Thermal loading.....

[mrvette]

1300' of house....4-12 pitch assfault single roof, the lightest gray 3 tab shingles available....

average temp on the roof in bright sun this morning...was measured with heat sink compound and a thermocouple.....

so it was burning in there almost directly at 11 this AM....so temp was ~138f on the surface.....

switching to a white painted shingle right near by...it was only 108f

so at a minimum a 30f temp difference.....

so the question is....IF I paint the whole roof, or at least the front/western facing slope bleach WHITE.....

what would be the % savings on a/c loading?? I assume attic temps would be dropped down to about shingle temps...what with no ventilation up there to speak of...just ridge vents....

anyone??

 

[68/70Vette]

so the question is....IF I paint the whole roof, or at least the front/western facing slope bleach WHITE.....

...what with no ventilation up there to speak of...just ridge vents....

anyone??

Sorry, I can't specifically answer your questions, but to try to be helpful......the white paint seems like a good idea, but will it start to flake off? It might cause the roof to look unattractive.

I'd think a good idea would be to install a fan to exhaust the hot air built up under the roof. This can be pretty easy to do, inexpenisve, and will - I believe -result in a noticeable drop in heat input from the roof airspace to the living airspace below.

My thermally primitive house here is one story with a peaked roof. There's about a 2 1/2 foot by 2 1/2 foot opening to the roof in my hall way. Normally the opening is blocked by a simple removeable piece of plywood. In hot weather, I remove the plywood and push a fan up through the hole and then lay the fan over the hole. This cheap fan is about 2 1/2 by 2 1/2 so it nicely covers the hole. It sucks air from the ground floor, blows it into the attic. This blows all the superheated air out of the attic. The ceilings on the ground floor are noticeably cooler and the bedrooms are not as hot at night.

 

[010752]

I thought you were going with the roof coating a few years ago.

Typically it will drop your attic temp around 30°, but it will also do more important stuff like bind your shingles together for the next hurricane. Contrary to popular belief, shingles down here pretty well dry out after 6 years or so and will blow off. In short it will make them last forever with coating every 7 years or so.

As far as attic insulation etc, the best insulation for a/c down here is WALL insulation, not attic. Doesn't make sense to me either, but that's the way it works with the energy software from the design engineers of the big guys like Trane etc.
Shade your windows, on the outside of the glass, as in awnings, not the inside, helps a bunch.

 

[mrvette]

so the question is....IF I paint the whole roof, or at least the front/western facing slope bleach WHITE.....

...what with no ventilation up there to speak of...just ridge vents....

anyone??

Sorry, I can't specifically answer your questions, but to try to be helpful......the white paint seems like a good idea, but will it start to flake off? It might cause the roof to look unattractive.

I'd think a good idea would be to install a fan to exhaust the hot air built up under the roof. This can be pretty easy to do, inexpenisve, and will - I believe -result in a noticeable drop in heat input from the roof airspace to the living airspace below.

My thermally primitive house here is one story with a peaked roof. There's about a 2 1/2 foot by 2 1/2 foot opening to the roof in my hall way. Normally the opening is blocked by a simple removeable piece of plywood. In hot weather, I remove the plywood and push a fan up through the hole and then lay the fan over the hole. This cheap fan is about 2 1/2 by 2 1/2 so it nicely covers the hole. It sucks air from the ground floor, blows it into the attic. This blows all the superheated air out of the attic. The ceilings on the ground floor are noticeably cooler and the bedrooms are not as hot at night.

ON the right coast they known as a 'whole house' fan, and with a/c it's not an option.....they do work well in certain situations, but this not one of them....humidity WAY too high....

and I have slotted roof peak vents up top of the ridge....and when they did the soffits over in vinyl plastic they didn't remove the damn plywood and small hole crap they had in there from OEM....so there is greatly restricted air flow...:hissyfit:

I could blow in extra insulation, but have no faith that stuff will do much good...really....

:ill:

 

[DC3]

How much insulation do you have now? There is a point of diminishing returns but if your insulation is the least bit marginal, adding more is a great bang for the buck. Payback can be as short as two summers. It's generally best to use the blow-in cellulose.

Painting the roof white will certainly help and the payback should be fairly quick but I'm not sure of the AC savings. There used to be a free heat loss/gain calculator somewhere on the web where you enter all of the parameters for your house (windows size, type & orientation; construction type; insulation levels; AC size; color of roof; energy costs; etc.). Once you get everything entered, you can play around with roof color, insulation levels, etc to see potential savings.

