Venting The Roof - Roofing/Siding - DIY Home Improvement | DIYChatroom


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Roofing/Siding

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 10-11-2010, 01:12 AM   #1
Member
 
Join Date: Dec 2009
Posts: 154
Rewards Points: 150
Default

Venting the roof


Background: My house was built in 1937, Block walls, all redwood roof, no tar paper, _ONE_ sofit vent, no other venting.
I've tore down the complete roof and ceiling in the back 1/2 of the house, the only damaged wood was a few ceiling supports (2x4 redwood) near the sofit vent (within 6 feet)
The rest of the redwood was in very good condition.
I added a vent (wirrly bird spinner type) near the front of the house and a whole house fan.

I live in Sacramento, CA and all the south exposure is covered with large trees (most of the house never sees the sun.

Questions:
How much venting do I need?
Is there something that I can/should do to keep out termites (note: there is no wood below the 8' ceiling, except new door side supports that I'll be adding and those will be redwood with steel risers)

Advertisement

KarlJay is offline   Reply With Quote
Old 10-11-2010, 01:19 AM   #2
Member
 
jlhaslip's Avatar
 
Join Date: Dec 2009
Location: Canadian Rockies
Posts: 1,280
Rewards Points: 500
Default

Venting the roof


Not sure about your code, but one square foot of venting per 300 sq ft of floor space works here.
A third of the square ft of vent needs to be in the top third of the roof or higher (ridge vent).

Advertisement

__________________
Quote:
Originally Posted by Bud Cline View Post
Go ahead and apply for a variance, those guys at City Hall can use a good laugh.
jlhaslip is offline   Reply With Quote
Old 10-12-2010, 12:27 PM   #3
I ask the impossible!
 
Join Date: Aug 2010
Location: Royal Oak, Michigan
Posts: 1,074
Rewards Points: 508
Blog Entries: 7
Default

Venting the roof


I'm no expert, but if the house was built in 1937 and has redwood shakes, it's probably loose construction and breathes pretty well on its own.

This sounds to me like it might be a situation that more of the big picture needs to be understood to say what is needed... You say you've torn off interior ceiling, what's the plan? And is there an issue that is causing you to suspect you don't have adequate ventilation?

Consider the house I'm working on now. Originally constructed in 1917 on a pier and beam foundation, then later an addition was added to extend the house 10 feet towards the rear of the lot, then a 10x10 mud room added on a slab. Later still, the house was insulated.

This house held up well in spite of construction methods that aren't found in the joist or rafter span tables used today. The loose construction used 90+ years ago meant it had airflow to remove moisture, and heating was cheap enough that you just made up with it by heating the world along with your house.

Then the insulation took away that free flow of air, trapped moisture and the wood suffered for it because the necessary increases in ventilation didn't happen at the same time.

The point I'm trying to make is that I think it's important to understand the underlying reasons why ventilation requirements are what they are, what kind of construction they're intended to go with, and with that knowledge it becomes possible to analyze whether your situation fits or not.

I found this link that discusses wood roofs, particularly cedar but I'd imagine the principles are similar:
http://www.oldhouseweb.com/how-to-ad...od-roofs.shtml
WillK is online now   Reply With Quote
Old 10-12-2010, 01:18 PM   #4
Member
 
Join Date: Dec 2009
Posts: 154
Rewards Points: 150
Default

Venting the roof


Actually the redwood is in the form of boards that cover the roof, then the shingles go on top of that. I have loose fill insulation, but don't know when that was put in.
Just based on what I'm learning so far... my roof was VERY under vented. with the house being about 1100 sq ft, I'd need about 4 sq ft of vents. probably a combo of sofit/ridge.

Last edited by KarlJay; 10-13-2010 at 01:20 AM.
KarlJay is offline   Reply With Quote
Old 10-13-2010, 12:06 AM   #5
Registered User
 
Join Date: Mar 2009
Posts: 9,993
Rewards Points: 2,052
Default

Venting the roof


Here's your CA Code:
Vent each enclosed attic & each enclosed rafter bay ____________________1203.2*
(UBC left issue of enclosed rafter bays up to local BO)
1/8in to 1/4in mesh screen over openings___________________________ 1203.2.1*
(UBC did not allow 1/8in mesh)
Min net opening area 1/150th of vented area OR _______________________ 1203.2
1/300th if 50-80% in upper portion _________________________________ 1203.2X

From: http://docs.google.com/viewer?a=v&q=...h1W5lElSFXE4_w


Gary
__________________
If any ads are present in my answer above, I do not condone/support/use the product or services listed, they are there against my permission.

