeowner with a small roof, due to the chance of fire when using a torch.

I guess we all have our preferences. My first encounter with Mod Bit was with Rhoflex, which was a hybrid Mod bit, containing both APP and SBS. The roofs I installed back in the 80's with Rhoflex in a single ply over a glass base sheet are still performing well. They had good drainage, and have been coated with fibered aluminum twice.

I think Rhoflex was sold to Firestone quite a few years ago.

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