Sealing/Insulating Cinder Block House
Last Post 29 Nov 2009 04:35 PM by grnideas. 11 Replies.
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thunksalotUser is Offline
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17 Nov 2009 10:45 PM

First off, I'm in the Raleigh/Durham area of North Carolina.

The question:
What can I do to seal-up and insulate my cinder block house without creating or worsening moisture issues?

The story:
The house I bought last year is made up of a cinder block 1950's 4 room house with a 1997 stick-built addition. (It really is cinder block, not concrete block.) I recently had the crawl space of the house sealed because of moisture control and mold problems. I thought the mold and moisture was coming up from the crawl space (and given how it looked down there, I'm sure some of it was). Since I closed the crawl space, I've still been having trouble keeping the moisture in the house under control. This may be because I heat passively (wood heat) and run a dehumidifier rather than using central air, but I think it has more to do with the leakiness of the house.

The house is very leaky. Before and after I had the crawl space sealed I had a blower door test done. Before the sealing job the CFM50 reading was 4913 and after it was 4050 (a 17.6% improvement). The house is a 2200 sqft ranch.

Today, I started popping off some of the vinyl siding to work on sealing around a window and discovered that there is no insulation, vapor barrier or anything between the vinyl and the cinder block. This surprised me because when I was buying the house, the builder that did the renovation in 1997 came over (he lives next door) and told me that he had put 1 inch insulation board around the whole thing. Hoping that I'd just misunderstood him, I went and pulled off some dry wall inside in order to see if there was insulation board on the inside of the wall. None. Which is pretty much par for the course on a renovation job that clearly cut every corner that hadn't already been sawed off.

Is there anything I can or should do about the cinder block situation, or should I focus instead on other air infiltration problems, like windows and doors that don't have an ounce of caulk around them?

Thanks in advance for any guidance you can give me!

BTW - Some people have told me that the things I'm finding out suggest that the 1997 renovation on this house was not done to code. Is there anyone that I could/should hold responsible for this mess? Like the inspector who told me "it's a great house!"?!!!

G ManUser is Offline
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17 Nov 2009 11:23 PM
Try going to Neptunecoatingscorp.com I working on a ICF house and they used this product on 80' by 15' cinder block retaning wall tied into an icf house wall. They will be back filling next week. There is a 100'hill that butts right up to this wall. Product Name is Wetsuit.
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18 Nov 2009 09:16 AM
Posted By thunksalot on 11/17/2009 10:45 PM
First off, I'm in the Raleigh/Durham area of North Carolina. The question: What can I do to seal-up and insulate my cinder block house without creating or worsening moisture issues? The story: The house I bought last year is made up of a cinder block 1950's 4 room house with a 1997 stick-built addition. (It really is cinder block, not concrete block.) I recently had the crawl space of the house sealed because of moisture control and mold problems. I thought the mold and moisture was coming up from the crawl space (and given how it looked down there, I'm sure some of it was). Since I closed the crawl space, I've still been having trouble keeping the moisture in the house under control. This may be because I heat passively (wood heat) and run a dehumidifier rather than using central air, but I think it has more to do with the leakiness of the house. The house is very leaky. Before and after I had the crawl space sealed I had a blower door test done. Before the sealing job the CFM50 reading was 4913 and after it was 4050 (a 17.6% improvement). The house is a 2200 sqft ranch. Today, I started popping off some of the vinyl siding to work on sealing around a window and discovered that there is no insulation, vapor barrier or anything between the vinyl and the cinder block. This surprised me because when I was buying the house, the builder that did the renovation in 1997 came over (he lives next door) and told me that he had put 1 inch insulation board around the whole thing. Hoping that I'd just misunderstood him, I went and pulled off some dry wall inside in order to see if there was insulation board on the inside of the wall. None. Which is pretty much par for the course on a renovation job that clearly cut every corner that hadn't already been sawed off. Is there anything I can or should do about the cinder block situation, or should I focus instead on other air infiltration problems, like windows and doors that don't have an ounce of caulk around them? Thanks in advance for any guidance you can give me! BTW - Some people have told me that the things I'm finding out suggest that the 1997 renovation on this house was not done to code. Is there anyone that I could/should hold responsible for this mess? Like the inspector who told me "it's a great house!"?!!!

Did that include a full ground moisture vapor retarder?  (6mil poly, mastic sealed at the seams, overlapped 12" at the seams,  mastic sealed to the block wall at least 12" up from the floor.)  If not, that's priority-1!  If the foundation walls arn't insulated,  2" of XPS or 2.5" of EPS bead board (with no poly or foil facers) can be applied to the interior at the same time, and will earth-couple the thermal envelope, reducing both heating & cooling loads.  (You may be required to leave a 2"  inspection gap a the top, below any sill plates etc. for termite inspection if you're in termite prone area.  But if the joists are just hung on hangers mounted to the cinder block this is less of an issue.)

