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 Attic Venting In Your Home

 

         The importance of venting your attic cannot be overlooked. In cold climates improper venting can lead to moisture buildup which causes mold to grow or wood rot in extreme cases. 
During the summer, stagnant, superheated attic air can dry out your trusses, increase your energy costs due to the demand on the air conditioning unit, and make your house uncomfortable.

         How did we become experts on attic venting? Our patented reflective insulation products reject the infrared heat emitted by hot roofs which in turn builds up in the attic and makes it even hotter. Getting rid of this waste heat then forced us to look at not only how homes are vented, but how best to address this challenge. Turns out a powerful, efficient fan made on the other side of the planet was the answer.

         Using a tracer gas and smoke generators we have documented all types of attic venting, the appropriate sizes that work in hot climates and have posted our findings below. This is not a scientific study but observations made over the study of hundreds of homes in all types of climates.
 

 

Our  proven field results and recommendations (if using a radiant barrier material and passive vents):

 

        Ridge venting, placed at the peak of the roof while attractive and easy to install does not allow sufficient air to exhaust as this, defies gravity, physics and logic.  Hot air rises, this is a law of thermodynamics yet a ridge vent consists of an inverted "V". This creates a thermal check valve which does not allow the hot air to escape properly during the summer and once covered with 2" of snow are rendered useless (check ice dam page for more info). Puffing tracer smoke inside the attic at 2pm just under the opening shows the air in the attic to be stagnant.  We have found through experience that homes with ridge venting are historically the hottest, and correspondence from our customers who have read this site reinforce this over and over. Ridge vents are very effective in areas where this is a steady breeze.

        We get letters and emails like this one every week from home owners all over the country:
 

         "Last fall I had a new roof installed.  My old roof was shake.  My new roof is a TAMKO American Heritage series laminated fiberglass asphalt roof.  My old roof had approximately 12 Pot vents.  With the shake shingles the attic was hot in the summer, but not 135 degrees like it is now on 100 degree days.  Most of my attic is accessible from the inside.  My new roof has ridge vents.  The old vents were disposed of!  My roofer reassured me several times that the new ridge vents would perform better than the pot vents because they had more square footage of opening for heat to dissipate through!  Maybe so, but my attic is hotter that it ever was.  Asphalt shingles are hotter that shakes.  My contractor dismissed this as an issue because of the additional square footage of venting available from the ridge vents. Any help would be greatly appreciated."

Thanks Doug M

What works, what doesn't:   CONTINUOUS SOFFIT VENTING
                                          
    Continuous soffit venting is typically a 2" or 3" slot cut into the soffit into which is placed on a manufactured venting system made from plastic or metal.   The plastic is typically molded with thousands of small holes (1/32" in diameter) to keep bugs out.  Great idea, easy to install but falls short of offering sufficient net free area to allow enough air to move.

      Another popular type is an aluminum strip with small louvers pressed into them. 
BENEFITS:  Easy to install and attractive.
PROBLEMS: The holes are too small (see photo below), to pass sufficient air preventing the attic from aspirating naturally.  Most often these are covered with insulation or partially plugged over time with dust/pollen/spider webs .  
   See our formula belo
w for how many to add per square foot of attic area.
 
         This vinyl soffit covering is very popular as it completely eliminates the need for painting and/or maintenance on your home.  Great idea! Unfortunately, it starves the attic for air and costs you higher utility bills and comfort.
SOLUTION:  Cut in larger openings (8" x 16"), in the soffit and cover with a screened, louvered grill available on our online energy store! Click here.

WHIRLYBIRDS
         The correct term is "air motor", also called roof turbines. It is thought that the spinning turbine creates some sort of suction which induces air movement.  This has not been proven.  They are often used in large commercial applications for venting smoke and fumes from a manufacturing plant.  The wind spins the turbine which is connected by a shaft to a fan blade below which spins and pulls the air from the building. Turbines used in the residential market do not have these fans and therefore can exhaust only what the roof opening dictates.   Mathematically, Pi times the radius squared equals the area, (A=3.14 x r x r)  A 10" unit offers 78.5" of free net area, a 12" unit offers 113" square inches.   Venting an attic using natural aspiration is based on net free area.   Use this to calculate the size of intake vents (soffit) and exhaust vents (at the top of the roof).  We recommend Aura Vents for natural venting.  Whirlybirds are better than most vents but in my opinion, make a house look like an industrial building.  
Despite the small area of these vents, the vertical stack of this vent allows for the fastest flow of air from a hot attic.  For best performance, these vents should be placed as close to the peak of the roof as possible.

          O'Hagen Vents (typically for tile roofs): Somehow meet code, but attics with these vents that we smoke tested, showed little to no air movement.

"Pop" Vents:  Better than nothing, but the openings are not big enough for air to efficiently move out of them.

Ridge Vents:  Totally useless unless you live where the wind is consistently blowing.  If there is no wind, a ridge vent does not allow the hottest air to  escape.

