I know this is a nutty idea, but I'm really bugged with having so much heat gain in my attic. I started thinking of this after a friend installed a sprinkler system on his roof to protect against wildfires. Why not do the same to reduce the heat?

A quick bit of internet research shows that some have tried it and the results are dramatic, dropping attic temps from 130 to 85-90. Most who have tried it set it up on some sort of timer so that it works only 5 minutes out of 30 or something like that. The amount of water used is minimal and if one sets the volume of water correctly there is little to no drainage.

The major negatives that I've discovered so far are:

• It's ugly and weird looking.
• If you have lots of minerals in your water, it may leave mineral deposits on your roof
• It may or may not reduce the life expectancy of your shingles (Argument for decrease is the frequent application of water to your shingles. Argument against decrease is that reducing the heat of your shingles may actually extend their life expectancy.)

Has anybody tried this? Any thoughts, comments, or, better yet, ideas and suggestions?

Would think a fan in attic would be better. Does work for fires.

HDeathstar said:

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Would think a fan in attic would be better. Does work for fires.

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Thanks for chiming in. I have no side eaves, so I have no room for an attic fan, except possibly those roof mounted ones. However, everything I've heard about them is that they don't actually work that well and invariably the motor burns out after 3 years or so.

Again, thanks for replying.

Several responses and questions.

First, what is the evidence that a thermal barrier and/or more insulation would do better? I already have R38 (or something like that) insulation in my attic.

Second, where I live it's impossible to find anyone to install radiant barrier and I'm too old to do it myself. And again what is the evidence it would do better?

Third, the quotes I've gotten to spray foam my attic are in the $15k-20k range. That's ridiculous. A sprinkler system would cost $100-200 to install, cost only a few dollars to operate, and may be more effective.

I've seen misting system on greenhouse roofs to help regulate indoor temps, so I suppose there's no reason this wouldn't work with a traditional asphalt shingled roof as well. But there's probably no data out there to give you an idea of what the typical offsets may be in water use cost and initial investment vs. current HVAC use costs.

I vote you try it out and document all of your findings for science.

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I vote you try it out and document all of your findings for science.

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Absolutely! No sacrifice is too great when it's for science.

sts7049 said:

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there are many better ways than wasting water on your roof

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Such as? Looking for constructive critiques, or alternate ideas, here, fellas.

As with all evaporative cooling, it would work better in dry climates than humid climates. Unfortunately, the drier the climate, the less available cheap water is (generally). If you can't afford to repair your AC and can't afford better or more insulation, it can be a good option. Best implementation would probably be a soaker house at the peak of the roof on a timer to where you don't have much runoff from the roof. It will work best on mostly sunny days and not as well on cloudy days. Of course if the hose or the timer breaks, you will wash all your savings down the drain. If your HOA and/or City are good with it, try it out.

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He's saying it's a massive waste of water, which is already in short supply throughout most of the state. That's it. It's not a viable option.

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But it is not a massive waste of water, especially if you are running only a few sprinklers for only a few minutes each hour. Most of the systems I've seen on the Internet are only using a couple of gallons an hour or so.

In addition, you have also assumed that I live in Texas. Believe it or not, not everyone on the site does. I do not, and water is not in short supply where I live.

But thanks for the constructive suggestions anyway.

Jabin said:

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HDeathstar said:

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Would think a fan in attic would be better. Does work for fires.

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Thanks for chiming in. I have no side eaves, so I have no room for an attic fan, except possibly those roof mounted ones. However, everything I've heard about them is that they don't actually work that well and invariably the motor burns out after 3 years or so.

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I had an electric fan that vented out of the roof in the attic at my old house. I replaced one about 5-8 years in and it was still going strong when we sold over 10 years later. I got busted about the connection when the inspector came in when we sold. I don't have any solid data on savings on electricity, but I seem to remember a bit smaller bills in the worst of summer. If you don't have those side vents I guess the turnover wouldn't be good enough to make a difference.

Jabin said:

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He's saying it's a massive waste of water, which is already in short supply throughout most of the state. That's it. It's not a viable option.

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But it is not a massive waste of water, especially if you are running only a few sprinklers for only a few minutes each hour. Most of the systems I've seen on the Internet are only using a couple of gallons an hour or so.

In addition, you have also assumed that I live in Texas. Believe it or not, not everyone on the site does. I do not, and water is not in short supply where I live.

But thanks for the constructive suggestions anyway.

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you did ask for thoughts and comments as well...

anyway, what is your end goal? to reduce heat in the attic? or to help keep your home cooler inside?

if it's the former, but your home stays cool as you like it, then what does it matter what is happening in the attic? all you really need to make sure is you have the attic space ventilated correctly to keep the airflow, and you're good. why waste water on reducing attic temps a few degrees (i'm highly skeptical that only a few gallons would make any sort of difference in attic temp, especially if it's 100+ outside)

if you are having issues with the heat indoors and a/c not keeping up or something, you would be better off focusing elsewhere. stop air leakage to/from the attic. are the windows in good shape, consider some shading/screens/ceramic tint to reduce the heat gain into the house. is HVAC performing correctly.

anyway, what is your end goal? to reduce heat in the attic? or to help keep your home cooler inside?

