Many thanks for all of the great information and discussion on the previous threads on these topics, including
I have some feedback from my positive experience so far with radiant barrier in a current project, and a specific question about roof fans for the next step.
I'm having our attic rebuilt (1903 Victorian in Seattle), originally motivated by finding mold when we replaced the soffits for all of the eaves. The insulation had been stuffed in tight along the roof when a previous owner did an amateur build-out of the attic interior, leaving absolutely no ventilation inside the roof. (Oh, and even earlier, depression-era construction used 2x4s for rafters, instead of 2x6 or 2x8s!) The attic was unlivably hot on even overcast days.
Here's what we're doing: The new soffits have covered vent holes spaced all the way around the house, under the eaves. At the top of the roof, there's a ridge vent all along the peak. And then (here's the fun part) we're making the following layers, from the roof inwards.
- two inches of air space for ventilation, connecting the eaves vents to the ridge vent
- radiant barrier (see below)
- four inches of insulation
Our incredibly competent contractor says the radiant barrier has an R value of 15. I don't know what that means, really, except in the earlier discussions here there was skepticism that a thin barrier would have that much heat-stopping power.
In practice, even the contractor was surprised at how effective it is already. With the radiant barrier installed half-way up the south roof face, on a sunny day, I could put my hand in that two-inch ventilation space between the roofing and the barrier. Toasty. Then move my hand out, just to the other side of the radiant barrier. Cool.
OK--it's probably not actually the difference between a toaster oven and an iced glass of lemonade. But it was a bizarre, weird experience, like doing something impossible. I have no mental model from anywhere before in my life for something that hot and something else so cool being that physicaly close to each other. I had to move my hand back and forth again and again to really believe it!
Now for the question. To aid even further in ventilation, we want to add a small roof fan. Because we're finishing the attic, most of the roof will have just the two inches of air. But at the peak, the flat interior ceiling will leave a small (less than two feet) triangular open-air space. That's where I'd like to exhaust hot air.
Most "roof fans" or "attic fans" seem to be big hulking, industrial, poke-through-your-flat-roof style, like:
Standard Aluminum Dome Roof Mount Attic Vent
I'd like instead to to put a smaller fan on one or both ends of the roof, out through the wall below the peak rather than through the roof incline. So there will be a long, triangular prism of hot air at the peak, with a fan on either end, as well as the ridge vent at the top, sucking cool air up from the soffits.
So here's my questions:
- Am I going overboard having both the ridge vent and also the fans?
- Will two fans be better than one? I only want to make sure that the air keeps moving.
- Recommendations for a *smaller* vertical-mount fan for this use? Maybe 8" or less in diameter? I'd like one that's reliable and quiet, and it's worth spending more on the "Cadillac" of fans while everything is open and easy to install. Can I just use any bathroom fan? How are they different? Heck, could I just get a "whisper-quiet" PC fan, 3" or 5", with a power transformer??
So far on Amazon, I've seen some attic fans like these:
But there isn't much information on some of them, even to tell whether they're appropriate for our use.
What do you recommend? Thanks in advance.
Recent discussions in the Home Improvement forum (500 discussions)
|Vintage St Charles Kitchen Cabinets Available (Set of 20) Excellent Condition||8||17 days ago|
|Pot Filler||27||21 days ago|
|porch light with electrical outlet||51||25 days ago|
|Help - Blower Motor for Carrier Furnace||15||Jul 12, 2017|
|best deck treatment/sealer for Pressure Treated wood - Tennessee||159||Jul 9, 2017|
|The tragedy of Ryobi tool ownership||52||Jul 3, 2017|
|Insulate a bath tub?||1||Jul 3, 2017|
|Granite Sink vs. Cast Iron||219||Jun 29, 2017|
|Granite or Zodiaq/Silestone?||42||Jun 26, 2017|
|Air filters and air flow||25||Jun 14, 2017|
|cast iron bathtub vs. steel||83||Jun 1, 2017|
|Best backup power source for a sump pump?||27||May 23, 2017|