Insulation For Your Home - Moisture Control
Part 3 of 3 - Vapor Barriers and Installation Tips
Vapor barriers... to use or not to use? THAT is the question!
Moisture within the walls of your home can cause serious problems. In the colder months, moisture tends to move from the inside to the outside of your home. As it passes through the walls, it may condense within them, causing the potential for rot and mildew. In walls with insulation, the water may condense within the insulation decreasing its R-value. In the worst case, moisture can actually freeze within the walls, accumulating until a thaw melts it and causes visible damage to your home such as wall or ceiling staining!
A vapor barrier is designed to keep moisture in your home from getting inside your walls. As mentioned earlier, batt and roll insulation come with a vapor barrier attached. However, leakage can occur where the facings meet. This is especially true if you do not staple the facings to the front of the studs, but instead either just press the insulation into place or staple it on the inside of the stud... a common practice with foil faced insulation. For the best possible vapor barrier, supplement the facing by installing a 4mil or thicker plastic tarp over the entire framed wall before tacking up the wallboard.
Attics present a special problems for vapor barriers!
Consider this... in the winter, there is a constant rising of heated air in the home. This warm air carries large amounts of moisture which attempt to pass through the ceilings and walls. To completely stop this movement of moisture is ludicrous... it will find a way out! So it is thought that it is better to allow some of the moisture to escape into the attic area. If your attic is properly ventilated, the moisture will quickly be removed by the circulating fresh air with no harm to anyone... you, your home... or your pocketbook! Using a kraft paper faced insulation laid between the ceiling joists... paper facing down, of course... will provide a slowing of the vapor movement without completely stopping it.
Vapor barriers are generally not needed in climates where the temperature is normally above freezing. Having a vapor barrier is not a negative... it is just unnecessary. Consult with your local building supply store or building inspector if you are unsure whether you need one!
Installing insulation... wisely!
Installing insulation is easy and quick... probably the easiest part of any renovation except for laying on the chaise lounge after the job is done. OK... installing the switch plates may be a LITTLE easier. Anyway, as a do-it-yourselfer, you know (from reading the brilliantly written sections above) that your product choices are limited... either loose fill or batt, blanket and roll insulation.
In a brief format, I am going to tell you what you should know to install insulation wisely. I say "wisely" because the mechanics of insulation installation are simple. Unroll the batt or blanket. Press it into place. Unfold the edges of the facing and staple it in place, if necessary. Done.
But it is the little things... the finesse if you will... that makes a simple job a great job. If you follow these guidelines, you will get the best insulation bang for your buck and minimize the chances of insulation related problems.
- The vapor barrier on insulation is always installed towards the living
space. "Oh... I thought having the pretty paper facing up
in my attic was pretty!" Don't let me ever catch you doing this
or I'll strip you of your Handyman Union Card!!
- Vapor barriers in attics should only be installed on one side of the
insulation. Since some leakage of moisture into the insulation in
inevitable (Murphy's Law), you want it to be able to freely escape from the
insulation into the attic... not be trapped inside!
- Never compress or fluff your insulation. Even if it asks you to...
"Fluff me... fluff me now!" But remember R-values?
They are computed with the insulation in its "natural
state". For example, fiberglass batts will expand after a batt is
unrolled. Blown or poured cellulose will tend to settle over
time. These events have been taken into account in computing
their R-values. If anything, squeezing or fluffing it will decrease their
R-values... not a good thing!
- For basement walls, a vapor barrier should be installed on the walls
first, before the framing is installed. This common sense step that is
often skipped in basement renovations will considerably lessen the migration
of moisture through the foundation walls.
- Though fiberglass batts can be used successfully for basement walls, foam
boards are also a good choice for insulation in basement renovations, since
they have the advantage of not absorbing water... in case of a water
leak! Some of the major manufacturers make a foam board product
specifically designed for basement applications. Check it out before
you hammer that first nail!
- If you use batt insulation with a reflective aluminum facing, you must allow some space... around an inch... between the facing and the wallboard. This air gap will significantly increase the amount of thermal energy reflected back to the home. To achieve this gap, staple the insulation to the inside of the stud instead of the edge. Don't compress the insulation excessively... a little air space is all that is needed.
Special insulation considerations for attics...
- When adding additional insulation to an attic that is
already insulated, NEVER USE INSULATION WITH A VAPOR BARRIER!! If you
do, there is a chance that moisture that has slipped by the first vapor
barrier will become trapped by the second vapor barrier, decreasing the
value of your insulation. If you have to use insulation with a vapor
barrier because your Uncle Harry gave it to you, slice the vapor barrier in
numerous places with your utility knife to allow moisture to pass through
it. And then thank Uncle Harry!
- Never jam insulation against the roof line of your attic. You
know... into that tight place where the roof meets the attic floor.
This can cause a cold spot on the roof in the winter months or a hot spot in
the summer. The cold spot could lead to ice damming... and the hot
spot could lead to overheating and possible damage to the roofing material.
- If you have a ridge and soffit ventilation system, do not interfere with
the flow of air by blocking the soffit vents. You can build little
dams out of wood to hold the insulation back, or use a commercial product
instead. For example, Owens Corning manufactures a plastic foam
barrier designed to keep the insulation back from the soffits and provide an
- Be careful installing insulation over the tops of recessed light fixtures, exhaust fans and other attic stuff! Though the insulation product you are using may not be flammable, overheating of fixtures could occur with tragic consequences. There are certain recessed fixtures that are designed for zero clearance from insulation. They are rated "IC", shorthand for "insulation contact". If you are unsure about your fixtures you can either 1) replace them or 2) build small open-topped boxes around them to keep the insulation at least 3" away!
Problems insulation and vapor barriers can cause...
As many benefits are there are to insulation, there are also skeletons in the closet. I have been asked many times over the years about unusual mildew growth on walls and ceilings or wet areas on walls where there is no apparent roof or plumbing leak. Since these events occur only in the winter months, the obvious culprit is a poorly planned or poorly installed insulation/vapor barrier system. Unfortunately, this can be a problem without an easy fix; cutting open the walls may be required to find out just what inside the wall is causing the problem.
To complicate the situation further, there may be culprits on the outside of your home, too. Oil paints are natural vapor barriers and they can cause moisture that would normally pass through the wood siding to linger and condense. Blistering exterior paint is a sure sign of moisture within the walls... yearning to be free!
Oh, your house has artificial siding? Well, aluminum or vinyl siding installed over a non-breathing insulation board can also be a suspect here, decreasing your home's natural ability to breathe.
Before you get the wrecking ball, here are a few less expensive things you can try.
- Don't add extra moisture to the air by using a humidifier.
- Use your bathroom and kitchen exhaust fans religiously.
- Eliminate sources of moisture in the basement and crawlspace.
- Use a vapor barrier paint to slow down the movement of moisture into the trouble spot.
- Install small circular plug vents between the studs on the exterior of the house... top and bottom. They will allow some needed air circulation within the wall, and give the moisture an escape route. These are the easiest vents to install... just drill a hole of the proper size for the plug vent you choose and press it into place.
- Peeling paint? Besides doing everything above, use latex paint or latex stain for your next paint job to allow for more vapor movement.
Visit these websites for more information...
Owens Corning, at http://www.owenscorning.com, has a wealth of information on installation of their fiberglass and plastic foam insulation products. Love that Pink Panther... even if he has become crassly commercial!
GreenFiber, one of the leading producers of cellulose insulation, makes their case for cellulose's superiority. One interesting twist is that they use some recycled paper and wood products in their manufacturing process, making their "fiber" even more green. You be the judge, at http://www.greenfiber.com.
If you are interested in insulating foam... polyurethane to be precise... visit North Carolina Foam Industries website at http://www.ncfi.com. They not only product foams for insulation, but also for mattresses, roofing and marine floatation. Amazingly enough, their foams are used to insulate the fuel tanks of the Space Shuttle!