Cool Roofs - Arguments for

[NigelW]

Just some thoughts / arguments on what evidence I've seen looking at water consumption in cities.

 

A common method for dealing with increasing temperatures in a building is with air conditioning.

Air conditioning takes energy.

Higher energy means higher cost.

Therefore higher temperatures means higher costs.

 

Water usage necessarily goes up if there is a temperature increase through things like maintenance etc.

Buildings materials, in general, absorb radiation and radiate heat outwards.

Building materials that are whiter in color reflect radiation.

Buildings that reflect radiation don't require as much cooling.

Therefore buildings that reflect radiation prevent water usage.

 

Buildings that are side by side will heat each other.

Buildings that become higher in temperature require more energy and water for air conditioning and human health/comfort.

Therefore the more compact a city becomes the more energy and water is required.

 

As cities get more compact, more energy is required to maintain occupant comfort, health and bank account.

With energy use, water consumption will go up as well due to more occupants per unit of space compared to before.

 

My argument is that to maintain a standard of living while compressing cities to more compact spaces you require methods of preventing energy and water consumption to make the building more efficient and cheaper to live in.

 

A method of dealing with a roof that absorbs large amounts of heat is to apply a reflective and weather resistant layer of paint called a cool roof.

 

My arguments are straight forward, if there are any inconsistencies I would appreciate that they be pointed out.

 

[wdiaz03]

Just some thoughts / arguments on what evidence I've seen looking at water consumption in cities.

 

A common method for dealing with increasing temperatures in a building is with air conditioning.

Air conditioning takes energy.

Higher energy means higher cost.

Therefore higher temperatures means higher costs.

 

Water usage necessarily goes up if there is a temperature increase through things like maintenance etc.

Buildings materials, in general, absorb radiation and radiate heat outwards.

Building materials that are whiter in color reflect radiation.

Buildings that reflect radiation don't require as much cooling.

Therefore buildings that reflect radiation prevent water usage.

 

Buildings that are side by side will heat each other.

Buildings that become higher in temperature require more energy and water for air conditioning and human health/comfort.

Therefore the more compact a city becomes the more energy and water is required.

 

As cities get more compact, more energy is required to maintain occupant comfort, health and bank account.

With energy use, water consumption will go up as well due to more occupants per unit of space compared to before.

 

My argument is that to maintain a standard of living while compressing cities to more compact spaces you require methods of preventing energy and water consumption to make the building more efficient and cheaper to live in.

 

A method of dealing with a roof that absorbs large amounts of heat is to apply a reflective and weather resistant layer of paint called a cool roof.

 

My arguments are straight forward, if there are any inconsistencies I would appreciate that they be pointed out.

 

My only argument is in the science itself. Were the experiments properly done? or was government just eager for something else to mandate?

 

I'm thinking if these are so good then private owners will adopt them.

 

Maybe they decrease cooling cost but increase heating cost in northern areas...maybe the trick is not to reflect back to the atmosphere which will probably create an oven effect but instead to absorb the heat using plants or other means?

Maybe these roofs are harder to repair? less durable? create issues with condensation?

 

I don't know any of these answers. but I'm always skeptical when governments jump into a trend.

 

Hope this helps.

[JohnH.]

"Water usage necessarily goes up if there is a temperature increase through things like maintenance etc."

 

Can you explain this to me?

 

 

"Therefore higher temperatures means higher costs."

 

Not always.  Higher temperatures in cold cities means lower costs because less heating is required.  

[NigelW]

My only argument is in the science itself. Were the experiments properly done? or was government just eager for something else to mandate?

 

I'm thinking if these are so good then private owners will adopt them.

 

Maybe they decrease cooling cost but increase heating cost in northern areas...maybe the trick is not to reflect back to the atmosphere which will probably create an oven effect but instead to absorb the heat using plants or other means?

Maybe these roofs are harder to repair? less durable? create issues with condensation?

 

I don't know any of these answers. but I'm always skeptical when governments jump into a trend.

 

Hope this helps.

 

I want to be clear that I am not advocating the use of force to impose this on anyone.

Why do you think its government that is initiating it?

Urban Heat Islands are the result of current and past construction methods and infrastructure. I am simply pointing out that if Urban heat islands are a concern that people consider painting their roof white.