Both. Reducing heat in the attic will keep my home cooler.

if it's the former, but your home stays cool as you like it, then what does it matter what is happening in the attic?

Hot attics make the AC work harder than necessary. It also bugs me that, in my house at least, the coils, return ducts, and supply ducts are all in such an intensely hot part of the house envelope. It may not matter to you, but it does to me.

all you really need to make sure is you have the attic space ventilated correctly to keep the airflow, and you're good.

Not necessarily, and it's difficult to vent the attic correctly. I currently have ridge vents which are grossly inadequate given that my roof has very short ridges. Every roofer I've talked to has recommended replacing the ridge vents with turbine vents, but in looking at their capabilities vs. recommended exit venting, I suspect that they will not significantly cool my attic either. They simply do not allow that much air flow. An owner of an insulation company I talked to says that ventilation really doesn't make that big a difference. He stated that every attic in the state right now is at 130+ degrees. I'm reluctant to go spend $1500-2500 to do the replacement and it end up not making any difference.

I have plenty of soffit vents.

why waste water on reducing attic temps a few degrees (i'm highly skeptical that only a few gallons would make any sort of difference in attic temp, especially if it's 100+ outside)

From what I've read and the people that do use roof sprinklers (primarily commercial uses but some residential), it doesn't take that much water. For example, it takes 8000 BTU to evaporate 1 gallon of water. The residential users I've found online claim that simply setting a timer to sprinkle your roof for 5 minutes every 30 minutes reduces their attic temps from 130 to 85-95.

if you are having issues with the heat indoors and a/c not keeping up or something, you would be better off focusing elsewhere. stop air leakage to/from the attic. are the windows in good shape, consider some shading/screens/ceramic tint to reduce the heat gain into the house. is HVAC performing correctly.

I've already done those things. Plus, I'm now focusing on the attic heat, which dwarfs all of those other factors you've mentioned.

By starting this thread, I was hoping for insights into design and use of a roof sprinkler system, and perhaps specific reasons not to use one from people who might have had experience with them, not comments on general AC issues.

OP, what's your location?

Watching this thread. Took an Infrared picture of a random house around 2pm yesterday in Dallas suburbs. Outside asphalt shingle roof is 175 to 180 degrees. Been randomly checking attic temps. Newer homes with radiant barrier and typical ventilation (likely inadequate to the letter of the recommendations) run 130 tob140 at the top of the attic and 120ish at the floor. Houses without Built in radiant barrier or really obviously poor/no ventilation run about 30 higher.

Think I am in the camp that his isn't really feasible on a constant all day basis. Not all of that heat for evaporation is going to be coming from the roof surface. I think it will cool, but 80 degree attics from it seem like a stretch with no other changes.

To me it seem like it would work best to do at sundown as a way to jump start cooling the attic by removing the latent heat from the roof, then the other parts of attic efficency work to cool the attic faster.

For us in Dallas with water costing what it costs, and doubting that it would not take a lot more water than the op suggests on most houses, i would suspect you spend more in the water.

As with most efficiency improvements no single thing is likely to be the magic answer. It seems the the right combination of different factors makes the biggest improvements. So spraying down a roof in a house with bad insulation, bad ventilation, bad ac etc isn't going to help much overall. If all those things are in pretty good shape, then adding this might make a positive noticeable difference.



Eot
If someone near by wants to experiment, I'm happy to come do the infrared to check temps. Don't think my roof is a good candidate as I have a foamed attic.

Here's my off-the-wall answer:
If I were in your situation, I'd install solar panels.

Your roof would be shaded by them, and you'd pick up the extra electricity benefit. I'm guessing they'd be more money than the spray foam quote, but you'd get the palpable ROI (I'm not going to speculate whether that ROI is higher than spray foaming would be, just that you could see the actual number every month.)

I lived in a house for a dozen years or so that had a tile roof. It bugged me when I noticed after moving in, that there was no radiant barrier, given the price of the house. BUT, the attic was cooler than any house I'd lived in (until now, a 1-year-old custom build with spray foam). Not sure if it was the air gap under the tiles, or insulation quality of the tile material, but it was definitely noticeable. I wonder if having solar panels shade the roof would be the next best thing?

Has anyone here used a laser temp gun or similar to measure the temp of the roof sheathing under solar panels, compared to bare roof areas?

What type of camera are you using? Been thinking of wasting money on one. Since I'm in attics daily I'd love to start a log of various roof temps, attic temps, venting styles etc. I could really create a killer spreadsheet to prove or disprove a lot of things.

I'd like to comment on this but I've never seen such a system for watering your house. Does anyone have a photo of this system? I can't think of a single reason off the top of my head why this would be good or OK for a roof for a "lifetime" setup.

In almost all cases, you'll be better served by adding the proper amount of ventilation. If your case, a solar attic vent setup would be a better long term solution and not waste water. It just seems unnecessary. If you want to try newer tech, GAF makes hip ridge vents. You will certainly have enough of that to make the numbers work.

We all know the attic being hot makes the AC work harder, but I've yet to find any empirical data to determine how much cost savings there is to be had. I suspect that's because there is enough variability that the difference is negligible.

I guess the next question is….what are you going to do in the winter? Are you going to add a heater?

As you can see, if you're goal is to temper the attic climate, you would be best served spray foaming the entire thing and sealing it 100%. You are essentially wanting to change the thermal envelope of the house to be the roofline instead of your ceiling.

I'm not sure what it would look like either since I've never done it. But the systems I've seen online seem to be modeled after rooftop fire suppression systems. Here's an example of a fire suppression system:



It appears that that would be relatively easy to put on your roof at the beginning of the summer and remove at the end.

The quotes I've gotten to foam my attic are in the $15-20,000 range, which is a nonstarter.

Here are some discussions from people who have tried what I'm asking about:

hvac - Would putting a sprinkler on my roof help cool my home? - Home Improvement Stack Exchange

Roof Sprinkler Cooling Systems (builditsolar.com)

Roof sprinklers | BUILD

Consider evaporative roof cooling to reduce your HVAC load | Plant Engineering

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If you want to try newer tech, GAF makes hip ridge vents. You will certainly have enough of that to make the numbers work.

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Thanks, Jason. You had previously suggested those to me. I mentioned them to 2 or 3 roofers where I live and they had never heard of them, even though at least one was GAF certified! They were very skeptical, especially about the ability of those types of vents to prevent rain from leaking in. Every roofer I talked to here recommended instead that I seal up my existing ridge vents and replace them with 2-3 wind turbines.

I'm somewhat skeptical of those recommendations, however, because in looking at the data, that number of turbines would not be sufficient to adequately vent my attic either. In these hot days the wind barely blows, further reducing the turbine effectiveness. The local roofers seemed to be recommending the turbines and the number simply because that's what they typically install on a house the size of mine.

I see. Yes, many roofers just kind of "know what they know" and that's about as far as they go. There is a lot of tech ology with roofing, as with any industry and it takes a little doing to keep up or at least seek out new solutions to old problems. The fact you're reading and searching is good. I've no doubt you will arrive at an acceptable solution whatever it may be.

The sprinkler system will cool the attic. No doubt about it. It's simple physics. What concerns me is the wear and tear and water usage. If you are going to make this removable then they will be loosely sitting on the house. The impact sprinkler sill vibrate that piping and frame and it will wear the grains off in less than a month I'd think. On top of that those impacts are at least 1.5GPH maybe more, so figure how much water is running through if it runs 10 seconds every 3 minutes or whatever. All the minerals in your water (that aren't present in rain water) will be corroding the shingles. It just doesn't seem ideal. To be fair, it's the same way I feel about misting the HVAC system. It just corrodes and ages the item way faster.

The other concern is that your roof will be wet most of the day. The roof isn't designed for that. Roofing is not waterproof. It is designed to be shed and dried. As shingles age, their ability to shed water and not absorb it is decreased. That's why we saw so many leaks during Harvey. A 4 hour rain storm is one thing, a 2 week rain storm is another. The roofing surface simple absorbed some of the water to the point it soaked the underlayment (most were tar paper at the time) and it eventually soaked through.

I'd be worried that concoctions wetting of the surface might cause the same issue. It might not, but I couldn't say with confidence.

I use a fluke ti400. Which was pretty pricey and is probably overkill. There are cheaper middle units that work, but there are also really cheap units that are a waste.

I have had great luck with the Fluke brand. The only otther brand I would consider is FLIR.

If you want to contact me directly, and discuss what you would be doing with it, I could help you zero in on a level.

Absoluteinspections@gmail.com

Absolute said:

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I use a fluke ti400. Which was pretty pricey and is probably overkill. There are cheaper middle units that work, but there are also really cheap units that are a waste.

I have had great luck with the Fluke brand. The only otther brand I would consider is FLIR.

If you want to contact me directly, and discuss what you would be doing with it, I could help you zero in on a level.

Absoluteinspections@gmail.com

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Does anyone make a cheaper version that is wireless that will basically display on a mobile device? I figured the brains of the device is the IR part and sending that to a superior display of a phone would be cost effective and better in every way???

Great points.

A completely different approach on those 110 days were the HVAC can't keep up is to just slap a couple of window units in and call it good.

Right now, based on what I know, if I were designing a house from the ground up I'd go with lots of mini splits, or even window ACs, rather than central air.

Intentionally putting water on your rain barrier system seems like a bad idea. Yah you get some cooling benefits but I hope your membrane, shingles and flashing envelope is tight. Been dealing with too many rott and mold projects lately to even want to think about taking a hose to my roof and hoping everything works out.

There is one that goes on an iPhone I believe. Pretty cheap. The issue is resolution and sensitivity of the ir lens and processor. If those are not good enough you just get a colorful blob that tells you nothing. Pretty sure the phone just displays what it gets from the unit.

Just depends on what you are trying to do and what kind of differentials you will be dealing with.