How to keep an attic cool? Radiant Barrier?

[portlandatheist]

So I live in Portland Oregon and we had some really nice weather this last week but unfortunately, the hot weather turns the upstairs bedrooms into ovens. I live in a Cape Cod style house and the attic floor has spray in insulation (I don't know its R value) and am considering putting in a radiant barrier (http://en.wikipedia.org/wiki/Radiant_barrier) on the attic ceiling. In some ways, I think the insulation makes things much worse for summertime weather, as I have an attic fan, but the heat radiates from the attic insulation most of the night.
I found some data on radiant barriers here:
http://www.ornl.gov/sci/roofs+walls/radiant/rb_02.html
Basically, there are so many variables (weather, existing insulation, etc) that it is hard to make any meaningful calculations. I'm curious if anybody has had any success/failures with radiant barriers or any other strategies to keep their attic/upstairs cool.

[JoeTheJuggler]

I'm doing something sort of in between in my tiny little frame house. Basically, I had no insulation under my roof at all. I'm planning to sort of finish the attic and climate control it. I love the spray in foam, and I'd like to do that little by little as I can afford it, but I've got some pretty bad solar gain right now (radiant heat gain). I know it's radiant heat and not convection (what insulation would block) because the inside surface of my roof decking was at 120°F on a sunny day when the outside air temperature was about 70°.

I've got a bunch of 1/2" rigid open cell foam panels. I'm cutting them to fit between roof joists, and I'm putting the radiant barrier foil on the upper side--facing the inside of the roof deck. I'm putting it in to leave a little airspace between the roof deck and the foil. Then, I'll foam insulate underneath (inside) the foam panels as I can afford it. So far, I've only done a small part of the attic this way, but I think it's helping already.

I realize this is creating a tiny super-heated space under my roof decking. From everything I read, the shingles can handle that. If condensation becomes a problem, I'll but a vent up near the ridge. (I'll probably tear out a section and inspect it in September when it's really hot.)

Oh yeah--the radiant barrier foil doesn't qualify for the 30% tax credit. : (

For your situation, if you're not going to occupy (climate control) your attic, you could just put the radiant barrier over the inside of the roof joists in a continuous sheet. (The radiant barrier need not be a vapor barrier--in fact, the kind I bought is perforated so it definitely is not, no matter how I install it.) That would bounce some 95% of the radiant heat out before it gets to the insulation on your attic floor. It should help. Also, it's not very expensive. (I got 1000 sq ft. for $128 shipped.)

[madurobob]

So, there is no attic airspace above the second floor? Just joists with spray-in insulation and the roof above that?

I'm no expert, but I wouldn't expect the spray in insulation to have enough thermal mass to hold much heat into the night. Does the ceiling feel warm when you touch it - warmer than the air up there?

Anyway, what I do in NC to keep the second floor cool at night is put a big box fan in one window upstairs, blowing outward. Then, I open the opposite upstairs window about 1/3 of the way and one window downstairs all the way. In 15 minutes the fan blows out all the upstairs hot air. The benefit is I don't need to run the AC at night to keep the upstairs cool. If I don't do this, and don't turn on the AC, the upstairs gets miserably hot at night (actually, it remains hot, everything else just cools down in comparison).

[madurobob]

I realize this is creating a tiny super-heated space under my roof decking. From everything I read, the shingles can handle that. If condensation becomes a problem, I'll but a vent up near the ridge. (I'll probably tear out a section and inspect it in September when it's really hot.)
Here in NC a ridge vent (and accompanying soffit vent where appropriate) would be required by code in that situation. Its very humid and the temperature fluctuates quite a bit so we'd be eyeballs deep in mold and mildew without some ventilation under the roof sheathing.

[lumos]

I have radiant barrier in my new home on the gulf coast in Texas. It's basically a perforated foil attached to the roof sheathing. I believe is does cut down on some of the attic heating by reducing radiation entering the attic. It does nothing for the conductive heating. The shingles are dark grey and they abosorb so much heat, it'd burn skin in the summertime. I'd get much better results by painting the roof white. The attic is still very hot in the summertime but between the radiant barrier, dual-pained, vinyl frame windows, fiberglass insulation, insulative house sheathing (foam), and efficient air-conditioning, my house is relatively efficient.

I can't really say if it's worth the money or effort and I suspect it only saves a small amount of electricity in the summertime.

[portlandatheist]

For your situation, if you're not going to occupy (climate control) your attic, you could just put the radiant barrier over the inside of the roof joists in a continuous sheet. (The radiant barrier need not be a vapor barrier--in fact, the kind I bought is perforated so it definitely is not, no matter how I install it.) That would bounce some 95% of the radiant heat out before it gets to the insulation on your attic floor. It should help. Also, it's not very expensive. (I got 1000 sq ft. for $128 shipped.)

