Ridge Vents and Power Vents

[DaveTheWave]

My first post here...

When I purchased my current home, the inspector mentioned that you shouldn't run ridge venting and power vents at the same time. I've sense replaced my A/C systems and the A/C guy suggested adding additional venting to the attic. I mention what the inspector said and he thought that was bogus.

Any ideas?

I currently have ridge venting only above the bedroom areas of my ranch style home. The living and garage areas are under a different ridge and there is no ridge venting on that ridge. This is a new roof, replace after Katrina by the original owners. I'd like to add either passive or active venting to the living and garage attic areas. I could add a gable vent to the garage attic.

Any suggestions?

[Fischer]

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You don't say how the garage is connected to the house, but if it shares the roof it would help more than if it didn't. If you have a composition roof, you have a huge thermal storage facility on your roof. A dark comp roof will absorb better than 80% of suns rays. The best thing you could do is provide as much ventilation as possible to keep the higher temperature associated with attics in the summer from heating your living space ceilings.

Insulation will help with the garage, but ventilation will help more, and a powered roof vent or gable vent coupled with eave vents will do much more for your whole house. Most powered vents will come with a thermostat that you can set to activate when the attic space starts to overheat. The powered vents do not work all that well without flow through ventilation, so if your eave or sophitt vents are not adequate provide the side opposite of the powered vent with an gable vent.



I would add to the above to vent both areas, and the more that can be vented the better. I can't, well I can, believe that a new roof wouldn't be vented by a contractor, so you better check on the whole roof system and eaves, because they may have been covered up, and until you can have airflow you will be stymied.

[DaveTheWave]

The garage is attached.
The shingles are lite brown composite.

Can ridge venting be installed after the fact? Can this be done by the homeowner? Of course there are issues with climbing the roof and what not, but can the job be done by the home owner?

What about running ridge and power vents, any issues with that? Obviously we need to have enough soffit/gable vents to feed the ridge/power vents.

[CraigFL]

Ridge venting systems are easily installed-- see the manufacturers recommended way. It's best to install with the new roof but you can istall afterwards too. It involves using your circular saw to cut a slot in the peak of the roof, laying down the vent assembly and then covering it with cut shingles.

[Wgoodrich]

Incomplete venting as you discribe suggests other areas not done right either.

very important;
Do you have any cathedrawl ceilings that are roof / ceiling combination ? I mean do you have any rooms that have a slanted ceiling with the drywall attached to the bottom of your rafters?

The building code required 1 vent for every 250 square feet of attic space.

If you install either ridge vents or attic vents you need soffitt vents equal to the area of roof of soffit vents.

Power vents and ridge vents would fight each other. Power vent would suck easiest flow of air. Power vent would suck high from the ridge vent instead of where it is supposed to suck low from the soffitt vents. This would be wasting your time.

Power vents are not required and venting is adequate if you install as many soffitt vents with open air flow across the top plate of your outside walls from soffit into attic and installing either ridge vent or roof vents. This way you are sucking by the principle heat rises from teh soffit vents as inlets and the roof vents as outlets sucking the heat out of your attic.

MOst often ridge vents are installed where you have roof decking on the top of the rafters and ceiling attached on the bottom of your rafters for a cathedrawl type inside ceiling being sloped. If this exists then air comes in the soffit vents down low but when it travels up the rafter space it hits a dead end with nowhere to floor unless a ridge vent is installed being continuous serving each rafer space to allow air flow between the insulation and the bottom of the roof decking where a minimum per code 1" air space is required.

Good Luck

Wg

[mks4fun]

I had gable vents and the roofer installed vents along the roof line. Bad deal.

I read that you should not have more than a 25 degree temperature differential between outside air and inside attic temp.

I tracked it down to the mixing of two different methods for venting. i.e. you either do one or the other, don't mix.

I had to go inside and block the gable vents and then changed the fixed vents to turbines and then had to put extensions on them to raise above the ridge.

Seems most roofer installed vents are not correct... Hmmmm....

