Attic ventilation - real world eye-opener.

[SoonerDave]

After noting that my AC power consumption was a bit higher than I expected, I started taking some stock of my 13-year old home. I never realized that my builder installed exactly *zero* attic vents beyond those in the soffit (beneath the eave). When I started measuring attic temperature a few days ago, and found the floor temp to be about 115, and the temp eight feet off the floor to be 134 (40 degrees higher than the outside air), I was stunned. Always knew the attic was hotter, but never measured it.

Turns out that a difference *that* great is, in reality, *too* great. The consensus of a few roofing/HVAC sites is that the best you can generally aim for in practical terms is about 10-20 degrees difference (excepting things like complete spray-foam insulation, etc). It was then I started reading about attic venting, and realized my attic had none.

I talked to a retired builder, called a couple of local roofing companies, and opted to have two simple passive vents (not fans) installed. Jackson Roof came out yesterday and put them in around lunchtime. The result? Later that afternoon, measured at the same time of day, at the same location, with an outside temp of 91 instead of 94, my attic measured 114 at eight feet from the floor. That's a real-world 20-degree drop in attic temperature - heat that's no longer hitting my AC ducts or ceiling.

I may have done fractionally better with turbine vents or powered fans, but the former may be against my covenants (and I didn't want any neighborhood hassles) and the latter were consistently not recommended by folks who have them and seemingly are constantly repairing them because the motors go out.

We'll see over the next few days/weeks if that translates to some true power savings, but my wife and I both agreed the house felt much more comfortable even when the A/C was off. Maybe that's psychological, don't know, but for the moment I'm happy.

I've got an insulation contractor coming out to give me an estimate on a "refresh" blow-in of a few new inches of insulation given that the house is 13 years old. I was also considering a radiant barrier, but given that I may have knocked a huge chunk of extra heat merely by adding the vents, I may opt against it for now. We'll see.

Moral of the story: Make sure your attic is vented. I didn't even know to look until I realized the homes built by my builder over a decade ago were the only houses on my street without any venting.

[BBatesokc]

We utilize both attic fans (pulling air through the house and into the attic (creates a nice air flow in the early mornings and at night - while also venting and cooling the attic). Plus, we also have solar powered attic fans on the roof that kick on when the temperature in the attic heats up (about $200 at Sam's). The combination of the two is really nice in our older (70's) home.

[RadicalModerate]

The importance of proper attic ventilation cannot be overestimated. If you have a house with a significant amount of straight ridge areas--such as a house with an L-shaped or H-shaped footprint--continuous ridge vents are a good choice. Our house had two turbine vents and built-in vents at the top of the three gables. BUT IT DIDN'T HAVE ANY SOFFIT VENTS. (Can you believe that?) I cut in a soffit vent every eight feet and when we get the house re-shingled (after the latest hail storm) I plan to lose the turbine vents and put in the continuous ridge vents. Another thing to note here is that it is important to make sure that your attic insulation doesn't block the air flow from the soffit vents.

BTW: I'm astounded that the City Building Inspectors passed your house on the final with no attic ventilation. They can sure be picky about other things. =)

[SoonerDave]

The importance of proper attic ventilation cannot be overestimated. If you have a house with a significant amount of straight ridge areas--such as a house with an L-shaped or H-shaped footprint--continuous ridge vents are a good choice. Our house had two turbine vents and built-in vents at the top of the three gables. BUT IT DIDN'T HAVE ANY SOFFIT VENTS. (Can you believe that?) I cut in a soffit vent every eight feet and when we get the house re-shingled (after the latest hail storm) I plan to lose the turbine vents and put in the continuous ridge vents. Another thing to note here is that it is important to make sure that your attic insulation doesn't block the air flow from the soffit vents.

Our house isn't purely rectangular, but its closer to than than a hard L footprint. We've got a good opportunity for a ridge vent when time comes for a new roof. Soffit vents were/are all clear, although there are a few corners of the house I'm not quite sure-footed enough to reach. That's what I want the insulation guy to check out and evaluate for me. Also, the guy who installed my vents said there was some hail damage along my ridge that will need attention sooner rather than later, and I fully expect that when time comes for a new roof, a ridge vent will be one of the things chief on my list. May even look into replacing the roof decking with the variety that has a radiant barrier on one side, but I've read mixed opinions on that, and it may end up being prohibitive cost-wise.

