Everything You Need to Know About Insulation’s R-Value

Spray foam insulation
R-value expresses how well insulation does its job.

How well insulation works is expressed by its R-value, which measures resistance to the flow of heat. The higher the R-value, the better it insulates per inch of thickness.

How Much Is Enough?

The amount of insulation recommended for your home is dependent on where you live, but here are some general guidelines:

  • Attic Insulation: Houses in a cold climate should have a minimum of R-49 in the attic, which is equivalent to approximately 16″ of fiberglass insulation. Warmer climates only require an R-38 or higher, or about 12″ or more.
  • Wall Insulation: While wall insulation is limited by the width of the studs, different materials provide higher or lower R-values. Fiberglass batts for standard 2×4 walls are now available in low, medium, and high-density products that range from R-11 to R-15. Sprayed foam insulation in the same wall cavity can range from an R-14 to an R-28 depending on the product that is used.
  • Floor Insulation: While there are additional considerations—such as venting and moisture problems—to take into account when you insulate under floors, the United States Department of Energy recommends an R-25 rating in cold climates and an R-11 in warmer parts of the country.

Fiberglass insulation.

Comparative Insulation R-Values

The R-value per inch for different types of insulation varies depending on the brand and how it was installed, but here are some general comparisons from the Department of Energy:

Insulation Type: R-Value per Inch:
Fiberglass (loose) 2.2 – 2.9
Fiberglass (batts) 2.9 – 3.8
Cellulose (loose) 3.1 – 3.8
Stone Wool (loose) 2.2 – 3.3
Stone Wool (batts) 3.3 – 4.2
Cotton (batts) 3.0 – 3.7
Cementitious (foam) 2.0 – 3.9
Polyicynene (foam) 3.6 – 4.3
Phenolic (foam) 4.4 – 8.2
Polyisocyanurate (foam) 5.6 – 8.0
Polyurethane (foam) 5.6 – 8.0

Installing Insulation

You can hire a pro to install insulation, or you can install insulation yourself in rolls and batts. If the attic doesn’t have any insulation, use faced insulation, with the vapor barrier facing toward the living space, and cut the batts to fit in the space between the ceiling joists. If the attic already has a layer of insulation up to the top of the joists, use unfaced insulation, with the new batts installed perpendicular to the joists.

Blown fiberglass or cellulose insulation is usually installed by an insulation contractor, but DIY blown cellulose insulation is also available. Loose fill cellulose insulation for blowing can be purchased at home centers and blowers are available to rent.

When installing insulation, wear:

  • Gloves
  • Goggles
  • Long sleeve clothing
  • Mask or respirator

Also, don’t work in the attic during the heat of the summer, and be careful not to step through the ceiling! Spaying expandable foam insulation is a job that should be left to professionals.

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  1. I prefer the ‘Johns Manville’ insulation over the ‘Pink’ insulation ,as the Johns Manville does not have as many loose itchy particles.
    But still wear the appropriate attire.

  2. Insulation R-value is only valid in still air. If you have a breeze going through your attic from soffit or roof vents it will degrade the R-value of exposed fiberglass insulation. The best results are gained by decking over the insulation, using a sheet product over exposed fiberglass insulation, or sealing up the attic completely and using a foam product under the roof deck to make the attic an enclosed space.

  3. A valid point, but I would be concerned that a sheet product, like plastic, on top of attic insulation could cause condensation to form under it in the winter.

  4. There are some sheet products I have heard about that are perforated to prevent becoming a vapor barrier. I don’t recall any brand names, but they were advertised for just this use.

  5. I am Finishing my basement and have come across moisture in the insulation that is wrapped around the basement walls and is wondering if that is common, also what I should do about it?

