Reduce electric bill by installing radiant barrier in attic?

[samclem]

Add in a car radiator fan @1800 CFM and a 20W solar panel and the turbines work even better.

This brings up an interesting problem. If there is any type of power ventilation, placement is important. Studies have shown that the power ventilators often cause air to be drawn in through other nearby high vents, and cause relatively little air to be drawn in through the soffit vents. This can significantly reduce their effectiveness of ventilating the attic.

Adequate soffit and ridge/gable/hat vents allow for natural convective airflow that is not subject to mechanical failure, costs very little, and has reduced potential to draw conditioned air from the dwelling through the hundreds of gaps and cracks existing in the typical home.

 

[Telly]

Well I plunked down $250 for 2000 sq ft of the stuff and just for kicks started to put a few pieces up in the attic. I swear by the Hammer of Thor, that is tough work! The ambient temp was 116 when I started around 6PM, and working with the material by yourself is definitely not the quickest way to do it. Hopefully as I get more up this weekend I'll notice some improvement.

The hardest part of the job is just getting around the attic without stepping through the ceiling, tripping over the A/C ducts, running into the trusses, or hitting your head on roofing nails.

Upon searching other home improvement forums, the usefulness of the radiant barrier material seems to be hotly debated. I am hoping that this project is not an exercise in snake oil installation...

Please keep us up to date as you go along on this. The radiant heat in a Southern clear-sky attic is incredible. When I replaced two HVAC units and adapted and reconfigured ductwork, I would start out about 7 AM, and work till it was just too hot for me. And that was early in a year! By 10 AM, if I was down on the attic floor, closed my eyes, and swiveled my head around in all directions, I could feel the radiant heat strongly on my face if I faced the roof surface that the sun was shining on. The underside of the roof deck was like a fire at a moderate distance.

What product are you using for the barrier?

 

[soupcxan]

I've been working on the project for a few days now and I think it's going to save me quite a bit of money - after working in the 120 degree attic (it's 100 outside), I have been cured of my desire to travel to the middle east, or anywhere that might be described as the "desert". I brought a metal ladder into the attic to reach certain areas and it's now too hot to even touch it without burning your hands.

Too early to tell if it will actually save me any money on my electric bill.

 

[travelover]

I bought one of those indoor/outdoor thermometers with a wireless remote and stuck the transmitter in my attic. It allows me an objective measure of how hot it is up there (without sticking my head through the access hole). I also installed a two speed gable fan with a thermostatic switch. I wired it so I can run it in any mode - hi/lo, auto/manual. It quickly cools the attic from 140 degrees to about 110 on a very hot day. I've noticed that my upstairs is noticeably cooler when I have the fan running - the ceiling even feels cooler.

I have a trussed roof support as well and I bought some used 1/2" plywood (thanks craigslist) and made a 2 foot wide track in the "V" of the truss that keeps me up off the insulation, but allows for headroom. I can crawl all over my attic on this track now, which really helped when I installed some tubular skylights.

 

[Nords]

I have a trussed roof support as well and I bought some used 1/2" plywood (thanks craigslist) and made a 2 foot wide track in the "V" of the truss that keeps me up off the insulation, but allows for headroom. I can crawl all over my attic on this track now, which really helped when I installed some tubular skylights.

We had a chicken/egg problem with the attic being too hot to put in flooring or tracks, and the lack of flooring made it tough to put in the insulation to bring down the temperature.

But now that the attic is cooler, our winter project is the "infinite attic storage system"...

 

[cute fuzzy bunny]

This brings up an interesting problem. If there is any type of power ventilation, placement is important. Studies have shown that the power ventilators often cause air to be drawn in through other nearby high vents, and cause relatively little air to be drawn in through the soffit vents. This can significantly reduce their effectiveness of ventilating the attic.

Adequate soffit and ridge/gable/hat vents allow for natural convective airflow that is not subject to mechanical failure, costs very little, and has reduced potential to draw conditioned air from the dwelling through the hundreds of gaps and cracks existing in the typical home.

Air is stupid...it doesnt know where you want it to come from or where you want it to go.

In some cases if you create too much negative pressure in the attic, you can draw conditioned air from the living space, which of course is replaced by unconditioned air through every crack and crevice.

The laws of unintended consequences are quite strong when any ventilation product is deployed...