I'm thinking I may have hit the sweet spot already for the biggest temperature reduction/cost "bang for the buck," because the vents were only $300, and my inference from the various sources I've read through that getting your attic within 10-20 degrees of the outside temperature is about the best you can realistically expect, and I'm just on the outside of that range. A $5K expense for a radiant barrier for, say, a 10 degree difference (which I'm thinking now may be waaay too optimistic a drop) probably goes outside the cost/benefit range, but maybe $1-2K for ~5" (?) new insulation to accomplish better in-house temperature control may be worth it. We'll see what the rep says on Thursday.

[RadicalModerate]

I still haven't made up my mind on how that radiant/reflective decking (that sounds good in theory) would affect the durability and lifespan of the shingles that cover it. I would imagine that there are some opinions expressed on some of the roofing manufacturers' websites, but I haven't really looked into the matter since redecking our house is not even close to being in the planning stages. Back in the 70s and 80s some builders used to use thin, reflective 4x8 panels for wall sheathing. One of the brand names was "Thermo-Ply". If the "reflectivity" is the main thing, I don't know why a layer of this light, relatively inexpensive material couldn't be applied over the existing decking prior to shingling. Still . . . if the sunlight isn't actually hitting the "reflective" surface (on account of being covered by roofing felt and/or shingles) I'm not really sure how any "reflective" material is supposed to do anything.

[HewenttoJared]

Radiative heat is light, RM.

[SoonerDave]

Still . . . if the sunlight isn't actually hitting the "reflective" surface (on account of being covered by roofing felt and/or shingles) I'm not really sure how any "reflective" material is supposed to do anything.

Keep in mind that the material is heat-reflective, meaning that it reflects the radiated heat (just light in a different part of the spectrum), which is initially absorbed by the shingle and then re-emitted into the attic space. The kind of radiant barrier that is stapled to the underside of the roof rafters simply reflects the heat right back to the decking material, which is why some express concern about additional heat aimed at the shingles. I've read/seen a few reports that suggest the actual temperature increase to the shingle is really only about 6-7 degrees, and as a result isn't quite as damaging to the shingle material as some sales folks are leading people to believe.

[RadicalModerate]

Correct. And if the LIGHT isn't hitting the reflective surface (because of the shingles and the felt covering it) how does the reflective surface actually do what it is supposed to do? It just doesn't seem the same to me as putting one of those reflective things behind your car windshield to "bounce" the "light/heat" back outside your vehicle. Or to buy windows with Low-E glass to "bounce" the radiant heat (light) back outside your house. It seems to me that light colored shingles or shingles with extra-reflective granules would be much more effective in this connection than any sort of foil-based substrate.

[SoonerDave]

I won't pretend to know all the physics on this, but I'm reasonably sure that "light" in this vein/region of the spectrum passes through solid objects, with some of the energy absorbed by the shingle, and that which passes through to the decking gets reflected by the radiant barrier.

The model I read which studied various kinds of RB's did indicate that the most effective kind is the one applied to the framing rafters, but I don't think it compared the performance of the decking material. The former resulted in an average attic temp decrease in their models and real-world tests of about 13 degrees, which is really, really startling.

[HewenttoJared]

Correct. And if the LIGHT isn't hitting the reflective surface (because of the shingles and the felt covering it) how does the reflective surface actually do what it is supposed to do? It just doesn't seem the same to me as putting one of those reflective things behind your car windshield to "bounce" the "light/heat" back outside your vehicle. Or to buy windows with Low-E glass to "bounce" the radiant heat (light) back outside your house. It seems to me that light colored shingles or shingles with extra-reflective granules would be much more effective in this connection than any sort of foil-based substrate.

