Cost of insulation in Florida

I need to have insulation installed in south Florida on a flat roof. I need to have 2 inch isoboard installed. I was wondering if anyone can tell me an approximate cost af the materials and installation per square. This is JUST for the isoboard and installation, NOT for the felt and top layer.

Thank You,

About a buck fifty a foot where Im at.

what system are you using ryan? I don’t know of any system that requires what you just said. I’m not saying there isnt one, I’m saying I can’t tell and I’m curious.

the roofers screwed up and installed a roof without insulation. they are proposing to install a second roof with insulation over the first. I am trying to find out what insulation at 2 inch cost with labor without there markup. since they should supply it at cost. not to mention that i dont even know if the system they are proposing is even viable.

I don’t get involved with pricing materials, so I can’t give you a good price. I will say, however, that iso was hard to get a few months back due to construction in China and the sunami they had in the Pacific, not to mention one of the companies that produced the blowing agent went out of business or something along those lines. Anyway, the point being, iso was hard to get, now it is a little easier but the energy situation has been driving up the cost of all roofing materials.

Now, to throw a wrench in to your plans, but first I suggest you read the link I’ve provided. I did a Google search for aged R-value of polyisocyanurate insulation, and this is one of the first links I read. … ue37a.html

Alright, assuming you read the link I guess you’ve figured out that 2-inches of iso will only give you an R-value between 11 and 12. To me, this is your one good chance to insulate your roof so I would bump it up to 3-inches. Furthermore, I would do it with two layers of 1.5-inch thick iso installed with staggered joints to help improve the insulating quality of the iso, and to help protect the roof membrane. With regard to the underlying mod. bit., if they want to leave it in place, I would require they at least remove all the mod. bit. installed around any penetrations in the concrete deck, and cut out the base flashings along walls and curbs. The reason being, if you ever have a leak you will want the roof to leak inside and not have the water get trapped between two roof systems. Although, to better advise you, I’d want to see photographs of your roof. If you want, take some digital photos, resample them to 3" x 4" size, and then contact me on this message board. I can then send you a PM with my email address so you can send me the photos, that is unless you can post them on the board. Photos I’d like to see would include an overview of the entire roof, perimeter shot(s), curbs, roof drain, soil stacks, vents, skylights, etc.

I would have to disagree with cerberus on the point that if you have a leak you want it to come in instead of sitting on top…

double ply modified bitumen systems are designed to be two roofs fully installed on top of each other instead of two-plied. This is for a redundancy in the system, so I do not beleive yours to be best-practice advice.

well here in indiana I can get 1.5 insulation at 21 dollars a sheet but I am not sure what 2.0 inch would cost I can look into it for you but florida is way different than florida

thats a good price ski.
real good.

and is that Aaronb talkin bout “if you have a leak you want it to come rite in, instead of sittin on top”.
nice. nice indeed.


No gweedo, that is me talking about wanting the leak to be active and identifiable instead of unknown. Apparently, Aaron would rather be ignorant of a roof leak rather than have it drip inside.

I was just checking the site out, I have to go do a leak investigation, I’ll be back later to expound on why I believe what I said is the best way to go.

Cant we all just get along?

Sure we can get along, Kevin. Cerberus and I have discusse things in the past. We can disagree. We are civil human beings. He has his reasons, I have mine. I, for one am open to hearing his reasoning when he gets back from fiinding that leak. :slight_smile:

Alright, I found the leak and performed a temporary repair until I can get a roofing contractor out to torch down some mod. bit.