 

[OAG]

We had a chicken/egg problem with the attic being too hot to put in flooring or tracks, and the lack of flooring made it tough to put in the insulation to bring down the temperature.

But now that the attic is cooler, our winter project is the "infinite attic storage system"...

That is a neat system and would work in my garage (which currently is uninsulated). Wonder if I can find some scrap metal strapping to make them myself (for less than the $129)?

 

[cute fuzzy bunny]

Do pay note to yet another possible unintended consequence...in many cases the trussing systems used in homes are not engineered to hold uneven weight bearing loads pushing down in the middle of the system...in particular in unsupported garage ceilings. They're made to hold a roof UP.

In my old neighborhood it was very popular to put in the stairs and the full storage floor and fill it up with stuff that people will never use again. Almost all of these had a bowed roof over the garage.

 

[samclem]

That is a neat system and would work in my garage (which currently is uninsulated). Wonder if I can find some scrap metal strapping to make them myself (for less than the $129)?

I think it would be tricky to make those yourself, as it appears they are stout enough to support the 2x2s (and the board over the stud bay, and a guy with a box of Christmas ornaments) without any other fasteners.

If you've got more time/enthusiasm than money, you could accomplish the same result by screwing 3x2's to the sides of your truss bottoms. Temporarily shim them up so they are in the same spot as the Infinite Storage hangers would have put them: 3/4" below the tops of the truss bottom piece. Then, just screw the floor pieces (3/4" OSB would be cheapest,3/4" plywood would be lighter and easier to handle) to the tops.

Waiting for Winter is a good idea.

 

[samclem]

CFB said:

Do pay note to yet another possible unintended consequence...in many cases the trussing systems used in homes are not engineered to hold uneven weight bearing loads pushing down in the middle of the system...in particular in unsupported garage ceilings. They're made to hold a roof UP.

True. I built a shop and added deep shelving up near the ceiling for storage. I hung the shelving with wood that went up to to the top of the trusses, rather than hanging them from the bottoms. That's what the engineers at the truss company recommended.

Also, (obviously) if you think you might ever want to insulate the garage, do it before you put the flooring in. Even just 3 " of cellulose or fiberglass (R-13 or so) will make a big difference compared to an uninsulated ceiling.

 

[cute fuzzy bunny]

Insulation is an amazing thing. We have a 3 car garage with bedrooms over top of it. Uninsulated garage doors that take direct sun all afternoon and get too hot to touch and I'm sure the builder put no insulation in the front or side walls. 6" of fiberglass in the garage ceiling/bedroom floor.

Used to get up to about 120-125 out there in the summer. The bedrooms over the garage got plenty warm late in the day.

When we stucco'd we put on an r-4 layer of foam first and we replaced the garage doors with insulated ones.

Maybe hits outside air temp (90ish) by very late in the day now. Noticeable difference in the bedrooms above.

 

[soupcxan]

I finished putting up the first 1000 sq. ft. roll of foil. The attic still hit 125 yesterday afternoon, but most of the foil I've put up so far is on the east side of the roof. I would say that the part of the roof under the foil "feels" cooler while I'm standing up there, but that may just be my imagination.

When I finish the radiant barrier, I'm thinking of adding a bit more insulation to the attic. Any thoughts on the following questions:

1) Is there any problem with adding a few inches of cellulose insulation on top of ~10 inches of rockwool insulation?

2) I'd only target a few areas of the roof for extra insulation, if I'm only doing 10-20 bags of cellulose can I just distribute it by hand? I'd rather not deal with the hassle of getting a blower (I know its a free rental, but still). I imagine that I could fluff up the insulation in a big plastic tub in the attic, then use a bucket to throw it where I need it. Other than taking longer than with a blower, any problem with this approach?

 

[samclem]

When I finish the radiant barrier, I'm thinking of adding a bit more insulation to the attic. Any thoughts on the following questions:

1) Is there any problem with adding a few inches of cellulose insulation on top of ~10 inches of rockwool insulation?

Nope, absolutely no problem. In fact, (as noted previously) the cellulose will do a lot to increase the insulating value of your already existing insulation by stopping the flow-through convective losses that rock wool and fiberglass are subject to on very cold days.

2) I'd only target a few areas of the roof for extra insulation, if I'm only doing 10-20 bags of cellulose can I just distribute it by hand? I'd rather not deal with the hassle of getting a blower (I know its a free rental, but still). I imagine that I could fluff up the insulation in a big plastic tub in the attic, then use a bucket to throw it where I need it. Other than taking longer than with a blower, any problem with this approach?