No, I'm saying that as those shingles heat up(from being struck by visible and non-visible radiant energy) they emit light in the infrared spectrum. Some of it goes outwards into the atmosphere, some of it goes below them into the house. If you have a reflective surface there a lot of it will just go back into the shingle and be re-radiated in all directions again. I saw a study that said having light-colored roofs would save the US a boatload on electric bills. You're definitely right about light granules on shingles, but the combination of reflector and light color would still be best.

[ou48A]

I know it’s not practical or affordable in every situation but the spray-foam insulation is a great product.
With new construction it’s probably the smart way to go.

[SoonerDave]

I know it’s not practical or affordable in every situation but the spray-foam insulation is a great product.
With new construction it’s probably the smart way to go.

A friend of mine just built a new house and put spray foam in the attic, and his temps are incredible. Its much more expensive than blown insulation, but since its a new house for him and he plans to be there for many years, it made great sense from all perspectives. If I were building new, I'd spray-foam in a heartbeat.

[SoonerDave]

No, I'm saying that as those shingles heat up(from being struck by visible and non-visible radiant energy) they emit light in the infrared spectrum. Some of it goes outwards into the atmosphere, some of it goes below them into the house. If you have a reflective surface there a lot of it will just go back into the shingle and be re-radiated in all directions again. I saw a study that said having light-colored roofs would save the US a boatload on electric bills. You're definitely right about light granules on shingles, but the combination of reflector and light color would still be best.

Bingo. As a kid, I remember living in a smallish house in SW OKC and it had white shingles. Wasn't until we got more "stylish" that we decided to start using black/dark shingles everywhere And I say that as someone who used to tease my wife for at one time having a black car in Oklahoma - man, was that thing H O T.

[RadicalModerate]

I won't pretend to know the physics either. =)
Especially the part about "light" passing through solid objects.

But don't let that detract from the importance of proper attic ventilation. =)

And thank you for that explanation, HWTJ. It helps to clarify the concept of "different kinds of 'light'".

So . . . Just out of curiosity . . .
Is the "radiant barrier" applied to the underside of the rafters, thereby creating "heat bays" (for lack of a better term) that could adversely affect the already less-that-top-notch lumber of which the rafters are composed (while interferring with the flow of "fresh" air from the soffit vents that helps to maintain something resembling an acceptable moisture content in the wood, that is, the rafters and the decking applied to them)? I suppose that if the areas where the rafters connect to the top plate were not obstructed, then fresh air could still surround these framing members, even if the rest of the attic space wouldn't benefit from the air flow . . .

P.S. Never try to work in an attic when it is very hot outside. It can literally kill you. (personal near-death experience)
P.S.2: Don't cover your turbine vents in the winter. This does nothing to save energy or increase comfort.

[Roadhawg]

I know it’s not practical or affordable in every situation but the spray-foam insulation is a great product.
With new construction it’s probably the smart way to go.

How heavy is the spray foam?

[ou48A]

How heavy is the spray foam?

I can’t tell you exactly what it is per square foot, but it’s very light. It’s about like a square foot of syrofome.

[ou48A]

A friend of mine just built a new house and put spray foam in the attic, and his temps are incredible. Its much more expensive than blown insulation, but since its a new house for him and he plans to be there for many years, it made great sense from all perspectives. If I were building new, I'd spray-foam in a heartbeat.

Spray foam will increase a home’s value.
If I ever move to a different house it will be a mandatory requirement for me.
I had a retro fit spray foam job done just over a year ago and I like it very much.

[RadicalModerate]

Spray foam insulation in the walls and ceilings is a GREAT idea!
Especially now that they have figured out how to make it without (eventually) toxic chemicals and/or the associated outgassing.

The only realistic caveat that I can think of is that all of your wiring will have to be run in conduit (as in a commercial building) and any later changes to the wiring will not be inexpensive. (Unless, of course, one has no objection to wiring chases on interior wall and ceiling surfaces.)