I've gone over why the heating load on a roof is avoided.

Roofs in the north are usually already covered in snow by winter anyways and I acknowledge that there may not be a need for things like this in remote areas. If I take a float plane to work I would not need an Austin Martin.. unless they started making jet packs!

I would be curious to know if an oven effect would happen.

I believe there may be an initiative in the USA to retrofit your home, but that doesn’t mean it doesn’t work.

 

 

Can you explain this to me?

 

Depending on where you live, maintaining a lawn could be really expensive. Dehydration is also more likely.

 

 

Not always.  Higher temperatures in cold cities means lower costs because less heating is required.  

 

True. Higher temperature doesn’t necessarily mean higher costs when comparing average city temperature to energy use. But it is the case that when people are uncomfortable, they will seek to adjust their environment. So, in that case, higher temperatures compared to room temperature means higher cost. If it is room temperature outside and 30 Degrees Celsius inside, you may find it more comfortable to exit the building or turn on the A/C. In winter, HVAC systems do a great job of maintaining the comfort level of the occupants. Building comfort is a requirement.

[wdiaz03]

I want to be clear that I am not advocating the use of force to impose this on anyone.

Why do you think its government that is initiating it?

 

I don't think I said you did, cool roof are being adopted by government build codes and subsidies. Not saying its an argument, the answer is in the science, but to me just a red flag.

[NigelW]

 

71F difference before and after applying the product 'Supertherm".

[WorBlux]

I think it's a great option for retrofitting, especially if you don't have deciduous tree cover on the south and west sides of your house.

 

For new construction thick green roofs may be the better pick, as they have a longer lifetime, provide a thermal mass, actively cool the roof in summer (via transpiration), and and reduce storm water runoff by up to and beyond to 90%.

 

Funny how in the video he talks about how cape cod houses are so hard to heat and cool on the second floor. Many houses and communities are poorly planned.  A bit of thought up front can save a lot of expense later.

I don't think I said you did, cool roof are being adopted by government build codes and subsidies. Not saying its an argument, the answer is in the science, but to me just a red flag.

 

 

Depends on what the code says. To really have a wide adoption you need to get your products into the code to contractors and designers know what it's final impact is.

[NigelW]

I think it's a great option for retrofitting, especially if you don't have deciduous tree cover on the south and west sides of your house.

 

For new construction thick green roofs may be the better pick, as they have a longer lifetime, provide a thermal mass, actively cool the roof in summer (via transpiration), and and reduce storm water runoff by up to and beyond to 90%.

 

Have you detailed or installed any green roofs? On the face of it, I see cool roofs as an easier fix for existing buildings, urban, sub-urban and rural.

I don't know if a green roof would be better in any setting for new construction. My focus of this post was on urban areas.

 

There are a lot of cool ways of designing buildings, that is for sure. Are you aware of any limitations of cooling via transpiration?

I know this is site specific, but do you know what effect freeze/thaw has on green roofs and the building envelope?

Compared to a cool roof, there is much more risk in building a green roof. How have you seen these issues addressed?

[WorBlux]

I've seen a few of them done well.  They are especially suited for urban settings. As their main limitation is they are very difficult to do on any significant pitch, and require additional structural materials.  Freeze/thaw isn't an issue. Additionally the reduced runoff reduced impacts on urban storm water systems.

 

To get an idea of the the effect move from blacktop parking lot to a sports field.  You still have to deal with ambient temps, but the transpiration + cover counters most solar gain.

[NigelW]

So if I understand you correctly, you are saying that for new construction a green roof is better because it has a longer lifetime, provides a thermal mass, actively cools in the summer, and reduces rain water run off.

 

I would be curious to know what application you are talking about and maybe you're correct. I know that for myself I would prefer to pay for a cool roof if I were somewhere hot, say phoenix, where the strain on water resources are a little higher than some place like Michigan.

 

My sources:

 

Water usage:

http://dogyears.com/edm/2007_guhathakurta_gober.pdf

 

Building Energy Consumption and the UHI

http://www.tandfonline.com/doi/abs/10.3763/aber.2009.0310#.U_F91mPCeh4

 

Limits of Evapo-transpiration:

http://www.tandfonline.com/doi/abs/10.1080/01944360903433113#.U_F-RmPCeh4

[WorBlux]

From a sustainability standpoint, keeping urban centres in deserts is absurd.

