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Old 04-10-2016, 12:28 PM   #1
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Wall Insulation in So. FL


I went looking for 1-1/2" Celotex (or comparable) at the local home centers and could find none. While looking online to see if I can buy it elsewhere I ran across something that goes like this:

The researchers monitored the two Florida houses, one with a setpoint of 73F and another with a setpoint of 79F. Although the cooler house used more air conditioning energy than the warmer house, the insulation saved 9%-14% of its preretrofit use. By contrast, the air conditioning energy use in the 79F home actually increased by 5% after adding wall insulation!

http://www.homeenergy.org/show/article/id/1293

Anyone with experience that supports this?
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Old 04-10-2016, 02:18 PM   #2
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Re: Wall Insulation in So. FL


Florida is a different beast depending on wall construction and orientation.

What does you wall consist of?
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Old 04-10-2016, 07:09 PM   #3
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Re: Wall Insulation in So. FL


It's a standard 8" cinder block wall that, as far as I can tell, has no insulation or mortar fill in the voids.

Before we stripped the interior, there was 3/4" PTL firring with fiberglass insulation and a vapor barrier over that. I have installed 2x2 firring and am ready to drywall. I was going to put in Celotex but that article has me wondering...
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Old 04-10-2016, 07:28 PM   #4
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Re: Wall Insulation in So. FL


The voids can be drilled and filled with foam.
Not a DIY job.
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Old 04-10-2016, 08:24 PM   #5
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Re: Wall Insulation in So. FL


I don't work with block homes and although the authors of that article are notable, I would still add the insulation. I didn't read beyond the first few lines, but can if you are really concerned. The basic principle that insulation reduces the heat transfer has to work in your favor. There are many other variables, but you shouldn't omit a fundamental improvement while those walls are open.

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Old 04-11-2016, 08:26 AM   #6
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Re: Wall Insulation in So. FL


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Originally Posted by Bud9051 View Post
I don't work with block homes and although the authors of that article are notable, I would still add the insulation. I didn't read beyond the first few lines, but can if you are really concerned. The basic principle that insulation reduces the heat transfer has to work in your favor. There are many other variables, but you shouldn't omit a fundamental improvement while those walls are open.

Bud
I completely agree with you, Bud, at least I did until reading the article in its entirety. After that, things got muddy.

Apparently, this is a very individual specific issue that, if insulating the entire house, would require inputting a lot of variables about your specific situation and needs. In my case I am only looking at the master bedroom.

In that room, neither of the exterior walls get much direct sunlight. So if I look only at passive heat transfer created by temperature alone, I imagine there would be more benefit in not insulating the walls, since only the outside temperature and not the effects of direct sunlight should be of major consideration.

With this particular situation there is already some insulation in the air void in the 8" block wall and the 1-1/2" void created by the firring. (FWIW, I firred at 1-1/2" to accommodate electrical boxes.) But the only way to really do an accurate calculation would be to monitor wall temperatures, interior temperatures and outside temperatures during the cooling period. That is still about a month away before it begins so that's not going to happen.

But the lack of wall insulation at the local home centers tells me they don't sell much. In rigid board insulation, some 3/4" can be found but not much. The original installers did 3/4" firring and knocked holes in the block to accommodate electrical boxes. They were also able to get 3/4" thick fiberglass insulation, something I have not seen here at the home centers.

Another factor is termites. Would wall insulation help create an environment attractive to termites? When we did the demo, we found termite tracks in tight spaces but not in air voids. (The termites were eradicated years ago by the previous owner. No sign of live termites today.) But it seems termites don't like open spaces.

If we had centralized control for the individual rooms I would insulate because I like to keep the bedroom cool at night. And if I could have found 1-1/2" rigid board insulation I would have installed it without even thinking about it.

Now, after reading that article, I am up in the air. Maybe using a dart board will make making the decision easier.
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Old 04-11-2016, 10:07 AM   #7
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Re: Wall Insulation in So. FL


Actually, my northern termites do not like open spaces and build mud tunnels when needed. Treatment for the termites is something you might want to discuss with the local exterminators in case they can do something simple while the walls are open. They would also have experience with any bug problems related to the foam. I know ants love it.

Although I am curious as to why they draw those conclusions, I have little interest/need to study the FL insulation problems. My plate is already full of northern issues, my apology.

As an energy auditor I can easily predict what an infrared picture of those walls would look like, with and without rigid insulation in the cavities, and you would not like the without images. A tight fit with a good tape over the seams between the rigid and the 2x2 would be my choice.

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Old 04-11-2016, 10:13 AM   #8
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Re: Wall Insulation in So. FL


I would still insulate.

What does the exterior finishing consist of here? I would just be cognizant of vapor movement and just making sure that if you put a foam in that wall, that is doesn't create a condensing surface behind the sheet rock.
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Old 04-14-2016, 12:54 PM   #9
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Re: Wall Insulation in So. FL


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I would still insulate.

What does the exterior finishing consist of here? I would just be cognizant of vapor movement and just making sure that if you put a foam in that wall, that is doesn't create a condensing surface behind the sheet rock.
They finished the raw cinder block with a mortar topcoat. It may be stucco but isn't finished like I am used to seeing stucco up north. It's smooth. On top of that is several coats of paint that has a rubbery consistency.

If I could have found 1-1/2" rigid board insulation, I would have installed it. All I can find is 3/4" and 2". The 2" 4x8 sheets are almost $60 each.

Doubling up the 3/4" probably wouldn't work because they are foil backed and you'd end up with two vapor barriers, something I have been told time and again is not good.

FWIW, I just did some thermal imaging takes and the bare block wall averaged about 76 degrees. The ceiling was about 2 degrees warmer.

When comparing the temperature of the bare block wall to an insulated, drywalled wall 2' away, the bare block wall was 0.7 degrees warmer. The wall outside was around 85 degrees with no direct sunlight on it. Between the overhang and the house next door, it's almost always shaded.

I'll do one more local search for 1-1/2" insulation, but if I can't find it, I'll just forget the insulation.
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Old 04-14-2016, 02:29 PM   #10
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Re: Wall Insulation in So. FL


2 points, using 2 layers of foil faced insulation would not be creating a double vapor barrier anymore so than one sheet with foil on each side, used all the time.

Second, I did a search for a Punta Gorda Home Depot and they have 1.5 inch rigid in 2x8' panels. They have a recess on each side for strapping, but I've visited friends in Sarasota and Clearwater and you have far more store selection in your area than I have way up north. If your box stores are not carrying it, email the mfg and ask who is carrying exactly what you want.

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Old 04-15-2016, 10:24 AM   #11
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Re: Wall Insulation in So. FL


RE: the vapor barrier, insulators on the job have told me many times there should only be a vapor barrier between the living space and the insulation. Dual vapor barriers create a sealed space in which condensation can build up. That's been drilled into my head over the years. And if there's condensation, termites might find it an attractive home.

As far as what's at the PG Home Depot, online I see no 1-1/2" at all. Maybe you're getting a different result. But on my visits there, rigid insulation stock is practically non-existent. I didn't even see what shows up online.

The other thing I don't know is how termites react to rigid insulation. There was one small section in the wall that had 1/2" Celotex. I saw termite tracks but I don't remember seeing termite burrowing in the Celotex.

There is a house being built near here. Maybe I'll stop by and see how they are doing it.
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Old 04-30-2016, 09:36 PM   #12
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Re: Wall Insulation in So. FL


So, what did you decide on?

http://buildingscience.com/documents...+humid+climate

http://buildingscience.com/documents...lligator-alley

Gary
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Old 05-01-2016, 12:57 PM   #13
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Re: Wall Insulation in So. FL


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So, what did you decide on?
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Believe it or not, nothing has been done in the bedroom. We've been spending all our time outside landscaping. We wanted to get that done before the oven here gets turned up too high.

I was planning on picking up the board insulation, along with the drywall, this week, but based on that Mold In Alligator Alley article you linked, now I'm not so sure.
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