The energy-saving and comfort-increasing benefits of spray foam insulation FAR outweigh the negatives.
Plus it's light. (it doesn't weigh a lot =)

Related Side Note:
Maybe eight years ago, I attended a seminar about building energy-efficient housing systems. One of the "Takeaways" that I still recall today is how stupid it is to run supply or return air conditioning ducts in non-air conditioned spaces (such as attics). The suggestion was made that duct chases--e.g. down hallway ceilings or [decorative] furr-downs around the perimeters of rooms within the air conditioned envelope--made a lot more sense and would save a lot of dollars. It might make a home seem more "motel/hotel/apartment-like" but that would be a small price to pay and you would get used to it, especially if the concept was incorporated into Building Codes.

Heck . . . I still wonder why Building Codes don't require a 36" door on at least one downstairs bathroom adjacent to a bedroom. (For minimal wheelchair access without extensive remodeling.) No . . . I'm not in a wheelchair. But back when I was a Remodeling Contractor I visited the home of a well-known local celebrity to do a site check and provide an estimate on accomplishing the goal of providing bathroom access to a member of his family who was faced with that challenge.)

[SoonerDave]

Maybe eight years ago, I attended a seminar about building energy-efficient housing systems. One of the "Takeaways" that I still recall today is how stupid it is to run supply or return air conditioning ducts in non-air conditioned spaces (such as attics).

No kidding!! I felt like an absolute idiot after I built our current home and did not insist on slab-based ductwork. Our ducts are in the attic and I loathe it.

Now, that said, I know that some regions of the country (parts of Texas, maybe?) are starting to impose stronger codes on home foundations, in particular looking at post-tensioned concrete slab foundations. That's where they run steel cables through the slab, mechanically tension them after the slab is poured, and then lock them off. It makes the foundations significantly stronger, but the downside is that it mandates attic-based ductwork.

RM, I remember that early foam stuff going in years ago, but then they had the off-gassing problem and the stuff was pulled/remade. Didn't they have some of the same kinds of problems with the first kinds of adhesives used to make the big sheets of OSB?

[SoonerDave]

I can’t tell you exactly what it is per square foot, but it’s very light. It’s about like a square foot of syrofome.

Oh yeah, the stuff is nearly weightless. You can buy small cans of the stuff at retail, and I've used it to close up a gap on the outside part of my house between the brick and an eave that BEES were using to make a home, and sprayed that puppy shut after I got a bee expert to take care of them. It was almost freakish to see this liquid spray on to a surface, watch it contemplate its navel for a couple of seconds, then FOOOMM...it's like a can of root beer exploded. The stuff filled the entire cavity, and all I had to do was trim the excess. I bet if you pulled out a section from a framed wall, which would be about 15" wide and about 96" tall, wouldn't even weigh 3 lbs.

[RadicalModerate]

"Absolute Idiot"? . . .
So . . . How about a guy who doesn't really understand the cost/value benefits of dealing with "invisible" light and owns part of two vehicles that both have basic black paint schemes? Plus isn't totally convinced that three years down the line the EPA won't demand that all of your SprayFoam insulation won't have to be removed no matter how harmless it actually is? =)

FYI: Under-slab ducts are subject to the vagaries of weather conditions, mostly due to improper addressing, by developers and builders, of natural and unnatural occurances involving either a surplus or deficit of rain and ineffective measure related to drainage. (Under-slab ducts flood and rust. Really. They do. =)

Actually, I think that the root cause of most of these problem are Architects/Designers who are heavy and light on Imagination and Practicality. Not to mention Salesmanship. =)

P.S.: There were concerns about "active" clay soils (in Texas and Oklahoma) for example way back before '82 when I bought an expensive book about "Foundation Design Basics". The book had an entire section about the drawbacks and benefits of Post-Tensioned Slabs. So this isn't a "new" issue. It's about "failing to learn from the mistakes of the past (and not living long enough to make them all yourself =)". HWTJ might like that book. It had a lot of graphs. =) Just kidding, amigo . . . Yet, I wonder, do reflective roofs contribute to global warming . . .=)

[SoonerDave]

FYI: Under-slab ducts are subject to the vagaries of weather conditions, mostly due to improper addressing, by developers and builders, of natural and unnatural occurances involving either a surplus or deficit of rain and ineffective measure related to drainage. (Under-slab ducts flood and rust. Really. They do. =)

Semi-funny story in that vein: Our previous house had slab based ductwork and part of the refrigerant line from the AC was in the slab. Moved in during the winter, so had no reason to use the AC; first time I turned it on, hot air. Hot air. And more hot air. House was under builder's warranty, so the AC co came out and inspected it, and discovered that the concrete guys had inadvertently plunged a shovel into the copper refrigerant line and crushed it. So they had to run a new line just beneath the sheetrock and above the stemwall.

