Better attic insulation options

After re-reading the GRM home efficiency thread (http://grassrootsmotorsports.com/forum/off-topic-discussion/efficient-home-thread/48440/page1/), I need some thoughts regarding better attic insulation. We live in north Florida, so most of my concern centers on heat in the attic during the summer, but better insulation will help in the winter too (we usually have several nights per year of near or below freezing temps).

The house was built in 1999 and has typical blown-in insulation. It is a one story house, except for a bonus room built over the 2 car garage. There are 2 access points to the attic (one in a closet in a bedroom and another in the bonus room). I can move around in the attic but it is so cut up with trusses that it offers very little storage.

The roof line looks more or less like this picture, with typical eaves (not my house but similar roof):

In the summertime, I bet it is 140 degrees up there. It's so hot that it feels dangerous to be up there for any amount of time. The electric portion of our bill is by far the highest, as it powers the A/C and one of our hot water heaters.

Anyway, I've been researching lots of options to better insulate it and would love thoughts from the group. I'd love to do the highest ROI stuff first, even if it is a little more costly. And if there is something out there that I didn't list, please let me know.

1. More blown in insulation
2. Some sort of radiant barrier
3. Spray on insulation on underside of roof
4. Eco-shield blanket (recommended by a friend who swears by it - http://www.ecoshieldblanket.com/)
5. All of the above
6. Other?

As a Canadian, my problems are a little different from yours in terms of where the temperature differential is, but the physics is the same. Personally, I'd do the spray foam insulation, because it can't settle over time. However, don't overlook the fact that your house is now 14 years old, and you may be losing lots and lots of temperature-modified air around windows or doors, or though other gaps that have been caused by natural aging or settling. If I were window caulking, for example, and I had to sit in the Florida sun for 14 years, I'd shrink and crack too. My point is that the roof may not be the only, or even the biggest, problem. There are services that do an energy audit of a house – you might find it illuminating. (And the audit is frequently subsidized by your utility or the government, because less energy use because of reduced waste is a win-win.)

What is the current R value of your attic insulation? Once you reach a certain threshold it is better to put your money towards other options. Focus on the big energy loss areas first and then work your way down. I believe that the order of cost effectiveness is roughly - House insulation - Sealing air gaps in doors and windows - energy efficient appliances

Also make sure your attic ventulation system is working properly. If you have an attic fan check to make sure it still functions. A lot of them fail eventually and can lead to increased heating and cooling costs.

Stealthtercel wrote: As a Canadian, my problems are a little different from yours in terms of where the temperature differential is, but the physics is the same. Personally, I'd do the spray foam insulation, because it can't settle over time. However, don't overlook the fact that your house is now 14 years old, and you may be losing lots and lots of temperature-modified air around windows or doors, or though other gaps that have been caused by natural aging or settling. If I were window caulking, for example, and I had to sit in the Florida sun for 14 years, I'd shrink and crack too. My point is that the roof may not be the only, or even the biggest, problem. There are services that do an energy audit of a house – you might find it illuminating. (And the audit is frequently subsidized by your utility or the government, because less energy use because of reduced waste is a win-win.)

Good point. In fact, I have an energy audit request in with our local utility already. They do them for free! But I think there is a long lead team unfortunately.

Quasimo1 wrote: What is the current R value of your attic insulation? Once you reach a certain threshold it is better to put your money towards other options. Focus on the big energy loss areas first and then work your way down. I believe that the order of cost effectiveness is roughly - House insulation - Sealing air gaps in doors and windows - energy efficient appliances Also make sure your attic ventulation system is working properly. If you have an attic fan check to make sure it still functions. A lot of them fail eventually and can lead to increased heating and cooling costs.

Sheepishly, I'll admit to having no clue what the R value currently is. Is there some way to determine that after the fact? We did not build the house so I don't know how to quantify what we have. I know it's hot as hades up there in the summer though and some of that heat must make it through to the house because, when I'm up near the 9' ceiling inside the house, it's a whole lot hotter up there than at ground level.

We don't have an active attic ventilation system. Just eaves and roof vents. I've thought about a solar powered fan but am hesitant to cut a whole in our roof.

Appliances are all pretty (or very) new, so all at Energy star rated.