Once sealed & insulated, monitor the relative humidity down there  (Accurite makes a cheap battery operated desktop type temp & RH meter, available at some box-stores.  Just leave it down there and check it in the morning under different weather and heating/cooling conditions. ) If the RH is above 65% most of the time, put a small dehumidifier down there, or rig up a small blower & timer to do periodic air exchanges with the conditioned air of your living space (it doesn't have to be anything like continuous unless it's an extremely low flow blower.)  At 70% & up the mold potential begins to skyrocket.

In NC in summer most of the moisture comes in from outdoor air infiltration, but in the fall/winter heating season it's usually internal (or ground moisture.)

The vinyl siding over the bare cinder block is a problem.  Any wind-driven wetting is immediately transferred to the interior by the porosity of the masonry. It really needs an air barrier, and better yet, a drain plane. You should NOT put a vapor retarder on the exterior of this house or you'll be asking for even worse problems!  You can (and should) have a vapor permeable (or semi-permeable) air barrier on the outside.  If/when you get to that point, 3/4-1" XPS insulating sheathing (with taped joints) would be permeable enough, and put the thermal mass of the cinder blocks inside the insulation (good for both heating & cooling seasons.)  If you create a gap with vertical furring (to which the siding is mounted), you have a ventilated drain plane to handle any storm moisture incursions.  If it turns out that he DID put insulation board over parts of it was on the exterior, and hopefully it had no vapor impermeable facers, which could end up trapping moisture inside the wall structure. In NC it's best if the wall can dry both toward the interior (in summer) and exterior (in winter)- adding vapor retarders just complicate the situation. But blocking air infiltration on both the interior & exterior limits the amount of moisture getting into the wall.

Start by caulking/foam sealing all the windows & doors though- your summertime humidity from air infiltration is likely a huge latent-load.  If the interior finish wall is a studwall, caulking/sealing all of the electrical & plumbing penetrations count too.

Last, but never least, there's the big air leak in the sky:  Do you have recessed lighting and plumbing chases extending into the attic spaces? How about open-topped partition wall stud bays?  These often represent the largest air leaks in a house.  If there's a lot of it, along with numerous electrical penetrations for other stuff (ducts? air handlers?), the labor required for fixing it can be endless, and if it means swapping out 20 recessed light fixtures for gasketed air-tight insulation-contact versions it's cheaper/better to convert the attic to conditioned space by insulating the roof deck & gable ends with 4-6" of low density spray foam, sealing off all the soffits & vents.  (And even though foam installers may try to convince you otherwise, leaving any attic floor insulation is usually more than OK, but benefit.  Just pull it back wherever they need to be able to spray where the roof & walls meet.)
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19 Nov 2009 08:45 PM
"Today, I started popping off some of the vinyl siding to work on sealing around a window and discovered that there is no insulation, vapor barrier or anything between the vinyl and the cinder block. This surprised me because when I was buying the house, the builder that did the renovation in 1997 came over (he lives next door) and told me that he had put 1 inch insulation board around the whole thing."
Just a guess: is there a white foam behind the siding attached directly to the siding (not to the wall)? If there is, that is a popular way of installing new siding and telling the consumer "this will insulate your home from nothing to R- whatever". It helps minutely; but nothing like the 3/4 to 1" XPS Dana refers to.
richm
ps I live in Kerenersville!
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19 Nov 2009 08:45 PM
oops, mis typed..Kernersville
ICFconstructionUser is Offline
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24 Nov 2009 08:33 PM
InSoFast.com
Brad Kvanbek - ICFconstruction.net
thunksalotUser is Offline
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24 Nov 2009 10:57 PM

Wow, thank you Dana1 for your thorough and speedy answer! I can't tell you how much I appreciate it! Thank you, thank you. I apologize for taking so long in responding, I've been super busy and had to put this (depressing) project out of my mind for a little while for sanity's sake.

Did that (sealed crawl space) include a full ground moisture vapor retarder?

Yes, it included 10 mil plastic laid across the ground and up the foundation to the trusses with PSK R-13 on the foundation walls except in places where they foamed the walls. The plastic joints were overlapped and sealed. The crawl space doors were weatherstripped and insulated. Because all the ductwork is in the attic and I rarely use the AC or furnace, I opted to have them install a small dehumidifier with an expeller pump and a 20 watt fan that moves air from near the dehumidifier to far corners of the crawl space.

Start by caulking/foam sealing all the windows & doors though- your summertime humidity from air infiltration is likely a huge latent-load. If the interior finish wall is a studwall, caulking/sealing all of the electrical & plumbing penetrations count too.

