# Moisture dripping from vented soffit at high end of single slope roof



## gvanginkel (Feb 3, 2015)

Hi All - great forum. 

This is my first post - next post will have the details and links as I cannot post links in my first post. Please read next post.


Thanks

Gerard


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## gvanginkel (Feb 3, 2015)

*Venting single slope roof with pics*

Hi all - great forum for sure!

I recently built a new house in Calgary AB Canada (cold weather prone) and I used a series of single slope roofs, flat roof and shed roofs that meet walls. I have noticed that I have moisture being expelled from the highest point of the single slope roof where I elected to use vented soffit as exhaust. The water is dripping from the soffit holes and also running down the soffit and dripping lower down the slope during cold weather (-15'c).

Let me explain: The roof has solid soffit at the lowest point (fire code) and vented soffit at the highest point. For intake, I have 8x surface mounted vents installed: 4x of low box vents and 4x of these proventillator vents (the tall vents are for instances where deep snow covers the lower profile box vents). They are in a row at the lowest point of the roof. For exhaust, I have a 3' overhanging soffit at the highest point that is perforated continuously. The trusses are open web (scissor style). There is r40 batt insulation in the cathedral space and 10-12" of open air space above the insulation for airflow. There is 40mil vapor barrier and drywall on all cathedral ceilings of course. 

I believe the issue is that the moist air in attic is traveling to the highest point of the roof as per chimney effect (and design) however is condensing against the cold aluminum soffit and hence water is forming on the inside of the vented soffit at the exhaust point and traveling back down the slope via gravity. 

What is the correct way to vent this roof design? Should I add surface box vents at the high point on the sheathing so that the warm wet air can escape up and out instead of having to go down against the soffit to get out of the cathedral attic? Do I leave the vented soffit in place at the high point or close it off with solid soffit so as to avoid short circuting of the new roof box vents?



This is the first winter with this house and roof and so I want to solve this asap so it doesn't become a problem in the future.

Thank you so much.


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## gvanginkel (Feb 3, 2015)

Hi all - great forum for sure!

I recently built a new house in Calgary AB Canada (cold weather prone) and I used a series of single slope roofs, flat roof and shed roofs that meet walls. I have noticed that I have moisture being expelled from the highest point of the single slope roof where I elected to use vented soffit as exhaust. The water is dripping from the soffit holes and also running down the soffit and dripping lower down the slope during cold weather (-15'c).

Let me explain: The roof has solid soffit at the lowest point (fire code) and vented soffit at the highest point. For intake, I have 8x surface mounted vents installed: 4x of these







and 4x of these







(the tall vents are for instances where deep snow covers the lower profile box vents). They are in a row at the lowest point of the roof. For exhaust, I have a 3' overhanging soffit at the highest point that is perforated continuously. The trusses are open web (scissor style). There is r40 batt insulation in the cathedral space and 10-12" of open air space above the insulation for airflow. There is 40mil vapor barrier and drywall on all cathedral ceilings of course. For reference the roof I am referring to is similar to the high roof in this image :









I believe the issue is that the moist air in attic is traveling to the highest point of the roof as per chimney effect (and design) however is condensing against the cold aluminum soffit and hence water is forming on the inside of the vented soffit at the exhaust point and traveling back down the slope via gravity. 

What is the correct way to vent this roof design? Should I add surface box vents at the high point on the sheathing so that the warm wet air can escape up and out instead of having to go down against the soffit to get out of the cathedral attic? Do I leave the vented soffit in place at the high point or close it off with solid soffit so as to avoid short circuting of the new roof box vents?

Is this the correct solution to my design:









This is the first winter with this house and roof and so I want to solve this asap so it doesn't become a problem in the future.

Thank you so much.


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## rossfingal (Mar 20, 2011)

Hi!
Welcome to "DIY"!

Pictures would help!

rossi


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## gvanginkel (Feb 3, 2015)

*Repost with Pictures*

Here are pictures of the house drawings.


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## Windows on Wash (Aug 30, 2011)

Based on that design, I think your original assessment is probably spot on.

It's a bit of an odd designed to use what is typically an intake vent as the exhaust vent. You really want to allow that warm air the shortest direct pathway to leave the assembly. This would've been a scenario where some sort of strip vent or other type vent application at the actual peak of the roof would've been preferred.


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## gvanginkel (Feb 3, 2015)

Thanks for the vote of confidence on my assessment. So you are suggestin a strip vent be installed as the solution? Not box vents installed just before the upper vented soffit?

I believe I have solved the source as mentioned but I need advice on the fix. Do I leave the vented soffit up there or close it off?

Thanks


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## 1985gt (Jan 8, 2011)

Close the soffit up. 

What kind of roofing material is on that slope?


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## gvanginkel (Feb 3, 2015)

The roof is asphalt shingles. Why? I think I will add 4 box vents at the peak and cover the soffit with poly and tuck tape and see if it solves it. If it does, I will replace the soffit with solid

Agree?


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## 1985gt (Jan 8, 2011)

gvanginkel said:


> The roof is asphalt shingles. Why? I think I will add 4 box vents at the peak and cover the soffit with poly and tuck tape and see if it solves it. If it does, I will replace the soffit with solid
> 
> Agree?


I'm wondering if a ridge vent could be used. They work better then the box style vents. 

Definitely cover the soffit vents up when you add another vent method. The hot moist air can not escape through the soffit vents well.


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## gvanginkel (Feb 3, 2015)

A ridge vent ?? I'm not sure how that might work on a single slope. Got a link to a prouduct by chance?


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## Windows on Wash (Aug 30, 2011)

I agree with 1985 GT. There are Ridgevent applications that will allow you to run them one sided.

DCI makes a strip that they can be adapted and I also think that air vent make something similar.


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## gvanginkel (Feb 3, 2015)

*How much ridge venting? Balanced or unbalanced?*

Thanks for all the advice guys... I will add ridge venting and block off the soffit venting. My question is should I have equal or less exhaust venting than intake venting?


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## mgp roofing (Aug 15, 2011)

On this style roof, I just use normal ridge vent cut in half at the highest point. Always been effective provided there's clear air flow from low to high points of the roof.


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## 1985gt (Jan 8, 2011)

I figured there was a product out there or that a ridge vent could be modified to work like MGP suggested. I'm not up to date on all these new fangled products you shinglers have now! :laughing:


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## Windows on Wash (Aug 30, 2011)

http://airvent.com/homeowner/products/ridgeVents-specialtyFilter.shtml

http://dciproducts.com/html/smartridge_I.htm


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