I also read that 'new' information suggests that you have 1 inch ventilation per 100 square foot floor space. ie. 1800 square foot house requires 180 square inches of ventilation.

The screen reduces the 'net' (free) area of the vents so that needs to be taken into consideration. Bottom line is that I only had 1/2 the soffit vent area I needed.

I put a temp probe inside the attic and was amazed at the temperature! Seems that the AC bill can be impacted by (as much as) 40% by the temperature difference of the ceiling being so hot!

Anyway, the only real way to be sure is to install a temp sensor in the attic and monitor it to see if your attic is being cooled efficiently.

The more vents the less the temp. difference between inside the attic and outside the house. The less temp difference the lower your energy bills.

It's quickly becoming cost effective to spend the money making your house energy efficient.

[scuba_dave]

In the same roof you do not want to mix power & ridge/soffit vent. If you have a power vent it will suck air in thru the ridge vent instead of the soffits

But if the roofs are not continous & do not have air flow between them: Then you can have ridge on one & power on the other

You do want venting on every roof possible
A homeowner can do this
BUT, done wrong water will be leaking into your roof
I dormered the back of my Cape & added a ridge vent
Front roof stayed the same, I was able to buy matching grey shingles for the front/ridge. The dormer I used white shingles to reflect the summer sun as much as possible

[wd8dsb]

Numerous folks including this posting state that a power vent fan should not be used if ridge vents are also being used, but I have never been able to find "real data" to support this issue. Therefore last week I installed some instrumentation to record attic temperature in two different locations (one near the peak, and one 2/3 of the way down from the peak) and also installed an outside air temperature sensor. I record the temperature readings from these 3 sensors every minute 24 hours per day. I also compare the attic temperatures versus solar radiation since solar radiation is the largest factor that controls attic temperature.

I first recorded data in which my dual speed power vent fan was in service, and then yesterday I disconnected the power vent fan and blocked it so air could not flow through it. Today I already have data in hand that shows my attic runs cooler with the power vent fan in service, and this contradicts all the information that is floating around that has no supporting data.

It's very possible that I have inadequate air intake in my system because I see some of my baffles are blocked with insulation, and it's also possible that I don't have adequate ridge vents, and I will now work on improving my attic temperature without the power vent in service to see if it's possible to obtain attic temperatures that are lower than or equal to the temperatures I obtain with the power vent fan.

I will also post some data in the near future.

Don

[Wgoodrich]

The factors having people advise not to install both power vents and ridge vents is that the power vent will draw its air from the easiest source entering the attic. The ridge vent is most likely only a few feet from the power vent. The intended intake of air is the soffit vents to suck hot air in the lower section of the attic up to the exhaust being either the ridge vent or the power vent. When you have a power vent and no ridge vent the air intake to feed that power vent is coming from the soffitt vents where it is intended.

When you have both a ridge vent and a power vent most of the air that power vent is sucking through the attic is flowing between the ridge vent and the attic vent.. This power vent when running changes heat from exhausting out the ridge vent to sucking fresh air in through the ridge vent running directly to the power vent leaving the rest of the attic hotter.

We are not saying not to use power vents. We are saying not to use both ridge vents and power vents. What happens is the ridge vent cuts the productivity of sucking air from the low soffitt vents in 1/2 limiting the ability of the power vent to do what it is intended to do. If you want to create true data when you run your power vent block off the ridge vent. Then the power vent is forcing air to come from the soffitts. Then when you read data of power vent off to properly compare gravity without power vent properly install the styrofoam shutes ensuring open air path between attic and soffitt for intake air.

If true value is created the difference between power vent and soffitt vents versus ridge vent and soffitt vents properly installed will still show a cooler attic with the power vent. However there is argument how much advantage the cooler power vented attic would save in heating and cooling versus the cost of running the power vent itself.

Just my thoughts

Wg

[bmarrj]

Remember that the temperature just about the attic floor can be much different than the temperature near the ridge. A good scientific study would involve simultaneous temperature readings at several locations in the attic, i.e., high, low, near gable ends, etc. Just a thought. I am very interested in the results of your study.