DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Roofing and Siding > Cathedral ceiling - how much venting do I need?




Reply
 
Thread Tools Search this Thread Display Modes
Old 10-22-2012, 03:11 PM  
Shawner
Member
Join Date: Oct 2009
Location: Peachland, BC
Posts: 56
Liked 2 Times on 2 Posts
Likes Given: 4

Default Cathedral ceiling - how much venting do I need?

Guys, meet my roof. Well, part of it anyways. The raised part is the cathedral section.



Here's the exhaust side of the venting. Aluminum soffits are covering up cedar with holes drilled into it. Haven't pulled them down yet to see exactly how much there is.



Found a site about calculating proper attic ventilation (http://www.trinityexteriorsinc.com/1...n-5-easy-steps), wondering if you could check my calcs below and see if I'm correct.

Area = 25' x 23' = 575 sq ft

TFNVA = 575 sq ft / 150 = 3.83 sq ft

Convert to inches = 3.83 sq ft * 144 = 552 sq in

Intake = 60% = 331 sq in
Exhaust = 40% = 221 sq in


So if I pull down the soffits, count the number of joist bays I have, figure out the size of hole I need to cut in each to total 331 sq in on the intake side, I should be good, right? If that's ok, should I staple in some screen material over the holes to keep the critters out or do the soffits do that already?

I'm not positive but I don't think I have to worry about baffles (don't think the insulation is up that high in the "attic")

Thanks for any help!


Shawner is offline  
 
Reply With Quote
Old 10-22-2012, 03:37 PM  
nealtw
Contractor
Join Date: Nov 2010
Location: Upper Fraser Valley, British Columbia
Posts: 13,536
Liked 1354 Times on 1195 Posts
Likes Given: 2336

Default

If the white soffet was part of the original construction the cedar would not be there. If you are taking it down to drill more holes, I would just remove one peice of cedar all the way across
The lower roof is vented below the windows with 3 holes for bay, I think I would want more there and maybe better protection for that venting.


nealtw is online now  
 
Reply With Quote
Old 10-22-2012, 03:51 PM  
Shawner
Member
Join Date: Oct 2009
Location: Peachland, BC
Posts: 56
Liked 2 Times on 2 Posts
Likes Given: 4

Default

Don't think the aluminum was original. Think it used to have cedar shake roof, they probably put the soffits on when they sheeted the roof and put asphalt shingles on.

Good plan on removing one chunk, lot easier than cutting lots of holes.
Shawner is offline  
 
Reply With Quote
Old 10-22-2012, 04:13 PM  
nealtw
Contractor
Join Date: Nov 2010
Location: Upper Fraser Valley, British Columbia
Posts: 13,536
Liked 1354 Times on 1195 Posts
Likes Given: 2336

Default

I would take a close look at the lower one too. Those little hole give you min. venting at best but the top board looks level so you may have water sitting way to close to those windows. I'm sure something better could be done.
nealtw is online now  
 
Reply With Quote
Old 10-22-2012, 05:30 PM  
oldognewtrick
Moderator
HRT_ADMIN.png
 
oldognewtrick's Avatar
Join Date: Jul 2009
Location: Nashville, TN
Posts: 7,109
Liked 701 Times on 574 Posts
Likes Given: 222

Default

There is a exhaust vent that is applied from above. It's like half of a shingle over ridge vent, then you put a metal "L" flashing over the top of it. One brand is called Smart vent.

http://www.dciproducts.com/html/smartvent.htm
oldognewtrick is online now  
 
Reply With Quote
Old 10-22-2012, 05:36 PM  
AndyGump
Drawer of Homes
 
AndyGump's Avatar
Join Date: Mar 2011
Location: Orange, CA.
Posts: 56
Liked 5 Times on 3 Posts
Likes Given: 2

Default

I think you would be better off making the high end (exhaust) the 60%.

If fact, I know it would be.

Andy.
AndyGump is offline  
 
Reply With Quote
Old 10-22-2012, 06:20 PM  
nealtw
Contractor
Join Date: Nov 2010
Location: Upper Fraser Valley, British Columbia
Posts: 13,536
Liked 1354 Times on 1195 Posts
Likes Given: 2336

Default

Andy: You lost me, a little more detail?
nealtw is online now  
 
Reply With Quote
Old 10-22-2012, 07:16 PM  
Wuzzat?
Banned
Join Date: Jan 2010
Posts: 2,328
Liked 168 Times on 155 Posts
Likes Given: 94

Default

Quote:
Originally Posted by Shawner View Post
Intake = 60% = 331 sq in
sqrt(331) = ~18" on a side for a square vent. You may want to make two vents that add to this area.

I'd redo for the 300 ratio just to see what kind of latitude you have on these dims.

Quote:
Originally Posted by AndyGump View Post
I think you would be better off making the high end (exhaust) the 60%.
Andy.
If you're thinking stack effect that may already be in the 60/40 split.

Last edited by Wuzzat?; 10-22-2012 at 07:21 PM.
Wuzzat? is offline  
 
Reply With Quote
Old 10-22-2012, 07:49 PM  
AndyGump
Drawer of Homes
 
AndyGump's Avatar
Join Date: Mar 2011
Location: Orange, CA.
Posts: 56
Liked 5 Times on 3 Posts
Likes Given: 2

Default

Quote:
Intake = 60% = 331 sq in
Exhaust = 40% = 221 sq in
This is what he stated.

Should reverse those percentages.

Andy.
AndyGump is offline  
 
Reply With Quote
Old 10-23-2012, 04:36 AM  
oldognewtrick
Moderator
HRT_ADMIN.png
 
oldognewtrick's Avatar
Join Date: Jul 2009
Location: Nashville, TN
Posts: 7,109
Liked 701 Times on 574 Posts
Likes Given: 222

Default

First thing to check is the ability to free flow air from the eave to the peak, because if it's stuffed with insulation all the venting in the world will not help.


oldognewtrick is online now  
nealtw Likes This 
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter DIY Home Repair Forum Replies Last Post
Floor or ceiling venting? cdelsig HVAC 3 09-03-2012 09:26 PM
Condensation on cathedral roof being remodeled benbern125 Roofing and Siding 6 03-02-2011 05:57 PM
Cathedral Porch Roof iufan1978 General Home Improvement Discussion 1 05-27-2009 04:14 PM
How about a cathedral ceiling - Check it Out Andrews Framing and Foundation 4 05-12-2009 12:28 PM
Cathedral ceiling support? xdissent Framing and Foundation 4 10-03-2007 12:36 PM

Newest Threads

LATEST SPONSOR DEALS