Dryvit over Cinderblock? Good idea? Expensive?

Question

I'm considering a property that is built with painted cinderblock.  It was built in the 50-ies and there is little insulation (I doubt the blocks are filled with foam, etc).  Some of the interior is drywalled but doesn't look like they put in a lot of insulation between the blocks and the sheetrock either.  Other parts of the interior are just basically the (painted) cinderblock.

So, I'm thinking of adding a siding such as Dryvit in order to a.) improve insulation and b.) enhance the curb appeal.

Does anyone have advice as far as potential pitfalls and approximate cost of such a retrofit?  This is a small 2/1 800-900 sqft one-story building.

Cathy Svercl · Answer

we used injected foam insulation, very cost effective, gives R-20 insulation as well as reduces outdoor sounds (traffic, neighbors, etc).  for a 1200 sf house, it cost $800 3 years ago.  the installer came for 4 hours, drilled 1 inch holes in the CMU ("cinderblock") exterior, about chest height, 16 inches on center.  sprayed the liquid insulation through the hole, it solidifies inside the block shortly.  just fill 1 inch holes on outside with grout and paint, or stucco over.

we only had 1 problem, where there must have been a hole in the block on the interior side, and the foam pushed through and pushed the drywall out about 2 inches.  not a big deal - cut out 24 inch drywall square, scrape off extra insulation (which has solidified), put drywall square back in place.

p.s. i am also an architect here in FL.

Cathy Svercl · Answer

contrary to an above reply, "typical" block walls are not solid - only corners and either side of openings have vertical rebar and filled with grout.  in Florida, we also have additional vertical rebars for wind and flood strength - called "filled cells" every 4 to 6 feet along the wall.  other areas of the country may have different requirements.

the R-value is just as important as the air (flow) barrier.  the foam will do both by filling all the cracks in the block wall.

not familiar with "Dryvit" specifically.  this is a name brand for what the industry calls EIFS "Exterior Insulation Finish System".  EIFS should be installed by an experienced contractor to make sure water and moisture can still drain/dry out of the wall.

get quotes from local companies, as no retrofit job is the same as the next.

Andrew S. · Answer

Paul S.

No, I ended up just painting the cinder block, so I never got an answer.  Sorry.

I may re-visit this in the future because during the renting process, a good number of people gave feedback on the cinder block exterior and said they'd prefer some type of siding.  Purely a curb appeal issue though - nobody voiced concerns about energy efficiency.

Paul S. · Answer

@Andrew S.

Did you ever get a price on your project? I was just curious if you had gotten an estimate per/sqf.

Kimberly T. · Answer

(I realize this thread is a few months old)

Masonry is not required to be fully grouted, at least per the IBC.  Here in seismic country, it typically is fully grouted, but I know it is not done that way in other parts of the US.  As long as it is properly engineered, cmu can by partially grouted and still meet code.

The ICC report that Mike referenced above is for Hilti KB3 anchors.  The ICC report states that the anchors can only be used in fully grouted cmu (since it is a wedge anchor), and is not meant to imply that the code requires all cmu to be fully grouted.  There are post-installed anchors available that can be used in ungrouted cells of cmu, but the KB3 is not one of them.

I am a structural engineer in CA.  I am speaking based on the IBC, as I have not done any residential projects.  Although, from what I hear, the IRC is much more lax than the IBC.

Cathy Svercl · Answer

@ Mike Reynolds - the R609 you refer to is specifically "Grouted Hollow unit masonry", which is different type of construction from R606 "General Masonry Construction".  i would have to assume your local soils are full of clay, requiring a fully grouted wall.

Miami Dade as well as the rest of Florida follows the Florida Building Code, which is based on IBC & IRC.

Mike Reynolds · Answer

@ cathy, Do you have a code for that? Here is mine

http://www.icc-es.org/Reports/pdf_files/load_file.cfm?file_type=pdf&file_name=ESR-1385.pdf

3.2.2 Grout: The masonry units must be fully grouted

with grout complying with Section 2103.12 of the IBC or

Section R609.1.1 of the IRC, and having a minimum

compressive strength as indicated in the tables at 28 days.

I would like to know what they do in Miami Dade as we go by the IRC here in Texas.

Mike Reynolds · Answer

Andrew I am from Texas so the prices I pay may be similar and they may not be. It depends on your location in Fla. Palm Beach contractors may charge more than in the panhandle per say. But around here its 6-10 bucks a square foot of coverage area. I have worked in West Palm Beach (not EIFS though as I am a carpenter) and the prices there are about maybe ten percent higher in carpenter/roofing than they are here whereas the panhandle is actually about 5% cheaper than here.

Hope that helps some. The best thing to do is get estimates to vet it. Cathy will be better tuned into this question if she sees it. Maybe a PM to her will help as she might know a specific one in your area.

Andrew S. · Answer

Thanks @Cathy Svercl  and @Mike  Reynolds  for the info.  I'll certainly check whether they are filled or not.  Any idea what a Dryvit siding would cost for a house of that size?  2K, 5K, more?

Mike Reynolds · Answer

@matthew, The r factor is about 5 or so but here is the problem with that. It encapsulates the exterior and the best air sealing measures come from sealing the inside. R values are just one way to improve your rating. Stopping air flow (to a point so as not to make it too tight) is the best way to help your utility bill.

Dryvit over Cinderblock? Good idea? Expensive?

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