Insulation

[Cshama]

So, taking the advice here. Along with getting solar I am looking into energy conservation .

I just got a quote for attic insulation. I currently have a thin layer of worn out batt insulation on the floor. The contractor is offering to blow in open cell insulation into the roof rafters and the exterior walls to an r-21 depth.

There are 2 issues I want advice on. Firstly are there any attic condensation issues I should be worried about. Secondly, I will make only be able to cover half my attic and the rest of my roof area is essentially inaccessible. The contractor says it will still make s big difference.

[peakbagger]

Depends on where you are in the world and how leaky your house is. The standard approach is seal up air leaks then insulate. Ceilings are notorious leaky as folks run duct work and fixtures up through them. An energy audit (frequently offered at low cost from your utility) will identify the best bang for the buck improvements. Frequently the attic gets sealed with foam insulation rather than insulated. They can deal with fixtures pretty easily but if you have duct work up in the attic, its pretty notorious for leaks. In most cases they need to replace or reseal the duct work. Its still crappy place for duct work. In most climates you want air flow up from the lower edges of the house up through a high mounted vent. Installing a high vent is easy but making sure outdoor air flow up through the soffits is challenge. Insulators are somewhat infamous for blocking this air flow by insulating right up to the roof sheathing at the tops of the exterior walls. Nothing good comes of that. Another frequent source of issues is bathroom exhaust vents, instead of piping them to the outdoors, the pipe then into the attic. If there is not good air flow in the attic that can cause mold and moisture especially with blocked air flow at the lower edges of the roof. Up north they cause ice damming. There are things called proper vents that can be stuffed down in the cavity between the top of the wall and the roof sheathing that acts to make sure they do not blokc the air flow up through the soffits. In some cases the original builder did not install soffit vents or didnt put enough in. In that case you need to put in adequate soffit vents. Ideally they should be 2" wide the length of the soffit. If you have vinyl soffits, they should have a continuous strip of perforated soffits the length of the soffit. There are also round ones that fit in 3 or 4" diameter hole drilled with a shell cutter. Ideally you want them every stud bay but many folks skimp on them as they look ugly.

A professional energy auditor will look for all these things and my bet is most of their recommendations is air sealing first, then they will look at insulation. A insulator is in the business to insulate so of course he will tell you that insulating will make a difference. Good luck chasing him down if it doesnt.

[J.P.M.]

A couple of comments/points/questions: You will be insulating the roof and not the attic floor ? If you don't have 6" wall framing you won't get R-21 in the walls.

Short replies:
1.) Yes. See below.
2.) It probably will make a difference but not as much as the contractor would like you to infer from his wisdom. Big is a matter of opinion.


Condensation issues are a big deal, particularly with blown in insulation. The crux of the problem there is that there is simply no way to provide what is an absolutely necessary and 100% effective vapor barrier to any dwelling. A poorly done or absent vapor barrier can often, over time and maybe a short period of time result in sills rotting away, studs and rafters rotting, not to mention the insulation getting wet, and then losing effectiveness and smelling.

Several ways to attack it, all of which are usually considered and several used in concert. None are completely effective by themselves. Several used in concert and applied with attention to detail can be marginally adequate and at least postpone the problems.

An overview of what's an important but usually ignored and even if considered, a largely misunderstood aspect of insulation and energy conservation is how to deal with the problems that occur when water vapor (and its condensate) is not removed from places in a dwelling where it can cause problems.

One way to think of moist air in a home is as a river of fluid trying to leave your conditioned space by seeping through the walls, ceiling, vents or other holes in the building envelope. Once that air gets to the stud or rafter spaces, or any un - or under- heated spaces such as attics or crawl spaces via the unsealed or vapor permeable places where walls, ceilings, window frame gaps where corners ought to meet (but don't quite) it will cool during its journey to the unconditioned (and so cooler/colder) places. When it gets there, the moist air's ability to hold water vapor will decrease and the water vapor will condense as liquid (or frost if cold enough) on any colder surfaces and cause problems.

