I would like to respectfully disagree with the points made in this
article.
What you have provided is the same old tired methods for insulating attics.
In fact, you are NOT looking for R-value. R-value measures conductive heat
loss. Most heat loss - especially if you insulate the attic floor- is
convective. What you really want to do is carefully air seal the attic- to
stop air movement through the house. As you point out- sort of- this is
really hard to do when insulating the attic floor. You have pipes, wires,
ducts, chases, attic stairs, bath fans, recessed lights, etc, ALL of which
allow heated air from below blow through the attic. This decreases the
effectiveness of the insulation (fiberglass is nearly useless when air
moves across it) and it raises the temperature of the roof, causing ice
dams.
Modern thinking suggests that the far better approach is to insulate the
attic SLOPES, not the floor. It is MUCH easier to air seal the slopes than
the floor. Further, by insulating the slopes, any HVAC equipment in the
attic is now in conditioned space, making it much more efficient.
If you hire a professional to install either densely packed cellulose
behind a mesh stapled to the rafters or- better yet- spray foam insulation
in the slopes you will reap the rewards in a very few years. Most foams
are, in fact, not flammable. Some are, but they can be covered by fire
retardent building paper.
When you use either foam or cellulose in the slopes, you don't need roof
venting.
Don't believe me? Go to ww.buildingscience.com. These people are on the
cutting edge of modern building practices.
With respect, I say that it's time for our industry to stop doing things
the same old way and start educating ourselves and our clients.
Mark Landry
landmark Services
www.landmarkservices.com
Do-It-Yourself Attic Insulation
Summary:
Do-It-Yourself attic insulation is one way to save energy and money. Attic insulation is available in a variety of options - reflective attic insulation, foam attic insulation, radiant barrier insulation, loose fill attic insulation - to name a few. Check first to be sure you don’t have asbestos attic insulation.
| Be sure to read the special Author's Note at the end of this column. It provides updated information on this topic. |
DEAR TIM: I have to tackle an attic insulation installation at my home. Winter snuck up on me and my heating bills need to go down if at all possible. Is installing additional attic insulation hard? How can I tell if I have asbestos attic insulation now? Can you teach me how to install attic insulation like a pro so that I don’t hurt myself or my house? What are some of the things you discovered the hard way all the years you worked in attics? Leah W., Goffstown, NH
DEAR LEAH: If you’re thinking of replacing attic insulation and there is any chance it’s made from asbestos, stop now. Take a small representative sample of what you have now and send it to an independent testing lab in your area. They’re easy to locate, especially if you have access to the Internet. Do a search for “asbestos testing labs” and you should discover many that will allow you to mail them the sample. Asbestos is a sinister product that has killed many who’ve worked with it and others who were exposed in a secondary fashion by being near a worker or his clothes.
This attic storage area can be insulated in just a few hours by a serious do-it-yourselfer. PHOTO CREDIT: Tim Carter
Let’s assume you decide to use fiberglass. The first thing to do is determine if you’ll use blown-in fiberglass or batts. The blown-in fiberglass requires a heavy machine that chops up, fluffs up and blows the insulation particles through a large-diameter flexible hose. You typically have a person near the machine feeding it bales of fiberglass, while you’ll be in the attic broadcasting the fiberglass as it chutes from the end of the hose. Some call this loose-fill attic insulation.
Be sure to read all the instructions on the bales of fiberglass to ensure you take all the needed safety precautions. Wear all the right clothes, a fantastic mask so you don’t get the tiny airborne fiberglass particles in your lungs, and goggles. I urge you to have great lighting up in the attic so you can see what you’re doing. If you use batts, just roll those out according to the instructions on the packaging. It’s caveman simple to install residential attic insulation batts on top of an existing ceiling when you’re in an attic.
There are many things you have to take into consideration so you protect your home. This is but a partial list. You need to be concerned with ventilation. Don’t pack the insulation in where the roof passes over the exterior walls. You need to make sure air from any soffits can pass over the insulation on its way to the peak of the roof. A 2-inch space is usually sufficient for this.
Be very careful in the attic where you step. You don’t want to punch through the ceiling with your foot into a room below. Don’t step on any cables or wires in the attic. If you have an older home with ancient knob-and-tube wiring, you really will have a tough time. This wiring is easy to identify. Each wire has coal-black insulation on it and it’s strung between porcelain insulators that are nailed to the ceiling joists or rafters up in the attic. You are not supposed to cover this wiring with insulation as its original design was to dissipate heat into the air. Insulation in contact with the wires can cause it to overheat and start the black wire insulation on fire.
You also need to be on the lookout for any older recessed lighting fixtures. Many of these can have wires that feed them that can catch on fire if they overheat. Some older recessed lights were never intended to be directly covered with insulation. If in doubt, construct a box using plywood around each fixture allowing a minimum of two inches of air space between the wood and any part of the fixture. This air space will help prevent the fixture from overheating when you cover the plywood box with insulation.
Attic insulation costs, especially if you do it yourself, can be recaptured pretty quickly. The trick is to inspect for any air leak passageways where cold attic air can drop down interior walls. Look for these problem areas around plumbing vent pipes where they penetrate the top plate of a wall. Be sure the holes drilled in top wall plates for electrical wires and cables are caulked. You don’t want cold air seeping into the center of your home.
If you decide to get quotes from an attic insulation contractor, be sure you install depth gauges up in the area that will be insulated so you can pop your head up into the attic to see if enough insulation was installed across the entire area.
You may wonder what the best attic insulation might be. That’s really hard to say, as each one has different properties. In the end you’re looking for R-Value. Try to add enough insulation that you meet the minimum guidelines as set forth by the Department of Energy.
Fiberglass will not support combustion. I’ve received emails and comments at my website from contractors and firemen who’ve had fire problems with cellulose, even though the manufacturers say it’s fireproof. It’s possible the problems were from a bad batch. Foam is usually installed by a pro, and it almost always is flammable. Be sure to ask about that.
Routinely I am blessed to hear from professionals and industry experts who share in-depth and updated information about a topic. You'll absolutely want to read the letter I received from the President of NAIMA (North American Insulation Manufacturers Association). It really helps clarify some of the points I just touched on in the insulation columns.
....
We've received other emails with similar problems or questions. Here's one from Dawn W. of Parma, OH, regarding knob and tube wiring.
"Is it safe to use USA Insulation's Tyrpolymer foam in a 1950's house with knob and tube wiring?"
Dawn, as mentioned above, knob and tube wiring is designed to dissipate heat through the exposed wires. If the wires are covered with insulation, there is a possibility of overheating.
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Comments:Welcome! I, Tim
Carter, don't answer questions
here. If you post a question here in the Comments Area,
perhaps another visitor will help you. You need to go to the Ask
Tim page if you want a question answered. Once there, look
closely at how many weeks behind we are. Please be patient as you use
this free service. If you have an emergency and need to talk to me,
there is an option there for you.
Mark Landry 07 Dec 2009, 16:51
Mark Landry 07 Dec 2009, 16:56
One more thing. There are kits to allow anyone to spray their own foam
insulation. I wouldn't recommend this for an entire house, but we've
actually done attics ourselves with these kits, rather than hire a spray
foam company.
Wear protective clothing (the stuff is sticky and hard to remove), goggles and a dust mask or respirator. These kits are also great for sealing small crawl spaces. Expensive, yes, but you will reap the rewards through comfort and energy savings. We get ours from www.efi.org
Tim Carter 07 Dec 2009, 17:24
Mark,
Thanks for your comment. How about providing the costs to heat and cool that conditioned space you talk about when you switch to insulating the slopes? Doing it the way you suggest creates more cubic feet of space of air that's heated and cooled. That wastes vast amounts of energy the last time I checked.
Mark Landry 07 Dec 2009, 17:55
That's a common argument that I hear. You might think that it would cost
more to heat and cool the attic but the fact is that if the air movement is
stopped up in the attic- by insulating and air sealing the rafter slopes,
the entire house works much more efficiently. The air in the attic becomes
static and maintains a constant temp- it doesn't take much energy to heat
or cool it.
We've been insulating the rafter slopes for about 15 years and have had great results. Last year we had clients with an enormous historic house with no insulation. We insulated just the attic slopes and gable walls. We didn't insulate any walls or touch the windows, etc. Just by insulating the attic their heating bills were cut in half (!) the next winter. They actually recouped the cost of the spray foam insulation the first winter! There is no way that the savings would have been even close if we had rolled some batts on the attic floor. The truth is that fiberglass batts perform so poorly that they are as close to a hoax as exists in our industry (in my opinion). Because batts require ice dams to prevent ice dams, there is so much air movement in your attic that the heat loss is massive. Plus, as I mentioned above, if your HVAC equipment (air handlers, ductwork, etc) are in conditioned space, it works much more efficiently. In the winter, your air handler might be in a 60 degree attic instead of a zero degree attic. Think that will be more efficient. Likewise in the summer. Instead of AC equipment working in a 130 degree attic it might be 80 degrees up there. So, no, even though intuitively you might think that it would cost more to heat and cool that space, in practice it doesn't. Really. Here's someone else who backs me up: http://www.homeinspectorgeneral.com/building-green-michigan/truth-about-ins ulation-and-myth-r-value
Mark Landry 07 Dec 2009, 18:39
In fact, another way to look at it this: if you insulate the floor with
batts but do a less-than-perfect job of air sealing you're already sending
enough heat up into the attic to heat the attic space. But the heat just
isn't staying in the building.
If you air seal and insulate the slopes properly all of the heat stays in the building.
eric kelley 15 Dec 2009, 12:43
Tim; thanks for all the info and now I'm lost! Live outside Denver Co in
a 11 yr old house. No insulation in the wood floor of the basement or
ceiling. Just sealed the crawl space and was going to insulate the ceiling
in there also. Walls in basement and crawl space are insulated to code.
So am I understanding you correctly that there will be little cost value to
insulate these space and concentrate on my attic and air leaks in the
house?
Thanks Eric
Robert Post 15 Dec 2009, 22:56
Mark and Tim,
Tim, I love your columns, site, and spirit. I am also with you at the pit, every time! I am a BPI certified building analyst and I must say that Mark is exactly on point here. Having utilized this approach for years, I (and my clients) are converts to this thinking. The proof is in the pudding, and the pudding is GREAT. Granted, it is not intuitive for most builders and is not the traditional method, however the energy savings are really impressive. Eric- define your thermal boundary and do not introduce insulated planes within it. In addition, align your vapor barrier/retarder and thermal barrier so they are in the same plane, together. Example: do not insulate your crawl-space walls and floor system above. It's one or the other, and most times it's better to insulate the crawl walls so as to keep the water vapor and soil gases from entering the structure. GOOD LUCK!
Mark Landry 16 Dec 2009, 04:47
Robert,
Thanks. I wish more builders would get on board. There's an awful lot of energy being wasted due to incorrect building methods.
Robert Samuel 16 Dec 2009, 16:53
NRCA (National Roofing Contractors Association) states that a minimum of 1
inch between the insulation and roof sheathing must exist. All asphalt
shingle manufacturers specific require the 1 inch to exist for warranties
to be valid. So if you want your shingles covered by warranty, you need to
provide some venting.
The attic space becomes an “unconditioned -- conditioned” space (closed by without its own source of heating). As a result, the heat from below (in the house), will flow up into this space. The increase in “conditioned” space means an increase in volume of air. Consequently, the increase in volume of air will require more energy to heat --- therefore more cost. This is basic physics, which is why Tim Carter made his comment. That fact that the air is “static,” has no impact whatsoever – and is an inaccurate statement. The exception being is if your home was a vacuum. In a vacuum (where static air generally exists), Boyles law (law of thermodynamics) comes into play. The temperature of the volume of air would increase as you increase the pressure in the vacuum or decrease the space (same effect). Kynetic energy (from the air molecules slamming into each other) translates into heat (through friction). So for Mark’s answer to be correct, your home would have to be a vacuum --- which of course would make every living thing in the home die. Mark also mentions that heat is lost in your home through convection. This is misleading, but to be fair, is possible. Under normal conditions, convective heat loss through fiberglass attic floor insulation or any other form of attic floor insulation is negligible. But in extreme cases (i.e. Boston – where Mark lives), convection occurs at low temperatures; and is particularly bad with fiberglass insulation. Basically, the fiberglass insulation’s R value gets cut in half. However, this happens regardless of air infiltrations into the attic. This is the secret reason why fiberglass manufacturers and the DOE suggest R-60 in attics in cold areas. You only need to go this extreme with fiberglass --- not with foam or cellulose. Air Sealing is very important…I would agree with Mark --- for the same reasons cited above, except moisture because a larger component of the argument. If the attic floor is not properly air sealed, you are wasting your time insulating it. Overall, insulating the rafters themselves is the wrong answer. Unless of course you make the attic a “true” conditioned space with its own source of heating and cooling. Insulating only the floor is also the wrong answer. It is very difficult to do it right to get the savings (i.e. no air leaks, good vapor guards, right amount of insulation, etc.). The better approach (assuming money is not an issue) is to insulate both the floor and the rafters with a foam insulation (ideally a closed cell). But the cost is high and the payback is long (at least in retrofits).
Mark Landry 16 Dec 2009, 18:12
First, how many people do you know who have actually collected anything on
a roofing warranty? Have you ever read one of these? They are written in
such a way as to make it extremely unlikely that the manufacturer will ever
pay out. Also, we've been insulating the slopes for over 15 years and have
never seen any problems with the roofing shingles. But even if the lifespan
of the the shingles is reduced by, say, 10%, the energy savings would more
than offset this cost.
Second, I believe you're wrong about your assertion about "basic physics". This talk about about your home being a vacuum doesn't make sense to me. You don't need to create a vacuum or anything close to slow down the movement of air through your house from basement to attic. And, as I mentioned above, if you insulate the attic floor and have a lot of roof venting, you're losing more heat than it takes to keep the attic conditioned. If you stop the air movement and create (more or less) static air in the attic, the additional energy to :condition" it is less than the energy that you lose by insulating the attic floor. I have never heard anyone recommend insulating both the floor and slopes. Please, check out the info at buildingscience.com. They explain things in a much more eloquent way than I can. All I can say is that there are a lot more people who agree with me than you might think. As far as the payback period, I have first hand experience that it can be unbelievably short. As I mentioned above, we actually had clients who had a ONE YEAR payback. It cost them $12,000 to insulate their (very large) attic with spray foam. It was actually three separate attics. The next year their heating bill went from $24,000 to $12,000 (did I mention that this is a huge house). We've had similar results with other clients with more modest houses. View all comments |
