I live in FL and am renovating my concrete block house.  I've removed the drywall and will replace with new.  Before I do, is it worth putting rigid insulation between the furring strips behind the new drywall.  Will I gain enough to warrant to cost and effort.  The exterior walls are hollow core block.

If you have already removed the drywall, I would seriously consider installing some rigid insulation. I would also use a spray foam glue to seal the joints between the rigid insulation and the furring strips. Hollow core block have an insulation value of around a R-2, so it should help a lot. Also by sealing the joints on both sides you will tighten up the house, which should be better and quieter in the long run. Just my opinion.

renangle

wow, R-2. I didn't realize it was that bad - thanks. I have never heard of foam glue. The furring strips are only 3/4" thick. I was thinking of replacing them with 2 X 2's (or 2 X 4's layed flat) so I could double the space to be filled with insulation. Any suggestions on what type of rigid insulation works best.

Others may chime in with a different opinion, as that is what we are giving our opinino. A non-core filled concrete block has very little R-value and a core filled concrete block has very little R-value too. I think that if you are going to do the replace the furring strips with 2 x 2's or 2 x 4's it would probably come down to personal preference. I would not lay the 2 x 4 flat to save on insulation. Part of it depends on our utility bill for electricity (since you are in FL), it may not be that high. Also, it may depend on how long you look to live there.

Look for a rigid foam that has a R-value of about 3 per inch. The foam glue (foam to foam, quick stop) can be found at many hardware stores and will seal up the gap between the insulation and the furring (this is if you are a DIY). You could do spray foam, that stuff is your best bet, but expensive (hard to DIY). If you are DIY, go to Lowe's/Home Depot and get their advice or hire a well know insulation contactor in your area and get pricing from them.

bmancanfly, now that you've got the drywall off do you see any evidence of moisture problems on the furring strips or in the space between them?

Use InSoFast, it sounds ideal for your situation.

There doesn't seem to be any moisture issues.

I hadn't heard of InSoFast until now. But they sound great.

Just wondering if I need additional insulation in the walls here in FL. Everyone insulates the heck out of their ceilings but I've never heard anything about the walls.

Call or email InSoFast, ask for Ed. He will advise you on how to do it.

I was at the FL home show and met some reps from a company that injects minimally expanding foam into the hollow cores of the blocks for insulation. Sounds like a good idea. Didn't get any idea of price though. Anyone have any experience with this stuff?

bmancanfly, I don't have any personal experience, but the general consensus seems to be that insulation placed within the hollow cores of the blocks doesn't work very well. The webs and ends of each block are very thick and provide a direct path from the exterior to the interior for heat or cold (depending on season) to travel right around the insulation. So where the insulation should be placed for it to actually work is on one side or the other of the block wall - preferably the outside. But in your case I think it would probably be easier to insulate the inside. Don't take my word for it, lots has been written on this stuff. I think Oak Ridge National Laboratory did a study on this.

If you want to insulate this, use a 2x4 wall with close cell foam. CMU's have almost on r value.

I had the guy from the show come and give me a quote on filling the cells of my concrete block walls for my 1600 sq ft house - $7300. Seems a bit much to acheive an R-11. Esp. considering the concerns expressed above.

Yep, that would be like throwing money down the drain.

How deep are your furring strips? Should be pretty easy to place rigid foam boards on the block between the furring strips before you place new drywall. Comes in 4 x 8 sheets and it's easy to cut with a hot knife if you need to.

Current furring strips are 3/4 " deep. I may double that to add more rigid foam board insulation. Considerably cheaper than the spray foam.

Yes, and since it's a block wall you don't need the strengthening and gap-sealing characteristics of spray foam.

place 1" r-max(board) on wall AND COVER with 1 x fir.

you get R7 + R3 for 3/4 air gap.

be sure to seal board at joints and penetrations.

new windows, and spray foam (roof deck) would also be a good investment

mac

mac31313,
Are you saying to affix the r-max boards to the the block and then affix the furring strips the the r-max boards?

You get about the same R-value with the much easier and no wood InSoFast.

If InSoFast has a dealer in Florida they would seem pretty appealing (assuming they don't overcharge for it). But if they have to be shipped from Minnesota, well that's a different story.

yes,

nail the fir strip to the concrete (on top of rmax) with 2 3/4"case hard nails,
you can tack rmax in place with small blocks or glue, seal joints, then add fir strips
mac

I think I'll be doing it the way you suggested.

When you say seal the joints ,  do you mean with tape?

tape will work,

but i use foam in a can ....get the pro style(reusable gun with control...less mess)
seal to floor,between sheets as you go.... 1/4" bead
also foam around outlet and switch boxes, penetrations, doors and windows

mac

thanks for the info - very helpful. the insulation boards I bought have a tongue and groove joint, so they provide a real good conection.

Once last question. Do I have to use pressure treated furring strips since they will not have any direct contact with the concrete block?

re: pressure treated strips

the only one required to be treated is where you have contact with masonry
(sometimes i use one along floor)

mac