If the insulation is blown in (ie loose), then just measure for an average depth and try to identifiy the type of insulation. When you figure out what it is, you should be able to find a R-value per inch. Multiply the two numbers for your overall R-value.

Attic ventilation is a big deal in the summertime. If there's insufficient turnover of air it will cause the ceiling to get warm and that radiates heat into the rooms, adding to the A/C's load. If there is a way to add a powered roof vent that could help a good bit.

RossD wrote: If the insulation is blown in (ie loose), then just measure for an average depth and try to identifiy the type of insulation. When you figure out what it is, you should be able to find a R-value per inch. Multiply the two numbers for your overall R-value.

Awesome! I'll work on this.

Curmudgeon wrote: Attic ventilation is a big deal in the summertime. If there's insufficient turnover of air it will cause the ceiling to get warm and that radiates heat into the rooms, adding to the A/C's load. If there is a way to add a powered roof vent that could help a good bit.

This makes inherent sense to me. Even if the outside air is 90 degrees, that is significantly cooler than the super heated air in the attic. Given the style of roof we have, would I have to install it in the roof? I think our roof style is called hipped so we don't have logical gable spots for a fan. And if it is a powered fan, does it save more electricity than it uses?

Curmudgeon is on the right is on the right track. Roof needs to vent better, combined with better ceiling insulation. You need vents in your eves and at the ridge of your roof. You may even find putting a small fan in the attic space will make a huge difference up there circulating the air. Poor venting will kill your roof. Lots of times blown in insulation will end up covering the vents, so make sure those airways are clear and it will make a huge difference.

My understanding is if the venting system is designed adequately a power ventilation fan is not needed, and in fact can mess up the proper air flow through the attic space. Since hot air rises, air will be drawn in through the vents at the eaves and exhausted out through the vents at or near the peak, but you need to make sure you have enough vents at both locations.

You also need to make sure there are no air leaks from the conditioned space inside the house to the attic.

Cover your roof with bedliner.

stuart in mn wrote: My understanding is if the venting system is designed adequately a power ventilation fan is not needed, and in fact can mess up the proper air flow through the attic space. Since hot air rises, air will be drawn in through the vents at the eaves and exhausted out through the vents at or near the peak, but you need to make sure you have enough vents at both locations. You also need to make sure there are no air leaks from the conditioned space inside the house to the attic.

That is true if proper vents are in place and not obstructed.

Lots of times eve vents are omitted for some stupid reason, but it depends on building codes in your area. If you don't have them, they aren't terribly hard to add after the fact if you have a ladder tall enough to reach the area.

Lots of good attic venting advice here. Get the temp down up there and shingles last a whole lot longer too.

stuart in mn wrote: My understanding is if the venting system is designed adequately a power ventilation fan is not needed, and in fact can mess up the proper air flow through the attic space. Since hot air rises, air will be drawn in through the vents at the eaves and exhausted out through the vents at or near the peak, but you need to make sure you have enough vents at both locations. You also need to make sure there are no air leaks from the conditioned space inside the house to the attic.

This is where I'm stumped. Our eaves (or at they soffits?) are entirely made up of this material:

And we have lots of roof vents like this:

Yet the attic is still brutally hot in the summer.

4 things that will be going into the home we plan to build in the near future

1. Metallic radiant barrier. Looks like a quilted mylar blanket you see them drape over marathon runners or people rescued from a frozen lake or something. We were at a home and garden show, and a simple heat lamp had just a section of this stuff - no other membranes or insulation of any kind - stretched out under half of the lamp, about 10" or so from the exposed elements. You could put your hand right under that barrier, approx 12" from the lamp, and feel no heat. Move your hand under the lamp at the same distance from the elements, but without the barrier, and you couldnt keep it there for long before the pain became intolerable...sold

2. Attic troughs (not sure if thats the real name) - these are ABS "tunnels", about 18" long, that mount along the bottom of your roof sheeting, just above the soffit. They keep bat/blown insulation from cutting off flow coming in from your soffit vents

3. 6/12 pitch roof - steeper pitch gives more "chimney" effect in the draw of heated air out thru the ridge vents.

a 4th possibility that Im not sold on yet would be a solar powered gable fan...

dyintorace wrote:

stuart in mn wrote: My understanding is if the venting system is designed adequately a power ventilation fan is not needed, and in fact can mess up the proper air flow through the attic space. Since hot air rises, air will be drawn in through the vents at the eaves and exhausted out through the vents at or near the peak, but you need to make sure you have enough vents at both locations. You also need to make sure there are no air leaks from the conditioned space inside the house to the attic.