Last edited by Gary in WA; 10-15-2010 at 12:39 AM.
Gary in WA is offline   Reply With Quote
Old 10-13-2010, 01:16 AM   #6
Member
 
Join Date: Dec 2009
Posts: 154
Rewards Points: 150
Default

Venting the roof


I'm not sure I understand what that means, code wants me to have a vent on each enclosed rafter bay?
So what is an 'enclosed rafter bay' sounds like everywhere you have an enclosed section of roofing, you need a vent.
I wonder if a ridge vent and 1 sofit vent on each wall would be correct.
KarlJay is offline   Reply With Quote
Old 10-13-2010, 09:43 AM   #7
I ask the impossible!
 
Join Date: Aug 2010
Location: Royal Oak, Michigan
Posts: 1,074
Rewards Points: 508
Blog Entries: 7
Default

Venting the roof


Well, whatever the case, too much is generally better than not enough. Unless it's a hip roof without gables, you can always add exhaust ventilation with gable vents too without disturbing the roof - and powered gable vents may be an option as well. Soffit vents would be good for providing intake, you want intake at the bottom and exhaust at the top, and a balance of having more intake is better than more exhaust. What you don't want is the ventilation trying to pull air from inside the house, this can defeat gas appliance ventilation in the worst case.
WillK is online now   Reply With Quote
Old 10-13-2010, 07:16 PM   #8
Registered User
 
Join Date: Mar 2009
Posts: 9,993
Rewards Points: 2,052
Default

Venting the roof


Enclosed attic is different attics that are separate from each other. Enclosed rafter bay is a cathedral ceiling.Figure you NFVA here: http://www.airvent.com/homeowner/pro...it-specs.shtml

http://www.buildingscience.com/docum...on?full_view=1
While you have the attic open, seal the air leaks from below: http://www.rd.com/how-to-seal-attic-...icle18158.html

Gary
__________________
If any ads are present in my answer above, I do not condone/support/use the product or services listed, they are there against my permission.
Gary in WA is offline   Reply With Quote
Old 10-13-2010, 11:10 PM   #9
Member
 
Grumpy's Avatar
 
Join Date: Dec 2003
Location: Chicago
Posts: 588
Rewards Points: 500
Send a message via AIM to Grumpy Send a message via MSN to Grumpy Send a message via Yahoo to Grumpy
Default

Venting the roof


Quote:
Originally Posted by jlhaslip View Post
Not sure about your code, but one square foot of venting per 300 sq ft of floor space works here.
A third of the square ft of vent needs to be in the top third of the roof or higher (ridge vent).
Actually to the best of my knowledge the code is 150 sq ft, but you can go 300 sq ft if you are splitting it equally between intake and exhaust. This 150 BTW is also a requirement of several shingle manufacturers.


If each rafter bay is seperated from the rest, then each rafter bay becomes it's own ventilation zone. You can bore holes at the center of each rafter to create cross venting between rafter bays. Please do not notch rafters as this will weaken them. Then holes must be placed center and no more than 1" diamater preferred. A ridge vent is ideal for this type of design, when a ridge vent is adequate exhaust. Ridge vent doesn't work on every building.
__________________
-Grumpy
Chicago Roofing Chicago Gutters

Sometimes the savings that comes from doing it yourself can be blown away with one mistake.

The information found in this post is not to be considered legal advice. All information should be considered relative, not specific. Never attempt any repairs you are not comfortable with. Always maintain safety! The author of this post takes no responsibility for any losses that occur. Use at your own risk.

Last edited by Grumpy; 10-13-2010 at 11:12 PM.
Grumpy is offline   Reply With Quote
Old 10-14-2010, 12:42 AM   #10
Member
 
Join Date: Aug 2010
Location: metro
Posts: 1,310
Rewards Points: 852
Default

Venting the roof


if your roof is sealed with spray foam though, then no ventilation is needed
federer is offline   Reply With Quote
Old 10-14-2010, 10:15 AM   #11
Member
 
Grumpy's Avatar
 
Join Date: Dec 2003
Location: Chicago
Posts: 588
Rewards Points: 500
Send a message via AIM to Grumpy Send a message via MSN to Grumpy Send a message via Yahoo to Grumpy
Default

Venting the roof


Quote:
Originally Posted by federer View Post
if your roof is sealed with spray foam though, then no ventilation is needed

Yes but with some shingles if there is no ventilation, as in the case with spray foam appliled to the bottom of the roof sheathing, your 30 year warranty will be reduced to 15.
__________________
-Grumpy
Chicago Roofing Chicago Gutters

Sometimes the savings that comes from doing it yourself can be blown away with one mistake.