I lived in that house for eight years and the ductwork was clean as a whistle when we sold it - a photo inspection of the ductwork was part of the buyer requirements. Now, on the other hand, my mom's house is pushing 40 years old, and she's already had to cover up two outlets because sand and even some moisture started blowing in, although I'm not sure that isn't part of some foundation shifting going on. Not sure.

Another reason I'd like to throttle the guys who put in the AC in our current house - ALL, repeat, ALL the air registers are located incorrectly. Rather than placing them near the region of greatest heat loss/gain (typically near a window), they stuck them in what appear to be arbitrary locations in each room. The register in our bedroom is just inside the door, which is not three feet away from the big return duct. You can literally feel a gust of air from beneath our bedroom door as the ductwork tries to pull in that air I've paid so dearly to cool. We've taken to plugging an old towel at the bottom of the door. Same thing in the kids bedrooms, vents nowhere near the windows, along with two arbitrary vents in the middle of our living room - again, nowhere near the windows. I was uneducated on all this until I had some work done one day, and the guy asked me "Who did your AC on this house" I didn't recall, but he offered, "well, they've really screwed up the placement of all your air registers, and used the wrong kinds of vents." He then gave me a 25-cent education on how they're supposed to be placed, and went room to room and showed me how wrong all the vents were. Said he'd never seen anything like it. It simultaneously infuriated and embarrassed me that I didn't know better. I consider myself to be a bit better educated about the details of home building than the average person might be, but this little bit of info made me feel really stupid in a hurry.

LOL on the EPA coming in and demanding spray foam be removed "no matter how harmless it is"...would be a funny idea if I didn't think it were possible

[Wambo36]

No kidding!! I felt like an absolute idiot after I built our current home and did not insist on slab-based duct work. Our ducts are in the attic and I loathe it.

We built our house 5 years ago and went away from slab based ducting due to our experience with it at the old house. We had a pipe burst one evening while we were out and when we returned there was water running down our driveway and about 2" of water covering the whole downstairs. The short version is this, the water in the duct work leaked into the sand under the slab causing it to shift around some. 5 years later we were noticing some cracks around some doors and thought we'd have it looked at by one of the foundation repair companies. Imagine our surprise when he told us we had no foundation problems but our slab was sinking in the center of the house (along the main trunk of the ducting), something akin to a taco shell. He informed us that with the flooding, our insurance company should have had us on the lookout for this kind of settling since our ducting was flooded. We had this confirmed by a structural engineer and the 9 month battle with our insurance company began. After $36,000 worth of pier and repair work, we opted for no slab based duct work in this house.

[SoonerDave]

Ugh, Wambo, what a horrible story! Sorry you had to go through that.

Certainly don't blame you one bit for being snakebit re slab ductwork based on that, but if I had it to do over again, I'd still put my ducts in the slab.

I can't help but wonder if in your case perhaps you had a poor grade on which your slab was poured. I mean, think about it; it would take an astonishing volume of water to erode the sand around a leaking duct, but for it to shift so much that it caused the slab to *fail* almost has to suggest that the grade on which the slab was poured was really sandy/loamy or shallow to begin with.

Reason that occurs to me is that I know of a development near where I used to live, and the developer basically backfilled a dump with some topsoil for an entire street of houses. I knew that was a horrendous place to build a house because, over time, that fill would erode and fail just as you've described. Wonder if there was something just below grade that the water exacerbated in your case...

Isn't homeownership fun?

[onthestrip]

I was recently told by a green building architect that new homes should never insulate just above the ceiling but should always insulate just below the roof/shingles.