DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Roofing and Siding > Can I cut off these prywood board in order to increase air circulation




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Old 04-17-2014, 11:27 AM  
q0987
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Default Can I cut off these prywood board in order to increase air circulation

Hello all,

Some sections of my attic have poor ventilation. One roofer suggested that I should install ridge vent on these sections and also cut through the prywood under the roof board in order to increase air floor to the roof board.

Q1> Is it safe to cut those prywood which is directly above my open attic area and under the roof board?

Q2> If I can cut those prywood without damaging my house, why the builder put those prywood between the attic and roof board at the first place?

Q3> Instead of cut all the prywood square by square, I decide to simply use hole saw to cut holes to increase the air flow. Does that make sense?

Thank you



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Old 04-17-2014, 11:39 AM  
Wuzzat?
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Quote:
Originally Posted by q0987 View Post
Q2> If I can cut those prywood without damaging my house, why the builder put those prywood between the attic and roof board at the first place?
If the plywood is not deflected at midspan it is not carrying a downward force so then you can cut holes if you want.
Use a straightedge or taut string to check this.

If you cut a hole and start getting deflection then there is a force on these panels/this surface. Cuidado!


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Old 04-17-2014, 11:49 AM  
q0987
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Quote:
Originally Posted by Wuzzat? View Post
If the plywood is not deflected at midspan it is not carrying a downward force so then you can cut holes if you want.
Use a straightedge or taut string to check this.

If you cut a hole and start getting deflection then there is a force on these panels/this surface. Cuidado!
Hello,

Thank you for the quick response.

Question> I don't quite understand how to check whether the prywood holds downward force or not. Can you give me some examples. I will post more images to illustrate the situation when I get a chance.

Based on my initial observation, most of the bottom part of the prywood has been cut between the stud.

Thank you
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Old 04-17-2014, 12:09 PM  
Wuzzat?
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The plywood comes from the store flat/planar. If it's bent downward there must be a force doing this.

I also remember PV=nRT, so
for a fixed attic volume V
as T (attic temperature) goes up due to sunlight hitting your roof,
the air pressure (P) in your attic will increase.

Ideally this hot air will be forced out your roof vents but with no vents the high pressure air could be forced downward through the plywood holes into your conditioned space.
So just cut one hole to start.

Using the same formula with politicians who occupy a fixed volume and have constant body temperature, something else must be forcing the hot air out of them.
If I had to guess I'd say they are full of decomposing ca-ca, which gives off heat and noxious substances.

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Old 04-17-2014, 12:26 PM  
nealtw
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No problem, when building this, a framer has a choice to put the valley set up or plywood the main roof and then add the set above. He did the latter.
So yes you can cut has many holes as you like and yes it is a good idea
He did miss a step, there should be a 2x4 on flat just up against each of those trusses on the lower side, but it has stude the test of time so I wouldn't worry about it.
Just don't cut into trusses below.

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Old 04-17-2014, 12:29 PM  
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Quote:
Originally Posted by Wuzzat? View Post
The plywood comes from the store flat/planar. If it's bent downward there must be a force doing this.

I also remember PV=nRT, so
for a fixed attic volume V
as T (attic temperature) goes up due to sunlight hitting your roof,
the air pressure (P) in your attic will increase.

Ideally this hot air will be forced out your roof vents but with no vents the high pressure air could be forced downward through the plywood holes into your conditioned space.
So just cut one hole to start.

Using the same formula with politicians who occupy a fixed volume and have constant body temperature, something else must be forcing the hot air out of them.
If I had to guess I'd say they are full of decomposing ca-ca, which gives off heat and noxious substances.
This may help you understand where this plywood is. It is between the main roof and the valley set built above.
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Old 04-17-2014, 12:46 PM  
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Hello all,

Thank you so much all great comments and helps.

The roofer told me to do it as a DIY job rather than pays him to do for several hundreds and he is the only roofer who point this problem to me. Originally, he suggested that I should cut all the board out just as the bottom part done by the builder. But I thought use hole saw is easierly and get less chance to damage the trusses.

I have purchased DEWALT DWD112 8.0 Amp 3/8-Inch VSR Pistol-Grip Drill with Keyless All-Metal Chuck

http://www.amazon.com/DEWALT-DWD112-...drill+3%2F8%22

I will buy the following tools to help do the job:

1> DEWALT DW1803 Heavy Duty 7/16-Inch Shank Quick Change Mandrel (Fits Hole Saws 1-1/4-Inch - 6-Inch)

http://www.amazon.com/DEWALT-DW1803-..._bxgy_hi_img_y

2> DEWALT D180066 4 1/8-Inch Hole Saw

http://www.amazon.com/DEWALT-D180066...+inch+hole+saw

Thank you all for your great helps.

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Old 04-17-2014, 12:50 PM  
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Hello all,

One more question:

Should I do anything to prevent possible fire hazzard?
In other words, should I wet the prywood first before I start to use the hole saw?

Thank you

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Old 04-17-2014, 12:53 PM  
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Do a little test drilling first, those things bite in the wood and will take your wrist apart if you are not ready for it.

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Old 04-17-2014, 01:38 PM  
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The urge for most beginners with a hole saw is to go straight thru the wood cutting on all the teeth at once, and it will rip your wrist out of the socket when it grabs. I have found that rocking the saw in a slight orbit so it’s only cutting on one side helps and it also helps with getting the sawdust out.



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