Thread: Sheathing thickness - measure twice, cut once

Installing a roof for a screened in porch (14'x15') in New England. Rafters are 2"x6", 16" oc. Rafters will first be covered with 1"x8" T&G for aesthetics on the underside of the roof. Will install plywood sheathing over T&G, not OSB.

What size sheathing is recommended given the T&G layer? 15/32" or ?

For nails:

For sheathing - Will use 8d galvanized steel ring shank nails

For felt - What type and size nail is best?

For architectural shingles - felt + shingle + sheathing + 1/4" past sheathing. Not sure how much to add for felt and shingles. What size nail is best. 11 or 12 gauge?

Thanks

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your 1x8 is your subroof (deck) you would not need anything over that . Unless I am misunderstanding your construction.

I suspect the plywood sheathing is going to be used as the nailing base for the shingles so no nails show through the underside of the T&G ceiling.

Basically, 1x8 T&G will be 3/4" thick, the 15/32" plywood is basically 1/2", for a total thickness of 1-1/4".

Add 1/8" for the underlayment, about 1/2" for the shingles (nails go through two layers of the double layer part of architectural shingles), and you will want a minimum penetration of 3/4" because you are not 'going through' the roof sheathing (the T&G and the plywood together) ... all that is 1/8" + 1/2" + 3/4" = 1-3/8" or a 1-1/2" minimum length roofing nail.

Now let's add the above two things together: 1-1/4" roof sheathing + 1-3/8" roofing - 2-5/8" total thickness, which means a 2" roofing nail will still not penetrate through or show through the underside of the T&G ceiling ... it should end 5/8" up above the bottom of the T&G underside surface.

Maybe Garry or someone else will double check, and possibly even revise, my numbers for accuracy?

all the math hoopla is unnecessary & appears wrong
required nail length should be no different than the minimum for new material installation
using the maximum length in the chart below
nails should not penetrate through the t&g

roof nail length.jpg

Originally Posted by BARRY ADAIR

all the math hoopla is unnecessary & appears wrong

As I asked for - corrections to the math ... "appears wrong" is a useless response.

"Unnecessary" is incorrect as the math exercise was to show the maximum nail length TO NOT penetrate through the T&G ... which is what you also confirmed:
- "nails should not penetrate through the t&g"

Please explain why you think determining the maximum length to NOT penetrate through is useless ... that was one of his concerns.

Originally Posted by jdbs32

Installing a roof for a screened in porch (14'x15') in New England. Rafters are 2"x6", 16" oc. Rafters will first be covered with 1"x8" T&G for aesthetics on the underside of the roof. Will install plywood sheathing over T&G, not OSB.

What size sheathing is recommended given the T&G layer? 15/32" or ?

For nails:

For sheathing - Will use 8d galvanized steel ring shank nails

For felt - What type and size nail is best?

For architectural shingles - felt + shingle + sheathing + 1/4" past sheathing. Not sure how much to add for felt and shingles. What size nail is best. 11 or 12 gauge?

Thanks

****Now, since you are in New England, think about installing a "Cold Roof system". A bit more work and expense but well worth it in the long run. Note: use 5/8" plywood with H-clips.****

The following is for normal roof system:
***This is assuming that you have an unheated attic and there is insulation in the floor of the attic..***.

****Prior to doing anything you must have correct ventilation to the attic.****

1) You are installing 1x8 T&G to rafters. I use nail gun with 10 or 12 common coated nail.

2) The sheathing you are installing will become the nailing surface for the shingle. So I would use nail gun with 12 common coated nails attaching on rafter line. Also using H-clips on plywood. The thickness of the sheathing is not that critical since the 1x8s are making the first roof deck that will provide support/stiffness to the roof surface, the sheathing over it just add thickness and additional support (belts and suspenders approach). So 15/32" or 1/2" is fine.

3) Install Ice and Water Shield on lowest 3ft of roof deck.

4) Then underlayment over rest of roof 15# felt is ok, 30# felt is better (will tear less from walking on it) or synthetic underlayment of your choice, I prefer plastic cap/button cap nails to attach the underlayment. You can use staples or most any other roofing nail if you want.

4) Install shingle with 1 1/4 galvanized roofing nail by hand or roof nail gun per manufacture instruction on placement.

5) Install ridge venting.

The shingle is being nailed to the plywood and the length of the nail should be long enough to penetrate the plywood which is all that is required for attaching the shingle.

Think again about doing a "Cold Roof".