 

You'd be looking at green roofs in climates were prairie/grassland communities can form.

 

https://agronomy.unl.edu/c/document_library/get_file?p_l_id=4128278&folderId=5114339&name=DLFE-65734.pdf

 

https://agronomy.unl.edu/greenroofs

 

http://www.greenroofs.org/index.php/about/greenroofbenefits

 

And what I said is that green roofs may be better for those reasons.  As you said there are a lot of site specific and use specific considerations to be made.

 

I also don't think the aesthetic and  restorative aspects of green roof spaces should be overlooked either.

[NigelW]

From a sustainability standpoint, keeping urban centres in deserts is absurd.

 

Can you define sustainability?

[SueBee]

Sustainability involves consideration of the ecological, economic and societal impacts of activities humans initiate. (Just to jump in here...)

The greatest benefit imo of green roofs is the improved food security, when indigenous food bearing plants are utilised in the greenroof design.

[Brentb]

The primary function of a roof is to keep the elements out. This means that the roof is going to need to sealed regardless if it's a "cool roof" or a "green roof".

 

So a cool roof can be no more expensive than a typical roof if a white-colored sealant is used. 

 

A green roof is going to be more expensive since in addition to the sealant, you'll have to have the roof designed for added load of whatever volume of saturated soil and vegetation you have. The environmental benefits of a green roof over a cool roof are negligible if any. I don't see any purpose for a green roof beyond aesthetics, or if someone wants a penthouse with a garden.

[WorBlux]

Can you define sustainability?

 

 

Not exactly, but I know it when I see it.

 

A few possible question to ask though.

 

Is it still a positive for people born 7 generations from now? 

 

Does it refrain from using resources faster then they are replenished?

 

Does it increase or maintain resilience? Resilience being a measure of how many parts can be disturbed before a total system collapse.

 

Does it minimize externalities.

 

Is it usable and healthy for people now?

 

Anyways for specifics in relation to buildings or site development, one can reference the LEED standards or the sustainable site initiative.

The primary function of a roof is to keep the elements out. This means that the roof is going to need to sealed regardless if it's a "cool roof" or a "green roof".

 

So a cool roof can be no more expensive than a typical roof if a white-colored sealant is used. 

 

A green roof is going to be more expensive since in addition to the sealant, you'll have to have the roof designed for added load of whatever volume of saturated soil and vegetation you have. The environmental benefits of a green roof over a cool roof are negligible if any. I don't see any purpose for a green roof beyond aesthetics, or if someone wants a penthouse with a garden.

 

You don't have to live in a penthouse to appreciate a green space in the middle of an urban center.

 

Storm-water management is another big one. You can also gain air quality improvements. And in areas with enough rainfall you can gain an increased energy saving over white or cool roofs.

 

An yes there is a higher upfront cost, but is minimized with new construction to the point it can compare to upscale conventional roofs Additionally as the lifecycle can be 50+ years compared to the conventional 10-15. 

[NigelW]

Not exactly, but I know it when I see it.

 

Fantastic. Well I've got my answer. hah

[WorBlux]

Well you were trying to claim that people living in a desert is absurd and you still have not made the case that it is unsustainable. People still live there.

 

I think it would be helpful to find a sustainable definition of sustainability.

 

People also snort cocaine off of a hooker's ass.

 

What does the supply chain for water and food look like?  It's long and fragile.

 

Yes people can sustainable live in a desert, but not a million in a half people stuffed into 500 square miles. 

[SueBee]

Hey Brentb!

 

From your post above...

"The environmental benefits of a green roof over a cool roof are negligible if any. I don't see any purpose for a green roof beyond aesthetics, or if someone wants a penthouse with a garden."

 

Can you tell me how you reached this conclusion? I am curious about the evidence that you have seen that would support a lack of environmental benefits. Also, do you mean that morally, the choice to utilize green roofs or cool roofs is just an aesthetic one? Or, do you mean perhaps that people who make this choice base it simply on whether they prefer one look to another, and no other factors (such as the energy savings and resource capturing/producing potential)? Thanks, in advance.

 

Regards,

SueBee