Now, back to the insulation sandwiched between two roofs. First of all, it should be noted that the membrane on the concrete will act like a vapor barrier. Many years ago vapor barriers were all the rage, and people were installing them without needing a vapor barrier until it was determined that un-needed vapor barriers could be detrimental to the roof system. In general, you don’t need a vapor barrier unless you are installing a roof over a cooler, freezer, swimming pool, ice rink, etc. So, I have to ask you why you would want to install a vapor barrier on a residence? I mean I guess it would be alright if the homeowner kept the thermostat at 32 degrees, but I doubt that is the case. For the sake of argument (since I’m not a weatherman), lets say the homeowner keeps his themostat at 72 degrees and it is 98 degrees outside. If the dew point is 74 degrees (I don’t know if that is possible with my example, because I’m not a weatherman), then water vapor in the air will turn to moisture (condensation) at that temperature. So, somewhere between the 98+ degrees of the roof surface and the 72 degrees of the interior temperature condensation will form, although humidity also plays a factor in this. If the 74 degree temp is attained within the concrete, no problem. If it is attained at the underside of the first layer of membrane, you wil have moisture between the concrete and membrane. If the 74 degree dew point is attained within the insulation, then that is where the condensation will form. Naturally, this moisture can also revert back into a gaseous form, and that is why some people install moisture relief vents. My one concern in the example we are talking about though, is that trapped between two roof membranes the moisture likely would contaminate the insulation. That is why when a roofer installs a roof system for me, and then wants to install a cricket/saddle overtop the roof membrane I make them perforate the membrane that will be beneath the cricket/saddle material. That way the insulation and the air space have a way to breathe.

With all of that said, dew point and moisture contamination is not the primary reason I would cut the membrane from around penetrations and along walls. The main reason is that I would want to know when the roof has begun to leak. If the top roof membrane leaks, and it eventually will leak, the underlying membrane will likely not leak. So, you will have a roof system that takes in water and releases very little of the moisture back out except as water vapor on sunny days. You can eventually end up with a “water bed” for a roof system. When you take into consideration that water weighs approximately 62 pounds per cubic foot, you are talking a lot of weight on the roof. In addition, the water saturated insulation (whether it be closed-cell or open-celled, unless you are using insulations like extruded polystyrene or foamglass) will lose its R-value. Why do you think people like me can find leaks in a roof by scanning them with an infrared camera? We are looking for hot spots in the roof where insulation has become wet and lost its R-value. Not to go too far off on a tangent, but the way an IR scan works is ideally you want a day with temps that vary at least 20 degrees from day to night. The roof system heats up in the day time to lets say 90 degrees for this example. At night the insulation and roof system are on their way back down to lets say 65 degrees; however, the wet insulation that has lost its R-value will retain the heat longer than the uncontaminated insulation. So, when you start a scan you are looking for hot spots, or areas that are retaining heat.

Anyway, not to get too far off the subject and to wrap this whole thing up, I just would not want a roof system that can trap water. Furthermore, the water trapped within the roof will attack anything that is exposed. So, if there is exposed metal or perimeter walls, these will be subject to attack from the water. Now, I will say this, if the concrete is solidly poured up to all pipe penetrations and walls, then there may not be any advantage to cutting the first roof. However, if there are openings, I would want them to be a conduit for water so I would know if the roof were leaking.

Once again, I’d want to see pictures of the roof and know more about it before I could absolutely say whether I’d want the first membrane cut or left intact. That is not to say you are right or wrong about my advice Aaron, give certain circumstances you may not want to cut the membrane in which case you would be right, but that doesn’t mean my advice was “whack.”

Nice post, cerberus.

I have just one question on the dew point. If you have a vapor barrier on top that is sealed 100% and a vapor barrier on bottom sealed 100%, were does the moist air come into the roof assembly from?

Also, bi-annual roof maintenance and inspection can find if your roof is leaking. A miniscule price to have to pay for double waterproofing protetion, IMO.


I would think that any material has moisture in it, especially in Florida with such high humidity. Also even a waterproof material has some amount of seepage over a long period of time.

But anyways there is some moisture content in almost any material. That moisture wont form into condensation until it reaches the proper conditions. At least that is my understanding. At night when the AC cools down the insulation it will form condensation.


well sure there is moisture in everything. was cerb talking about this moisture or was hje talking about more of a vapor drive scenario?

The moisture that Ryan80 is talking about is the general moisture content of each and every material, but that is not what I was talking about. No, moisture is going to get into the system one of two ways. First of all, unless both of the roof membranes together are not only watertight but also airtight, moisture will get in with air passage. Second, there is the permeability of the roofing and building materials, which can allow moisture into the system in vapor form.

I will say this Aaron, if the homeowner truly does follow through and has his roof inspected at least once a year, if not more often, then the two systems probably wouldn’t be too bad. My only concern is that most building owners have the out-of-sight out-of-mind mentality. If that happens in this case, then by the time the homeowner is aware he has a leak, he will have one hell of a mess on his hands.

Well, I sure do agree with you on that. :slight_smile: