Attic ventilation in Phoenix area homes ? (Tucson: new house, transfer, scorpions)

[veritased]

New to the area. As I look towards moving into my purchased home in the area, I am wondering about what is the common way to ventilate attics during the summer to reduce the temps in there, so as to not bake the living spaces in the afternoon/evening ? Would it even be effective given the ambient outdoor temps in the AZ valley of the sun area ?

My home inspection report says there is R-30 fiberglass insulation up there, so that's fine.
And some sort of attic ventilation, which I have not personally inspected.

What is the best way to optimize your insulation and venting of attic for savings on cooling costs ?

Thanks for any advice and experience.

p.s. in CA where I am coming from, the trend is to use whole home fans to bring in rapidly cooling outside air as evening approaches, via open windows, throughout the home, then pushing that air through the attic and outside attic vents. Not sure if this approach would work in AZ.

[JGMotorsport64]

Originally Posted by veritased

New to the area. As I look towards moving into my purchased home in the area, I am wondering about what is the common way to ventilate attics during the summer to reduce the temps in there, so as to not bake the living spaces in the afternoon/evening ? Would it even be effective given the ambient outdoor temps in the AZ valley of the sun area ?

My home inspection report says there is R-30 fiberglass insulation up there, so that's fine.
And some sort of attic ventilation, which I have not personally inspected.

What is the best way to optimize your insulation and venting of attic for savings on cooling costs ?

Thanks for any advice and experience.

p.s. in CA where I am coming from, the trend is to use whole home fans to bring in rapidly cooling outside air as evening approaches, via open windows, throughout the home, then pushing that air through the attic and outside attic vents. Not sure if this approach would work in AZ.

I don’t think there is an approach here. Most attics have open air vents to the outside and you don’t go up there because it’s miserable. The homes all central air here.

[veritased]

Looking at some research done by building councils in Tucson, turns out that insulating the roof, then sealing the attic, and letting the HVAC ducting cool (or heat in the winter) the attic as it goes from air handler to various rooms, allows a non trivial cost savings. Compared to a traditional vented attic.

Big surprise to me. But I guess the different is in insulation being applied not only above the ceiling, but also on the underside/inside of the roof, typically some time of expanding foam type of product. That provides a much higher temperature gradient to the attic, and then from there, the leakage of heat from attic to HVAC ducting causes the attic to cool down, and net-net, you save money on the cooling costs to the interior space, as the ceiling is no longer transferring heat to the living space, as the attic is no longer at 160deg F or whatever, it's more like below 100deg F, the studies show.

[DougStark]

I read in a building journal recently that having adequate attic insulation is much MORE effective than attic air ventilation as far as energy savings go. My attic insulation is lousy (91 built home), so I have the unpleasant task of either doing it myself with rented equpt. or hiring someone.

[veritased]

Yes there are all kinds of theories and test buildings being done in humid/hot and dry/hot climates, trying to figure out the right way to minimize energy costs in heating/cooling.

Not clear what the ideal situation is for AZ remodels and new homes.

[DougStark]

Forgot to mention: the OP asked about whole house fans. They work fine here for a relatively short window of time, IMO. Some places, like Denver or Sacramento where they have hot days and cool summer nights, they're very very effective.

Problem is, in Phoenix our period of cool evening/night temps and hot days are relatively short. The more typical scenario is hot days and very very warm evenings/nights, so a whole house fan just isn't effective under that scenario. Not enough cooling.

Better option, IMO, is to install an evap cooler (preferably a ducted one with adequate CFMs). The evap cooler, even on "fan only", will do the same thing a whole-house fan does--it blows all the hot air out of the house and replaces it with fresh, cooler outside air. Plus, the added option of the evap cooler is its "cool" mode, when you want cooling even if it's 100 outside.

Not much $$ difference between the two either, assuming you don't demand a lot of evap duct work installed.

[veritased]

Thanks, I'll look into it... this is what I was looking for... the local hacks to keeping cool without burning megawatts doing it.
If possible.

[Burning Madolf]

I went through a similar thought process when I first moved here. My house was a "bubble build" with an oversized a/c unit and ok but attic insulation. The house just always felt hot.

I put an exhaust fan at one end of the attic where there was a large triangular gable vent. My thought was that I could turn it on say an hour after sunset to exhaust the hot air built up during the day.


I can't give any conclusive info as to it working because I sold the house like a month later and took the fan out. However, I will say the house I moved into has better sized a/c units, better insulation, better roof vents and I've made sure every soffit vent is free and clear. It definitely feels better. You can go nuts in the attic with all kinds of ideas but I'm not sure of the return on time and investment.

[KurtAZ]

Evap coolers only work well when there is no humidity...so May/June would be fine but once the humidity picks up in July, usability would be spotty at best. Some homes have a hybrid AC/Evap set up so you can use one or the other depending on the humidity levels...not sure how well they work though.

There was a concept a few years ago of creating a chimney effect by using specific underlayment and roof tile configuration that would vent hot air underneath the tiles towards the peak of the roof. Personally, I think the best approach (maybe the most cost effective?) would be passive attic vents and making sure you have enough insulation. Don't underestimate the insulation in your walls either...especially the side of the house taking the afternoon sun. Windows can make a difference as well as sealing any leaks to the outside world. This is a double benefit as it keeps scorpions out of the house...they like to sneak in through bathroom vents, under doors and windows...pretty much anywhere they can squeeze through. These intrusions are also leaking air.

[veritased]

Burning Madolf, yes thank you for that data, indeed. Can you provide any insight as to what ade the roof vents better, please?
Thanks.

KurtAZ, thanks for your insights, too. Much appreciated. I have seen a somewhat similar concept, but on the inside of the roof, with a radiant barrier stapled to the roof rafters, from within the attic. But then that would reflect heat and further heat up the roof underlayment and tiles... I am sure it does not help roof life, but does it shorten it either, appreciably ?

Agree about sealing. I've looked into that alot for both reasons of not losing conditioned air, as well as the evil scorpion. I'll be working on further sealing the home, for sure.

Overall I'd just like to see if there is some reasonable method to cool down the attic so it does not conduct heat towards the living space. Seems like venting the attic would do that... with good soffit vents (haven't checked my new house to see if they have them), and a good A/C fan (apparently solar powered fans don't move enough CFM) blowing for a few hours, maybe I can make the home more efficient and net-net save electricity ?