hurricane prooof roof glue for plywood

[nota]

I am trying to 150++mph hurricane proof my roof by adding 2 layers of 5/8 plywood SCREWED AND GLUED
I just got the wood from an over bought large condo project in the keys

to add my existing roof that has a single layer of 1/2 plywood now to make a 1 3/4'' solid plywood no gaps no leak strong roof

would love to use epoxy BUT IT COSTS WAY TOO MUCH as I need to do 1300sf twice of glue area

I am in the ANDREW eyewall area, south dade near the bay, so it is a question of when not if we get a cat 5 storm again

glue needs to be strong water proof and cheap to cover 2600sf so many gals needed ruling out epoxy for costs

top con strong screws will be used so some clamping force, could add weights to added clamping force if needed

but I am searching to find a good strong/cheap glue with good penetration and eazy to spread/work with available in 5 gal or larger sizes

metal steel panels will cover the roof after the code required tarpaper BS

[tcar]

Screwed and glued to what??? Screwed through to the rafters/trusses?
Is the existing roof ply glued to the rafters/trusses? If not, it won't help to glue new ply to the existing ply.

Check that the roof structure itself can carry the additional weight...substantial. Plywood / OSB are heavy.

That's only part of it, maybe...

Make sure the entire roof does not come off as a unit... are hurricane clips/straps enough? Maybe not.
Hurricane straps down to studs?

Just some thoughts.

[mepstein]

Liquid nails?

[1990C4S]

What tcar said..Do you hurricane straps?

Don't overthink the wood glue...yellow wood glue by the pail.

[red-beard]

What does adding 2 layers of plywood do to increase the wind resistance? It would seem to me that the roof structure, more roof trusses, with better attachment, would be better than a thicker roof. Also look to strengthen the over-hung areas, so the wind cannot come from underneath.

Someone had a video showing a roof slowly being ripped off a building. It was a 30 minute video posted here by someone in a hotel. Take a look at that for what the wind actually did.

[drkshdw]

Adding two layers of 5/8 to 1/2 inch won't give you 1.75 because plywood is now nominal thickness. You'll be at 1.5" with those 3 layers. If I were you and I hadn't gotten the extra 5/8, I would rip off the 1/2" and do one layer of 1" plywood. Stronger and easier than multiple layers that will cause problems when (not if) water gets between those layers.

But before you do anything, take note of what tcar said. If your rafters are any more than 16"OC, you have some engineering to do. If you were further north and had snow loads to accommodate then it wouldn't be such a big deal but your roof is only as strong as the rafters holding it up (and the nails holding it to the walls and the bolts holding the walls to your foundation).

[onewhippedpuppy]

You would probably get the most bang for the buck gluing directly to the rafters then screwing the hell out of it. Plywood eventually de-laminates when bent, and keeping it from bending will be much more on the screws than the glue. With two sheets you'll gain some stiffness to prevent bending, so that's a positive. If I were doing this I would use an exterior grade wood glue, stagger the seams, and screw the hell out of it with a 4" structural screw to get good penetration into the rafters. If you glue then immediately screw, there's no need to weigh it down for the glue to dry.

It's an interesting idea, but I really wonder if your rafters and exterior walls are designed to carry that much load. Most homes are built no more heavily than required, and my guess is that you are easily doubling your roof weight. With a wind load and more weight on the roof, now your walls may be more prone to buckling in a strong storm. You'll also need to consider rafter attachment to the wall and wall attachment to the foundation.

[Evans, Marv]

What those guys said. Seems to me you want to maximize the integrity of the building rather than adding a huge amount of weight to the top, which might just be a liability under stress. I'd put my effort into securing what you have to the rafters/trusses and adding hardware to increase the structure's rigidity and securing it to its base.

[nota]

yes the trusses are hurricane strapped to the concrete cap on the top of the CBS walls
that is required by code here roof and trusses were redone after ANDREW IN 92
GABLE end walls are CBS block up to the wall concrete cap
no studs no stick built home

by doing 3 layer we can lap the joints 2 ft leaving no gaps to leak seams will be sealed
between the ply sheets puting the ends on the 24'' trusses
and screws [strong topcons] will be into the 24'' trusses 6'' wood about 2'' in

I would NOT use OSB on a dog house real 5 core plywood only

weight is not a problem many similar roofs have heavy concrete tile in the area
steel top panels are much lighter then concrete tiles so total weight will be in the same ballpark

[ckelly78z]

If I were strengthening a roof to prevent lift off, I would use 2x4 or 2x6 hangers underneath the rafter lumber, and bolt through the hanger with large stay washers, and stay nuts. I would then strap down the overhangs to prevent wind from lifting at the edges, and also strap vertically from the rafters, to the joists inside the attic. Of couse a well secured metal roof might be a better plan to start with.

[LWJ]

1) what is your over-hang / aerodynamic profile? Does your roof want to fly? If so, extra glue and plys may not help.
2) What if you do all the work and your house is still trashed?
3) I think I would consult an expert first, before taking action.

Sorry to be a little negative. I saw what Michael can do. There is serious power in these storms.

Good luck! Thanks for being proactive!

