best Insulating method for Florida house
| Posted in Energy, Heating & Insulation on
looking for some expert advice on insulating a house in Fl. Our builder suggests foam
insulation sprayed into the CBU cores but I was thinking using DOW foam board foil faced under the furring strips to create a thermal break. I suggested this to the builder and the formen but they did not think it would work as well. ALso I may just do both, maybe over kill. Any FL builders out there that could help me out with this?
Thanks budd344
Replies
BUMP
You bumped while I posted....what a team!!!
Saw it and bumped you. Didn't know if you had seen it.
Bud,
We either use foam board between the furring strips or AlFoil stapled to the strips as the air gap left between the foil and block helps. I have seen guys glue the foam board to the block then shoot the furring strips thru it but that leads to future nail pops in the drywall from what I have seen. No matter what the combination you are looking at R values of less than R - 9 or so.
I wouldn't go wioth the foam in the CMU as its actually overkill. Folks used to use vermiculite and that was the same way. In addition, many of your cells are going to be filled solid with grout (concrete) and rebar so those break up your insualtion pattern. I mean it won't hurt anything but that initial cost is going to be pretty high.
Look at your energy calcs and you'll see what I mean. The temp differences between interior and exterior in FL are never that great that wall insulation really has to be that high. Its not like up north where it might be -10 and you want it 68 in your house. Here it might get to 20-30 for a few hours in the late night -early morning and the next day is up to 50 or 60 again.
I would beef up the ceilingattic insulation to R-30 to keep the heat in the attic and out of the living space. And use good windows with Low E coating. Best bet is Impact glass with Low E as then you protect yourself from hurricanes too and get the insurance break in the process.
Mike
Would it help to have some form of insulation on the OUTSIDE of the block/cement walls? Keep the heat out of the walls?
Also,
I would beef up the ceilingattic insulation to R-30 to keep the heat in the attic and out of the living space.
R-30 doesn't sound like enough these days. Whether it is cellulose or foam, something to keep radiated heat from the roof structure from penetrating into the living space. Fiberglass wouldn't be useful with radiated heat gain.
I'd want to keep the sun's heat from getting into the attic space in the first place. Spray foam under the roof deck or structural foam panels for the roof itself. Does such a construction exist that is code rated for Florida's hurricane building codes?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Spray foam under the decking? The windload is calculated on the assembly so why would that make a difference?
I would think anything engineered for 140 mile uplift would be acceptable.
Spray foam under the decking? The windload is calculated on the assembly so why would that make a difference?
I don't know, that's why I asked. Some areas are very fickle about what they allow.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Catfish,
They are doing this as a retro on a lot of older homes. Like you said, any newer home already would meet the windload uplift requirements so the benefit likely wouldn't be there for any structural aspects...just insulation and secondary water barrier.
Mike
Exterior insulation might work but you have to find the right material. Moisture and rain are high and most block homes are stucco on the exterior so a means of application is tricky. Have to keep the moisture (and termites!) out of anything on the exterior.
I have siding on my block home and considered something like Celtoex board on the exterior underneath the siding but the material costs seemed to exceed the benefit for something like R3 on the exterior so I passed on it.
Sure, many folks like the spray foam that serves as both a seconday water barrier, an adhesive to retain the roof sheathing and an insulation below the decking. Only problem is its about $2 per sq ft to spray. Once again a great product just not cheap.
The ongoing debate is if the insulation like a radiant heat barrier at the roof decking retains too much heat at the roof deck and reduces the life of the shingle.
I have always used R30 with good results. Obviously more might be better but at what cost?
The underlying aspect to always consider is I have a 2,895 sq ft home and in the hottest parts of the summer with both my upstairs and downstairs AC units running, my electric bill is $260. per month. Not sure how much lower it could get even if I would have spent a ton more on insulation.
What type of insulation is in your attic (assuming you have an attic)?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
R30 batts
Is cellulose used much in your area?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
It is as a blow in style. Not common as fiberglass but I have seen it.
Cellulose has a bad habit of becoming gray slag. The accumulation of moisture is exactly the opposite of what it is up north, the cellulose gets waterlogged and rots.Quick question, where is the "warm moist side" if your A/C season is 9 months long and the ambient outside humidity is usually 75 or higher?BTW if you think that is wrong, Email me an address and I will send you some gray slag [email protected]I have an attic full
Edited 10/27/2009 1:23 am ET by gfretwell
Sounds like you have so much moisture in your attic that fiberglass would be wet too.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
I am doing a better job of ventilating than we had before but I still bet it rains up there now and then. I really think the whole vapor barrier thing is backward.
If I was doing this all again I would put foil backed FG up there, foil side up. That would also radiate the heat away from the house.
The problem is, getting the blown in gray sludge out of a 2:12 attic is almost impossible. I didn't put the cellulose up there but the guy who did was an idiot.
Maybe you should block off all the vents up there to keep the moisture out! Then run a de-humidifier up there, 24/7 for a month.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
I know folks will cringe when they read this but I have NO soffit vents on my house. I have off the ridge vents to let hot air out but no soffit vents to let cooler moist air up in. Never a believer in air flow thru the attic.
Been this way since I built it in 2000-02 and have had no moisturemold problems.
I don't know where you live (didn't see it in your profile), but if I lived in a super humid locale like Florida I'd NOT let humid air into my attic.I'd also try to block radiated attic heat gain from getting into my living space. I do not think fiberglass alone is good at blocking radiated heat. I'm wondering how the moist Florida air could condense and soak cellulose insulation in gfretwell's attic. Leaky air conditioner ducts causes the moisture to condense? Leaky roof was/is the actual culprit? Wind blown monsoon rain getting into the ridgevent? Combo of a/c leak and wind driven rain?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
I'm wondering how the moist Florida air could condense and soak cellulose insulation in gfretwell's attic
Well, along the Gulf coast it's not uncommon to have average RH's in the 60+% range for all of the cooling season. Couple that with dew points in the upper 60s and lower 70s for a similar amount of time, and it's very easy for the temperature in the attic to pass through the dew point, and condense as water.
Air leaks from the a/c ductwork will not help any at all, either. Especially on marginally-designed systems with can't-be-bothered thermostat settings--get the a/c running 40-50 minutes of every hour from 0600 to 2400, and you are putting a lot of 60-70º air at <5% RH into the attic. That will condense water out of water vapor in a steady, incremental, way. Do that for months, years, at a time, and it will add up.
Until you live for a stretch in a high-humidity environment, it can be an odd thing to think about. I know it can confuse folk when I describe my spring and fall, not as calendar times, but as the time of year it passes through the DP twice a day, not once.
For the 7-8 weeks of my heating season last year, I had only 7 days where the reported RH was under 20%. Only 62º today, RH is 66%, though--with a dry DP of only 51º after three inches of rain yesterday.Occupational hazard of my occupation not being around (sorry Bubba)
I wish it would get down to 60% RH here.
72% right nowhttp://esteroriverheights.com/esteroweather.jpg
86% here
I actually do appreciate the humidity problems you have being I live near the ocean here. But it's not for nearly as long a time in a years worth of seasonal changes. Every Summer we get a period of time where the humidity is so very high yet not hot enough to run the air conditioning much. Toilets sweat so much you think there is a plumbing leak. Beds, sofa, all feel damp. Unless you run the a/c to low enough temps to store sides of beef! <g>With the situations you describe for the Gulf Coast, sounds like it's been known for a looooong time that an attic could get saturated. Why aren't homes built to avoid the problems like qfret has? Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Edited 10/28/2009 1:15 am ET by PatchogPhil
Why aren't homes built to avoid the problems like qfret has?
Because the rules were written to prevent ice dams in the midwest.