  6. If you have visible moisture in a fully enclosed under ground basement.
    1 .Is it a new house?
    2. Is the moisture beads of water? or dark wet spots?
    3. Do the walls have white efflorecencent
    ( salts in the water that form on the surface) lines on the walls: which would be from outside in?
    If # 3 is yes than the water is coming from the ground and the water proofing is compromised on the exterior of the concrete wall, in which you need to stop the water.
    If # 2 is yes then the moisture is condensation from the inside,which can be altered by a dehumidifier.
    Over all the source needs to be determined so you know what to fix.
    John Cannamela

  7. i have 1500sq ft of attic space. thier is very little insulation in thier now. i was told blown in cellulose is better than roll in insulation. is that true? which is better and cheaper and easier to put in myself.i know how to blow insulation but im confused whick one or the other would be energy efficient as well as savings for my home. i also have a full crawl space under my house. do i use roll in insulation or what? and how much would it take and cost in material?

  8. I’m trying to add insulation to my home. It was built in ’81 and is raised about 36″ off the ground. I want to insulate the floors, but am just figuring all this out. What would be the best thing to use under the house? Is 3/4″ expanded polystyrene (R-2.9) good to use? Do I just nail/staple it to the bottom of the house? Any suggestions are welcome since I really have no idea what I’m doing…

  9. Lani H and others
    Te insulation that is there now may or may not me adequate, so add to it-use reflective backed foam board if in doubt- alter the seams then tape them with foil tape.you can’t loose.
    Don- blown in is great however you will have more control over the batting and if you ever store stuff in the area ,it won’t ge moved out of the way so easy.Which helps to
    know how much has been compromise in case a tradesmen has to work in the area at a later date.Bating is more likly to get put back than that fluffy stuff.
    sometimes you need to think of what would happen if you are not there because noone will worry as much as you about your house.

    I hope I helped an not confused anybody
    Thanks again Danny for a great site
    John Cannamela
    Charlotte, NC

  10. I need to insulate a 12×24 steel framed workshop. It’s a sweatbox in summer and an icebox in winter! I live in central Georgia. Any thoughts on how to best accomplish this and choice of insulation is greatly appreciated.

  11. I forgot to mention that the building is clad in aluminum siding. Also, moisture control is important as my area is very humid most of the year

  12. I live in Raleigh North Carolina and would like to insulate my attic. My house is approximately 1600 sq feet and was built in 1963. The attic has had no upgrade of insulation since. It now has roughly 3 to 4 inches of blown cellouse insulation. I am leaning towards insulation of pink fiberglass with a R-38 rating. The thickness would be 12″ and a width of 16″. Is this enough insulation? I’m not sure of the square footage of the attic yet but I’m assuming it will take between 25 and 30 rolls. Thank you. Ellis Farris

  13. I inherited my grandfathers farmhouse built in 1900. Although I grew up playing there and visiting since then, it is now my responsibility to take care of it. We have spent the last year working on the obvious and last year we only had a fireplace for heat. After purchasing a propane tank I thought my heat problems were over, Wrong! After examining under the house with about a 16 inch crawlspace, I have discovered that there is no insulation or sub floor. Only hardwood floors over the 2X6 joists. I have been researching insulation and after seeing your show on the weather channel I still have questions. Would an R-19 with facing be sufficient? Also, since this is literally off the ground (no basement) should I enclose the insulation? It appears that I should put in batting face side to floor and am considering using a basic plywood across the joist. There are also insulated sheats that say they are indoor/outdoor with “R” ratings and they state that they even hold up to immersion in water, but I am unsure of these for an exterior surface. Since I have 6 inch joist, should my insulation be 6.5″ (R-19) and would the plywood or the insulated sheaths be best? How much improvement in comfort and utility bill should I expect? There is nothing blocking the wind from coming underneath the house. Thanks

    • Hi Jenn,
      If possible I would start by closing in the foundation around your home, then add insulation between the joists with 6″ insulation (which should be plenty), holding it in place with specially made support wires. Check out the article and video from our Scariest Utility Bill episode to see how to go about insulating under a floor.

  14. Hi Ben,

    I can’t close in the foundation because there is a creek about 200 or so feet away; water has only entered the house once, during Hurricane Camille and only because of storm surge backed up all rivers and creeks. Just in case the creek were to ever rise that high again, I need water to have the ability to flow versus rising. I am going to check this weekend to verify if I have 2 x 6 or 2 x 8 joists and if they are 16 or 24″ centers so that I can buy the right size of insulation. If I buy faced and staple with facing close to floor, at most I will leave an inch and half from the bottom of the joists. This air flow should assist with moisture evaporation, so I think the 6.5 inch, R-19 will be ok. I am looking at osb board to put on the bottom of the joists, what do you think?

    Also, I will ck this weekend to see how much, if any, insulation is in the attic. Since warm air rises, I think my first attack should be in the attic and then the floor. I used a calculator and it said to insulate to R-49 for this area. The farm is in Wayne County Mississippi about 5 miles from Millry Al. Currently, there is no attic access, but it has a metal roof. I am thinking of blowing insulation in by removing sections of roofing. Any advice would be appreciated.

    • Jenn,
      Since most heat and cool loss is through the attic, you’re right to tackle it first. If possible, it’s important to provide adequate ventilation in the attic to remove hot air and prevent condensation (see our articles on Attic Ventilation and Soffit Vents), which it sounds like would be hard to do in your case. As far as under the house goes, it would be okay to attach OSB to the bottom of your joists. You might want to screw them on with drywall screws and a cordless drill so you could easily take it off in case it floods and the insulation gets soaked. Good luck with your project!

  15. Thanks Ben!
    My son and I got into the attic this past weekend and guess what we found??? NO Insulation whatsoever!!!! Just wood ceilings and rafters with Tin overhead! We have measured and are getting ready to get started. Most of the rafters are logs, the others 2×6. I plan to lay R-30 down first inside the logs (30″ in between so will use 2 x 15″ rolls)and go back another time and add more cross the logs. It appears that R-30 is no longer the standard minimum. Looks like R-38 to R-49 is more the current minimum. Since I have no insulation, I should see a huge difference in comfort and bills just from the R-30! Will tackle underneath later as you suggested. Thanks for your help. Now if you can tell me how to keep the pipes from freezing under the house, I am all ears!

    • Jenn,
      Keeping your pipes from freezing isn’t easy if the crawlspace under your house isn’t enclosed, but here are some tips:
      Use pipe (like PEX) that resist breaking when the water freezes.
      Bury the pipes and run them straight up to the plumbing fixtures to reduce the amount of pipe you need to insulate.
      Wrap heat tape around hot and cold pipes (unplug when above freezing) followed by foam insulation.
      Drip faucets when the weather is below freezing.

  16. I am finishing my basement and live in the foothills of NC. I have sealed the walls with three coats of drylock. My basement has always been fairly dry. I have 2×4 studs for walls. They are not in direct contact with the walls. Now to my question. Do I need to put insulation with paper face or no paper. Some people are telling me that the paper would trap moisture and paperless would allow it to breath. Im lost please help.

    • Hi Allen,
      If your masonry basement walls are dry, I would use faced insulation, with the paper facing in toward the living space to prevent moisture from the warm inside air from condensing on the cool masonry walls.

  17. OK, I guess everybody understands this but me. I do know that R-21 insulation is more effective than R-21, but that’s all I know about the material. How much more insulation do you get for those two points? How do I determine what is worth the addional cost of R-21 for new construction in WA State on the Puget Sound. I don’t want to spend a dollar to get a dime’s worth of more efficiency. Can you explain the rating/grading system to me. Is it roughly a 5% improvement? And does that relate directly to energy/heating cost savings directly? The builder is saying R-21 is better but he has no clue as to how much better it is and I have no clue whether it’s worth the addition cost.

  18. We have a cathedral ceiling in the log home we are building with 2 X 10 rafters. We are not able to get an R-38 insulation at the 10 1/4 thickness in a timely manner. How horrible would it be to use the 12″ thick R-38 material with the rafter vents? Will it lower the R value that much and/or create other problems being compressed? Thanks.

  19. I want to upgrade the underside of an enclosed porch and have a question about the existing insulation. The wood paneling does not currently cover all of the fiberglass insulation and there a few spots where you can reach in through a hole and stick your entire hand in…the fiberglass will have been exposed to humidity and blacksplashing rain. Does it need to be replaced? I see two different arguments online: 1. If fiberglass has been fully dried out then it is ok and you can re-use and 2. it has lost R-Value and needs to be replaced. Any thoughts would be appreciated!

    • Hi Rachel,
      Just my personal opinion, but I would say if it’s dried out, isn’t moldy, and is still fluffy, use it. It’s an inert material, so unless it’s been compressed, I can’t see why it wouldn’t be okay to use. Good luck with your project!

  20. We have a 700 square foot enclosed room that used to be a balcony. The roof is flat and the square that is the roof/ceiling is 8 feet shorter all the way around the room than the floor. There is a 4 ft wall that rises from the floor. From there, the walls angle back toward the roof. We would like to use this room as a greenhouse since it has so much space. The angled walls are about 6 ft in height, but because of the angle, the ceiling height is still only 8 ft. The siding needs to be replaced on the angled walls as it is, so I was thinking about using 4X8,1/2 inch sheets of plexi-glass as siding. I have three questions regarding this design. I understand if not all three questions can be answered through this site.

    1) How much “insulation” will 1/2 in thick plexi-glass provide (if any at all).

    2) Should we use plywood at the top two feet? Or the bottom two feet of the angled wall? I was thinking the bottom because then the water could come down the roof edge onto the plexi-glass which would be 1/2 and then down onto shingle which would be attached to 1/2 in decking.

    3) We are planning to pre-drill holes and screw through those holes to attach the plexi-glass to the studs. How can we seal the holes so that no water penetration occurs? I was thinking of filling the predrilled holes with silicone and then screwing in???

  21. I live in central Alabama and have a cabin with a gambrel roof, which is constructed with 2x6s.
    The roof is metal amd attached to 2×4 lathing, no sub roof. I cut 1/2 inch pick foam strips to fit the 14 1/2 inch space and attached therm to the under side of the lathing and plan on using R19 batts on top of the foam.Is there more efficent way other than using expandable spray foam?

  22. I am a farmer in Missouri that just built a wookshop 40×60. Wooden posts and metal painted tin exterior. I am looking for the most bang for the buck but I want quality that will last under semi-industrial conditions. Welding/metal working with exposure to torchs/cut off saws/ect in the building. I want to box in the walls to protect the insulation. We can get to 0 degrees on the cold nights in the winter. I need it to stay 50-60 degrees in the shop in the winter. I am considering Spray poly from Tiger industries. or doubleing the stringers and using 3.5 foam board. Can I spray it myself? or is the board better. Money to a point is no problem. but I would prefer to do my own labor. I am not afraid to try anything once. but I don’t want to screw it up.

  23. We are having our old pink fiberglass insulation removed (due to raccoon family damage) and replaced. I’ve been getting estimates and didn’t realize all there is to the process and all the different kinds. So, which is the best for my area (NJ shore)? One man started talking about r49 and r42 and spray in versus fiberglass. Can you please just give me a quick overview of what I need to know and should be asking? thank you.

  24. I am remolding a 1950’s house cottage in southern California and have 2 x 6 rafters 16 on center. My bays are now 14 inches on center due to Engineer required sister-ing a 2×6 strengthening structure to the existing frame for a cathedral ceiling. My dilemma is that I do not have enough depth for R19 6 ¼ in each bay. Are you aware of any product on the market that is high density batt that will give me the 1 inch air flow.
    I have found 4×8 rigid foam board at $60 a sheet….any other alternatives?

    Any words of wisdom? Thanks in advance for your insight!

  25. I recently removed some Weyerhauser Balsam-Wool insulation from the unfinished attic in my Pennsylvania home. I am considering installing fiberglass vs blown cellulose insulation myself. Any recommendations?

  26. I live in a mobile hom ewith vaulted/cathedral ceilings…my heating bill in the winters is terribly high. How can I add insulation to the ceiling has no crawlspace or attic access. This mobile SOMEHOW made it through County inspections and has insulation and roofing for a lower elevation area. Therefore the decreased amount of insulation. difficult to tel what is under the mobile due to the bottom covered with plastic under. there is a 30″ H crawlspace under the mobile.

  27. k i know there is a formula and such… i know what r value is needed in each area of the house… what i want to know is what is the trasfuranse rate of heat through r values?… example… *80 outside and i have stud wall 3/4 sheeting and r13 how cool will the inside of the wall be?… give or take for unknown veriables

  28. My 1953 low-sloped-roof home in Pasadena, CA, needs a new roof (to cover the aging asphalt sheet roof which leaks in one area) and which sits over some rigid insulation — we’re guessing .5 or 1″ thick. We want to employ “cool roof” technology to bring down the summer heat effect, which radiates into the house making the interior temperatures high (85-87 degrees)and expensive when we run the central AC. One roofer suggests putting white 45 mil TPO over LOW E 3/16 inch insulation foam. 1) Will this have a noticeable/significant effect on our interior temperatures? 2)How does this scenario compare with the utilization of 1″ spray polyurethane foam system?

  29. Re the above, I neglected to include the fact that most of the house has open-beam ceilings and very little attic space.

  30. I live in South Florida were the weather is warm and high humidity and I’m looking at having insulation put in my attic. A few local contractors have given me the option of R21 blown in Cellulose or R30 blown in fiberglass for the same price. Which one should I choose?

  31. I live in Chicago and a pipe located in an exterior wall freezes every winter (and bursts when we neglect to leave the tap open- twice last winter) even in relatively mild (for Chicago) temperatures like 20 degrees F. In addition to upgrading the plywood from 1/4 to 3/4 inch, I’m debating on whether to use foam panels or spray (fluffy rolls were in there but provided too many spaces for air to enter)? I really want to seal this up right. I was also considering covering the wall in some kind of Tyvek as it is located in breezeway and it gets very windy. Any advice you have is greatly appreciated, thanks!

  32. What happens in a loose blown in R38 attic when radiant barrier is stapled to the 2 x 4 attic floor? The insulation is compressed to 3 1/2″ and has higher density, but lower air volume. Is R value decreased?

    • Katherine,
      The comment section under each post on our website is for comments that visitors would like to post. These can be general comments, feedback about the post, questions about the topic, or answers to questions posted by other visitors. While it’s not possible for the Today’s Homeowner staff to respond personally to the thousands of comments posted on our site, we do read every one and try to respond when we can. In this article alone, there are numerous replies from our staff, as well as responses posted by other visitors to the site.

      If you have a specific question you would like answered, submit it at Ask Questions to have it answered on our Today’s Homeowner Radio Show.

  33. Last comment form staff on this particular thread is December 2010. 10-12 questions submitted since then, cannot find comments from staff or other visitors helping. I understand you are busy…but my question from 1/8/2014 still goes unanswered as do 10 other questions on this thread since December 2010. Also figure you will delete me from this thread etc…just looking for an answer. Thank you again

    Thank you for your time.

  34. Jean, in response to your question, if you need access to the insulated area ( say in an attic you store stuff in, or for repairs) I would go with the cellulose, as you will not have issues with fiberglass getting in your skin. ( it itches like crazy from all the little threads of glass). If you need no access, go with the fiberglass and enjoy the higher R value. I have put helped my dad add fiberglass batts years ago, and I wore heavy jeans, dust mask, gloves, etc, and showered after and still got the itch. Johnson Manville makes a low itch fiberglass that has plastic on the faces, but not sides, I have used it to insulate walls and it is easy to use.

  35. Rich, in response to your question, you do not want to compress insulation, it will lose its R value. Insulation works by creating dead air space which heat travels very slowly thru. Also, a radiant barrier under or over insulation is a waste of money. If you have sufficient insulation, it doesn’t matter if you reflect the radiant heat. The claims for the savings for radiant barriers are often inflated, or under special conditions. Think of it like this, if you put aluminum foil in your window, it will reflect the sun and some radiant heat, but if it is 100 degrees on the other side of the window, and 70 inside, the heat will still get thru. The last time I looked at a radiant barrier it was about $75 for 500 square feet. I lined my attic floor with heavy duty aluminum foil for about half the cost, before I found out about the radiant barrier uselessness. It does no good in the middle of the day, and has had very little if any effect.

  36. I converted a deck to a sunroom. The deck extends out about 3 feet on all sides of the sunroom. There is no vents in the deck or sunroom. Having problems with moisture in crawl space. Floor is not insulated. Water enters the crawl space from cracks in the deck. How do i eliminate the problem?
    Tom Hancock

  37. I live in a double wide mobile home in Central NY, for the past two years I have had little to no heat at one end of our home, we found animals got under the home(no basement) and destroyed part of the under belly. We are preparing to re-insulate, I need to know what R-rating Insulation I should use, Can I use tarps to hold it to the bottom of home? We will have skirting all around the home. Any suggestions on how to proceed is appreciated.

  38. What would you recommend for Mississippi, crawl space of an 1950 house? The contractor brought some rolls for the walls – #16. And some needles – to hold the insulation up.
    What would you say?

    Thank you so much for your time,

  39. I’m in Australia and our R values on insulation start at 2 for walls and R-3.5 for ceilings. I was told R6 is as high as you can get. I’m confused by the massive difference I see talked about on American based websites where people refer to anywhere up to R60. Is there a different scale? Or different climates require different strengths? Surely the higher the R value the better regardless of climate?

  40. Thanks all for your input. On North Fork of Long Island I have 1921 home, attic tongue and groove floor over 2×6 joists. How can I achieve R49 rating with only 6 inches of joist space? Can I insulate rafters and floor to achieve recommended R49 value ( or close as possible)? Thanks.

  41. How do I determine my final r factor when i use different types of insulation material? For example. .. if I have R11 of rock wool and I add a layer of r19 blow in fiberglass ?

  42. There is a steel container of 20’x8’x8’6”(lengthxwidthxheight). inside temp is 20 and outside is 55.so how we can maintain temp 20 inside by 3” insulation to inside. can anybody calculate this and which insulation will be best insulation?

  43. In need of advice ASAP. I’ve bought celluse blow in and going to isulate behind bedrooms in story and a half older house. There is some fiberglass bat between floor joist upstairs, I cant get at it all. There are knees causing more issues for access. The number one concern, do i put platic vapor on top of fiber and blow about 20 inches or more, or blow the celluse on top of fiberglass with no vapor barrier? The next, do i insulate roof board and vapor? If so, I live close to Atlantic Ocean in high wind area in winter. I am going to tackle this week as the temp. is starting to climb. Any help or comments appreciated.
    Alan Spinney

  44. Is there a real difference between 1/2 Vs 3/4 Dow foam board on a house being sided? holding more heat in is always a goal of every home owner. Thanks

  45. what is the thinnest product that you have out there that can achieve a R = 16.8? It will be placed over waterproofed densglass and behind a rainscreen system out of porcelain cladding materials

  46. I have access to insulgard 2″ 4×8 sheets of reclaimed roofing insulation and am going to put this under the concrete floor with the px water tubing to heat the basement. I understand that the R rating on this is R-7 per inch. this gives me an R-4 over the preferred foam that was recommended. Is there any reason this is not a good application for this system?

  47. For those of you insulating a crawl space, try the Roxul brand made out of spun stone slag. It maintains its r value when (if) wet, is impervious to mold and insects, and can be friction fit between the joists and will not sag or come out without having to use strips to hold it in place. It also has a little bit more R value. I used it in the remodel on my 1958 ranch and it is pricy, but the best stuff out there short of spray foam- cuts with a bread knife into any shape needed!

  48. I built a porch on my house. It has a flat roof built with all 2x4s. I would like to insulate with r-19. I want to keep as much moisture out as I can. Any suggestions?

  49. Hi,

    I need R30 Polyurethane Panels. What thickness i should buy ?

    Can you provide the chart showing different R values for PU?

  50. In response to Karly: This response surely comes too late to benefit you, but others may be wondering the same thing. Yes, you are seeing R-values expressed in different scales. The US has not converted to SI units of measure. You are correct in saying “Surely the higher the R value the better regardless of climate?” I would add, “The higher the R value the better, regardless of which scale you use.” Just don’t add so much insulation that it becomes compressed and loses its effectiveness.

  51. A comment regards “Rock Wool” it’s likely that this is asbestos and a problem.
    It may be expensive to remove and this is the best option. The area has to be sealed off and an amateur should not be opening up such an area only professionals with the proper protective gear; Mask, eyes, clothing.

  52. Roger, if you don’t know your facts don’t say anything.
    Rock wool insulation is made from grounded Balsamic rock, it has no asbestos, is itch proof, and is fire resistant to 2000 degrees F, I am an engineer who specifies this on all my projects.

  53. I am doing moisture control in my crawl space (1000sf) –moisture is coming in from ground because crawl space is lower than outside of house–I am putting down plastic on crawl space and insulation under the floor and want to know if it should be turned up against the inside of foundation and around the support pillars and taped to make a complete barrier?? I am also going to use a dehumidifier to dry out what wood is wet–I had this home built and have lived here 50 years, John West

  54. R-Value, while an industry standard and is one the general public readily understands to some degree, unfortunately, is somewhat of a mis-statement. The better measurement is actually U-Factor. What is the difference. R-Value actually stands for “resistive” value. U-Factor is a measure of a component assembly in its conductive and radiate capacities. Let me explain… when the general public hears an R-13 wall insulation, they believe that in fact they have an R-13 insulation value in their exterior walls. The truth is this, studs have an R-value of 3.5. The net effect on the R-value of the wall, with the studs transferring heat/cold thru conductive properties, is the actual rating of that wall system is some where around an R-9. U-factor is a unit of measure used in assembly of building components like windows and door units that have multiple components which have varying conductive and radiant values.
    One of the posts above indicated they needed an R-30 polystyrene. When looking at U-factors, the conductive and radiant values don’t change much with a thickness greater than 2.5″ – 3″. So, while the R-value may increase in rating, the benefit received for your expenditure drops dramatically.
    A window assembly rated at U-factor .21 or less is virtually non-conductive and zero radiant in its properties. 3″ of polystyrene has a U-factor of approx. .10, 4.5″ has a U-factor of .07 eventually dropping to somewhere around .03. The point is this, conductive and radiant properties of an assembly are much more important and relative to the measure of effective insulation properties. R-value is a simplified term used for the general public but is not necessarily descriptive of an efficient building system.

  55. People that say thermal reflective barrier doesn’t work have never been in a properly installed attic area. In Texas we see attic temperatures of what….140 to 180 plus degrees on a 110 degree day. (yes, that is correct, up to 190 degrees!)

    Install thermal reflective barrier, we see the one to three degrees or so over ambient temperatures (the same temperatures found under a shade tree). a 110- degree day will give us a 112 attic temperature.

    Reduce the thermal heat load and you reduce the AC requirement. This is a fact. Even attic ventilation can not end the radiant thermal load from a hot roof, only thermal reflective barrier can. Heat radiating from your roof to your insulation heats the insulation (and your ac system as well), it does NOT matter that there is “some” dead air space in your insulation, there IS PLENTY of mass in mass insulation (as in rock wool or fiberglass). Heat that mass, and it will heat your ceiling. Then you have to pay to cool the air, the ceiling and the mass insulation again. I have felt ceilings in the south in summer and they were well over 110 degrees! AC systems running constantly. Yes, fully insulated attics and insulation and the ceiling was over 110 degrees!

    Many older homes do not have the space available for R30 plus insulation. they can and do have room for thermal reflective barrier.

    Stop the radiant heat from hitting your attic insulation and you stop the house from heating, period. Radiant barrier does this and when installed under the rafters it will retain its reflective properties for many, many, years.

    There are too many people that sell mass insulation that just don’t want the facts to be known. Thermal reflective barriers work, when installed and used properly.

    Ask any of the tens of people I have installed reflective barrier for; they have no hot or cold spots in their homes. They have significantly lower utility bills. Their homes are actually quieter!

  56. It seems there is a lot of confusion over radiant barrier. Firstly it does work very well when installed correctly. That means not laying it over your insulation so it can conduct. Staple it under the trusses below the underside of the roof, start at the bottom and work up overlapping as you go then tape seams with foil tape. You must have air flow, so soffits and ridge vents are necessary. Or go one step further use 2 inch foil faced foam board with an R13 rating. Again attach to underside of trusses and foil tape seams, soffit and ridge vents required, now when your roof tile/ shingle is baking at 160-180F and that conducts to the underside. The radiant heat will be reflected at 85-95% conductive heat will dramatically reduced, and the baking hot air will exit through the ridge vent, while pulling in cooler air from the soffit. So the air in the void is the same as the out door temp, you can go a step further and use spray adhesive, to attach your R30 fiber glass to the foam board. Done correctly, you no longer need insulation on the attic floor, unless it’s a tall attic. 1 ton of ac is 500 sq ft floor space at 8 ft ceilings.

  57. When I asked for help with my bathroom remodel, the guy suggested I didn’t apply insulation. Im really having a tough time figuring this out. I live in North Dakota, I would think insulation would be rather important

  58. Question: I have a church flat roof and I want to put insulation between the joists which are 8 inches deep. I was recommended to use R19 FSK batts to do the job. this is a Church and I was wondering if the R-19 FSK batts would be sufficient Would Rock wool be better to put between the joise than regular Pink insulation

  59. I need to replace all of my insulation due to problems with critters. I was told to replace with cellulose as the R value is highest. But I am worried about moisture problems and mold. I also wonder if any type of insulation is treated with boric acid to deter critters.

  60. SO glad you shared this; I’ve been planning to have my house insulated (can you believe I never did this?!) because I heard that it can provide energy efficiency.
    I’ll keep in mind to have a minimum of R-49 in my attic since my house is located in a place with cold weather…Brrr, brrr and BRRR!!! I’ll also make sure to have an R-25 rating for my floor insulation. Awesome tips. Makes it SO much easier.

    • We’re glad you enjoyed these tips, Rachel.
      Please share them with friends, if you think they’d enjoy them, too. 🙂

  61. I learned something new today – that attics should have an R-value of at least 49!!! My husband and I want to save on energy bills by having new insulation installed in the attic of our older home, hopefully within the next few weeks. Any information I can get before that happens is EXTREMELY appreciated!

    • Glad to hear you enjoyed this content! Please feel free to share it with friends — that’s how we’re able to create similar content.

  62. I have an interior wall between my bedroom and kitchen and sound come through. Would it help to insulate and what is best, blown in or foam?

  63. I like this idea! Sounds brilliant to me! I wonder if this is actually doable or if there’s some unforeseen reason it is not feasible?

    • Totally doable, Nikki-Autumn! Once you understand R-value, you can just head to the home center, purchase insulation and take it from there. 🙂


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