Roof cooling issues.


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Old 06-28-21, 04:08 PM
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Roof cooling issues.

We are dealing with our 3rd major heat wave already this summer with several months still to go.

It was 95 degrees here today and the AC can not cool the upper floor less than about 77 degrees.

I have a tar and gravel flat roof.
I am going to try and coat the roof with Durock Coolflex white roof treatment.

Would it be a waste of time, or would it help reduce the heat transfer from the attic to the upper floor if I added a 300 or 400 CFM fan in a goose neck vent to reduce the oven effect in the attic?


the attic is about 1100 sq ft and from what I see sticking a cell phone down the goose neck vents, there is ZERO insulation. That will need to be dealt with soon.
 
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Old 06-28-21, 04:11 PM
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It's too hot to coat the roof.
Not sure what a goose neck vent is but maybe a fan will help with circulation.
 
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Old 06-28-21, 05:09 PM
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It all comes down to the insulation. If there is good insulation then anything like painting the roof or installing an attic fan won't have much affect as the insulation effectively isolates the high temperature away from the people space. If you don't have any insulation then painting the roof or a vent fan could be worth a try but my first choice would be to insulate. It will be the most expensive option to lowering temps but it will also provide the biggest benefit both now and during winter.
 
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Old 06-28-21, 05:21 PM
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Three things-

First I've heard of some benefits of doing a white-wash of simple lime-mortar mix.

Second, I remember that in Philly there has been a program to do white roof or a silver reflective roof.

Third, a simple black tarp, to put the roof in shadow, is apparently also effective.
 
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Old 06-28-21, 06:08 PM
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This is not my roof, i just grabbed this picture to show the vents that are used here. I have 4 very small vents like this on a tar gravel roof, and they are the only access to the attic! Once I can get things together, I would like to add a 5th vent and try to blow fiberglass or cellulose in and cover as mush as the surface as possible. This spring I stuck my arm in to the space and took a few cell phone pictures, absolutely ZERO insulation!
 
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Old 06-28-21, 06:21 PM
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Pilot Dane wrote:

It all comes down to the insulation. If there is good insulation then anything like painting the roof or installing an attic fan won't have much affect as the insulation effectively isolates the high temperature away from the people space. If you don't have any insulation then painting the roof or a vent fan could be worth a try but my first choice would be to insulate. It will be the most expensive option to lowering temps but it will also provide the biggest benefit both now and during winter.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I agree the insulation must be dealt with asap!

It would cost about $170 to white coat 40% of the roof, I am willing to try it just to see if it works and if so, do the rest to give my daughter some relief until we can insulate.

I have a skylight the connects the two bathrooms, they are stinky hot today and I can smell the tar on the roof in the bathroom "service shaft" that connects the two floor to the skylight. I have been here 10 years and have never experienced that before this heat wave.

AS PJMax says, it is too hot now to coat the roof, and this heat wave is here for several more days at least.
Hal's idea of a tarp is worth a try in the short term.










 
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Old 06-29-21, 07:05 AM
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Hal_S Second, I remember that in Philly there has been a program to do white roof or a silver reflective roof.
Thanks,

I looked in to this, seems Toronto, the next big city down the road has grants to convert to a white roof. Not here in Montreal.

All new roofs must be white roofs here. But there is no program here from the city of the state to help push it along.
 

Last edited by Kiton; 06-29-21 at 08:26 AM.
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Old 06-29-21, 10:17 AM
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Won't a black tarp laid on the roof and weighted down with bricks either do nothing or increase the heat in the attic?
And a tarp suspended upright or like a hammock to shade the roof would rip apart in the wind, no?

 
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Old 06-29-21, 03:12 PM
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Won't a black tarp laid on the roof and weighted down with bricks either do nothing or increase the heat in the attic?
Yes, I should have clarified "shade tarp" or "shade mesh"- which is partially open and made to not blow away, suspended above the roof - COVER-TECH | Shade Mesh | Shade Cloth | Mesh Tarps for Everything
Some Philly homeowners reported that the combination of a reflective roof + shade mesh a foot above it made a huge difference in their roof temps and house temps.

Another issue is radiated heat- example - I've got a 3rd floor attic I use as study / library.
I've had good results in reducing the temperature by layering some left over foam vent baffles

across the collar ties. What that does is prevent the radiated heat from the underside of the roof from warming the floor level.
 

Last edited by Hal_S; 06-29-21 at 03:51 PM.
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Old 06-29-21, 04:59 PM
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I have covered the skylight with a white tarp in the short term. It is nothing but a magnifying glass of heat and sun down in to the bathrooms.

At 10am this morning before leaving work I took a few temperatures.

My neighbours white roof at: 106.8 F

My BUR roof at 131.3 F

BUR test patch at: 143.2 F

A small test area that treated in preperation for white roof coating in the spring with sealant, to soften out the sharp edges of gravel and in fill in gaps etc
But now I need a cool rainless day to apply the white coating, it may be fall before that comes.






 
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Old 06-29-21, 09:03 PM
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A quick fix for Kiton is with good squirrel cage ventilation fan set to activate at 85F attic space temperature.

Along with fan it is important to install air inlet vents to roof area twice size or more of fan opening.

Most ventilation fans are activated at 100F to 120F are not fully effective.