Have fun

Originally Posted by BARRY ADAIR

all the math hoopla is unnecessary & appears wrong
required nail length should be no different than the minimum for new material installation
using the maximum length in the chart below
nails should not penetrate through the t&g

Originally Posted by Jerry Peck

As I asked for - corrections to the math ... "appears wrong" is a useless response.

"Unnecessary" is incorrect as the math exercise was to show the maximum nail length TO NOT penetrate through the T&G ... which is what you also confirmed:
- "nails should not penetrate through the t&g"

Please explain why you think determining the maximum length to NOT penetrate through is useless ... that was one of his concerns.

JP
i never said your math was useless...you're the one throwing that word around
it's just unnecessary when there are published industry standards that can be cited for different deck & roofing material thicknesses

send me the bill for today's dose of xanax

Originally Posted by BARRY ADAIR

JP
i never said your math was useless...you're the one throwing that word around
it's just unnecessary when there are published industry standards that can be cited for different deck & roofing material thicknesses

send me the bill for today's dose of xanax

The common roofer uses galvanized 1 1/4" collated nails in their guns. they never get caught up in the math, they just use what works day in and day out. You buy nails by the case and they become universal for applications. The chart is nice but I have to say that I never spoke to anyone that has ever used one. It is about experience, you may think through the length the first time you lay a roof and then forget about it from there on out. Or if you are learning from someone they say we use the nails in those boxes and you trust them and emulate it from there on.


The math from Jerry and the chart from Barry take you to the same place. Nails that go through the sheathing and not just into it for up to 5/8" sheathing. Jerry's math is correct in that 1 1/4" nail will do the job needed fulfilling required specifications. The 2" nail may not go through the 1x8 but it may cause it to split at some time.

I typically have used 1 1/2" collated nail for roofing since they will work for one and two layer applications (roof over). 1 1/4" is what most roofers use day in and out. 2" nail is used for the ridge cap when using ventilation.

As always "don't worry....be happy" https://www.youtube.com/watch?v=d-diB65scQU

As for vapour barrier atop the sheathing.
#15 pound non perforated organic felt.
Note: You can use Grace ice shield if you wish ti be practical. It seals fastener penetration.

Metal: Drip first, felt atop.
Galvalume apron at the wall abut. You can use lead for the apron well but it depends on the veneer.
Boxed Eave. Gutters with a downspout around the periphery.

All that I just got a headache. Trying to understand it looks good from everyone's comments. So, if the construction is going up then probably your local regional building folks have something to say. I mean as an example, when I built my deck I had to pull a permit and submit architectural drawings of the material being used before a permit was issued. The folks at regional in my area changed a few items in the materials being used which was minimal, it was a long time ago I believe I had to change out some nails for the cross beams for support and use nails that regional recommended. No big deal. Can't wait to see some pics when the project is completed

Originally Posted by Garry Sorrells

****Now, since you are in New England, think about installing a "Cold Roof system". A bit more work and expense but well worth it in the long run. Note: use 5/8" plywood with H-clips.****

The following is for normal roof system:
***This is assuming that you have an unheated attic and there is insulation in the floor of the attic..***.

****Prior to doing anything you must have correct ventilation to the attic.****

1) You are installing 1x8 T&G to rafters. I use nail gun with 10 or 12 common coated nail.

2) The sheathing you are installing will become the nailing surface for the shingle. So I would use nail gun with 12 common coated nails attaching on rafter line. Also using H-clips on plywood. The thickness of the sheathing is not that critical since the 1x8s are making the first roof deck that will provide support/stiffness to the roof surface, the sheathing over it just add thickness and additional support (belts and suspenders approach). So 15/32" or 1/2" is fine.

3) Install Ice and Water Shield on lowest 3ft of roof deck.

4) Then underlayment over rest of roof 15# felt is ok, 30# felt is better (will tear less from walking on it) or synthetic underlayment of your choice, I prefer plastic cap/button cap nails to attach the underlayment. You can use staples or most any other roofing nail if you want.

4) Install shingle with 1 1/4 galvanized roofing nail by hand or roof nail gun per manufacture instruction on placement.

5) Install ridge venting.

The shingle is being nailed to the plywood and the length of the nail should be long enough to penetrate the plywood which is all that is required for attaching the shingle.

Think again about doing a "Cold Roof".

Have fun

Originally Posted by ROBERT YOUNG

Metal: Drip first, felt atop.
Galvalume apron at the wall abut.

Depends.

In high wind event Florida you should put the underlayment down first, then the metal drip edge (helps hold the edges of the roof covering down), then a minimum 4" wide bed of plastic roof cement over that joint to help seal it.

Metal for flashing is typically (99% of the time) galvanized sheet metal (steel) with the remaining 1% being copper (typically within 1500 feet or so of the coast - typically as even that varies.

Originally Posted by Chris Roth

All that I just got a headache.............

Yep.... alot of bla-bla-bla-bla for those who have built /installed a roof before.

I figure the OP wanted to get directions/specifications as to either what he was doing or was having done by someone else. I hoped he would come back after my 1st post to see if he was really interested in obtaining assistance.

The thread started to bog down in the minutia of nail length. Figured I might take a shot at covering the OP questions in one fell swoop without trying to teach him how to drive a nail. I didn't get into flashing and nit-ti gritty unless the OP returned. Though I did take in the direction of a roof over a conditioned structure as a over kill in description.

Sorry for bringing back your headache with more bla-bla-bla.

Originally Posted by Jerry Peck

Depends.

In high wind event Florida you should put the underlayment down first, then the metal drip edge (helps hold the edges of the roof covering down), then a minimum 4" wide bed of plastic roof cement over that joint to help seal it.

Metal for flashing is typically (99% of the time) galvanized sheet metal (steel) with the remaining 1% being copper (typically within 1500 feet or so of the coast - typically as even that varies.

Most of the standard practice for the mid east cost and north have been to install a membrane the first 3 ft or more of the roof against ice damming. Mastics on the starter to bed down for wind if location required.

Most of the east and north east coast use aluminum flashing either preformed or custom formed on site. Copper costs have drastically reduced its' presence. As always it is about location - location - location and budget.

Originally Posted by Garry Sorrells

Yep.... alot of bla-bla-bla-bla for those who have built /installed a roof before.

The reason for some of the "bla-bla-bla-bla" regarding nail length is that his decking was going to be 1-1/4" thick ... which requires a nail length long enough to penetrate into the decking a minimum of 3/4" (which does not count the point).

Other parts of the math was intended to give a thickness of what was to be installed above the decking - this thickness plus 3/4" is minimum nail length - 1-1/4" would be too short (if my math was correct or close - Garry confirmed that my math was correct/close).

The other factor which needed to be known was maximum nail length.

Regardless of what a roofer may typically use.

Originally Posted by jdbs32

Installing a roof for a screened in porch (14'x15') in New England. Rafters are 2"x6", 16" oc. Rafters will first be covered with 1"x8" T&G for aesthetics on the underside of the roof. Will install plywood sheathing over T&G, not OSB.

What size sheathing is recommended given the T&G layer? 15/32" or ?

For nails:

For sheathing - Will use 8d galvanized steel ring shank nails

For felt - What type and size nail is best?

For architectural shingles - felt + shingle + sheathing + 1/4" past sheathing. Not sure how much to add for felt and shingles. What size nail is best. 11 or 12 gauge?

Thanks

Hi jdbs32,
Specifics for local area snow loads, wind shear and lift, roof pitch, eave tail overhang , eave facia and wall posting/beam data support is needed please. Is the span support 15 ft or is it building length 14ft @ 16"oc? Does either key structure dimensions include the over hang(s)? These definitions physically set which type of shingle/shake/ three tab loading used and span permitted. Appears that the 16 oc could be excessive for an ice roof over an open porch. More structure detail could fill in the critical construction data? Tx Ben

First, thanks for all of the feedback, including Jerry Peck's - I prefer to underrstand the why behind an answer so I can learn something.

Again, this is a screen in porch - no need for ice and water shield, no ridge vents, just a 15'x14' roof.

The old rolled rooing was removed, and about half of the 1"x8" T&G was replaced. Interestingly, there was NO plywood on top of the T&G; for some reason, I though there was.

The roof has leaked for years, but that was (I expect) mostly due to the 2 plastic skylights that were not flashed on 3 of the 4 sides, and age (~25 years). While I don't know where the leaks originated (e.g. possibly further up the roof from the skylight), where the rain dripped down was all around the skylights. And yes, the skylights are now gone.

I'm still planning to go with 2 layers of #15 felt, and Ownes Corning Oakridge architectural shingles.

I do have one decision to make - whether to add the 15/32" plywood, or not.

If I do NOT add it, then the roof is similar to what was up there, just architectural shingles instead of the rolled roofing. But Owens Corning would give no warranty since I have 1"x8" roof board; their warranty says 6" maximum. This saves me about $300 on materials and labor.

If I do add the plywoord, then I meet the warranty.