          Since our reflective attic insulation products increase attic temperature by rejection instead of absorbing infrared heat, attic venting plays an important part of our system.  Getting rid of this waste heat is essential to reduce energy consumption and increase interior comfort.  If your home is like most and severely under vented, the most effective and cost effective way to increase venting is using our imported German attic fan.  Install it in the hottest side of the house (South or West), so it will draw the coolest air possible (East or North side), into the attic. 

VENTING IMAGES


 





 
 
If you see these balls of sap boiled out of your rafters, your attic has inadequate venting. This makes your home hot, dries out your structural framing and is an indication your may be spending too much  to maintain interior comfort.


 
 
 
 
 
 
 
 
 
 To place an order click here 
 
 
 
 
 
We now recommend the Aura Vent as it allows for better air flow in either wind or no wind conditions and is specifically designed for use with our
German made powered attic fans.


Ridge Venting vs. Dormer Vents

        Having installed our reflective radiant barrier in homes for over 25 years, we have found that the rejected heat, (previously absorbed by the insulation and passed on later), winds up in the attic making the attic hotter; much hotter in fact than an attic without a radiant barrier.   This means the attic must be properly vented by natural aspiration (adequate soffit vents and properly sized and placed exhaust vents).  If it is not, then a homeowner should install a quality attic fan (seen below) to exhaust the excess heat.  A properly vented attic,  naturally or with a powered attic fan, should be only a few degrees above the outside ambient temperature regardless of roof color or composition.

       Ridge vents are very attractive, easy to install and makes all the sense in the world...but as we stated above, they just don't work.  Everyone thinks it best to put an attic exhaust vent at the peak where the attic air is the hottest.  Sounds logical except for one basic fact:  Hot air rises, it doesn't go down.  A ridge vent design dictates hot air must fight gravity and travel down from the peak of the roof in order to escape.  Even if it only has to travel a short distance, it will not happen.  This is unrealistic and so is expecting this type of vent to be effective.  The only "driving force" that makes hot air leave an attic is the differential density of the 140 degree  lighter attic air compared to the more dense ambient outside air.   Prove it for yourself:  buy a 2000 CF smoke canister, place it in a coffee can in the center of the attic and light it.  Then go outside and wait for the smoke to come out of the ridge vent.   Better bring a lunch, plenty of water and a good book....you will be there awhile.

        The roof you see above was built using a continuous ridge vent.  When the hot weather came in April to this Phoenix home, the attic was like an oven despite the fact the intake venting (soffits), were doubled to insure good flow.  We cut the first hole in this roof about noon to install the dormer vents you see above and the air came out so fast if you kicked the sawdust into the hole it would hit you in the face!  Proof that the hot, stagnant attic air is not being vented properly and being trapped by the ridge vent design.  Furthermore, the steeper the roof pitch, (like homes in Texas or the older Cape Cod homes in the Midwest),  the less the ridge vent will work.  This observation is based on fact, physics and common sense.  Hot air does not fight gravity.  Further, in cold climates, it only takes a few inches of snow to render ridge vents completely useless....when you need them the most to keep the roof from getting warm, melting the snow and creating ice dams.  Inadequate venting is a major contributor to costly ice dams.

UPDATE ON THE ABOVE HOUSE: 5/11

         As you just read, we installed the ridge vent on this home in 1990 and found it to be absolutely worthless.  Puffing smoke up under the vent in a hot, stifling attic showed NO movement of air up through the vent.  So we went back and added the six dormer vents.  The attic was still too hot so we blocked off all the dormer vents, installed a 16" German fan in the center, blocked off the oversized gable vents and now drawing cool air in through the soffits.  Over 20 years of testing and we finally get it right?  I once thought that passive vents would be suffice when using a radiant barrier which makes attics hotter.  On this home the passive venting was many times what the minimum USB code required and was still not enough.  With summer soon upon us, we will be doing more attic temperature testing but one thing is certain:  after having experimented with every type of vent combination available it appears the best way to remove hot, stagnant air is by using  a reliable powered ventilator. 


Dormer vents installed on the back side of a home in Dallas where the hottest attic air temperature was ever recorded by our NRG Auditor.  Two reasons:
1) The underside of the roof decking was sprayed with silver radiant barrier paint thus lowering the emissivity and increasing the convective currents in the attic space.
2) Ridge vents trapped the hot air inside. The dormers shown here dropped the attic temp by 42 degrees. Solution: TCM6 over the insulation and increased venting.

 

 

SOFFIT VENTING
       Many homes do have soffit vents but are blocked by improperly installed insulation. Proper attic ventilation is necessary and the products listed below will help.


 

 

This is what you may see when you look at your venting around the perimeter of your home
"My attic has hundreds of holes around the perimeter, we don't need any more venting"


 


 

 

 

 




Remove the blocking and you can see the fiberglass blocking the vent holes.  Very common problem found during our NRG Audit inspections.

 

 

 

 

 

 

 

 

        This is what is recommended on the outside of the home if you  do not have a soffit.  If you have a soffit, add 8"x12" screened  vents every eight feet of soffit.   We offer screened soffit vents on our online store.

This procedure gives your attic the air it needs to properly vent.  In cold climates this equates to adequate moisture removal and the elimination of the associated problems, like mold growth and wood rot.  In hot climates, the super heated attic air can flow out the upper vent (if you have them), and draw cooler air in around the house.  This is what your architect and builder expected.  However, in most homes the insulation contractor may have plugged up some or all of your soffit vents.  Our home energy auditors have found most homes have this problem.  Check yours or click here to schedule an energy audit for your home (if you live in the Phoenix area).  If you have questions about your existing attic vents, take a few digital pictures and send them to us for evaluation.  Take advantage of our knowledge and free advice!  Please, no more than six pictures.  Take one of each side of the home noting to make photos of the soffits vents (if any), gable vents (if any), and one or two shots of the attic.

 

 

 

 

 

Step by Step Soffit Venting

 
 
 
 
        The soffits on this home were completely blocked making the attic like an oven increasing energy costs and making
the upstairs unbearable during the summer.
This is very common in homes of all ages, even brand new homes across the country. 

 

 

 

 
 
 
 



 
 
      Cutting holes in the plywood soffit to allow intake air to cool the attic.  The first thing you need to do before cutting
any holes is snapping a chalk line so the vent holes are cut straight
.
 

 
 
 
 
 






       Once you get the holes cut, simply cover them with 8"x16" louvered intake grills available at our online store. 




 
 
 

 
 
 





        The completed installation. Efficient, inexpensive and lasts forever.   Paint the grills after the installation to match
the soffits and they blend right in.






 


 
 
 
         Homes we have upgraded attic vents on have significantly reduced attic temperatures during the summer.  This means lower A/C bills (and stress on the
equipment), and more comfort!  In cold climates, these vents allow for the egress of accumulated moisture which is the source of many problems.
  
 

       This is an 18" Aura vent installed on a pitched roof on the island of Oahu Hawaii.  This is the vent we use when
installing our 
solar powered attic fans in tropical applications.
 
 

 

 

 

 

 

 

 

 

 

         Dormer vents installed correctly on the back side of an apartment building.  The lower vents on the roof are intake ventsand the upper vents are exhaust vents. 
If correctly sized to the volume of the attic this type of venting can adequately vent the hot air out during the summer and moisture during the winter.  These are not
seen from the front of the building and therefore do not detract  aesthetically
.

POWER VENTING

Photos of what not to do:

 

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 This shows a typical home store attic fan installed on a gable vent inside the attic.  Although the mounting looks secure, the application is incorrect
since the space around the fan is not blocked off.  Air will always take the path of lease resistance. The fan will draw air from the closest point, in
this case, from vent openings around the side of the fan. This means very little air will be exhausted from the attic!  
      The open area around the fan shroud (the round ring), needs to be blocked off with cardboard or wood to make
this type of installation effective.  This is the recommended installation by Home Depot per their advertising.

 

 

       Here is a solar gable fan just wearing itself out and doing nothing to vent the
attic.  99% of the air the fan is blowing out is coming in the vent next to it.

 

       "Attic fan?  Don't need one, I have one already and I installed it myself"
Here's a DIY job where the fan is mounted in the center of the
attic just using power.  Nowhere near a vent to the outside.

 

Virtually every attic fan we see installed is done like this.   

      Great idea, improper installation.  Without blocking the
area around the blower, most of the air is going to be
coming in around it. 

       Summary: Think of the fan installed as an air pump.  The fan will exhaust air from the rear of the fan and push it through the vent.  The key is understanding where the intake air is being provided.  In all of the photos above, most of the intake air is being drawn in around the fan since this is the path of least resistance.  To make this work correctly, all the area around the fan needs to be blocked off as well as roof vents or soffit vents that are too close to the fan.  When designing a venting system that employs a powered fan, the goal is to evacuate the hot air from the attic and bring in the coolest air possible.  This dictates mounting the fan on the hottest part of the home (the South or West side), so the coolest air possible (the North or the East side), will be drawn into the attic.

Power Fans:

      STAY AWAY FROM UNDERPOWERED SOLAR ATTIC FANS, THEY JUST DON'T MOVE ENOUGH VOLUME OF AIR.  Great idea, not enough power and does not match the needs of the task.  Attic venting is most needed between 1pm and 7pm and the solar fan reaches max power at noon.

 

      We import a vibration free, powerful, reliable powered attic fan manufactured in Germany.  This attic fan is unlike any other available.  This fan features an external rotor to which the fan blades are welded.  This unique design reduces blade flex and vibration, and eliminates one of the shaft bearings.  The bearings are sealed and never need maintenance.  We include an adjustable thermostat and an optional mounting box with this system. Install it, set the thermostat and forget about it.  It costs 2 cents per hour at  .10/KWH to operate. This equates to approximately $6/month!

14" 1800 CFM fan shown here

To visit our online store to order  click here

Warning: In homes that have gas appliances such as water heaters or furnaces in the attic, great care must be taken to insure adequate intake venting (gables/soffits), is provided so as to not create a negative pressure that will draw combustion gasses down the chimney of gas appliances.   Installing an attic fan in this application has the potential for fire or filling your attic with carbon dioxide.  Just make certain there is sufficient intake openings to circumvent this potential hazard.      

Construction Features of the 14" model (other sizes below)

  

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