Posted By thunksalot on 11/17/2009 10:45 PM
First off, I'm in the Raleigh/Durham area of North Carolina.
What can I do to seal-up and insulate my cinder block house without creating or worsening moisture issues?
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.)