The realistic first line of defense is to first remove the amount of water vapor put into the air at the source by effective intentional venting such as bathroom and kitchen vents with stress on the word effective. For many reasons, most vents for such applications are better at making noise and looking pretty than removing moisture, but that's a somewhat separate conversation. Also, if a little off topic, if the exhaust for such vents is to an unheated and/or unused attic space, that's a sloppy and lazy but expedient and so all too common way of venting that can easily cause problems.

Next measure is to create what's called a vapor barrier - actually a vapor barrier system, one of whose purposes is to keep moist air from getting to cold places you own where it can condense and cause problems. As a general rule, in most climates, the vapor barrier is placed on the warm side of a building envelope, particularly in colder climates that have a winter.

One caveat of many to all this: Homes with aluminum or vinyl siding with some types of crap foam backing that's touted as insulation but does a poor job as an insulator while doing a pretty good job as a vapor barrier in the wrong place, and which as a result, can then be pretty effective at trapping moisture in the unheated spaces where it can do precisely what a hot side vapor barrier is meant to protect and minimize. See below for a trick to partially deal with that which may seem counterintuitive.

An effective vapor barrier is actually perhaps better thought of as a vapor a sealing system that has two or more elements. The two main ones are a film barrier and gap sealing.

In general, the closer the barrier elements are to the heated space the better. For example, vapor barrier paint (with a low vapor permeability) placed on the (heated) interior side of exterior walls and ceilings is probably the easiest and about the only way to apply the film portion of a vapor barrier system when used in conjunction with blown-in or loose fill insulation such as treated cellulose for your blown in application where plastic sheeting, or better yet a continuous aluminum foil barrier cannot be used in any practical sense. BTW, wallboard by itself is not an effective vapor barrier. It needs more than just itself to stop vapor migration through it.

The other very important (but not the only), and probably more evident part of a good vapor barrier system is sealing gaps.

In general, when there is a change in direction of a surface such as a corner, or where two surfaces meet (or don't quite meet), caulk or seal the seam, and when doing so keep in mind that attention to detail is the name of this game. Think of how tight the hull of a boat needs to be and go that way.

A couple of comments about blown in insulation when used for walls and to some extent with any non horizontal surface like sloped roofs: The stuff settles. Gravity is not loose fill's friend. For non vertical surfaces like sloped roofs, the thickness will decrease a bit. All that settling means that sooner or later gaps in the insulation will develop at the tops of stud spaces, below firestops in the stud spaces, and under windows, electrical boxes and probably any penetrations. Over blowing (packing the stuff) at installation helps some, but probably not much, particularly if the stud spaces are only blown from the bottom and the spaces above things like electrical boxes wind up with a non insulated "shadow" above them. Sometimes, places like the the spaces above high windows are missed entirely or intentionally skipped. SWAG: Expect ~ 4 % volume loss in any vertical space from settling, maybe a bit less if packed tight. BTW, you don't want too tight packing as that will decrease the R value a bit. Life is full of compromises. I suppose there's a "goldilocks" packing density that may well vary with each application and probably geographic area but the folks I know who deal with such things either don't know, or ain't telling, or, in their opinion it doesn't matter spit or they don't want to talk about as it is an unpleasant subject for them to deal with.

If a vapor barrier is not used for any reason, or if you want more insurance for what is a good attempt at a vapor barrier system on a retrofit, one way to get it is to loosen up the outside surface of an insulated wall, roof, or any surface.

Now, back up a minute. One goal (of many) in all this energy conservation business is to not solve one problem (large heat loss/gain) by creating others (in this case moisture problems from inadequate sealing methods). The way to mitigate if not eliminate the moisture problem entirely is to keep water vapor from condensing in an enclosed and under/un heated space - say a stud space. One way to achieve that is to prevent moist air from the dwelling from getting into the stud space in the first place. The other way is to get the moisture laden air through the exterior wall and out of the stud space as quickly as possible, faster and easier than it got in. That can be achieved to some degree by doing the opposite of what's done to create a vapor barrier in the warm (interior) side. That is, by loosening up the exterior surface.

In practice, it takes some thought to try to ensure the exterior remains an effective barrier to rain, bugs and critters while giving the exterior surface a vapor permeability that's about an order of magnitude greater than the interior. That way, water vapor that does get into the stud space will have an easier time getting out than it did getting in while the (probably) dryer outside air will mix with the house originated air that does make it to the stud space and the mixture will have a lower dew point and so produce less condensation, maybe none. For exterior walls, vents at the top and bottom can work. Or for siding such as wood lap, 1/4" holes on the underside of the laps with plugs made for the purpose inserted in the holes under the stud space fire stops can work well while being mostly unobtrusive. For aluminum, vinyl and stucco siding, top/bottom vents are available. For unheated attics, adequately sized and positioned soffit and ridge vents can be very effective. The wall venting method extracts a bit of a penalty for heat loss if the inside walls are loose, but not as much as you might expect with water vapor transport mainly by vapor species diffusion rather than fluid (air) transport or movement.

I had blown in cellulose done to the walls and (unused) crawl space floor in my first home in Buffalo that I essentially rebuilt. In the process I also really sealed the interior side and loosened up the exterior side of the exterior walls and also sealed the 2d floor ceiling with vapor barrier paint and caulking of the at the wall/ceiling joints as well as weatherstripping at the crawl space access and plumbing and HVAC penetrations. In the winter, the attic was colder than a well diggers ass and dry as a popcorn fart. No ice dams on the roof or eaves but as a somewhat unexpected consequence, I had to go up there a couple of times after really bad snow storms and push several feet deep snow off the roof. As for any moisture problem, when I bought the home I was told it was impossible to keep paint on it. That's often a sign of a moisture problem. After the insulation and interior sealing (and the weatherstrippng that went with it) I repainted the exterior. When I left town 18 years later, having sold the home ~ 10 years prior to that, the paint job was still tight as a drum and looking good with no peeling. I took that as an indication that the moisture problem was gone or at least under control.

Take what you want of the above. Scrap the rest.

[Cshama]

Thanks for all the good responses.

I spoke to my hvac guy and apparently due to all the leaks in my ducts in the attic, the air will effectively be conditioned.

He sees no issues and he's not getting a penny out of it so I kind of trust him.

[reader2580]

I had the "floor" of my attic sealed with closed cell spray foam. The builder had used fiberglass batts with kraft paper as the vapor barrier. That is a terrible vapor barrier. The contractor took out all of the original insulation before putting in the spray foam and making sure the attic was properly vented. Blown-in insulation was placed on top of the spray foam.

I don't have ductwork in my attic and it is extremely rare in Minnesota.

[J.P.M.]

I had the "floor" of my attic sealed with closed cell spray foam. The builder had used fiberglass batts with kraft paper as the vapor barrier. That is a terrible vapor barrier. The contractor took out all of the original insulation before putting in the spray foam and making sure the attic was properly vented. Blown-in insulation was placed on top of the spray foam.

I don't have ductwork in my attic and it is extremely rare in Minnesota.

Yea, kraft paper is a crappy/no vapor barrier, particularly and especially the way most batts are installed. Simply stapling the batt paper flange to a stud or joist will hold the batt in place, but without sealing, what's already a lousy vapor barrier becomes no vapor barrier at all.
If it was me, I'd check for cracks in the foam caused by shrinkage in the body of the foam, mostly at the edges of the foam that can create gaps. Such cracks that develop in the edges of the foam near eaves can increase the likelihood of ice dam formation. Proper venting of the attic ought to keep the dams in check, but if they still form, or are sporadic in the their location, cracks or other gaps in insulation may be the culprit.