How many holes in blocking?

Patrick Allen · 12-31-2012, 03:08 PM

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 · 12-31-2012, 05:19 PM

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.

**Gary in WA** · 12-31-2012, 10:56 PM

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

12-31-2012, 03:08 PM	#1
Patrick Allen Newbie Join Date: Dec 2012 Posts: 1	How many holes in blocking? 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?

12-31-2012, 05:19 PM	#2
Windows on Wash Exterior Construction Join Date: Aug 2011 Location: VA, MD, DC Posts: 3,861	How many holes in blocking? 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. __________________ To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

12-31-2012, 10:56 PM	#3
Gary in WA Moderator Join Date: Mar 2009 Posts: 8,851	How many holes in blocking? 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 __________________ Clothes taking longer to dry? Clean the dryer screen in HOT water if using fabric softener sheets. They leave a residue that impedes air-flow, costing you money. Clean the ducting in the last six months? 17,000 dryer fires annually!

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How many holes in blocking?