Same way the original "solar" guidelines were really only good for southern new england. (There's a house in Dallas built to those guidelines, low roof on the north, huge windoes to the south and limited overhangs on E, S, & W--have no idea what that costs to a/c, especially with the south side facing a six-land boulevard street, too . . . )
Occupational hazard of my occupation not being around (sorry Bubba)
...and also folks are convinced you have to have positive airflow from the soffit up through to the ridge vents in your attic.
I don't believe that myself. Let the attic get as hot as it wants...I don't care. I can insulate between it and my living space. It may get too hot to store things up there and maybe reduce the life of the shingles by a few years but at least mold and mositure will never be a problem.
Let the attic get as hot as it wants...I don't care. I can insulate between it and my living space.
Yeow, to each their own.
It gets to 130-140º in attics in the summer in my part of Texas, and not just for a couple days. That can be 3-4 times the deltaT between the outside walls vice that ceiling plane. And, that oustide wall has a lot more planes in it to help seperate conditioned space from non-conditioned.
Keeping the roof deck from heating the framing, which then radiates all through the attic looks more and more like a sensible solution for my climate.
Now, if more people around here would just "believe" that letting moist air into crawlspaces is as bad as having a slab only 2-3" above grade . . . Occupational hazard of my occupation not being around (sorry Bubba)
Cap,
Florida attics get just as hot but with the off the ridge vents on mine, I have it down to 115-130 in the middle of the summer. The off the ridge vents allow the hot air out but the lack of soffit vents prevent the moist air from below being pulled in from below. I just don't buy the "air flow thru the attic concept".
I don't know that we have the conduction issue of the framing you mentioned as most of our homes are concrete block and the average CMU transmits heat very poorly.
I guess I just see it as I would rather spend a bit more on energy to cool my house than have to combat mold, moisture and associated problems from that high humid air moving through the attic? Most summer days here the humidity ranges from 80-95% URGH!
Maybe I'm wrong scientificallyt but the house has been this way for 9 years since I built it and have been happy thus far.
Do you have a wood framed roof with asphalt shingles? That does transmit a lot of conductive and radiated heat gain into an attic space.If money weren't a concern, would structural foam panel roofs with standing seam hurricane-proof (OK, resistant) metal panels be the best roof in a very hot, very humid locale like Florida and Gulf Coast homes?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Well yeah structural foam and metal would be better but the extra you spent on those (especially using one that are hurricane resistant) will outcost the extra you would ever spend on energy unless you ran the numbers over a 30-50 time span. Metal in out area goes for $750-1000 a square! Shingles are $200.
Keep in mind as I mentioned before, as my home stands now, my electric bill for running TWO AC units full time over the summer is around $250 give or take. In the fall winter and spring my electric bill is like $80 a month and we have no gas nor heating oil costs. Thats it!
So yeah there are alot of things that one (me) could improve on from, an energy standpoint but why? I wouldn't recognize the savings until after 20-30 years. By then I want to have enough money to not worry about it! :)
I really think the answer is to put in foil backed insulation, foil side up. The "cold" is not coming from blown open ductwork. It comes through the ceiling below the insulation and the vapor barrier below the insulation doesn't accomplish a thing.Again the operative question is "where is the warm moist air"?
In Kansas (winter), it is in the house. In Florida(summer/fall) it is in the attic.
The "cold" is not coming from blown open ductwork. It comes through the ceiling below the insulation and the vapor barrier below the insulation doesn't accomplish a thing.
Then your insulation is not doing it's job. And/or you have a very poor air sealing situation at the attic/ceiling plane.
If you have no air leaks thru the ceiling plane, where cold dry air is being pushed up into the attic then what is probably happening is that the heat is radiating downward towards the colder ceiling/attic floor. Heat goes to cold. Unless cold is "pushed" via higher pressure.
Fiberglass insulation is not very good at blocking radiated heat gain. The moisture from the hot humid air comes along for the ride and condenses on the colder attic floor.