The information found in this post is not to be considered legal advice. All information should be considered relative, not specific. Never attempt any repairs you are not comfortable with. Always maintain safety! The author of this post takes no responsibility for any losses that occur. Use at your own risk.
Grumpy is offline   Reply With Quote
Old 10-14-2010, 12:04 PM   #12
Newbie
 
Join Date: May 2010
Location: Langley, BC Canada
Posts: 16
Rewards Points: 10
Default

Venting the roof


Quote:
Originally Posted by jlhaslip View Post
Not sure about your code, but one square foot of venting per 300 sq ft of floor space works here.
A third of the square ft of vent needs to be in the top third of the roof or higher (ridge vent).
This is what I heard too, of course each Province/State could have its own rules.

Our house is about 2000 sq. feet, but we just have two whirlybirds. So we should have 6 or 7 vents. It gets incredibly hot in the summer, but we use portable a/c units in our bedroom. I've contacted several roofing companies but nobody seems interested in my "little" project to add vents.

One guy came out to look, but of course he came at the wrong time when nobody was home. He was supposed to quote me on either a ridge vent or more whirlybirds, I haven't heard anything yet. Must be nice to have so much work you can turn people down or ignore them.
Scott Stevens is offline   Reply With Quote
Old 10-14-2010, 02:29 PM   #13
Member
 
jlhaslip's Avatar
 
Join Date: Dec 2009
Location: Canadian Rockies
Posts: 1,280
Rewards Points: 500
Default

Venting the roof


Quote:
Originally Posted by Scott Stevens View Post
This is what I heard too, of course each Province/State could have its own rules.
We share the same code. I live in Golden, BC.
Grumpy is absolutely correct. The 150th rule applies unless the ventilation is available both top and bottom.
Each Whirly Bird vent has a stated rating of how many square feet/inches it supplies for the calculation of venting space. See if you can find the make/model and source out that information.
Also, can you see in your attic if the bottom of the rafter bays are blocked off? Some home owners actually stuff insulation in the vents to stop air leaks, which defeats the purpose of the venting space.

I was in Langley/Abbotsford/Mission last weekend. You should have called...
__________________
Quote:
Originally Posted by Bud Cline View Post
Go ahead and apply for a variance, those guys at City Hall can use a good laugh.

Last edited by jlhaslip; 10-14-2010 at 02:37 PM.
jlhaslip is offline   Reply With Quote
Old 10-14-2010, 10:40 PM   #14
Member
 
Join Date: Dec 2009
Posts: 154
Rewards Points: 150
Default

Venting the roof


Canada gets hot ????!!!! I wooda lost money on that...
The insulation that I have doesn't block the ends, in fact it was so compressed it didn't have but about 1" towards the edges. Overall my house has REALLY poor insulation. I'm looking forward to see what a 'real' house feels like this winter.
Two houses down just had a $4,500 roof re-do and he's now got at least two whirlybirds, I have the one I added and I think I'll be getting 2 or 3 more. I got mine because of the whole house fan and nowhere to push the air.
KarlJay is offline   Reply With Quote
Old 10-14-2010, 11:25 PM   #15
Member
 
Join Date: Apr 2007
Posts: 406
Rewards Points: 250
Default

Venting the roof


Quote:
Originally Posted by jlhaslip View Post
We share the same code. I live in Golden, BC.
Grumpy is absolutely correct. The 150th rule applies unless the ventilation is available both top and bottom.
Each Whirly Bird vent has a stated rating of how many square feet/inches it supplies for the calculation of venting space. See if you can find the make/model and source out that information.
Also, can you see in your attic if the bottom of the rafter bays are blocked off? Some home owners actually stuff insulation in the vents to stop air leaks, which defeats the purpose of the venting space.

I was in Langley/Abbotsford/Mission last weekend. You should have called...
Right on some more local Bcers.I live in Chilliwack but do most of my work in Abby,Mission,Langley,etc

Advertisement

johnk is offline   Reply With Quote
Reply


Thread Tools
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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
venting my roof properly MLMIB Roofing/Siding 2 08-12-2010 08:14 AM
Roof Venting??? JoAnn Roofing/Siding 2 03-17-2010 10:42 AM
Proper venting of new roof on attached garage jlatulippe Roofing/Siding 1 11-26-2009 04:24 PM
The moving Ice Dams after using a roof rake ?? Canufixit Roofing/Siding 9 02-05-2009 08:33 PM
Roof Venting Issue, crawlspace supton Roofing/Siding 1 11-12-2008 07:44 AM




Top of Page | View New Posts