Ventilation in a Cape Cod style house?

chris davies · 07-13-2010, 09:48 PM

My ridge vent was merely asthetic for years since roofer did not cut away OSB prior to installing. Now the ridge vent is right, my attic is no cooler. Soffit vents are plentiful and not clogged. Insulation is adequate in 10 y/o home. Black roof with half day worth of sun.

I have heard on podcasts about Cape Cods being a challenge to ventillate since they have three heat chambers (attic and two knee walls). No one can shed more light on how to vent it, nor will anyone return a call to tackle it. Any suggestions? I am in Western IN. Thank you.

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**John Kogel** · 07-13-2010, 10:17 PM

Maybe a couple of turbine vents would help, but as a rule, they shouldn't be combined with ridge or gable vents.

**Trent Tarter** · 07-13-2010, 11:46 PM

Install a power gable vent on a thermostat.

**Michael Thomas** · 07-14-2010, 04:28 AM

Originally Posted by chris davies

I have heard on podcasts about Cape Cods being a challenge to ventillate since they have three heat chambers (attic and two knee walls). No one can shed more light on how to vent it, nor will anyone return a call to tackle it. Any suggestions? I am in Western IN. Thank you.

Take a look here:

www.dom.com/about/conservation/pdf/rooms_over_garages.pdf

You have the same general situation.

David Bell · 07-14-2010, 07:37 AM

Be sure that there is a unobstructed path for air to move from the soffits in the knee wall area to the peak.

Philip · 07-14-2010, 08:19 AM

My experience tells me that you have to vent the knee wall spaces seperately.

David Bell · 07-14-2010, 02:12 PM

Originally Posted by Philip

My experience tells me that you have to vent the knee wall spaces seperately.

Not true. If properly done both knee walls can be incorporated with a ridge vent to provide proper ventilation.

Bob Spermo · 07-14-2010, 02:27 PM

Chris,

Proper venting is not a guarantee of less heat. The true reason for venting is to let the moisture out of your house. Much of the heat in your attic is from radiant heat of the sun which comes through the roof and hits objects in the roof which then emit heat. The radiant heat does not heat the air in between the roof and objects it strikes. Attic fans when used in conjuntion with air conditioniong is a bad idea as the fan will also pull out conditioned air.

Your dark roof is partly responsible for the heat in the attic. If you have knee walls ensure they are insulated and an air barrier on the attic side is in place.

chris davies · 07-14-2010, 04:12 PM

Originally Posted by James Risley

Are All of the spaces open between the rafters and above the top plate of the knee wall? Now that the osb has been cut back Leaving 1.5 to 2in open on both sides of ridge...What is the type ridge cap over the shingles and the opening in that?

James-the majority of the spaces are open-at least the ones with foam baffles-I cehcked each one. The ridge vent is Tamko-roll version they offer. Manufacturer says 18 sq inches of NFA per linear foot. The ridge vent is about 34' long and straight. Thanks.

Ted Menelly · 07-14-2010, 06:00 PM

Being from the land of Capes and such and living in 4 different states and experiencing every type of attic I will say.......... Cape, 2 story home of any kind that incorporates knee walls with ceilings that are above the knee walls where the knee wall and the slope and or flat ceiling over a sleeping area and such meet definitely needs its own lower roof venting.

The homes I inspect here in Texas with lower (over the first floor) and upper (over the second floor) where the lower attic vents thru narrow slots that are mostlhy filled with insul (baffles or not) are always hotter than the upper attics. The ones I have inspected where the lower attics had there own vent it was always cooler and closer to the temp of the upper attic. Before we get into reflective barrier and all that this is with or with out radiant barrier. Where you are relying on a lower attic surrounded by interior walls to the living areas where all but a few slots come from the lower attic to the upper attic the upper attic is always hotter as well.

Restrict the natural upward draft and the upper and lower attics are always hooter.

My opinion and well thought out and logged in my reports is that any time there is a lower attic or knee wall space, what ever you wish to call it, and an upper attic the temperatures are always higher. Open attics that have no knee wall area and the attic has its average eve vents and roof top or ridge vents are always cooler.

The idea that air flow does not keep attic temp down because it is the radiant heat that is heating everything up is extremely flawed logic. Radiant heat has an extreme amount to do with attic heat in itself but can be combated with radiant barriers proper eve and roof top vents and insulation as well as lower attic ventilation combined with upper attic ventilation.....lets not leave out a tighter home to attic envelope.

Just a humble opinion.