Part 3 of 3 - Vapor Barriers and Installation Tips
Vapor barriers... to use or not to use? THAT isthe question!
Moisture within the walls of your home can cause serious problems. Inthe colder months, moisture tends to move from the inside to the outside of yourhome. As it passes through the walls, it may condense within them, causingthe potential for rot and mildew. In walls with insulation, the water maycondense within the insulation decreasing its R-value. In the worst case,moisture can actually freeze within the walls, accumulating until a thaw meltsit 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 insideyour walls. As mentioned earlier, batt and roll insulation come with avapor barrier attached. However, leakage can occur where the facingsmeet. This is especially true if you do not staple the facings to thefront of the studs, but instead either just press the insulation into place orstaple it on the inside of the stud... a common practice with foil facedinsulation. For the best possible vapor barrier, supplement the facing byinstalling a 4mil or thicker plastic tarp over the entire framed wall beforetacking up the wallboard.
Attics present a special problems for vapor barriers!
Consider this... in the winter, there is a constant rising of heated air inthe home. This warm air carries large amounts of moisture whichattempt to pass through the ceilings and walls. To completely stop thismovement of moisture is ludicrous... it will find a way out! So it isthought that it is better to allow some of the moisture to escape intothe attic area. If your attic is properly ventilated, themoisture will quickly be removed by the circulating fresh air with no harm toanyone... you, your home... or your pocketbook! Using a kraft paper facedinsulation 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 isnormally above freezing. Having a vapor barrier is not a negative... it is justunnecessary. Consult with your local building supply store orbuilding inspector if you are unsure whether you need one!
Installing insulation... wisely!
Installing insulation is easy and quick... probably the easiest part of anyrenovation except for laying on the chaise lounge after the job is done.OK... installing the switch plates may be a LITTLE easier. Anyway, as ado-it-yourselfer, you know (from reading the brilliantly written sections above)that your product choices are limited... either loose fill or batt, blanket androll insulation.
In a brief format, I am going to tell you what you should know to installinsulation wisely. I say "wisely" because the mechanics ofinsulation installation are simple. Unroll the batt or blanket.Press it into place. Unfold the edges of the facing and staple it inplace, if necessary. Done.
But it is the little things... the finesse if you will... that makes asimple job a great job. If you follow these guidelines, you will get thebest insulation bang for your buck and minimize the chances of insulationrelated 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 basem*nt 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 basem*nt renovations will considerably lessen the migration of moisture through the foundation walls.
- Though fiberglass batts can be used successfully for basem*nt walls, foam boards are also a good choice for insulation in basem*nt 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 basem*nt 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 air space.
- 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 thecloset. I have been asked many times over the years about unusualmildew growth on walls and ceilings or wet areas on walls where there is noapparent roof or plumbing leak. Since these events occur only in thewinter months, the obvious culprit is a poorly planned or poorly installedinsulation/vapor barrier system. Unfortunately, this can be a problemwithout an easy fix; cutting open the walls may be required to find out justwhat inside the wall is causing the problem.
To complicate the situation further, there may be culprits on the outside ofyour home, too. Oil paints are natural vapor barriers and they can causemoisture that would normally pass through the wood siding to linger andcondense. Blistering exterior paint is a sure sign of moisturewithin the walls... yearning to be free!
Oh, your house has artificial siding? Well, aluminum or vinyl sidinginstalled 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 youcan 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 basem*nt 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 foaminsulation products. Love that Pink Panther... even if he has becomecrassly commercial!
GreenFiber, one of the leading producers of celluloseinsulation, makes their case for cellulose's superiority. One interestingtwist is that they use some recycled paper and wood products in theirmanufacturing process, making their "fiber" even more green. You be thejudge, 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 andmarine floatation. Amazingly enough, their foams are used to insulate thefuel tanks of the Space Shuttle!