This is where I'm stumped. Our eaves (or at they soffits?) are entirely made up of this material: And we have lots of roof vents like this: Yet the attic is still brutally hot in the summer.

That's how most houses are built and it can be considered a 'thermosiphon' system. As hot air rises and escapes it draws cooler air in at the soffit. They do need help sometimes and that's where the powered vent comes in. If you get one with a thermostatic switch it will only run when needed.

The problem is the blown in insulation can cover the soffit vents over time. You almost want a chimney over the sofit vents to prevent the blown in insulation from migrating over those vents.

The vents in a typical home are there to allow just enough airflow to keep moisture from collecting and causing mold. If you want to get rid of the heat, you need a fan. Either something electric that you can turn on and off, or something wind-powered or solar-powered.

sachilles wrote: The problem is the blown in insulation can cover the soffit vents over time. You almost want a chimney over the sofit vents to prevent the blown in insulation from migrating over those vents.

thats the troughs I mentioned above...

sachilles wrote: The problem is the blown in insulation can cover the soffit vents over time. You almost want a chimney over the sofit vents to prevent the blown in insulation from migrating over those vents.

I think I'm okay here. While I haven't checked all the attic, there doesn't seem to be too much that has blown over into the soffits.

pinchvalve wrote: The vents in a typical home are there to allow just enough airflow to keep moisture from collecting and causing mold. If you want to get rid of the heat, you need a fan. Either something electric that you can turn on and off, or something wind-powered or solar-powered.

So the theory is that it is pulling hot air out, right? So, hopefully the hot air is being replaced by cooler air drawn in via the soffits?

Correct. If you can remove the 140 degree air and replace it with 90 degree air, not as much heat will radiate down into the living areas. Part of this is all those exposed boards ('joists') you see in the average attic are attached directly to the Sheetrock and wood does not insulate very well, meaning this causes the Sheetrock to get warm.

Ignore the orange boxes, they don't mean a thing in this context.

If you can get insulation over those joists that would help too.

pinchvalve wrote: The vents in a typical home are there to allow just enough airflow to keep moisture from collecting and causing mold. If you want to get rid of the heat, you need a fan. Either something electric that you can turn on and off, or something wind-powered or solar-powered.

This is what you need. I had soffit vents with the "tunnels" and ridge vents put in when we redid the roof years ago. Also have vents in all 3 gable ends. The AC still ran a lot and this is in MD. Had one of these powered attic fans(probably the exact one in the pic) installed and saw the difference immediately. It is hard wired and has a thermostat so it only comes on when the attic temp gets over 120.

There is a lot of pretty good general info in this thread, but a lot of it doesn't apply to your house.

Let me interject a couple of things...

The things previously referred to as "troughs", "tunnels", and "chimneys" are correctly called baffles. They are available in both styrofoam and cardboard. One correction... in most cases, these may not help with ventilation. They keep insulation in place. If they are not there, most of the time your insulation has fallen into the soffits, so you have plenty of ventilation (but lousy insulation).

You said you have lots of "off-ridge vents". It is unlikely you have enough with a hip roof. You would need something like 30 of them, all in the top 1/3 of the roof. Since there are none on the front, my bet is you don't have enough. But it doesn't matter. Read on...

A hip roof is a trap for natural ventilation. There is insufficient ridge area for the volume of the attic, especially in FL. It is NOT POSSIBLE to have adequate natural flow-through "chimney" ventilation. Don't bother trying.

Your solution will be those powered mushroom style roof vents. You will probably need 2. Buy ones with thermostats, as previously mentioned. They make them solar powered too, which will mean no power consumption (but reduced efficiency when they get dirty).

After you deal with the ventilation, consider insulation. You should have R-30- R-38. That would be 14"- 18" of loose filled fiberglass. Stick a ruler in it, and see how thick it is. I'd be shocked if you have more than 8". Don't try foam. It is almost impossible to retrofit well. Just blow more fiberglass on top of what you've got.

I'm not working these days, so if you need an installer, give me a call. Don't mind a road trip.