[dad911]

Well, you could ask on a car forum..... or go to the miami-dade website and use an approved method for roof sheathing.

https://www.miamidade.gov/permits/hurricane-mitigation.asp

Roof Sheathing
Roof sheathing shall be attached in compliance with the Florida Building Code, Florida Statute 553.844 and the Hurricane Mitigation Retrofit Manual........

[nota]

less the a one foot over hang except on the front porch door area that is about 4 foot
that may get cut off and replaced with a awning to reduce lever action
house is simple single peak no gables no dormers ect low vee
in ANDREW most locals losses were shingles and tar paper with minor plywood dammage
except on the bigger over hangs that did damage the roof plywood
problem is if you lose the tarpaper the roof leaks like a sieve destroying the drywalls ect

[GH85Carrera]

Originally Posted by dad911

Well, you could ask on a car forum..... or go to the miami-dade website and use an approved method for roof sheathing.

https://www.miamidade.gov/permits/hurricane-mitigation.asp

Roof Sheathing
Roof sheathing shall be attached in compliance with the Florida Building Code, Florida Statute 553.844 and the Hurricane Mitigation Retrofit Manual........

Hey wait, we have lots of opinions here! We don't need to be covered up in logic and facts. What are you trying to do?????

[dad911]

Originally Posted by nota

........
in ANDREW most locals losses were shingles and tar paper with minor plywood dammage
except on the bigger over hangs that did damage the roof plywood
problem is if you lose the tarpaper the roof leaks like a sieve destroying the drywalls ect

If plywood damage was minimal, why add more plywood?

As to roof leaks, you need secondary water barrier protection, examples and more info here: https://www.miamidade.gov/permits/hurricane-mitigation.asp

http://www.floridabuilding.org/fbc/thecode/secondary_water_barrier_revised.pdf

https://apps.floridadisaster.org/hrg/content/roofs/roofs_index.asp

[JeremyD]

we did interlocking plywood (splined butt joints) at our initial construction - and tied to our foundation with concrete rebar and metal ties. We also went with upgraded plywood - I think either inch or 3/4 inch at the minimum.

[Zeke]

Originally Posted by drkshdw

Adding two layers of 5/8 to 1/2 inch won't give you 1.75 because plywood is now nominal thickness. You'll be at 1.5" with those 3 layers. If I were you and I hadn't gotten the extra 5/8, I would rip off the 1/2" and do one layer of 1" plywood. Stronger and easier than multiple layers that will cause problems when (not if) water gets between those layers.

But before you do anything, take note of what tcar said. If your rafters are any more than 16"OC, you have some engineering to do. If you were further north and had snow loads to accommodate then it wouldn't be such a big deal but your roof is only as strong as the rafters holding it up (and the nails holding it to the walls and the bolts holding the walls to your foundation).

Lots of good thoughts here. However, if the new layer (I would be satisfied with one) is glued well, then it essentially will be one layer with the added advantage of staggering the joints differently than the first layer. As mentioned, the new layer must be screwed into the rafters below the first layer. And one more thing: I seem to recall the nails are superior to screws in many applications. I'm in CA so I won't speculate on what FL approves. A good ring shank nail is all but impossible to remove.

Metal attachments on the attic side would be ideal.

If all 3 layers are going to be applied, consider running the 2nd layer perpendicular to the first and 3rd layers. Now you'd really have stagger.

For glue, I'd look into something that can be troweled on with a notched trowel about 3/8 x 3/8 notches. Screw (or nail, or both) from the center out doubling up on the edges. Around here our side wall sheathing is nailed 3" OC. That's too much IMHO as it can weaken the membrane. Stagger opposite nailing on edges.

That's all I know.

[nota]

Originally Posted by dad911

If plywood damage was minimal, why add more plywood?

As to roof leaks, you need secondary water barrier protection, examples and more info here: https://www.miamidade.gov/permits/hurricane-mitigation.asp

http://www.floridabuilding.org/fbc/thecode/secondary_water_barrier_revised.pdf

https://apps.floridadisaster.org/hrg/content/roofs/roofs_index.asp

by doing a 3 layer plywood lapped 2' so water proof
if the roofing metal and tar paper is blown off
we still will NOT LEAK at all even if some top plywood is damaged
there will still be 2 layers to seal the leaks
unlike a single layer of plywood that leaks with damaged tarpaper let alone removed TP + metal/shingles or tile

cat 5 eyewalls require much more then the local code wants
we have a strong code for cat 1-2 storms it will help limit cat 3 damage
but cat 4-5 is a whole other animal and the code does NOT limit damage

I worked the post ANDREW recovery helped my boss and others
with torn up roofs that leaked destroying the interior dry wall electrics and furnishings
plus mold and mildew everywhere
I am trying to avoid that mess

I decided a better plan is needed
a roof with extra layers to redundantly seal the leaks
so it can and will take damage and still NOT LEAK even in a cat 5

[gtc]

3m 5200

[onewhippedpuppy]

In a strong tornado, often times it's the pressure differential that knocks out windows as opposed to wind or debris. That can be mitigated (somewhat) by correctly venting the attic. Does a hurricane have similar effects?