The weight of the snow in NE has never beeen an issue for the roof. Also 4 of the 12 rafters are double rafters with 1" between them. I had this idea of running lighting there some day and did not want the wires to show.

So the real question is, is a rofing warranty of any real value.

Ah, I think I just answered my own question.

Shingles, including starter row and felt cost ~$300. So my $300 in materials and labor for adding the plywood can be viewed as an insurance policy in case the shingles which cost $300 fail.

When viewed like this, I thnik I'll skip the plywoord. And note, that this is what Garry Sorrells said.

And, using the handy chart, I would use 1" roofing nails.

Please feell free to comment; I'm always opening to others thoughts and learning something also.

Thanks!!

A 1" nail might pop through the T&G in a few places. Try a row and see if they are ok. Hot-dipped galvanized nails are the best for rust resistance and they grip way better than the electro-plated nails they use in nail guns.

Take your time on the first course. Let the shingle overhang the edge of the wood about two inches. Read the instructions on the package.

BTW, for the masses, the proper way to nail down a roof on plywood is to have the nails go right through the plywood or OSB.

Originally Posted by John Kogel

A 1" nail might pop through the T&G in a few places. Try a row and see if they are ok. Hot-dipped galvanized nails are the best for rust resistance and they grip way better than the electro-plated nails they use in nail guns.

Take your time on the first course. Let the shingle overhang the edge of the wood about two inches. Read the instructions on the package.

BTW, for the masses, the proper way to nail down a roof on plywood is to have the nails go right through the plywood or OSB.

John,

Did you miss where he has 1/2" plywood over 1x T&G?

Originally Posted by jdbs32

First, thanks for all of the feedback, including Jerry Peck's - I prefer to underrstand the why behind an answer so I can learn something.

Again, this is a screen in porch - no need for ice and water shield, no ridge vents, just a 15'x14' roof.

The old rolled rooing was removed, and about half of the 1"x8" T&G was replaced. Interestingly, there was NO plywood on top of the T&G; for some reason, I though there was.

The roof has leaked for years, but that was (I expect) mostly due to the 2 plastic skylights that were not flashed on 3 of the 4 sides, and age (~25 years). While I don't know where the leaks originated (e.g. possibly further up the roof from the skylight), where the rain dripped down was all around the skylights. And yes, the skylights are now gone.

I'm still planning to go with 2 layers of #15 felt, and Ownes Corning Oakridge architectural shingles.

I do have one decision to make - whether to add the 15/32" plywood, or not.

If I do NOT add it, then the roof is similar to what was up there, just architectural shingles instead of the rolled roofing. But Owens Corning would give no warranty since I have 1"x8" roof board; their warranty says 6" maximum. This saves me about $300 on materials and labor.

If I do add the plywoord, then I meet the warranty.

The weight of the snow in NE has never beeen an issue for the roof. Also 4 of the 12 rafters are double rafters with 1" between them. I had this idea of running lighting there some day and did not want the wires to show.

So the real question is, is a rofing warranty of any real value.

Ah, I think I just answered my own question.

Shingles, including starter row and felt cost ~$300. So my $300 in materials and labor for adding the plywood can be viewed as an insurance policy in case the shingles which cost $300 fail.

When viewed like this, I thnik I'll skip the plywoord. And note, that this is what Garry Sorrells said.

And, using the handy chart, I would use 1" roofing nails.

Please feell free to comment; I'm always opening to others thoughts and learning something also.

Thanks!!

jdbs32,
Thanks for the quick reply. From the information, I might hesitate to give a course in professional framing to remodeling bootleg methods. The mention of roll roofing indicates the original pitch would be below code requirements. The info requested would be helpful for new construction from UBC or IRC code methods. The rafter scabbing described is not what I would consider copacetic nor compatible with 1 x 8 T&G.

In actuality a 2 x 6 or 2 x 8 T&G would be considered a real open ceiling 'decking' without using sheathing for a sunshine roof. A 15/32 OSB sheathing would be the minimum over what exists without seeing a sketch or a photo of what you have now. A 30 lb felt under an architectural grade 20yr three tab will work using cooler nails on a minimum pitch. Good luck.

Originally Posted by John Kogel

A 1" nail might pop through the T&G in a few places. .

Agree, there was penetration on a few places on fhe existing rolled roof. Thanks for the comments.

As noted, I have decided to redo the roof as it was before, just with architectural shingles, not rolled roof, and with 2 layers of felt - there was no felt under the rolled roof.

Thank you for all of your input.