I think you'll be sorry. The blower is easy to handle, the hose is long enough to allow the unit to be placed outside, and the blower does the job of moving the insulation up to you. It also fluffs it up and distributes it more evenly than you can do it by hand. Also, you can shoot the stuff a good distance with the blower, which will save you from having to crab your way all over the attic. Probably not a big deal unless your roof pitch is low.

The job goes very quickly with the blower (it digests a bag in a couple of minutes). It's a good, satisfying project. Wear a good dust mask (N95--with an exhale valve. Spend the 5 bucks). I think you'll find using the blower (if you've got a helper) a lot simpler than hoofing those bags up to the attic and then trying to hand spread the cellulose. But--it's possible to do it that way. Some folks do it.

If I were going to do this by hand, I'd probably use unfaced fiberglass batts. And I hate those things/that stuff.

 

[cute fuzzy bunny]

I only tried doing one bag of cellulose by hand, if that helps.

Ends up chunky, you dont get as much coverage, and you'll be covered with the stuff.

If you get a blower, make sure you dont block any vents or cover any recessed lighting thats not rated to be covered with insulation.

 

[Nords]

That is a neat system and would work in my garage (which currently is uninsulated). Wonder if I can find some scrap metal strapping to make them myself (for less than the $129)?

I think the cost of the metal will pale in comparison to the cost of the wood!

Do pay note to yet another possible unintended consequence...in many cases the trussing systems used in homes are not engineered to hold uneven weight bearing loads pushing down in the middle of the system...in particular in unsupported garage ceilings. They're made to hold a roof UP.
In my old neighborhood it was very popular to put in the stairs and the full storage floor and fill it up with stuff that people will never use again. Almost all of these had a bowed roof over the garage.

We'll have to see what happens with our hurricane-strength trusses. I think our attic storage is living on borrowed time with all the things that are propped between the trusses. I know that in 20 years I'm not gonna want to shimmy across the trusses.

It's an interesting thought about spending the $$ to improve the storage of crap. Some of it is valuable crap-- like spare parts for our 19-year-old stove scavenged from all the ones put on the street a few years ago. But otherwise this is about the only way that we're going to get a good look at all of our stuff. Spouse has floor rugs from houses that she lived in 20 years ago but heaven forfend that we should get rid of them-- we might need them someday! Once we price out the project it might make more sense to actually divest ourselves.

The most popular stupid truss trick around here was replacing shake or composition-shingle roofs with ceramic tile without installing additional trusses. You can actually see the waves on some roofs.

 

[cute fuzzy bunny]

Oh yes, thats another bad idea. A bunch of older homes in a neighborhood near here seem to have all been attacked by the same roofing company who put in some kind of composition/clay tile on homes that formerly had asphalt shingles.

Ripple and bow.

I have to admit having lived in a house with a concrete tile roof that the idea of three or four tons of rock hanging over your head is a mite concerning.

 

[Nords]

I have to admit having lived in a house with a concrete tile roof that the idea of three or four tons of rock hanging over your head is a mite concerning.

On a fault line.

But, hey, at least California outlawed those [-]attractive, lightweight, affordable[/-] dangerously flammable cedar shakes...

 

[cute fuzzy bunny]

Believe it or not, you can still install them in my county, which has one of the highest fire rates around.

Many of the local cc&r's restrict homes to either shake or concrete tile, no alternatives. Obviously you dont need to replace a concrete roof for at least 50 years, and putting tile on a non sheeted skip lathe roof would be a very bad plan.

 

[soupcxan]

Update: The radiant barrier is installed. I achieved about 80% coverage, the remaining 20% would require taking down the A/C ducts and due to the layout of the attic and all the insulation I've already crushed, I'm unwilling to do this. The attic still gets quite hot, although with the variations in outside temp and lack of pre-foil baseline data, it's hard to make an accurate comparison.

I purchased the foil from Radiant Barrier Foil Insulation Do-It-Yourself Radiant Barrier Tips. It was the best price I found online (with local pickup in DFW) and the product seems to be high quality. I can't tear the foil with my hands, it's quite sturdy.

