Attic ventilation in Phoenix area homes ? (Yuma: contractors, living, costs)

[veritased]

Just to follow up on this, having lived in this house and hitting some 90-100 degree days here, seems like the house stays relatively cool on it's own, before having to kick the AC on. I went up into the attic and there seems to be like at least 18"+ of blown insulation, vs what we see in California, which is like rolled insulation.

In any case, this 5 yr old house seems to be built reasonably insulated. The roof does have these very thin slits/vents, which I suspect are designed for AZ climate. Can't explain why they are in that form factor myself. But the opening do seem unique compared to what little I know about building science.

So let's see what happens in August with weeks on end of 100+ degrees beating down on this place. But so far, don't see the need for extra expense to move air through the attic. There's really not that much volume of open air space, left over, after the volume of attic space taken up by the blown insulation.

[DougStark]

BTW, I'm seeing several homes in my neighborhood being re-roofed (tiles taken off, stored, for re-use later.) Is it likely they were having water leaks? My house (same builder and year) hasn't had any water roof leaks (knock on wood.)

But, I haven't noticed the roofers installing shiny foil radiant barrier OR sheets of rigid insulation on top of the roof. Strange?

If my house needed a re-roof, I'd opt for the extra 4'x 8' rigid foam board insulation sheets (expanded polystyrene) before the tar paper and tiles went back on. That's GOT to make a difference, no?

Slightly off topic, but have you seen (or would a home look good) with porcelain clay roof tiles that were glossy white? Seems like the glassy white tiles would be excellent at reflecting radiant heat during the day, and it might look very sleek and modern (retro almost.)

Another roofing material I don't see here (valley) is metal roofing. I've had a home with metal roofing before, and man, they are DURABLE!! Our punishing heat wouldn't bother them as long as the coating (porcelain, enamel, or whatever) was done correctly. And since they're lighter weight than concrete tile roofing, it might save on framing costs (??) not sure.

[veritased]

Good questions Doug. After having obsessively researching this topic, I realized that within the building science community, the options and consequences of the various claimed optimal solution are not all that well understood. So I took no action, and still my house seems to stay pretty cool. I was up there in the attic again during a recent breezy day, and I did notice a fair amount of air moving through those little slits... the way they are oriented, they tend to pick a decent amount of air and move it through the attic. Don't know what happens on a still air day. But hey, the more insulation there is, the less air to be overheated, so I think the people that say just blow more insulation probably have the right idea.

God forbid you have to do any work up there rewiring or repiping... man that would be a bear.

[gemstone1]

"God forbid you have to do any work up there rewiring or repiping... man that would be a bear."....I did just that to facilitate a home sale......in July....in Yuma. Powered, thermostatically controlled attic ventilation fans are good....when they work. Turbine fans work OK....if you have sufficient soffit vents. But in my opinion, nothing works like closed cell spray foam, which makes the attic space part of the building envelope and it becomes semi-conditioned space by virtue of the heated/cooled air traveling thru the ducts within the attic. In my current home, it was money well spent.

Regards
Gemstone1

[veritased]

Gemstone1, I can imagine the experience you had... the polar opposite of those cryogenic treatments one can get these days.

Closed cell foam would imply a material property of stickiness... so the closed cell foam would stick the ceiling drywall and rafters ? Making it hard to do any electrical or plumbing work from the attic space ?

[Hal Roach]

Originally Posted by gemstone1

"God forbid you have to do any work up there rewiring or repiping... man that would be a bear."....I did just that to facilitate a home sale......in July....in Yuma. Powered, thermostatically controlled attic ventilation fans are good....when they work. Turbine fans work OK....if you have sufficient soffit vents. But in my opinion, nothing works like closed cell spray foam, which makes the attic space part of the building envelope and it becomes semi-conditioned space by virtue of the heated/cooled air traveling thru the ducts within the attic. In my current home, it was money well spent.

Regards
Gemstone1

IMO, that is a huge waste of energy.. Basically you are increasing the cubic feet to be cooled by a lot. As building science guy would say.. only for mitigation of serious design problems.. One of which is having ducts in the attic to begin with. They do the same thing with crawl spaces, and there are even formulas they follow on how much hvac to leak into the crawl space. In the attic, if you can simply get close to the outside temp, you are doing well.. the key is to having a properly sealed ceiling decking.

And to add, I live in Bangkok and it has been hotter than Phoenix every day this year.. so I deal with many of the same issues... but the Germans started offering spray foam on the underside of the roof decking fifteen years ago... part of the sales pitch was it would eliminate roof leaks from the 60 inches of annual rain we get. It was overpriced, just like every other over engineered German contraption, and not a total failure, but you hardly hear of it anymore... pairs of spinners are as popular as ever, along with ceiling drywall that has a radiant barrier built in.. and insulation bats on the ceiling deck. AC is 98% point of use here, and the last thing they would do would be to cool the attic with air con.. it simply defies logic.

[gemstone1]

Originally Posted by veritased

Gemstone1, I can imagine the experience you had... the polar opposite of those cryogenic treatments one can get these days.

Closed cell foam would imply a material property of stickiness... so the closed cell foam would stick the ceiling drywall and rafters ? Making it hard to do any electrical or plumbing work from the attic space ?

No, the closed cell foam is sprayed on the interior surface of the exterior walls and roof deck. In my case, the foam was about 4" thick (about 7 "R" per inch), less thickness than the 2x6 rafters and end wall studs...which are clean, ready for drywall. As a side benefit, the foam completely sealed the attic space, no more wasps, or wintering lady bugs, no drafts. Yes, running wire or pipe through foamed space would be a pain, plan ahead to eliminate that chore. Again, in my case the attic is huge, 12' from floor to the peak, 12/12 pitch, no crawling required, so application was not difficult. If and when I close in the attic, there will be plenty of room above the ceiling for wire, and behind knee walls for duct work/wire.

And yes, it was hot in that Yuma attic in July...outside about 115 degrees, attic maybe 140-150.

Regards
Gemstone1

[gemstone1]

Hal...I never stated it was wise to fully air condition the attic space, which only makes sense if it would be finished living space. What I said was that merely by running ducts thru the foam sealed attic, a semi conditioned space would be the result. Heating and cooling loss thru poorly insulated ducts is measurable. I'd also suggest a major portion of homes in AZ have ducts in the attic, albeit a poor design, there are few if any cost effective alternatives.

Regards
Gemstone1

[Hal Roach]

But you are losing 20% of your cooling in the attic.

[gemstone1]

"But you are losing 20% of your cooling in the attic."....my point exactly Hal. Wouldn't it make sense to capture that loss within the home's envelope by insulating the attic space with foam (or other material) rather than let it escape into the atmosphere ? The only discussion to have at this point is the cost benefit analysis....IMO.

Regards
Gemstone1