Originally Posted by jdbs32

................
I'm still planning to go with 2 layers of #15 felt, and Ownes Corning Oakridge architectural shingles...........................
.......
I do have one decision to make - whether to add the 15/32" plywood, or not. ..................
.....
When viewed like this, I thnik I'll skip the plywoord. And note, that this is what Garry Sorrells said...........................................
....
And, using the handy chart, I would use 1" roofing nails.
.............................!

Originally Posted by John Kogel

A 1" nail might pop through the T&G in a few places. Try a row and see if they are ok. ........................
.....
BTW, for the masses, the proper way to nail down a roof on plywood is to have the nails go right through the plywood or OSB.

Originally Posted by Jerry Peck

John,

Did you miss where he has 1/2" plywood over 1x T&G?

Jerry,
Jdbs seems to have decided to go with the T&G decking and no plywood. Not hard to miss the flip flopping and nail length differing.

The issue of nail length with 1/2" or 5/8" plywood over the T&G the only real need was to go through the plywood to attach the shingle, which is why the comment on what roofers typically use comment. The T&G is not really part of the consideration for the shingles attachment. The T&G is only a spacer above the rafters. The idea was to go through the plywood only and not through the 1x8. Not an argument as to maximum length calculation you did. Whether the nail goes into the T&G 1/8" or 1/2" is not the issue, just not through the T&G.

The bla-bla-bla was an apology for Chris's head ache reading my long post, that's all.

xxxxxxxx

Jdbs,
I assume your thinking for 2 layers of 15# felt is as a spacer for nail length or to flatten out the variations in the T&G surface. Do not think that the felt will do anything to prevent water leakage, it will not. If you want to to prevent potential water leakage use the Ice and Water Shield as your underlayment and skip the felt.

I think that you are now leaning toward looking at the porch as less of an addition to the house and more of just an outside space with a roof cover, so why spend any more money than absolutely necessary.. But I bet at some time in the future you will start thinking of making it an addition to the house and the added money spent now might pay off later. Just a thought.

I think that you are now leaning toward looking at the porch as less of an addition to the house and more of just an outside space with a roof cover

Yes, it has been a screened in porch for 25+ years; no intentions of doing anything else with it.

I assume your thinking for 2 layers of 15# felt is as a spacer for nail length or to flatten out the variations in the T&G surface.

Owens Corning installation instructions for a low slope roof call for 2 layers of felt. Not sure why though.

Do not think that the felt will do anything to prevent water leakage, it will not. If you want to to prevent potential water leakage use the Ice and Water Shield as your underlayment and skip the felt.

I had considered Ice and Water Shield, but I'm not concerned about ice dams on an open scree porch; I've never had one yet.

I agree that it will prevent water leakage, but if the felt and shingles are installed correctly, why won't they also prevent water leakage as is true for my house that only has felt and shingles after the first 3' that do have Ice and Water shield?

Originally Posted by Garry Sorrells

Jerry,
Jdbs seems to have decided to go with the T&G decking and no plywood. Not hard to miss the flip flopping and nail length differing.

Garry,

The real quote ...

Would have included the ...

"IF" ...

Aa in IF I don't install the plywood ... and IF I do install the plywood wood ...

I recall John's post being the post before mine, and the post with the "if" being the post before John's.

I may have missed the 'I'm not installing plywood" post ... and if I did, then I missed it again going back through the posts just now - if I have missed it please point out the post number and my post number to make it easier for the old guy to find, thanks.

BTW, did you mean "Not hard to miss ..." or did you mean the opposite?

Originally Posted by Jerry Peck

........
BTW, did you mean "Not hard to miss ..." or did you mean the opposite?

Ment that easily lost in the post,,,,

Originally Posted by jdbs32

....................
I had considered Ice and Water Shield, but I'm not concerned about ice dams on an open scree porch; I've never had one yet.

I agree that it will prevent water leakage, but if the felt and shingles are installed correctly, why won't they also prevent water leakage as is true for my house that only has felt and shingles after the first 3' that do have Ice and Water shield?

If you have a low slope roof, forget about ice damming. Porch(unheated), forget about ice damning.

By using the Ice and Water shield you have a sealed roof under the shingle. The nails that penetrate the shield seal around the nail. Nail through felt have no real seal. Using 2 layers will have little effect. Roof slope may be your issue. Added bonus is that if you make a mistake installing the shingle you have backup insurance.

Your house roof that is over a conditioned space (heated) is far different than the porch roof. Sorry for commingling the roof structures/applications. Apples and oranges.