Plywood on roofing now?

[Thronester]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

[randomq]

Structural/sheer is a good guess. I will say I prefer spaces with plywood roof sheathing as they stay quieter and cooler, and don't drip on you on cold mornings...

[microage97]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

If you get a engineer stamp on your plans you can go w/o the plywood and 4' OC rafters

[Hotzcatz]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

Three or four decades ago, the plywood decking wasn't required at all.   It was just rafter/truss + perlins & add tin.  Then several decades ago, we had some hurricanes and everyone went nuts about roofs flying off.  So, loads of Simpson fittings and then plywood decking.  

However the decking was expensive and folks didn't like it. A contractor used the criss cross metal strapping and that was a good replacement for the roof decking for awhile.  I thought it was a bit odd that they never really had very many dimensions for the strapping.  It wasn't like at 4' o.c. or anything, just some metal strapping up there somewhere. Some roofs had the strapping at 4', some at 6' some just had one big 'X' and called it enough.  Now, the County has decided that's actually not good enough and we're back to the plywood decking again.

The rafter/ truss spacing has been getting smaller, although a lot of that has to do with what's used to span between them.  Way back when, it was 2x4 rafters at 5' o.c. w/ 2x3 perlins @ 3' and aluminum roofing. Much lighter than the current metal roofing. The old galvanized tin roofs were much heavier so the rafters became closer together. The current metal roofing is pretty light, but the rafter/trusses haven't gotten any further apart. However, the numbers used to size lumber have changed in the past twenty years so now the same dimension of lumber can't span the same amount that it used to.  Probably the difference between old growth timber and the newer faster growing species of trees.

Other than the roof decking, the foundations have changed a lot, too.  Along with more engineered hold downs and shear walls.  About every ten years there's usually some sort of upheaval in required construction methods.

After the Maui fires, I'm expecting to see residential fire suppression systems required sometime soon.

[humble pi]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

Plywood is not strictly required.  
We are building a small house with 2x6 TNG planks for the roof deck.

[Durian Fiend]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

Plywood is not strictly required.  
We are building a small house with 2x6 TNG planks for the roof deck.

What's the advantage of these planks over plywood? I guess it will be your finished ceiling inside, so this is being done for aesthetic purposes.

[humble pi]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

Plywood is not strictly required.  
We are building a small house with 2x6 TNG planks for the roof deck.

What's the advantage of these planks over plywood?  I guess it will be your finished ceiling inside, so this is being done for aesthetic purposes.

Yes, it will be our ceiling, we like the look.  
Friends have something similar.  Shed roof, 3 in 12 pitch, made of 2x6 TNG, over 4x10 rafters @ 48"OC.  
The tallest wall has a row of long, narrow awning windows way up high to catch the trade-winds & let the heat out.  
The inside feels solid, symmetrical, old-fashioned, bright & bigger than it really is.  

If you plan to cover the rafters, there is no advantage to a plank roof.  More materials, and more labor.  

[Punatang]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

Plywood is not strictly required.  
We are building a small house with 2x6 TNG planks for the roof deck.

What's the advantage of these planks over plywood?  I guess it will be your finished ceiling inside, so this is being done for aesthetic purposes.

Yes, it will be our ceiling, we like the look.  
Friends have something similar.  Shed roof, 3 in 12 pitch, made of 2x6 TNG, over 4x10 rafters @ 48"OC.  
The tallest wall has a row of long, narrow awning windows way up high to catch the trade-winds & let the heat out.  
The inside feels solid, symmetrical, old-fashioned, bright & bigger than it really is.  

If you plan to cover the rafters, there is no advantage to a plank roof.  More materials, and more labor.  

---

You can get a similar look and save a pile of cash if you use t1 11 and flip the "outside" in.  https://www.homedepot.com/p/15-32-in-x-4.../202526444

[humble pi]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

Plywood is not strictly required.  
We are building a small house with 2x6 TNG planks for the roof deck.

What's the advantage of these planks over plywood?  I guess it will be your finished ceiling inside, so this is being done for aesthetic purposes.

Yes, it will be our ceiling, we like the look.  
Friends have something similar.  Shed roof, 3 in 12 pitch, made of 2x6 TNG, over 4x10 rafters @ 48"OC.  
The tallest wall has a row of long, narrow awning windows way up high to catch the trade-winds & let the heat out.  
The inside feels solid, symmetrical, old-fashioned, bright & bigger than it really is.  

If you plan to cover the rafters, there is no advantage to a plank roof.  More materials, and more labor.  

---

You can get a similar look and save a pile of cash if you use t1 11 and flip the "outside" in.  https://www.homedepot.com/p/15-32-in-x-4.../202526444

Yes, we've seen that.  There are many ways to get a similar look.  Paneling and such would be lighter, thinner, cheaper.  The house is a single box with a shed roof - fairly modest and practical.  This ceiling/roof is our one extravagance.  We enjoy the aesthetic.  

Did not mean to hijack the thread.  I think the code requires a roof deck under the metal roof.  You can make the deck in different ways (like sheets or planks), but it has to be a solid deck.

[tikicarver]

Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.

If you get a engineer stamp on your plans you can go w/o the plywood and 4' OC rafters

I don't know if that will work with the building permit dept.
I am building a garage, I had planned to build the roof just like  all the metal post frame buildings on the mainland.There are tons of Youtube videos about building them and lots of company's selling plans etc. They all build the roof the same basic way.
trusses, with purlins then put the metal roof panels directly on top. the metal roof panels are thick enought to handle the sheer loads required. You just have to get the truss and purlin sizes calculated correctly for the dimensions of your building.

But when I talked to the building dept in Hilo, they said " plywood decking is required."  Even after I pointed out that the code says decking is not required if the metal roof panels are rated to handle the sheer load. I figured it was not worth arguing with them and just went with the plywood, since I would have to convince the guy who drew the plans too..

This is the same building dept that would not approve my plans when I had no electircal planned. One guy kept saying I need to have an electircian on the declaration sheet. I told him there is no electircal, it says it on the plans and they were stamped approved. He kept saying code requiires electical installed.  I ended up having to go in person to the office with copies of the code in hand to prove to them there is no code requirement for installing electical in a detacted garage. the guy was misreading the code that said 'IF you install electical, there must be a min of one branch circuit with 2 outlets". Luckly there were 2 other guys there that day that said the first guy was wrong and the signed off my permit.   I don't think it would be that easy trying to get them to approve no plywood,, because everyone is doing it.

but once again they are not reading the code correctly or don't understand the engineeering.  There are 1000s of post frame buidings on the mainland with the roof and the siding just metal panels on trusses, purlins and girts. the metal panel IS THE sheer strength of the budiling. and they withstand huricanes....