That is pretty much what I intend to do, purchase perforated foil from Radiant guard or some other company. I'm doing this mostly for comfort than energy savings. My bedroom is upstairs and I just either deal with heat or avoid it by sleeping downstairs instead of using air conditioning.

[-Axiom-]

Insulation and roof ventilation is the answer.

Do you have a ridgevent on the ridge of your house?
Do you have soffit ventilation?

Soffit vents allow for intake and ridgevents are for exhaust, insulation inhibits heat migration from both inside and outside your home.

One or more of these things is missing or not done correctly in your home.

A radiant barrier will just mask the issue, if you are lucky...

How old is your roof?

[BenBurch]

I am told that re-roofing with white shingles works well.

[-Axiom-]

Lighter shades of shingles do have a lower exterior temperature but the effect on attic temperatures is negligible.
If there is inadequate ventilation the heat will still build up to uncomfortable levels.
Lighter color roofs show moss and algae much more than darker shades and they show their age sooner also.

If it is not possible to ventilate the attic the next best thing would be to insulate the roof with a spray in foam insulation such as Icynene.

In very warm climates such as the American southwest a radiant barrier is a somewhat common part of the roof structure.
I doubt this is the case in the Pacific northwest.
Putting a radiant barrier in a completed Cape Cod style home could be difficult.

[shadron]

What you want to do, as much as possible, is to keep the heat from entering in the first place, and then moving out what gets in. The former you do with white exterior roofing material (best would be a mirrored exterior roof, like the radiation barrier, but aviation authorities frown on that), with radiation barrier as high as possible. Then, inside the attic, a fan which exhausts the air drawn in under the eaves and insulation on the floor above the rooms below. Trees to partially shade the roof (as well as walls) are also great.

The whole point in a radiation barrier is to reflect radiation (uv, light and infrared) away from the house. The white roofing material reflects most (perhaps 70%?) of the light and UV. If it isn't reflected it is absorbed, and then it has to be convected - the job of the fan or ridge vents - or conducted away. If the barrier reflects from under the insulation, it gives the insulation a double shot at absorbing the remaining infrared radiation and converting it to heat.

[portlandatheist]

The house was built in 1951 and the roof was redone in the mid 90's. I did some snooping around and found two major problems:
1. The vents on the eaves are blocked by the spray in insulation
2. There is no ventilation between the top attic, where there is an electric fan and the side attic.
I think my time would be better spent solving the ventilation issue before I install a radiant barrier or perhaps I should tackle both at the same time.
Here are some poor quality photos but I thought it would be easier to snap a few photos than describe what is going on.
The roof with both passive and active ventilation:
http://www.freeflightcomps.com/images/p/roof.JPG
Here is the top attic:
http://www.freeflightcomps.com/images/p/top_attic.jpg
And the side attic with the blocked ventilation:
http://www.freeflightcomps.com/images/p/side_attic.jpg

Today was overcast and it was like a solar oven in the side attic. When it is sunny I'll do a temperature compare of outside, upstairs, top attic and side attic. The side attic gets much hotter than the hottest part of the day outside.

[-Axiom-]

That is your problem.

You need to put some rafter vents in at the wall line so you have an intake.
If you want your ventilation to work correctly you should remove all those can vents and install a ridge vent also.

Doing the above will do far more than a radiant barrier.

FWIW I have been roofing in Northern Michigan for 23 years, I fix this kind of stuff all the time, it is usually because of ice damming though.

If you are near Gearhart OR, I may know someone who can do this for you.

Edited to add: You should get rid of that power vent also, it is probably burned out anyway.
Your roof ventilation is done completely wrong.

[madurobob]

That's an odd set-up, but easy to fix.

The upper and side attics split where the roofline meets upstairs wall line, right? So the upstairs is boxed in by attic overhead and on the sides?

First you need to ensure there is ventilation between the upstairs and side attics. You can buy simply foam or plastic baffles that form a "U" shaped vent between the wood of the roof and the insulation underneath it (these things (http://www.idealtruevalue.com/servlet/the-168916/Detail)). From the looks of it you can easily push them into place from the side attic.

Then, you need to get the side attics vented all the way down to the soffit - where the roof overhangs the outside wall. Check to see if there are vents there already (should be). With a little more effort you should be able to slide those same plastic baffles down from the side attic to the soffit.

If there are no vents in the soffit you'll need to install them - that could be a pain depending on the soffit. They way I've done it is use a drill, a hole saw and round pop-in soffit vents.

As -axiom- points out, those four can vents near the ridge look like an attempt at ridge venting, but probably aren't working correctly (are there four more on the other side of the roof, too?). But, I guess they are better than nothing. The power ventilator isn't helping much, since it just draws air in from those can vents and blows it back out.

[aggle-rithm]

1. Plant pecan trees around house
2. Wait 30 years

[lumos]

From your pictures, it seems that your soffit vents are clogged/non-existent. As the air heats up inside the attic, it rises and runs out of the roof vets (air-hawks, ridge-vents, electric fans, turbines, hole in roof, whatever). This air must be replaced by more air entering the attic, hopefully through vents in the lowest part of the attic space (soffit vents). These are simply some type of hole to allow outside air to pass into the attic. If air cannot enter the attic from lower areas, air cannot effectively leave and your attic will bake.

[portlandatheist]

From your pictures, it seems that your soffit vents are clogged/non-existent. As the air heats up inside the attic, it rises and runs out of the roof vets (air-hawks, ridge-vents, electric fans, turbines, hole in roof, whatever). This air must be replaced by more air entering the attic, hopefully through vents in the lowest part of the attic space (soffit vents). These are simply some type of hole to allow outside air to pass into the attic. If air cannot enter the attic from lower areas, air cannot effectively leave and your attic will bake.

I have 6 soffit vents, 3 on each side of the house, all of which are totally blocked by massive amounts of spray insulation.

[madurobob]

I have 6 soffit vents, 3 on each side of the house, all of which are totally blocked by massive amounts of spray insulation.

For the record, judging from the pictures I think what you have is "blown in" insulation instead of "spray in", but that may be a semantic point for me alone. I've always interpreted "spray in" insulation to mean expanding foam that is sprayed on like a think paint. It expands to fill all cracks and crevices. Blown in would be loose fiber material that is blown in with a large hose and settles everywhere like falling snow.

Blown in is much easier to deal with when retrofitting proper ventilation. Since you already have the soffit vents, clearing the insulation from them should be a simple task that will make a huge difference.

[jasonpatterson]

It would seem that if you're feeling adventurous, you could solve much of the problem yourself by clearing the blocked soffit vents as mentioned previously. The benefit to this approach is the price...

[-Axiom-]

I have 6 soffit vents, 3 on each side of the house, all of which are totally blocked by massive amounts of spray insulation.


If that is the case you should add more soffit venting and clear out the cellulose insulation that had fallen into the soffits.
In addition to installing rafter vents and removing the can and power vent(s).

Do you have wood or aluminum soffits?
Perhaps wood with aluminum over it?

Your best bet for soffit vents is a continuous strip, if you have a wooden soffit.
If you have aluminum or vinyl soffits all you would need is to replace the non-vented panels with vented ones, after cleaning out the cellulose over blow.
2" - 3" round soffit vents are convenient and easy to install in a wood soffit but they are only a little over 3 and 5 sq inches apiece, so you would need at least 3 of them between every truss/rafter and 4 would be better.
And that still isn't quite enough...

If venting your soffits is a problem there are a couple of products that serve as intakes that are installed on the roof, one is called "smartvent", the other is "The Edge".
You would probably want to hire a roofer to install these vents as they involve removing shingles and cutting a slot in your roof.

Proper roof ventilation will decrease the workload on your air conditioner, saving on electricity in the summer months.
Ventilation also decreases or eliminates ice damming in the cold months, but that probably is not a big issue in your climate.

To fix your roof ventilation should cost anywhere between $1,000 and $3,000 depending upon what actually needs to be done and the roofing market in your area.

Removing your power vent and can vents involves putting up roof jacks to access the roof.
Then they must be removed with the hole being sheeted over and the shingles replaced.
The cap needs to be removed from your ridge and a slot cut if there isn't one there already.
Then a ridgevent can be installed on the entire length of your ridge.
That will fix your exhaust venting.

Rafter vents can probably be installed from the inside of your attic but your soffits will still need to be cleaned out.

We normally remove the first course of sheeting to install rafter vents, but we do it as part of a reroof since we are removing the shingles anyway, not a good option for you.

Adding soffit vents depends on what you have to work with since there are a few different options.

In my area the material to do all of this would be around $800 - $1000, based on what I can glean from your pictures.
Costs for this kind of stuff vary widely from region to region, the ball park estimate given above reflects the common costs I experience in my area.

[lumos]

I have 6 soffit vents, 3 on each side of the house, all of which are totally blocked by massive amounts of spray insulation.

As others have noted, I think you have hit upon a significant problem. I don't think you can have too many soffit vents but you can definitely have too few. I am fortunate to live in a new house with hardiboard soffits. The ventilation is built into the soffit by simply having hundreds of holed drilled into it. They are constant and they go all the way around the roof line. If I go into the attic, I can easily see daylight coming through the soffits, indicating they are open. If my wife grills outside and I am in the attic, I can smell the food cooking indictaing that there is air moving in from the soffit vents and exiting the roof vents (air hawks on my house). An air hawk is just a hole in the roof covered by weatherproof housing. (I count 6 of them in the picture of your roof.)

[portlandatheist]

Thanks for all the great information. I think for this year, I'm going to clear away the "blown in" insulation from the soffit vents but I will wait until next Spring to do the big project of fixing the overall lack of proper ventilation. Axiom, I may PM you with more questions later on.