Cellulose does a very good job at blocking radiated heat gain. If you have wet cellulose and no water leaks in the attic then I suspect you have cold dry conditioned air leaking into the attic. That would exasperate any dew point issues in the attic. Altho I am not yet convinced that an attic "naturally" cools down fast enough at night.... houses tend to retain heat gained during the day well into the night.
Then again, I don't get many months straight of very high humidity like the Gulf Coast, but I get a lot of humidity from Spring to Fall. So I could be thinking wrong about dew points in an attic causing soaking insulation. It would be likely that EVERYONE in that area would have soaking insulation in their attic.
I have one 1000 sq ft attic with 16" of cellulose. And another 700 sq ft attic with very old (1950's)fiberglass. Same house. Neither one sucks up moisture to saturate either insulation. I have much better air sealing where I renovated and used cellulose.
P.S. This is a good conversation going on. :-)
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Folks, lets not make this too complicated. When the house was built, in the Kennedy administration, they rolled out foil backed insulation (r-11 or so), foil down, just like everyone else "up north". Air conditioning was not even a consideration. I am guessing sometime around the Carter administration they blew in "x" inches of cellulose over that.
That may have also been when they put the 3.5 ton Ruud package unit on the roof but I am not sure about that. There is also some evidence of window shakers (230v outlet in LR) so they may have made the A/C plunge earlier but I am not sure how they did that with awning windows.In 1984 when I bought the house the insulation looked to be about 6" deep. I didn't look at it much after that until the 90s when we got serious about some renovations. By then the cellulose was a matted slag up to an inch below the 2x4 chords of the trusses and the fiberglass was totally compacted. That is what I know.What I surmise is when the weather is moderate and the attic is "pumping" air in and out from expansion, humidity enters from the cool evening air. The cellulose absorbs this moisture. The part that is resting against the ceiling drywall eventually approaches or passes dew point from the A/C and starts to rot. The more it rots and collapses, the worse the insulation quality is, more gets below dew point and the process continues up through the cellulose. This happens over the years, not overnight but the result is I have no real insulation in my attic now and no easy way to get it.
If a cellulose blower guy ever knocks on my door I am going to punch him in the nose. All to do over, I would put in R-30 FG, foil side up and tape the joints but I am not sure how you do that in a 2:12 attic.
I have never actually seen a moisture problem except that the cellulose went bad. The wood does not show any signs of trouble. I suspect it is just where the cooling from the ceiling meets the attic air and even then, maybe only occasionally when conditions are right. The problem is cellulose will absorb the moisture more than fiberglass and it will rot with a very slight moisture content.I do believe good attic venting is a lot more valuable than simply putting in more insulation. If nothing else your roof lasts longer. Note, we are just talking about cooling here, We don't have furnaces.
My total heating "season" might be 35-40 hours spread out over a month or two using the toaster strips in the air handler or just the heater in the bathroom.
The grout and rebar issue was one of my concerns filling the block. The attic will be R30 and it looks like they use a good amount of vents for the roof also the roof is a lighter color. We have not started to build yet and have not pulled the permits.
I really think the foam board is the best way to go and I guess I was a little surprised when the builder did not agree so I thought I would so feedback. All the comments have been helpful.
In addition Bud, the actual insulation method should already be determined when he got the permit so the workmen shouldn't be making the call! Insulation is an inspected item in FL and all the specs like the Energy Calculations are required to be submitted at the time of permitting....
What I am saying is the builder should already have all this figured out before the house is ever started.
I wish it would get that warm here after those 20 degree nights. Rarely over 40 after one of those. Pensacola
You need to move south into more of the Florida Florida.....instead of the lower Alabama Florida. I have a friend that lives there and she says it gets REALLY cold there yet it will be in the 70s here. But it is a nice part of the state.
Budd,
You may be interested in reading this recent article on designing a house to handle a hot climate:
http://www.greenbuildingadvisor.com/blogs/dept/musings/hot-climate-design
Martin Holladay, senior editor
http://www.greenbuildingadvisor.com