To seal the windows and doors, it seams to me that I have to either take off all the interior trim (which isn't insubstantial given the depth of the window sills) or take off the vinyl on the outside to seal it from the outside. Is there any reason it would be better to seal the windows and doors from the inside or outside other than whichever one is easier to get to? If not, I think I may just try to do it all in one go all on the exterior - remove vinyl, seal windows and doors, put on XPS sheathing, add furring and replace vinyl.

If the interior finish wall is a studwall, caulking/sealing all of the electrical & plumbing penetrations count too.

I have done this kind of thing, but I just have to think that with an ACH of 14(!) there must be bigger air infiltration problems than those, right?

Last, but never least, there's the big air leak in the sky: Do you have recessed lighting and plumbing chases extending into the attic spaces? How about open-topped partition wall stud bays? These often represent the largest air leaks in a house.

Last winter, I discovered that there was zero insulation in the attic over the new (1997) part of the house. I spent a better part of 8 weekends sealing all the ductwork, vent boots, and electrical penetrations. I even took out all the recessed lighting that couldn't be insulated and replaced with ones that could be insulated. Then, I blew in 12" of cellulose insulation.

A wise friend of mine told me to seal the top-plates and I tried to look for gaps at the tops of walls but didn't really know what I was looking for so I didn't find anything to seal. Unfortunately, if the top-plates are my major infiltration source, they are all now buried under 12" of blown-in insulation. My friend is now recommending that I try to remedy the situation by installing an "attic blanket." It's an air, moisture and radiant barrier with R-16.8. It sounds like a good idea but I wonder if I need to do anything else first because once the attic blanket is installed I think it will be even more difficult to get to the ceiling from the top-side. What do you think?

I still have more investigating to do. I've been too afraid to look under the siding in the addition. And, I need to take a look at where the addition meets the old cinder block construction. I'll report what I find when I get up the courage to look!

-Sam

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24 Nov 2009 11:09 PM
Brad, it appears to me that the InSoFast product is intended for interior installation. If you are going to pitch a product, it would be helpful to provide some details of why you are recommending it. Are you trying to suggest that I should rip out all the drywall in the cinderblock part of my house and start from scratch witn InSoFast (leaving the cinder block outside the building envelope) or are you suggesting that the InSoFast should be used under the vinyl on the outside?
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24 Nov 2009 11:11 PM
Posted By richm on 11/19/2009 8:45 PM
Just a guess: is there a white foam behind the siding attached directly to the siding (not to the wall)? If there is, that is a popular way of installing new siding and telling the consumer "this will insulate your home from nothing to R- whatever". It helps minutely; but nothing like the 3/4 to 1" XPS Dana refers to.


I didn't see or feel any white foam on the back of the vinyl. But, I wasn't looking for it either. I'll look for that next time I pop some off. Thanks for the tip.
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24 Nov 2009 11:24 PM
Posted By G Man on 11/17/2009 11:23 PM
Try going to Neptunecoatingscorp.com I working on a ICF house and they used this product on 80' by 15' cinder block retaning wall tied into an icf house wall. They will be back filling next week. There is a 100'hill that butts right up to this wall. Product Name is Wetsuit.


Wetsuit looks pretty nifty but I'm not sure I understand how it applies to my situation. Are you suggesting that I take off the vinyl siding and spray wesuit over the cinder block? From what Dana1 and others I've talked to have said, it seems like that could make my situation worse as true cinder block that is built straight up from the ground wicks moisture and needs to be able to dry out. Am I misunderstanding how you were recommending this product would apply in my situation?
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25 Nov 2009 12:41 PM
They say it's "very low perm" but I didn't see a number.  Stuff like that could be safely applied as a sealer to say, a slab/rat-slab in a basement or crawl space, or on the EXTERIOR side of a sub-grade wall, or to a membrane roof. But definitely not to the interior side of a sub-grade wall or it'll drive the ground moisture higher. Consider it and it's placement as you would any other vapor retarder.

http://www.neptunecoatingscorp.com/wetsuit.htm

In NC, permeable insulation on the exterior with goop like this can be applied to either the interior or exterior side of the cinder block of an above grade wall as long as there is semi or high permeability of the rest of the wall structure (no vapor retarders, only permeable semi-permeable air-barriers like tarpaper-felt or housewrap) letting it dry toward the exterior.  If foil or poly faced insulation is used on the exterior, don't put low-permeability stuff on the interior surface or you'll have a classic condensation/ground moisture trap. 
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29 Nov 2009 04:35 PM
It seems green buildings are not as easy as they appear. When accounting for LEED and other such milestones it can get expensive and cubersome. Fortunately green forums and communities can help out and give people good DIY advice and ways to go green and save money at the same time. Great luck to you!
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