DH uses ordinary thermostat to activate fan, not the one on it. Today at 90F attic air was 96F.

Forced air attic ventilation is great way to improve air conditioning performance and lower costs.

In winter block off fan and inlet vents and use static attic space as insulation blanket. Best of both worlds.
 
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Old 06-30-21, 01:14 PM
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An even quicker temporary fix is to put lawn sprinkler on roof activated periodically by timer.
 
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Old 06-30-21, 02:11 PM
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Doughness wrote:

A quick fix for Kiton is with good squirrel cage ventilation fan set to activate at 85F attic space temperature.

I am looking at that angle too, I will try to make several small adjustments until I can get the attic insulated.
There is no access other than via the 4 vents on the flat roof, so I will need to bring 120 volt up and and make a custom mod job to one vent while the three others act as in let. I have ordered a fan with 400 CFM and will rig that up for the hot days that I can control from the service shaft inside my home.

Maybe I am over working it, would not be the first time, but I have an idea for a pretty decent setup, if 400 CFM is enough to make a a small difference, it is worth it.
 
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Old 06-30-21, 03:01 PM
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For cooling, fan ventilation keeping attic air a few degrees about outside ambient air temperature is more effective than insulation.

Look on insulation as slowing transmission of BTUs, not stopping it. Insulation key in winter, but in summer fans/ventilation is easy, additional way to reduce heat load.

For Kiton1100 square foot attic the 400 CFM fan would be token. That tight space, small openings so was why suggested more powerful sqierrel cage blower. Another way to improve ventilation is with second blowing in on inlets.

DH has 1600 sq/ft attic with 1500 CFM roof fan. Today with 94F outside temperature attic was 98F. Have elasped time clock on AC. Ususally run 8 hours/day in New York humid summer 90F weather.

Many years ago DH designed specialized industrial air conditioning systems. This residential stuff is simple, no large people count, machines, product loads.
 
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Last edited by doughess; 06-30-21 at 04:01 PM.
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Old 07-01-21, 05:42 AM
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Doughness wrote:
DH has 1600 sq/ft attic with 1500 CFM roof fan. Today with 94F outside temperature attic was 98F. Have elasped time clock on AC. Ususally run 8 hours/day in New York humid summer 90F weather.
When I search DH ventilation, or attic fans I do not find anything. The biggest fan I can find in Canada is 800 cfm.

I am willing to try 2 units of 750 cfm and use one as push in to the space and one as draw.

Sunday we get a break from the heat and I will add the white roof coating on the back 1/3 section.
The we go right back to 85 plus degrees on Monday.
 
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Old 07-01-21, 11:16 AM
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Kiton: There are endless ways to ventilate attics.

DH uses 1600cfm roof fan at upper section of split level with 24” window fan blowing in at other end of attic. One ordinary thermostat activates both, set just above local night time temperature, say 90F. For air intake, which should be twice fan area, have screened louvers under eves around house.

Would not use built in-switch on most fans. They often does not activate until 100F to 120F+.

Here is a link to wide collection of ventilation fans:

https://www.amazon.com/s?k=roof+fans...s_ts-doa-p_4_8
 

Last edited by doughess; 07-01-21 at 01:25 PM.
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Old 07-03-21, 04:44 AM
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Doughness,

Thank you, I misunderstood and thought DH was a particular specialized company which I could not seem to locate.

I have ordered 2 fans and will wire up a system that I can control them manually from the service shaft that houses all my plumbing and electrical feeds from basement to roof top.
 
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Old 07-04-21, 09:46 AM
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KITON: Anther way to improve home cooling and heating is sealing off interior air leaks to/from attic.

Weather strip attic doors. Caulk AC ducts where they pass through ceilings. DH uses water based spray foam to seal electrical fixture boxes, fans, etc..

While some may look at those as trivial, they are cost and comfort improvements.

DH a DIYer trying to help other find solutions in this age of misinformation.
 
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Old 07-05-21, 09:16 AM
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On the weekend we got a break from the heat, but heading right back up there today.

Thank you PJMax for reminding me to check the roof temp before applying the white roof. I manged to get the 2 coats on, one Saturday and one Sunday morning while cool and overcast.

In the spring I cleared the stones off 1/3 as a test section. Applied the flash coat as instructed, they say to wait 28 days before adding the white coat, but it took much much longer for the flash coat to settle down. Then it was too hot and/or too windy to advance the test.

The spread from white treatment to old gravel is huge, it was 11:30am and the day has not come close to peak heat yet and there is a 37 degree spread between most of the old gravel roof, and 47 degree spread with the front section of the house.

I have much to learn about how this all works.
The attic is all one open space.
There are no ducts or wiring that go through the attic, is a completely sealed off space that ranges from about 6 feet high at the edges and tapers to about 2 or 3 feet in the center when the roof drain is.

And yet the roof is 10 degrees hotter at the front section despite the sun hitting the roof equally???







 
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Old 07-05-21, 08:38 PM
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And yet the roof is 10 degrees hotter at the front section despite the sun hitting the roof equally???
If that front section is 6 foot high area, larger outside wall surface area may be reason for being hotter.

Basic heat calculation is square feet of wall X temperate difference = BTU transfer
 
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