I have been hearing many different views on wheter to use blown in insulation behind existing plaster walls. Some say that not to insulate is bad for the heat loss factor, others say that the insulation will only serve as a sponge for the water causing rot, mold and mildew and that I should seal all air penetrations and only insulate the attic.
I am still deciding, but I was wondering what people think and if anyone has had to rip out rotten wood because of wet insulation.
Replies
I've seen houses that were a hundred years old stuffed with cellulose that were starting to suffer from rot within ten years in this humid climate.
That doesn't prove that the insulation caused it but OI believe that any project like this should include a full plan for preventing moisture from getting into the insulation because it seems to me that if it penetrates to that point, it never seems to dry out enough
What is your climate and ground water situation?
Excellence is its own reward!
What Piffin said .
It would make a big difference where you are , such as Florida or Colorado. Always try to post where you are at in a post such as this one . Can you stop the moisture?
If you were living in a cold climate then you would have to address the moisture .
Tim Mooney
Edited 1/8/2003 8:26:45 AM ET by Tim Mooney
I am in Central VA. The weather can vary greatly, but never to the extremes of Colorado or Florida.
The ground water situation is not good. It is built on piers so water can easily get under the house, and the soil is clay, so everything sits right on top. One of my many major projects is dealing with that, but even with a good solution, water will still be able to get under the house. (I will be posting a question about weather to try to close in the open crawl space as well.)
Thanks a lot for you input.
Things get even trickier in a climate like virginia, which is a mixed climate, It has a fairly substantial heating season followed by a fairly substantial cooling season, which makes the use of vapor barriers on either side of the envelope a bad thing for half the time.
Will you be using air conditioning in the summer?
I highly suggest you look at Joe Lstiburek's "Guide to Building in Mixed Climates" to get a handle on the dynamics of the issue.
What it boils down to though, is that you will want to get moisture issues under control first. Then you need to build an air-tight yet vapor-permeable thermal barrier that will be able to dry via diffusion to either the inside or the outside of the envelope, as the moisture-movement dynamics will flip from season to season. There are not a lot of ways to acheive that particular mix of characteristics.
Steve
Edited 1/8/2003 11:35:51 PM ET by STEVENZERBY
Edited 1/8/2003 11:36:23 PM ET by STEVENZERBY
Ditto to what Piffin said. My folks place is over a century old and was structurally sound . It now suffers from rotted sills and floor joists after it was insulated. Coincidental? Maybe but I don't believe so. The house, although drafty, surviced for a century without any significant deterioration. After it was insulated under a Federal weatherization program, the deterioration was marked and noticeable. I suspect all those drafts allowed moisture/dampness to dry out before it could do any damage. If the basement problems had been rectified (dirt floor/ water), I don't believe this would have happened. This doesn't mean you should insulate; just that you should do your homework and fix any moisture/water problems wherever they occur.
Edited 1/8/2003 9:15:18 AM ET by jc
I am involved frequently in the renovation of very old buildings, HVAC systems design and troubleshooting and mold investigations from time to time. You have received some pretty good advice. Adding insulation to an older structure or adding AC to an older building without considering all factes of the ventilation and moisture control of the building can be disasterous. The books by J. Lstiburek are very good references. He has also written a few articles for the ASHRAE (Amercian Society of Heating, Refigeration and Airconditioning Engineers) Journal, one in particular deals with moisture control in houses. This is also a very good reference. It can be found on their website: http://www.ashrae.org
The question frequently comes up, for instance, "Why was this building/school/etc., fine for 50 years but now I have mold growing?" The answer, in a nutshell, is almost always "incomplete or poorly performed weatherization/insulation". Do the research first, then insulate.
You said where you live but nothing about the construction of the house other than that it is on a pier and beam foundation with a vented crawl space (do not close this up). How its built, the existence and location of vapor barriers and weather or not you use air conditioning all matter.