One thing you probably do need to do is open up your soffits. One quick and dirty way to do that is to go to Lowe's and buy some 2" aluminum soffit vents and a 2" hole saw if you don't have one. Drill a hole in the soffit, press fit in the vent and you'll be done in no time. You can't put in too many. I'd put one at least every 2'. There are also some 16" x 8" soffit vents available but you need to cut a hole with a jig saw. Probably need two or three of them on each side of the house. You'll need to make sure your new vents are not blocked by insulation.

There is a lot of info on the web regarding proper home construction and energy savings. Here is one website I use: http://www.buildingscience.com

Hope this helps.

DC

 

[mrvette]

Eh, the house is 40 years old, facing directly west...was a basic L shape as you see from the sites, but the back end is a room addition now...we did replace the roof with white metal about 1.5 years ago..so it's fine...

I hear the awning suggestion, but due to trellis tricks over the deck and various other coverings, it seems a marginal return at this time...

at this point, I wish I knew that shingles were THAT short a life span in Florida....I had hoped being the lightest color around...gray...that they would have lasted much longer being NEW 13 years ago when I bought the house...

so to paint the roof white, drop the attic temps...and maybe blow in extra insulation soon enough....

simply not going to replace the roof...

:hissyfit:

 

[JPhil]

Insulation on the ceiling--R30 at least (10-12"). Open up the soffits, open up the roof. "Code Requirements" are one square foot of ventilation per 150 sq ft of roof area, but, especially in SoFlo, more is better. More more more.
A whole house fan may not be your answer down there, but I bet an attic fan will help a lot--especially if you have enough square feet of opening for good even flow.
You want a canopy for your living space---like a hammock under shade trees, with a breeze above to carry away the heat. The airflow from ventilation, especially induced airlow, will carry the heat out of the attic and thus away from the ceiling, reducing the broiler effect at the end of the day. It will help keep the entire mass of your structure from absorbing heat so it will have less to radiate into your living space.
Reflective roof covering, awnings to shade your fenestration (& exposed south walls if you can) to reduce solar heat gain, insulation on the surfaces most susceptible to it (good low-E windows help a lot---throw those ubiquitous Florida jalosies in the trash) , ventilation to carry the heat out & away.

Here's website for a company that can help explain a lot of it. This guy is a real kick in the ass, I've been to a couple of his seminars. He'd be right at home in any garage drinking beer, swearing like a stevedore, and castrating lawyers & engineers with finesse. But he knows his shit. Look in the 'Building Science Information' section for readable stuff which pertains to the real world we live in. 'BS Digests' (yeah that's what he calls 'em too) are more for builders & studious types, 'BS Insights' are humorous & yet very enlightening. I urge you to read "The Top Ten Dumb Things to do in the South" and for anyone, anywhere, "The Building Science of Bourbon". And many more .......

http://www.buildingscience.com/index_html


(Huh--I just read through some of Top Ten Dumb Things to do in the South,and he says that what I just said is bullshit---I'd trust him more than me......use your judgement)

 

[big2bird]

Just been thru most of this Gene.(Over time of course)
Seer 13 A/C with new high R ducts/insulated plenums
Light(Copper Canyon) shingles
R-30 Attic and floor
R-13 walls
Added 3 whirly birds and maybe 30-40 eave vents, and doubled the gable vents.

I have Noonies rafter vents here to install in fall (Took forever to find online)

I attribute the A/C to the 1/3 power usage reduction.
Statically, the added attic ventilation helped enormously.
As John attests, the attic should be a "canopy". (Think tent fly)
I wonder sometimes if the roof was post and beam, with a 12-18" vent continuous around the perimeter would solve much energy demand.

 

[mrvette]

Just been thru most of this Gene.(Over time of course)
Seer 13 A/C with new high R ducts/insulated plenums
Light(Copper Canyon) shingles
R-30 Attic and floor
R-13 walls
Added 3 whirly birds and maybe 30-40 eave vents, and doubled the gable vents.

I have Noonies rafter vents here to install in fall (Took forever to find online)

I attribute the A/C to the 1/3 power usage reduction.
Statically, the added attic ventilation helped enormously.
As John attests, the attic should be a "canopy". (Think tent fly)
I wonder sometimes if the roof was post and beam, with a 12-18" vent continuous around the perimeter would solve much energy demand.

makes me wonder if I should rip off the vents in front at least and tear off the plywood/screens from the OEM, and reinstall the plastic mesh....

it's a ton of work much of it on a ladder...

not that I mind all THAT much, but wonder if I am wasting my time for the results obtained, if any....

I have decided to paint the west exposure/street side bleach white to help save the shingles, and reduce loading....in a few months maybe the rest of the house too...

is a memory now....:stirpot::sos:

 

[010752]

Just been thru most of this Gene.(Over time of course)
Seer 13 A/C with new high R ducts/insulated plenums
Light(Copper Canyon) shingles
R-30 Attic and floor
R-13 walls
Added 3 whirly birds and maybe 30-40 eave vents, and doubled the gable vents.

I have Noonies rafter vents here to install in fall (Took forever to find online)

I attribute the A/C to the 1/3 power usage reduction.
Statically, the added attic ventilation helped enormously.
As John attests, the attic should be a "canopy". (Think tent fly)
I wonder sometimes if the roof was post and beam, with a 12-18" vent continuous around the perimeter would solve much energy demand.

makes me wonder if I should rip off the vents in front at least and tear off the plywood/screens from the OEM, and reinstall the plastic mesh....

it's a ton of work much of it on a ladder...

not that I mind all THAT much, but wonder if I am wasting my time for the results obtained, if any....

I have decided to paint the west exposure/street side bleach white to help save the shingles, and reduce loading....in a few months maybe the rest of the house too...

is a memory now....:stirpot::sos:

Gene, I think I posted this before, you should use an elastomeric of some type, regular white paint won't do anything, especially for wind resistance.
Homey Depot handles this stuff down here, not the best , but priced ok.
http://www.lancopaints.com/english/products/4.3_elas_latex_roof_coating.html

The recommended process.
Pressure clean,
bleach and rinse (kill mildew)
fill tab gaps with a slurry of stucco mix and bonding agent using squeegee,
paint enough coats to fill pinholes and cracks

I did one that had older shingles with a bunch of tabs missing from Katrina, glued just new tabs down for looks. These shingles were way past their life. Finished with the roof coating.
Along came Wilma (a lot stronger than Katrina here) and any house that had asphalt shingles lost most of them if not all, even a lot of tiled roofs had substantial damage. This roof had absolutely no roof damage at all, but lost a bolted down shutter/awning.
Same house lowered the attic temp about 40° in summer sun because of the coating alone.

As far as the soffit vent, check ASI in Jax, they should have a pvc continuous vent, 4" wide x 10 ft long, 1/2" deep with lips made for adding to wooden soffits. You have to saw a 4"+ strip out of the soffit covering. They also make one for stucco soffits, that will work in a pinch. Under 10 bucks a length. Use a 4" circ saw, set to covering (plywood?) depth, and rip away, pita, but I've done it.

 

[mrvette]

Just been thru most of this Gene.(Over time of course)
Seer 13 A/C with new high R ducts/insulated plenums
Light(Copper Canyon) shingles
R-30 Attic and floor
R-13 walls
Added 3 whirly birds and maybe 30-40 eave vents, and doubled the gable vents.

I have Noonies rafter vents here to install in fall (Took forever to find online)

I attribute the A/C to the 1/3 power usage reduction.
Statically, the added attic ventilation helped enormously.
As John attests, the attic should be a "canopy". (Think tent fly)
I wonder sometimes if the roof was post and beam, with a 12-18" vent continuous around the perimeter would solve much energy demand.

makes me wonder if I should rip off the vents in front at least and tear off the plywood/screens from the OEM, and reinstall the plastic mesh....

it's a ton of work much of it on a ladder...

not that I mind all THAT much, but wonder if I am wasting my time for the results obtained, if any....

I have decided to paint the west exposure/street side bleach white to help save the shingles, and reduce loading....in a few months maybe the rest of the house too...

is a memory now....:stirpot::sos:

Gene, I think I posted this before, you should use an elastomeric of some type, regular white paint won't do anything, especially for wind resistance.
Homey Depot handles this stuff down here, not the best , but priced ok.
http://www.lancopaints.com/english/products/4.3_elas_latex_roof_coating.html

The recommended process.
Pressure clean,
bleach and rinse (kill mildew)
fill tab gaps with a slurry of stucco mix and bonding agent using squeegee,
paint enough coats to fill pinholes and cracks

I did one that had older shingles with a bunch of tabs missing from Katrina, glued just new tabs down for looks. These shingles were way past their life. Finished with the roof coating.
Along came Wilma (a lot stronger than Katrina here) and any house that had asphalt shingles lost most of them if not all, even a lot of tiled roofs had substantial damage. This roof had absolutely no roof damage at all, but lost a bolted down shutter/awning.
Same house lowered the attic temp about 40° in summer sun because of the coating alone.

As far as the soffit vent, check ASI in Jax, they should have a pvc continuous vent, 4" wide x 10 ft long, 1/2" deep with lips made for adding to wooden soffits. You have to saw a 4"+ strip out of the soffit covering. They also make one for stucco soffits, that will work in a pinch. Under 10 bucks a length. Use a 4" circ saw, set to covering (plywood?) depth, and rip away, pita, but I've done it.

BINGO man, BINGO!!! that roof finish is just what I was hoping for, and so to be done soon enough....

my soffits have been covered over with vinyl mesh, and the old wooden crap left in place, so the OEM screened holes are blocked by this vinyl there now....I need remove all the vinyl and cut the ply out and reinstall the vinyl...talk about a PIA, on this hillside with ladders and large bushes on the north end....less critical there, surely but a PIA....just the same....

 

[Yellow73SB]

I found this in a google search

Seems promising

http://www.metalroofing.com/v2/content/news/inthenews/inthenews_florida_cont.cfm

 

[mrvette]

I found this in a google search

Seems promising

http://www.metalroofing.com/v2/content/news/inthenews/inthenews_florida_cont.cfm

Yes, I redid my room addition roof about 1.5 years ago, had put on rolled roofing of shingle material....BIG mistake...buckles up like mad, not worth messing with...leaked like crazy....no matter how many buckets of elastrometric coating went on, it still leaked...it's mostly flat, that's why....
so it's metal now, and no leaks...

thanks man....

 

[010752]

I found this in a google search

Seems promising

http://www.metalroofing.com/v2/content/news/inthenews/inthenews_florida_cont.cfm

Yes, I redid my room addition roof about 1.5 years ago, had put on rolled roofing of shingle material....BIG mistake...buckles up like mad, not worth messing with...leaked like crazy....no matter how many buckets of elastrometric coating went on, it still leaked...it's mostly flat, that's why....
so it's metal now, and no leaks...

thanks man....

FPL is our power company down here and they did studies like that or maybe even that was theirs, but they have it all on their website and the GOOD elastomeric was the highest in energy savings. They also give some kind of rebate for using the stuff (all types of energy roofing materials), even listing different brands.
I ended up putting a fairly flat patio roof on the back of our house 3" slope in 14' and used foam sandwiched interlocking panels that are 4' wide and almost any length you want. 4" thick foam sandwiched in white aluminum both sides and with that span I can walk on top with no problems. Refrigeration rooms at Costco are the same stuff. In the noon day sun the bottom is ambient temp, too bad the main house roof isn't that stuff. Materials for a 14 x 25' roof were less than 1000 bucks. Pretty good deal, I thought.

Gene, I'll tell you a little story about that elastomeric stuff.
Have a rental house that has a flat roof over the garage with a little area about 6' dia that ponds mostly because of the dido that put the roof on used curbed flashing instead of flat. Hadn't been inside for years and the tenant didn't tell me that it leaked and dropped some sheetrock. So I pressured cleaned etc, recoated the roof with a couple coats of the cheaper elastomeric, then hung some new rock, finished and painted it. After a couple of rainstorms, some new bubbles in the ceiling paint. So I cleaned again and put more roof coating on and fixed the ceiling. Well this happened again a third time.
Luckily, I found a 5 year old bucket of the really GOOD eleastomeric stuff I forgot I had. Just enough to do one coat. Many thunderclappers since then, and hasn't leaked a drop. Big difference between the good stuff and the other, but I stopped using it because of price, he wanted 150 bucks a 5 for it when the others were only 60 bucks five or so years ago.
Talked to a friend of mine that makes some concrete coatings and his son is a chemist. Coincidentally, he knows the expensive guy fairly well and he told me his stuff is so much better than the others because he uses twice the amount of resins in his coating thus the higher price. So now I build up the mil thickness with the cheap stuff and use the good stuff for the final coat.

Here's another interesting little tidbit. My house has flat tile that was painted white. In the noonday sun, it feels very, very warm to the touch. When using the good stuff (very high gloss btw), I checked it side by side and it was very cool to the touch compared to the white paint on the tile.

 

[mrvette]

Noonie, I been very reluctant to do anything to the roof because of various sun loading factors, up here we can get rather cold in winter, too cold for me, but not moving anymore, still a hell of a lot better than Maryland anyway....

the house faces directly west, and with the sun really lo in winter there is a lot of tree shade on the north side, and if I paint the entire roof white, I get no heat help....so the thoughts were ambivalent about it.....but now that the shingles are in trouble, I need do something, that much is rather obvious....

so I finally got tired of waiting for freeking RAIN and got up there yesterday/thrusday AM early and hosed off the roof in front, hoping to paint it today, and wooden you know, it RAINED......I was standing there hosing it off thinking that it is going to rain pretty good NOW that I have done this....sure enough....:lol::lol: TFF, Typical Freeking Figgers....

