I've got a home in CS, built in the 80s. Utilities (electricity) kills us in the Summer. The a/c is plenty large enough, and is only four years old (Trane). I'm looking for inexpensive, yet effective, insulation in the attic. I've thought of several ideas. So, my question has several parts.

1) Would polystyrene panels installed between the roof joists effectively keep some heat from entering through the composite shingles into the attic?

2) Would it be better to simply add new roll-out insulation over the living area in the attic?

3) We've got an attic fan that works, but we only got it working this past August. Will it do more harm than good?

Roc96 said:

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1) Would polystyrene panels installed between the roof joists effectively keep some heat from entering through the composite shingles into the attic?

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That sounds like a good idea if you have soffit vents along with a ridge vent. Install in the middle of the joist to give a couple inch air gap for it to escape out the ridge vent.

That's not exactly what I've got. I've only got soffit vents. Thanks!

edit: I didn't read your message correctly.

I've wondered how one could use discarded styrofoam and press/mold them into thick panels for insulation, to give it a long-term use, and keep them from landfills.

What's your ceiling insulation like now?

There have been several discussions about attic insulation recently that have some good info. Check out the first few pages worth of threads.

Biggest bang for the buck will be to blow in insulation until you reach minimum code in CS which is r38 for ceilings.

How deep of insulation is in the attic now ?

Attic fans work but from my experience any electrical savings gets eaten up from the fan running nonstop in the summer. Also often the attic fan will pull conditioned air through electrical box penetrations in the ceiling causing the air conditioning to work harder.

Current attic insulation against the ceiling is less than six inches in depth, and appears to be original.

Polystyrene between the roof rafters is a lot of work. I just did it for a new room that we added above the garage and it was a PITA. Google "cut and cobble insulation" if you want to read more. If you still want to do it, look for a local supplier of recycled polyiso insulation instead of polystyrene. Repurposed Materials is such a place in DFW.

Roc96 said:

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Current attic insulation against the ceiling is less than six inches in depth, and appears to be original.

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With 6 inches or less you are only looking at roughly r19 so blowing a overlay on top to get to r38 will help greatly with heat transfer from the attic. If you want to diy you can buy the bags at lowes and the machine rental is usually free but it takes to people, 1 to run the hose and 1 to feed the machine down low.

Thanks, JP. This is very helpful.

JP76 said:

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Roc96 said:

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Current attic insulation against the ceiling is less than six inches in depth, and appears to be original.

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With 6 inches or less you are only looking at roughly r19 so blowing a overlay on top to get to r38 will help greatly with heat transfer from the attic. If you want to diy you can buy the bags at lowes and the machine rental is usually free but it takes to people, 1 to run the hose and 1 to feed the machine down low.

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Same applies with Home Depot...

JP76 said:

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Roc96 said:

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Current attic insulation against the ceiling is less than six inches in depth, and appears to be original.

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With 6 inches or less you are only looking at roughly r19 so blowing a overlay on top to get to r38 will help greatly with heat transfer from the attic. If you want to diy you can buy the bags at lowes and the machine rental is usually free but it takes to people, 1 to run the hose and 1 to feed the machine down low.

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Agree, if your insulation is only 6 inches deep you can see big changes by adding another 6-8 inches for cellulose or 8-10 fiberglass. (I think I did the math right to get to R38 or better)

I did the blown in insulation over the winter. Almost 18 inches installed (which came to ~R40). Took one day. We aren't even into the heat of summer next and I already love it.

Agree with most here that blowing extra insulation above your 6 inches is going to be your best bang for the buck.

Having seen a number of 80's homes built in BCS the following "checks" of air infiltration or ex-filtration could prove interesting:

-make sure someone sprayed foam into the holes where the electrical cables enter the walls in the attic.
-consider throwing some large styrofoam coolers over the top of any original can light fixtures still in the house from the 80's that aren't meant to be covered with insulation (and not rated to be covered). Many of them are notorious for leaking. A large styrofoam cooler with at least 6 inch of air clearance from the fixture will help a lot and not cause the heat overload to trip and shut the light off occasionally.
-check your door thresholds to the outside and make sure the weatherstripping isn't gone or shows 1/4 inch or more of light under the door when you look.
-You may have windows that leak like crazy around the frame (in the wall....not the window itself). Not much you can do there until you are needing to remove trim or drywall during update and then check the framing.

I've been amazed at how bad some of the SWV homes built during the boom times in the 80's leak air around windows, doors, lights, etc.. With the AC on use a smokestick and walk around the inside of the exterior walls near doors and windows and lights in the ceiling if you can get close. The smoke will show you where the larger leaks are and you can consider the best way to address them....or not until you remodel, etc.

Thanks, Ranger!

you only have soffit vents? nothing else (besides the fan)?

sts7049 said:

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you only have soffit vents? nothing else (besides the fan)?

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There's a regular attic vent at each gabled end, and three turbine vents. Just no ridge vent.