Edited 1/10/2003 8:54:40 AM ET by Tim
tim, i went to the ashrae site you linked and looked for joe's article but couldn't find it..
any more info on how to find the article ?Mike Smith Rhode Island : Design / Build / Repair / Restore
I'll have to look and I'll get back to you. I don't remember when it was published and I don't know what kind of access non-members have to published articles.
Tim
Thanks for the advice
What are the potential downfalls of each. If I don't insulate do I risk anything more than high energy bills or could it effect the structure one AC is put in (if it is to be done).
When you say do my research, I have tried and always come up with conflicting answers. what sort of professional would be good for this. I am a GC myself, but I have done mostly commercial work. I now work for a renovation contractor and everyone ay my company says to blow in insulation. We just did it on a historical renovation of a framhouse similar to mine (against the advice of some). Another colleague who has been doing this for years (in Mass.) just did it to his own house (again similar to mine). My father-in-law who is an architect and professor of architecture advises against.
Sorry for the long list but I have very good sources saying both ways and I am not sure what direction to go next in terms of research or advise or professionals.
you asked about vapor barriers. I cannot see how there would be one, but I cannot verify that yet. I haven't closed on the house yet.
I have been advised by soimeone who advises against insulating the walls to use semi-rigid insulation under the joists to insulate and provide a bit of vapor barrier under the house, but I have 12" max under the house to work.
The concern with vapor barriers, when installed in the typical fashion (on the inside of the insulation), is that in a mixed environment, during the air conditioning season, moisture will move from outside to inside. If a barrier is placed in its path, the moisture needs a way out. If you do not use an air conditioner in the summer, then its less of a concern.
My house has fiber cement siding, an air barrier, osb/plywood sheathing, two 2x4 stud walls with fiberglass batts and a small space between, a vapor barrier and drywall. The space between the stud walls is open to the vented attic, wherever possible. In the summer, moisture will pass through the siding, air stop, sheathing and first wall of insulation (which has no vapor barrier or retarder) and out the vents. In the winter, any moisture that gets past the VB, will do the same.
BTW, plaster with and oil based paint will serve as a fairly effective vapor barrier. Under or between the joist over the vented crawl space, you can use regular fiberglass batts and cover it over with rigid foam or a vapor barrier. The crawl space will be a source of moisture in the winter, in most cases, and keeping the moisture out as oposed to keeping it in, is one way to do it.
There are people who make their living doing this stuff (insulating and weatherizing) and I'm not one of them. There is a great difference of opinion on vapor barriers and insulation as well. I don't know if there is a single right answer for you.
our house is double walled also... 2x4 exterior with r15 glass & poly vapor barrier.. 1" airspace, 2x3 interior wall with electrical devices and fiberglass r13 batts & poly vaporbarrier...
attic is 18" of cellulose with soffit & ridge ventsMike Smith Rhode Island : Design / Build / Repair / Restore
Mike,
Did you build the home? How long have you been there? In RI you don't see subzero temps often, I would think, how are your heating costs?
I renovated a 1971 constructed house, that originally had 2x4/r-11 walls and 2x6/r-19 ceilings and all electric heat. Although, I worked for the electric utility at the time, the first $400 electric bill made it real obvious something had to change. (I did not get a discount on my electricity) The previous owner had installed an LP furnace and about 1000' of 6" flex, that effectively heated a single room.
I decided on the double wall approach, probably for the same reasons that you did: no penetrations, wiring, etc., in the outer "shell" and double the insulation for an existing structure. In my case (the house is WAY too big) the loss of some floor space was insignificant.
So far, I'm able to heat an almost 6000 sf house for what a "normal" house half that size would take. I have a single 125,000 btuh furnace that easily handles the heating.
Would be interested inyour results.
Tim
tim .. here it is.... 18 years later...
front ....................................................................and back..Mike Smith Rhode Island : Design / Build / Repair / Restore
Very nice, Mike!
I really like the glassed cupola/belvedere. I have photos being developed and will post you a pic next week. I have almost the same over my central stair. Opened up the attic to let in the light, though mine is not hexagonal.
Tim
Well Tim, your heating costs seem to bear out that you can't be losing too much heat compared to what you were losing before. What's the climate like where you are?
Steve
North central Illinois. Design low temp is -15, ASHRAE 99.4% low temp is -10. I usually keep the house between 60 and 65. Supplement with electric "tile warmers" and 3 fireplaces. Walls are R-25, ceilings are R-45, catherdrals are R-35, all with continuos soffit and ridge vent, and argon-filled insulated low-e glass. I have a 94% AFUE 2-stage, variable speed LP furnace with a Honeywell programmable thermostat, and a Bosch Aquastar tankless water heater.
So far, so good.
JOBYG,
You have hit the wall that we all hit when we become interested in doing things well. There are pros and cons to everything.
What are your average annual energy bills? A leaky uninsulated house will be less suceptible to moisture problems. But if you understand the dynamics of your particular climate and your particular house, you should be able to insulate in such a way that you will minimize the potential for trouble.
Your house on piers actually could be a plus. The source of a lot of moisture in houses is the cellar. If your house is on piers and the skirting is relatively open, then most of the ground moisture will simply be carried away on the breezes. If you start to enclose that perimeter, however, you raise a lot of issues. Not the least of which is that in hot humid climates a tight, unvented crawlspace is better than a vented one (depending on who you ask, of course). Unless there is significant ground moisture, then enclosing it without dealing with the ground moisture is asking for trouble.
I would probably do as one person suggested you do and cover the bottoms of the floor joists and blow the floor joist space full of cellulose. The delimma there is what to cover the bottoms of the floor joists with. Should it be something vapor permeable? (ie: housewrap) or something that's a vapor barrier. In the winter, a vapor barrier on the outside of the envelope is not a good thing. The pressure dynamics of the structure are such that air will want to move from oustside to inside (stack effect) but the moisture diffusion dynamics are such that the moisture will want to move from warm to cold and from humid to dry--both of which would have it moving towards a condensing surface (whatever you cover the bottoms of the floor joists with) at the cold side of the envelope--not good). Will the the air pressure from outside to in conteract the moisture pressure from inside to out? Who knows. Lstiburek says that you you move 100 times more moisture via gross air movement through a 1 inch hole than you do via diffusion through a 4x8 sheet of sheetrock. If you use a thick enough sheet of ridgid foam to cover the bottoms of the joists, will the first condensing surface the moisture encounters (the inside of the sheets of foam) be above the dewpoint anyway, so it won't matter? What's the net effect of all these factors at floor level in Virginia in the winter? Your guess is as good as mine.
Or you could put a vapor barrier on the ground, enclose the perimeter and insulate the perimeter, but you better be sure you have the ground moisture under control if you go that route.
What you decide to do ultimately depends on your level of comfort with the knowledge you have. You should carefully scrutinize the sources of whatever recommendations you weigh. What is the basis of their recommendation? Is it backed up by research? Anyway, I would start with Joe Lstibureks books.
Best of luck to you.
Steve
Tim,
Seems to me that with the airspace between your double walls being open to the vented attic, the outside studwall and its insulation is effectively outside the thermal envelope, thereby rendering it pretty useless. In addition the interior studwall has its fibergalss essentially exposed as well, with resultant excessive convective heat loss. Or am I missing something here?
Steve
Edited 1/12/2003 3:14:44 PM ET by STEVENZERBY
Edited 1/12/2003 3:15:09 PM ET by STEVENZERBY
The air space is less than an inch, and is not really open to the attic but to the joist space over the top plates, through unfaced insulation. It is a path for vapor and I'm sure some heat is lost through this path with the vapor, but not any significant amount.
Here is a link to Joe Lstribrk's books that other posters were talking about. Apologies for mispelling his name. http://www.buildingscience.com/
This was an education by itself reading the excellent responses you got to your question.
Eric S.
Edited 1/29/2003 3:17:26 AM ET by ESVENDSON