Replies

1. 
   iLikeDirt | Jun 15, 2015 02:44pm | #1

   Pea gravel won't insulate; it'll increase the mass of the wall, which is a good thing in Florida, but there are better ways to do this, like filling the cores with rebar-reinforced concrete, which will also increase the strength of the wall. The father south in Florida you are, the less insulation outside a block wall is necessary (compared to in colder places), but can still be beneficial. The place where you really want a ton of insulation is in your attic or roof, to reject all that solar heat! Your primarily enemy is the sun, not the air temperature. So keep the sun off the windows and walls with deep roof overhangs, porches, awnings, big trees, etc.

2. Expert Member
   Dana Dorsett | Jun 15, 2015 03:10pm | #2

   Nate has it right: Wall-R just isn't very important for energy use or comfort in US climate zones 1 (south Florida) & 2 (the rest of the state.) Thermal mass is good, but it needn't be excessive, and having that mass completely inside the insulation layer utilizes it to maximum benefit. To hit code-min with a CMU wall in zone-1 only takes an inch of exterior EPS. To hit code min in zone 2 takes an inch of exterior polyiso. If you wan't to knock it out of the park on wall-R, double that and call it a day.

   A layup of 2" foam on the exterior held in place with 1x furring through-screwed to the CMU with 4.5" masonry screws would provides something to attach metal-lath onto for a hard-stucco wall. If that's too expensive, there are EIFS stucco finishes designed to work with EPS (but not polyiso) without the air gap. With foil faced foam, a foil facing the air-gap provides provides some thermal benefit during the cooling season beyond simple R value, but it's not necessarily enough of a benefit to be worth paying extra for.

   Attic/Roof R counts, as does managing the solar gains from windows, and air sealing to minimize the latent cooling loads of humid summer air. West facing windows drive peak cooling loads skyward- if you can't keep the west wall blank, minimize total glazed area on that side. Overhangs can work on the south side, but in hurricane country overhangs (and vented attics) can be a liability. Awnings can be a better solution.

   With the ducts & mechanicals in the attic it's better to insulate at the roof deck, but it's often cheaper & easier in new construction to build-in a service chase for the equipment above the ceiling but below the structural attic floor, which allows you to air-seal & insulate the attic floor with the requisite amount of fiber insulation. R40-50 cellulose (11-14" ) isn't insane in that climate, even though code-min is only R30. For a good starting point on where the R-value economics may need fine-tuning, see Table 2 p10 of this document:

   http://www.buildingscience.com/documents/bareports/ba-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones

3. 
   iLikeDirt | Jun 15, 2015 03:57pm | #3

   Others may pooh-pooh it, but for new construction, also consider radiant barrier roof sheathing if you're putting insulation on the floor and the uncharge isn't much. My neighbor and I have near-identical houses with near-identical amounts of attic insulation, but I have a red shingle roof while he has a white metal roof. The difference in the amount of heat in the attic is intense and this difference does matter, since it represents a dramatically lower amount of heat that's trying to get through the insulation and down through the ceiling. The manual J calculated difference in ceiling heat gain between our two houses is about 1,000 BTUs, which represents about 7.5% of my house's total cooling load. I will maintain that it makes a difference.

4. 
   user-4994651 | Jun 16, 2015 08:54am | #4

   Why not investigate Hempcrete? It provides all you are asking for and more - there is much to be learned and very positive results are bringing this technology to the forefront very quickly...Good Luck! This house is in FLA -

   http://www.americanlimetechnology.com/clayton-house/

   http://www.industrialhempny.com/home.html

5. Expert Member
   Dana Dorsett | Jun 16, 2015 05:57pm | #5

   Nate is right again: CRRC rated cool roofing with a high SRI makes a difference in the cooling load, as does foil-clad roof decking. It's not worth paying a lot extra for, but it's usually not much of a cost adder either.

   The biggest complaint about high SRI roofing is about visual aesthetics- that it can looks "dirty" in short years when the algae & pollen collect on it, whereas with a darker finish roof the crud sorta blends in. But there are cool-roof finishes other than titanium-white that still make a difference.

   Roof pitch also makes a difference. Anything below 2:12 has effectively zero convective cooling to the outdoors, whereas pitches higher than 4:13 convection cool to the exterior relatively well, independent of it's solar reflectance. I recently measured the temp of a 2:12 pitch roof with a dark EPDM membrane north of 160F on a ~73F outdoor temp late morning on a not-super-clear day. With even a modest SRI cool roof finish it would have been no more than 130F, and had it been a 4:12 roof it might have been cooler than that, due to the convective cooling.

6. 
   heidner | Jun 17, 2015 12:54pm | #6

   If the area of Florida has termites and ant's... look at a rock mineral insulation for the OUTSIDE wall. Roxul Comfort IS... About 1 and 1/4, roughly R5...termites ignore it... water runs off it.

7. 
   iLikeDirt | Jun 19, 2015 11:18pm | #7

   Dana, would you mind explaining the whole angle-based nighttime cooling thing? I thought radiational cooling was enhanced on flatter roofs whose normal vector was closer to vertical.