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August 31, 2007

Question: Can I insulate the floor over a vented crawl space?

James writes from Tuscaloosa, Alabama: "If I live in the South and have a vented crawl space. Should I insulate my floor or will that stop the house from cooling off at night?"

Answer: You can insulate the floor. Make sure you check with your local building code regarding the vapor retarder. High humidity regions can differ on the use and placement of a vapor retarder.

Click here for general instructions on the Owens Corning Web site for insulating crawl spaces under floors.

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August 30, 2007

Question: Can I put a vapor retarder over sheathing before I install the sub flooring?

Warren writes from Winnipeg, Manitoba: "My cabin is 18" above grade on piers, no skirting. The joist cavity is uninsulated and there is no vapor barrier under the floor sheathing. If I were to insulate the floor cavity, could I put vapor barrier over the sheathing before I install the sub flooring? Putting vapor barrier around the joist cavities from below sounds like a chore."

Answer: Yes. You want the vapor retarder closest to the floor towards the warm side of the living space, not facing down below towards the ground.

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August 29, 2007

Question: What insulation do you have to meet my code?

David writes from San Jose, California: "I have a vaulted ceiling with 9" x 2" rafters (6x2 + 4x2 added on). I need to follow code - which is R30. What can I do? What type of insulation do you have to meet my code?"

Answer: I recommend Owens Corning R-30C insulation. It is a high density fiber glass insulation that measures 8-1/4".

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August 28, 2007

Question: How should I insulate the walls of a brownstone house?

Edward writes from Brooklyn, New York: "Any product to insulate exterior wall of a brownstone house? What is the recommended installation procedure? Recommended contractor in the area?"

Answer: The proper product and installation method depends on the existing assembly. I recommend contacting a certified energy professional for help. They can be found in the Yellow Pages of your phone book.

There is one certified energy professional in your area:
 Seal Rite Insulation of NY Inc
 718-241-6611
 One American Way
 Brooklyn, NY 11201

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August 27, 2007

Question: Can I use FOAMULAR® insulation under a slab?

Brett writes from Topeka, Kansas: "Can you use Foamular® under a slab of a two story home? Are there problems with the weight of the wet newly poured slab compressing the foam board? What thickness would you recommend for such an application since there are no housing authority requirements?"

Answer: Yes, you can use FOAMULAR® insulation under a slab. Any questions about weight or load bearing will need to be answered by an architect or engineer. FOAMULAR insulation is made in five different compressive strengths - 15psi, 25psi, 40psi, 60psi and 100psi - and can be used in under-slab applications.

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August 24, 2007

Question: Do I need to put a vapor barrier between unfaced insulation and a subfloor?

Brian writes from Lafayette Hill, Pennsylvania: "I am insulating the floor above an unheated crawl space with a concrete floor, so I do not have any ground moisture. I bought R-25 fiberglass roll insulation. Do I need to put a vapor barrier between the unfaced insulation and subfloor? If so, what is the best way? 6 ml plastic stapled to the joists?"

Answer: Click here to see information on the Owens Corning Web site about insulating crawl spaces under floors.

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August 23, 2007

Question: Should exterior insulation panels be installed before or after new windows are installed?

Ronald writes from Sharon Springs, New York: "I'm building a garage studded with 2x4's, covered with 7/16 OSB and wrapped with TYVEK. I'm planning on installing 3 1/2" insulation inside and am considering rigid foam insulation outside and finished with 1" board & batten siding.

Should the exterior insulation panels be installed before or after the new windows are installed? I'm concerned that the windows may appear too recessed if installed before the insulation panels but don't know if the panels will compress too much when the windows are mounted. Would furring the windows out to the thickness of the foam panels be a better alternative?"

Answer: The windows should be installed after the foam insulation. Most likely, the windows will have to be furred out.

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August 22, 2007

Question: We are curious as to how to insulate a floor?

Tom writes from Minneapolis, Minnesota: "I have a screened porch on a cabin in Northern Wisconsin that we will be converting into 2 bedrooms. Right now, the porch is raised about 1.5 feet off the ground, with 2x8 joists, no current insulation.

We are curious as to how to insulate the floor, without spending too much time crawling underneath to porch. Concerns: Rodents, warmth, sound, moisture, costs.

Ideas: Since there is a cheap thin floor on the joints, we were thinking that we could just rip up the floor, and put insulation in from the top. We would do this by nailing furring strips on the joists, and then lay plywood (Which we have plenty of scraps of) on the furring strips, then lay down the insulation on top of that. We were thinking we may need to prime and paint the 'suspension' plywood for moisture and rot. Is this necessary?

Do you think this system will work? What type of insulation should we use? It will be seasonal use. Perhaps heated a few weekends in winter. But since there will be two bedrooms, we are looking on cutting down the noise too. Please, give me your thoughts!"

Answer: I asked one of my friends at Owens Corning to review your note and he did not see any problems with the assembly you have proposed. You should use Kraft-faced insulation with the paper facing up. The only additional thing you may want to consider is installing some small screened vents in the band joist so there is ventilation.

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August 21, 2007

Question: Can we install fanfold insulation between studs?

A.D. writes from West Pawlet, Vermont: "We purchased the PINK OC fanfold 3/8" thick insulation and saw warnings about proper installation. We have a barn/shop with just studs and boards. We wondered if we can just install that in between the studs against the boards to make the building warmer in the winter and cooler in the summer or does something have to go against the boards before the insulation is attached? What if we want to put sheetrock over it eventually?"

Answer: The proper way to insulate your barn is similar to the process for a new pole barn. Use unfaced fiber glass insulation between the studs. Cover the entire assembly by stapling 4 or 6 mil polyethylene to the studs. The poly will act as a vapor retarder and help decrease air infiltration.

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August 20, 2007

Question: Can you have too much attic ventilation?

Jay writes from Mesa, Arizona: "Can you have too much attic ventilation? I am thinking about adding additional side vents off my gable ends. Do I need to limit the vents?"

Answer: Click here to check the Owens Corning Web site and determine whether you have adequate ventilation or need more.

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August 17, 2007

Question: Would roofing felt give me any vapor protection?

Jim writes from Nashville, Tennessee: "I am renovating a 100 year old house. The original siding is lap board that was covered with asphalt shingles. The shingles were attached to the house with nails that are no more than 3 to 4 inches apart. I am removing the shingles and nails and will patch and paint the lap board.

There is no sheathing or insulation of any kind under the lap board. I am removing the interior walls and will put insulation between the studs prior to installing the drywall interior walls. I am considering placing roof felt between the studs against the interior side of the lap board before installing the wall insulation. My reason for doing this is to provide a last line of defense against water penetration through the lap board wall. (With thousands of nail holes I will probably miss filling a few.) I hope this would keep the insulation sufficiently dry.

What do you think and if this sounds like a reasonable solution what felt weight would you recommend?

I know that roof felt is not a vapor barrier, but would it give me some protection? Given the age of the lap board I do not want to risk damaging it by removing it to put sheathing under it. I intend to leave the lap board siding."

Answer: If you take the siding off you will need to re-sheath the walls for structural strength. I don't think the felt will keep water out; it will probably only allow water to run down to the bottom of the cavity and saturate the bottom wall plate. While sidings will shed water, most are not intended to keep water out entirely and that is why a weather-resistant barrier has to be installed prior to the exterior finish. I don't see how that can be successfully done from the interior of the wall cavity and therefore my recommendation is to remove the siding and sheath the wall, install either taped foam board or housewrap and then reside.

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August 16, 2007

Question: What is the correct R-value to use in the ceiling?

Sean writes from Bella Vista, Arkansas: "What is the correct R-value insulation to use in the ceiling above a bonus room? As best I can tell, ours is R-19 and it's compressed."

Answer: Your local building code official can best tell you what R-Value is required in the ceiling joist. If it is greater than R-19 you will have to fur out the ceiling joist to achieve the proper R-Value. There is a Compression Chart on the Owens Corning Web site that indicates the R-values that result when insulation is compressed in a cavity.

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August 15, 2007

Question: Can I cover the insulation with plastic?

John writes from Flushing, New York: "My cathedral style attic roof has R-30 insulation with paper style vapor barrier stapled to the studs. It has roof vents installed under the insulation. Some of the insulation is missing the vapor barrier. Can I cover all of the insulation with plastic to be sure it all has a vapor barrier? Is any other vapor barrier recommended?"

Answer: The entire assembly can be covered as long as the plastic material is in direct contact with the Kraft paper. As an extra precaution, my technical friends recommend cutting the Kraft paper with a razor blade before installing the plastic.

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August 14, 2007

Question: Do I have to insulate the outside wall?

Kim writes from Lebanon, New Hampshire: "Help! I have a Cape style house built in 1950. I would like to insulate the attic spaces behind the kneewall, roof etc. Unfortunately, the upstairs heating pipe runs thru the bedrooms and then behind the kneewall. Do I have to insulate the outside wall treating this unused space as heated space or can I insulate the pipes with rubber tubing and then insulate the kneewalls and floor? I can send a picture if needed."

Answer: You just need to insulate the knee wall. Unfaced fiberglass insulation can come in contact with hot water pipes. You just need to work around them.

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August 13, 2007

Question: Can I add rigid foam insulation?

Steve writes from Saint Paul, Minnesota: "The sloping roof in our upstairs bedrooms consists of asphalt shingles, 3/4" board sheathing, 2 x 4 studs with Balsam Wool insulation between them, and untaped gypsum board at the ceiling. The face of the Balsam Wool where I can see it looks to be in good condition and I can't easily remove it because of a knee wall, so I plan to remove the gypsum board, leave the Balsam Wool in place and then add 2 inches of rigid insulation (Foamular 150) and new gypsum board to the room side of the studs. My concern is that the high R value of the foam insulation compared to the Balsam Wool insulation will put the existing vapor barrier of the Balsam Wool on the outside of most of the insulation value instead of on the inside. Do you think I will have any problems with this proposal? What about putting the rigid insulation and new gypsum board over the existing gypsum board instead of removing it?"

Answer: My friends at Owens Corning are not familiar with balsam wool, having never made the product, but they suggest you consider slitting the vapor retarder on the existing insulation before installing the FOAMULAR® insulation.

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August 10, 2007

Question: Do I need 2x12 rafters for R-38 insulation?

Max writes from Fairport, New York: "I am building a cabin in Dansville, NY and have been told I need R-38 in my cathedral ceiling to meet code. The building inspector told me this would require using 2x12 rafters. Is this true? Seems to me that's a lot of lumber to use."

Answer: Yes, you need to use 2 x 12 rafters. Or, you can use the lumber that would meet structural requirements and then furr them out to get the 2 x 12 space you need to accommodate R-38 insulation.

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August 09, 2007

Question: Will insulation "shed" fibres until it is covered up?

Darryll writes from Lacombe, Alberta, Canada: "We are insulating the ceiling of our unfinished basement for sound purposes and are using batts of fibreglass for this. My question is, if this is fixed in place but not yet covered by ceiling tiles will the insulation "shed" fibres until it is covered up? We want to wait a while after installing the batts and I do not want any cleaning or irritation problems."

Answer: With foot traffic impacting on the floor above, I would expect some dust to fall from the insulation, joists, pipe, ducts, etc. Normal cleaning should remove that dust. I would not expect enough fibers - size or quantity - to cause skin irritation.

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August 08, 2007

Question: How do I insulate a hybrid wall?

Mike writes from Canton, Georgia: "Got a newer ranch house on a full unfinished basement. The house is rectangle in shape. I want to finish the basement. One short wall is all poured concrete (below grade). The opposite short wall is all 2x4 (above grade). The long walls are a combination of concrete and 2x4 studs. Mostly below grade i.e. concrete. Now it gets tricky. The poured wall is about 10" thick which causes the 2x4 wall to expose a ledge because the 2x4 wall is flush to the outside. Thus I plan on building a complete 2x4 wall so that I can have a truly flat wall for the finished basement.

Doing that will give me about a 13" cavity above the poured wall and a 2x4 cavity along the poured wall.
1) How do I insulate this hybrid on the 2 long walls?
2) Do I build out the short 2x4 wall to something thicker to balance the insulating of the entire space?
3) Does the existing paperbacked insulation that is in the main floor (basement ceiling) needed to be removed?
4) Does that floor (ceiling) insulation paperback need to be removed or cut open?

I already scanned through the previous 12 months of questions. Didn't locate obvious answers."

Answer: 1) The two long walls should be insulated just like any exterior wall. We recommend Kraft paper facing rather than any plastic since the vapor retarder will be in a high moisture content area.

2) Building out is your discretion. Building out will let you increase the R-Value of the wall but keep in mind it will also reduce the living space in the room.

3) No. You will still benefit from the acoustic value between the floors.

4) No. Keep in mind that if you are finishing the basement you will need proper air handling or a dehumidifier to prevent moisture problems.

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August 07, 2007

Question: Should I install a vapor retarder over the fiberglass?

Brad writes from Interlochen, Michigan: "I'm building a new log home in Northern Michigan. The home has 2x12 rafters. The insulation contractor installed R-38 batt fiberglass with baffles from eve to ridge without a vapor barrier which is not code in this area. My questions - should I have them install a vapor barrier over the fiberglass before the finished ceiling material (tongue & groove pine) is installed? If so, will potential issues could I have with condensation with or without a vapor barrier?"

Answer: In the Northern Michigan area where you are building, a vapor retarder is normally used facing the warm air side of the assembly. There may be a special consideration here we don't know about. Perhaps your local building inspector may be able to help resolve your concern.

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August 06, 2007

Question: Can I insulate around an older type of insulation?

Steve writes from Saint Paul, Minnesota: "I would like to upgrade the insulation in an upstairs room that has knee walls and slant walls with Balsam wool insulation between the 2 x 4 studs. The facing of the Balsam wool appears to be in good condition, so I plan to carefully remove the existing gypsum board, but leave the balsam wool in place and then install 2 inch rigid insulation (Foamular® add generic 150) on the inside of the studs. I would then cover this with new gypsum board. Do you foresee any problems with this? My concern is that the Balsam wool has a lower R value than the rigid insulation, which would put its vapor barrier on the wrong side of the majority of the insulation."

Answer: Fiber glass insulation would be the best option in the situation you describe. It would be labor intensive to cut each piece of FOAMULAR® insulation and place it snugly between the studs. Also, the back side of knee walls would most likely have to be covered with a 15 minute thermal barrier because of building code requirements. Heat could also be a factor with the application being up in an attic or rafter assembly. I recommend PINK FIBERGLAS™ insulation.

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August 03, 2007

Question: Can cleaning ducts stir up air quality problems?

Gail writes from Pittsburgh, Pennsylvania: "We just had our heating ducts cleaned and were told that two of the returns (one in my bedroom) had insulation in them which they did not feel was supposed to be there. Apparently they vacuumed/cleaned/pulled out the insulation with their vacuum equipment (that lead outside the house). Is there any risk to our family/children in terms of air quality? I woke up with a headache the last two days (although no one else did). Would the process of 'cleaning' stirred up anything? What is insulation? Is it fiberglass?"

Answer: Your duct cleaner was referring to the insulation I am known for advertising - PINK FIBERGLAS™ insulation. Yes, it is fiber glass insulation. Since I cannot see the insulation he removed I am not sure it is ours, but if it is PINK in color it is Owens Corning and it is fiberglass. I am not sure why you would have insulation inside a metal duct, assuming it is a metal duct. In some cases metal ducts are lined with fiberglass duct liner which is typically black in color. Our products can be used in open return-air plenums like you find above many dropped ceilings in commercial buildings.

Owens Corning has conducted extensive fiber sampling research during both installation and use. The level of glass fibers found was 0.04 f/cc of air during installation and 0.0002 f/cc of air after the installation was complete.

Sampling in buildings over many years shows consistently that the materials found in dust are predominantly (a) cellulosic - fibers from newspapers, paper bags, paper boxes; (b) synthetic - fibers from carpets, clothing and furniture; and (c) biological - skin cells, hair follicles, insect parts.

Based on over 60 years of research, Owens Corning believes that its glass fibers are safe to manufacture and use. If you are installing new product, the company recommends that you follow the industry safe work practices to avoid irritation. We would be happy to provide information from Owens Corning, the North American Insulation Manufacturers Association and the American Lung Association with simple information about working safely and avoiding irritation.

In Summary:
- Glass fibers are safe to manufacture, install and use, and
- Installers should follow the industry safe work practices to avoid irritation

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August 02, 2007

Question: How should I insulate an older house?

Mike writes from Middlebury, Connecticut: "I have a Greek Revival farmhouse built in 1850. I have removed to floor and ceiling joist in the attic of part of the house and am converting the ceiling to a cathedral ceiling. The roof rafters are trus 2" X 4". We are going to put in a few more rafters for added strength. Is there a system where I can hang R-38 or higher insulation and also attach the ceiling drywall or do I have to put in all new 2" X 10" rafters?"

Also, I have removed all of the plaster and lath so the walls are exposed. The plan is to put in R-15 between the true 2" X 4" studs and cover it with 5/8" drywall using vapor barrier paint. We plan on leaving the old 7/8" sheathing and covering it with 1/2" plywood, 1/2" rigid insulation, housewrap and 1/2" clear vertical grain redwood siding.

After 160 years the old sheathing and studs are in good condition because there was no insulation and moisture could escape. I am concerned that I might trap moisture. Do you think this design is OK?

Answer: For the cathedral ceiling you will need to build the rafters out to 2 x 10. I am not aware of any system like the one you are looking for.

I do not see any problems with the assembly but remember that I am an actor and not an architect or designer. My friends at Owens Corning are insulation manufacturers and not the people to judge assemblies.

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August 01, 2007

Question: Is it worthwhile to add insulation in only part of the attic?

James writes from Arlington, Virginia: "I recently purchased a 1941 brick colonial. It has an unfinished attic with plank flooring covering the middle 60 percent or so (to allow it to be used for storage). The exposed portion reveals only about 4"-5" of old white insulation (unfaced) between the joists.

I'd like to do something in the short-term to improve the insulation. Is it a problem to install insulation (between the joists as high as possible, and then additional insulation perpendicular to the joists) only on the unfloored portion? This will mean the middle section of the attic has only the original insulation level, while the edges have a much higher R-value."

Answer: Your plan will be better than doing nothing but by your own estimate, you will not be increasing the insulation R-value in 60 percent of the attic. Most of a home's heat loss goes out through the attic so it is important to have that part of the home well insulated. There is more information about insulating an attic on the Owens Corning Web site at Adding Insulation to an Attic and Frequently Asked Questions.

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