How many holes in blocking?

Patrick Allen

I'm adding 2x6 blocking to an existing shop. The trusses are 24" O.C. I'm drilling three 2' holes in each block. My question is: Do I need to drill every block to get enough ventalation (I know there needs to be roof vents.) or could I get by with say every other one?

Windows on Wash

It is best to vent each one.

How much do you condition the space.

I would rather see 1 - 2" hole per block than 2 - 2" every other one.

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Gary in WA

Depends on how much ventilation you want. With an 18NFVA ridge vent, you need 9NFVA per side of building per foot for balanced system. 2' block is 18"NFVA or 2" circle with screen is about 3"NFVA X 3 = 9NFVA, per foot----- so 6- 2" per block for 1/150, if using a vapor retarder (faced) insulation, 1/2 of that (3-2") for 1/300.
You did say shop...


Gary

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