:sos:

 

[DC3]

Noonie, I been very reluctant to do anything to the roof because of various sun loading factors, up here we can get rather cold in winter, too cold for me, but not moving anymore, still a hell of a lot better than Maryland anyway....

the house faces directly west, and with the sun really lo in winter there is a lot of tree shade on the north side, and if I paint the entire roof white, I get no heat help....

I wouldn't hesitate to the block the summer heat. The roof heat gain in the winter is nothing compared to the summer so the white roof is still the best choice for your locale. The summer savings way more than offset any minimal loss in the winter. One good thing to do in the winter is to make sure you maximize heat gain through the windows when the sun is shining on them.

DC

 

[mrvette]

Noonie, I been very reluctant to do anything to the roof because of various sun loading factors, up here we can get rather cold in winter, too cold for me, but not moving anymore, still a hell of a lot better than Maryland anyway....

the house faces directly west, and with the sun really lo in winter there is a lot of tree shade on the north side, and if I paint the entire roof white, I get no heat help....

I wouldn't hesitate to the block the summer heat. The roof heat gain in the winter is nothing compared to the summer so the white roof is still the best choice for your locale. The summer savings way more than offset any minimal loss in the winter. One good thing to do in the winter is to make sure you maximize heat gain through the windows when the sun is shining on them.

DC

Wish I known that, or thought to search, TEN years ago, or better...

not a issue back then...but so to get that roof white soon as possible....

rained this evening...figgers, as I have help for early enough tmrw AM....

:noworry::wink:

 

[mrvette]

Well, today is a sunny day....and so the front and NORTH slope of the L to the garage is all painted white, first coat, needs another, cheep stuff from HD....

the north triangle in the hip and the south triangle/slope of the garage is not done, but the WEST and East is all done for one coat....

I know from long time ago that attic clocked 140f in the sunny south....

today, ~4-430 in the bright unrelenting SUN it clocked 110 f near the peak of the roof after about ten minits of the thermo being up there....

out front in the garage 92f very slight breeze.....

in the vette, backed out primarily to allow attic stair access.....setting in the sun in the drive....white top UP....thermo in the shade.....110f....same as the freeking ATTIC....

to boot the windows were down on the vette...so some air circulation did take place...not exactly a friendly island breeze, however, not 50 miles inland anyway.....

SO, for just one coat of varying thicknesses, and covering just the basic high sun areas, it's dropped about 30f in that attic....

good enough for now....

as I get more coating, and manage to suffer more work up there, I will post updates best I remember to....

results above tell me I was correct in my suspicions when moving down here, to paint that damn roof white and get OVER it already....

even IF just 30f is all I can get, that temp differential is 1/2 what it was before, gotta be worth 5000 bux/year in electric....

:suicide::rain:

 

[mrvette]

I have the north facing triangle to do yet, above the bedrooms on that roof hip, but it gets tree shade in the afternoon, and oblique sun at most all day long....so it's lower on the priority list.....I have more paint to do today, get the south end slope done....so the job is winding down for the first coat....

the 'livability' is interesting, the a/c runs a LOT less, and the feel of the house has changed, the humidity is higher inside, because of less a/c running all the time....so that's a negative...it's not super high, like outside, but noticeable....

the temp on the a/c could be dropped a degree or so, but the short smiley person objects, and we know how THAT turns out......:bump::quote:

 

[mrvette]

Well, just paid last month's bill.....the coating was not much on the house by the 8/15 reading date, so nothing evident in the savings on this last bill so 7/15 to 8/15 was 250 bux for electric, 1600' under HVAC....6/15 to 7/15 was 230 bux.....

so this month will be interesting as the entire roof has one coating on it now, I note the huge drop in shingle temps just by feel....been tracking the outside temp in the front yard....88f right now.....sunlight hitting the backyard thermo 92f.........I have my thermcouple wrapped around the trusses and hanging down outta the attic hatch way in the hall.....87.5 in the attic, more direct sun but a few clouds....

the entire roof has one coat on it now, and the thinner coating to my hands is warmer/darker to gray then the thicker white coating....

just pisses me off this wasn't done 13 years ago, could have saved a easy 50 grand in HVAC costs.....:mobeer: