Attic Ventilation Project


Well, my attic needs some ventilation. In fact, I don't think I have any substantial ventilation in my attic at all. The house had gable vents at one time, but when the previous owners installed vinyl siding, they completely removed the gable vents and left me with an attic with NO ventilation!

I decided to figure out what would be the best ventilation to install and do it. Apparently, not having any ventilation in the attic can be a very bad thing. It can warp boards in the roof (which it already has), cause your roof to age very quickly, and allow mold and fungus growth.

But, being an engineer, I needed to see a difference between what I have now and what I get after adding ventilation to consider the project a success. To that end, I constructed a house temperature recording system.

Attic Ventilation and my plan of action

By far, the best site I have found explaining the pros and cons of all sorts of attic ventilation is this one. It is a great site for someone like me who is investigating their options.

Another thing I noticed while running the cable in the attic is that my ductwork is in horrible shape. The ducts are splitting and cold air is spewing into the attic all over the place. Also, the ducts are plagued with tape trying to patch up holes and fix ducts that have come off of the vents they attach to. This is something I know I will need to do, but my initial estimates tell me that it will cost around $1800 to completely replace all of the ductwork. :(

So, the question is, what do I want to do to decrease my attic temperature and remove humidity? Here is my current plan:
  1. Reinstall my gable vents
  2. See if my attic temperature noticably decreases with respect to the outside temperature
  3. If not, have 2 turbine vents installed on the 2nd floor roof and 1 on the 1st floor roof.
  4. Begin saving money to replace the ductwork

Update 7/8/04!!! Well, I said I was going to reinstall my gable vents, but after talking to the "gable vent guy", he suggested leaving them closed up and installing a ridge vent. He said that when you install a ridge vent, you want to close up the gable vents anyway.

So, I started shopping around this week for quotes on ridge vents. I've gotten different stories from everyone I talk to. One guy said, "the more ventilation the better" when I asked him about leaving the one gable vent I have when installing ridge vents. However, reading on the web (and from the "gable vent guy") I thought I should have closed up any other vents so as to not steal from the airflow going up along the roof to the ridge vent.

Another guy came over, and gave me a quote on a ridge vent, but said if it were his house, he would put turbine vents. He said that turbine vents suck the air creating more airflow than ridge vents. I told him that from what I read that the ridge vent is better because it eliminates hot spots and creates a more even air flow to which he responded "that even flow crap is just a sales pitch anyway". I can understand his point, but I can also see how wind can create a low pressure by blowing over the ridge vent to also suck the air. Another thing is that ridge vents don't depend on the wind to still work well. According to this page, "Most builders agree that a ridge vent system is the most effective as well as the most cost-effective."

Part of me wants to do ridge vents on the second floor attic, and turbine vents on the first floor portion, add a sensor to the other side of the attic, and evaluate the performance so I could prove which one is more effective in lowering the attic temperature!

Since that is not very realistic, I am still leaning towards ridge vents. I have about 50 foot of ridge and have one quote of $600, and another for $500. I have one more guy coming from a bigger, older, more established roofing company tomorrow and I will get his take on things along with a quote.

Update 7/25/04!!! The ridge vent was just installed today. I'm looking forward to getting some new data and seeing if the average temperature of the attic becomes any lower. Here's a couple of pics of the installation. Click for a bigger image. Also, more pics can be found here.

Ridge Vent 1

Ridge Vent 2

Ridge Vent 3

I am looking into installing some radiant barrier in the attic and seeing if that has any effect. Stay tuned!

Update 8/5/04!!! I have finally got a few days of data that were hot and had no rain. I put together the following comparison to show the difference in the attic temperature with and without the ridge vent. This is three hot days in July without ventilation compared to three hot days in August with the new ridge vent:

Temperature comparison chart

The yellow line represents the difference between the outside temperature and the attic temperature, since one directly affects the other. This is the scale on the left y axis. The right axis is just temperature and is for the blue and purple graphs.

You can see that the ridge vent took about 10-15 degrees off of the peak temperature in the attic and that the average temperature difference (attic - outside) dropped by about 4 degrees. Also it looks as if the ridge vent helps the settle to the outside temperature more quickly. The benefit of the ventialtion that is not being shown here is the removal of built-up humidity in the attic (which is one reason I needed it, regardless of how much it lowered the temperature).

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