In retrospect, I should've started this project with the attic ventiliation. This weekend I'm going to check the soffit vents for obstructions (I suspect they're clogged with insulation). My understanding is that for a ~2000 sq ft attic area, I should have a ventilation ratio of 150:1, or about 13 sq. ft. free vent area (FVA). I have two 9 inch round vents at the peak of the roof which together give me about 1 sq ft FVA, and 10 4x16 inch soffit vents (28 sq in FVA each) which gives me about 2 more sq ft FVA. So I have a total of 3 sq ft of vent area when I should have 13...are my calculations off somewhere or did they build the house with way too little attic ventilation? If anyone has any thoughts on this, please share.

I guess the next quickest/cheapest way to increase ventiliation would be to replace the 4x16 soffits with 8x16 soffits. I probably need to add a few more vents at the top of the roof, but that may be more work than I'm willing to take on.

 

[HFWR]

Ideally, the free vent area should be evenly divided between upper and lower vents.

 

[Patrick]

I have two 9 inch round vents at the peak of the roof which together give me about 1 sq ft FVA, and 10 4x16 inch soffit vents (28 sq in FVA each) which gives me about 2 more sq ft FVA. So I have a total of 3 sq ft of vent area when I should have 13...are my calculations off somewhere or did they build the house with way too little attic ventilation? If anyone has any thoughts on this, please share.

I guess the next quickest/cheapest way to increase ventiliation would be to replace the 4x16 soffits with 8x16 soffits. I probably need to add a few more vents at the top of the roof, but that may be more work than I'm willing to take on.

The 9-inch vents actually give you about 0.44 sq. ft. FVA. Area = Pi X radius squared = 3.14 x 4.5 X 4.5 = 63.58 sq. in/vent X 2 vents = 127 sq. in.

127/144 sq. in. per sq. ft. = 0.88 sq. ft. This must then be reduced by any obstructions like screening that are in the way. Typically, a 50% reduction is used. So 0.88/2 = 0.44 sq. ft, unless there is no screening or louvers in the way of the air flow. If they are turbine vents, forget all of this because they actually extract air depending on local wind speed.

A 1:300 ratio may be adequate. See BSD-102: Understanding Attic Ventilation — buildingscience.com

So 6.5 sq. ft. might be adequate, but you are still way below that. Some building codes specify 1:600 - perhaps your house was built under that. And, as HFWR said, it should be equally distributed between soffit and peak.

 

[samclem]

Patrick is right--the "net free area" of the vents isn't just the area of the hole in your roof, because the screening and louvers really cut down on flow of air. Look at the vents in the home stores, the packaging will tell you how many sq inches/sq feet of vent area each one provides.

Yes, you have far too little ventilation. You aren't overlooking anything, like gable vents or ridge venting, are you?

Net Free Vent Area should equal at least 1/300ths of your ceiling area IF you have a very good vapor barrier in your ceiling. If you have a typical vapor barrier, 1/150th is sufficient. These are minimums, and help to assure that homes in cooler climates won't get excess moisture buildup/condensation in the attic. In the DFW area, I'd think the major issue is getting that heat out, and that more is better. I'd want at least 1/150th if I lived in Dallas. Of this total amont, 1/2 should be high, 1/2 should be at the soffits. Be sure the air can flow freely from your soffits into the attic and s not blocked by insulation/etc in the attic.

This ventilation will probably help a lot.

Some folks like the turbines, but I'm not a big fan due to their appearance and that fact that I've experienced more water infiltration from them than with typical "turtle vents (or "hat vents"). Just my opinion.

 

[cute fuzzy bunny]

This weekend I'm going to check the soffit vents for obstructions (I suspect they're clogged with insulation)

Ladder and a leaf blower will fix that. Just keep the air flow parallel to the roof line so you dont blow all the insulation away from that area of the attic floor.

In a perfect world they baffle the soffit vents with a piece of plywood a couple of feet up the rafters. Apparently soffit vents arent able to figure out the plywood.

I'm very sorry, the coffee is a little strong today.

 

[lets-retire]

Ideally, the free vent area should be evenly divided between upper and lower vents.

The house I had in Florida only had soffett vents, but they did add up to the minimum required sq/in for the house size. I cut the shingles at the ridge off and installed ridge vents. I was surprised by the amount of decrease in attic temperatures and electric bills for the summer.

 

[cute fuzzy bunny]

Yeah, soffit vents only wont do you any good. Nowhere for the air to go. It might have had some eyebrow vents or gable vents at one time but a prior homeowner might have removed them or covered them up when doing a roof or siding job.