Replies

1. 
   mycarwood | Dec 12, 2006 02:40pm | #1

   Here in New England it is the lack of insulation that causes the mildew/rot problems.  Blown-in foam insulation, in theory, will bond to all three sides of the stud bay.  This effectively eliminates the ability of moisture to make its way into the siding....in theory.  Blown-in cellulose insulation relies on the airspaces between the fibres to be effective, and it can settle, allowing your moisture issues.  I would go for the foam insulation wherever it is possible and practical.  It may be alittle more expensive, but it'll be worth it.

2. 
   user-217211 | Dec 12, 2006 03:15pm | #2

   My own house is a 30's West Coast bungalow with plaster walls, lap siding and empty stud bays.

   I've thought to blow in insulation, but I'd like to ask this of the experts first:

   The lower half of this  1 1/2 story house has no sheathing and no building paper of any sort.  The siding, 1x8 Dfir cut in a double V with a rabbet, is nailed directly to the studs.  The upper half has cedar sidewall shingles over 1x boards but still no tarpaper.

   Have you opened up the walls to inspect them? It is likely that you are getting small amounts of water entering into the stud cavities, especially around doors and windows. A drainage plane is essential to prevent this from occuring. Do not insulate a wall if any water can enter it even in small amounts.

   I am concerned that if I blow in insulation, the things won't breathe, moisture could become trapped in the walls and I'd get mold/rot issues.  This is rainy Oregon--it's hosin' out there right now!

   This is a valid concern. Many homes that were able to survive their lack of a watertight drainage plane by drying out after a rain event have not survived the addition of insulation. Insulation slows down the movement of air and heat in a wall cavity. These are the two primary mechanisms by which drying occurs.

   In this particular room, I'm going to pull down all the plaster anyway, so I thought I could use the fiberglass batts that are cased in film to prent any water that makes it into the walls from wetting the insulation.

   There are two problems with this strategy. It's the wood that you need to keep dry, not the insulation. The insulation will lose it's r-value if wet and mold can grow in fiberglass insulation although fiberglass is not a food source. The plastic film is perforated or otherwised designed to allow moisture to pass freely through it. Foam insulation is not a substitute for a drainage plane. It will promote rot from external water intrusion by slowing the drying potential of the wall perhaps more effectively than fiberglass.

   Any other thoughts?

   Pull the siding and add a drainage plane, carefully sealing around doors and windows and adding pans below the windows and flashings above. I won't detail how to do that here, but if you decide to do it, I or others can help with that. If you don' decide to do that, don't insulate. Air seal the crap out of the house from the inside to help with the energy losses. That is the most effective way to spend your money in any case.

   Thank you,

   Pat

   There is only one planet earth. How many chances do you think we get with her?
1. 
   Waters | Dec 12, 2006 06:39pm | #4

   Ray,

   Thank you.  I've been trying to get an informed response on this ? for some time and you have confirmed my suspicions.

   Pulling the siding is definitely out as it's old and fragile.

   I've had the walls open in several areas and it is apparent that there is/has been some infiltration.  The framing is all old growth Dfir full 2x4 and very solid.  There are no areas where it appears to stay wet.  I've replaced a few windows and doors and sealed best I can around the openings.

   Thanks again for your info..I'll have to think more and form a plan of attack!

   Pat

3. 
   andy_engel | Dec 12, 2006 04:37pm | #3

   Generally, I like cellulose, but not in your case. I'd consider open cell foam that allows some moisture migration.

   Andy

   "Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)

   "Get off your dead #### and on your dying feet." Mom

   "Everything not forbidden is compulsory." T.H. White, The Book of Merlin

4. 
   alwaysoverbudget | Dec 12, 2006 07:08pm | #5

   i really agree with your concerns and the idea's so far,what about when you pull the plaster down you fit 1-1/2" foam in the bays.this would give you some insul but would be away from the outside wall so if water comes in it would still get some air to dry. larry

   hand me the chainsaw, i need to trim the casing just a hair.

1. 
   Waters | Dec 12, 2006 08:36pm | #6

   That's actually a great idea.  Use rigid to seal and insulate the inside half, or more, of the stud bay--foam around the margins--and leave an air gap/screen outside to the siding to ventilate.

   Any cons on that besides price, Mr. Overbudget?

   Thanks,

   Pat

    

1. 
   DanH | Dec 12, 2006 09:10pm | #8

   Yeah, this occurred to me about the same time I saw OverBudget's post. You could pull the plaster and add maybe 1.5" foam board insulation (I'd guess you want at least 2" of airspace behind the siding) held towards the inside, then cover with plastic and drywall. You might consider a piece of flashing at the bottom of each cavity, to kick water towards the outside.This wouldn't be as good as pulling the siding and installing a rain barrier, but wouldn't be too likely to worsen the existing situation greatly.
   People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck

2. 
   DanH | Dec 12, 2006 09:12pm | #9

   If you can get a halfway tight fit and then you add plastic over it all, there shouldn't be any great need to foam around the edges of the foamboard. The plastic will prevent infiltration.
   People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck

5. 
   DanH | Dec 12, 2006 09:02pm | #7

   Fiberglass is the worst choice for this situation, unless some sort of air barrier is added -- the siding is virtually a screen door, and fiberglass needs to have an air barrier on both sides to maintain its insulating properties.

   Cellulose generally works well in this sort of situation, since it packs so tightly that air infiltration is minimized. Settling isn't a problem if installed by a competent contractor. The one downside of cellulose is that it is absorbant, and will retain more moisture longer than other options, if liquid water gets into the walls.

   Foam is theoretically the best, from an air infiltration standpoint, though not always from a moisture standpoint (depends on the situation).

   Moisture entry from the outside can be an issue with any scheme. Not a big problem in most of the country, if the house isn't falling down, but in a climate such as yours, especially with no sheathing, it's a concern. A lot depends on the exposure of the house (lots of wind-driven rain?) and how much eave overhang is present.

   In your climate (I'm assuming the coldest you see for any length of time is maybe 20F) condensation inside the insulation due to inside moisture isn't such a big issue. So long as there isn't plastic on the outside moisture from the inside will escape fairly easily.

   People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck