+ Reply to Thread
Results 1 to 6 of 6
  1. #1
    Join Date
    Feb 2011
    Posts
    2

    Default Whats the best insulation???

    Hello all,
    I am new to the forum here so please bare with me. I have a major dilemma and would love some input. I live in Michigan and just added a 25x40 addition with a full basement and a 15x25 bonus room on top. I am trying to make this addition as energy efficient as possible. The walls are 2x6 and the trusses are 2x6 as well. So here is the question. What type of insulation should I use? I have been trying to research this and it seems that it really depends on who you ask as to whether one is really better than the other. I will tell you that cellulose is definitely out. I am really considering spray foam and would like to hear what others have to say about it, I have had 2 contractors out but it seems like they wanted to push the foam because they made more money selling it. Some other questions I have on the issue of foam is in the trusses and walls. I was told that the best, is to do what they call a hot roof (I was told) and spray the foam directly on the sheathing under the shingles that way there is no need for roof vents and the shingles would actually last longer. The other is in the walls since I have 2x6 studs should I fill the cavity or just 3.5 inches? Also should I use closed or open cell? Or should I just go the way of bat insulation? Any advice will be greatly appreciated. Thanks in advance

  2. #2
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: Whats the best insulation???

    for the basement addition insulated concrete forms are your best bet, from there do standard 2x6 walls with R-24 batts in the wall cavity and 1" rigid foam on the outside which will give you a r-30 rating and the foam will create a thermal break on the outside of the house

    for proof the difference a icf can provide, this time last year i was one of the carpenters on a 4000 sq ft vet clinic built from icf. 6 months after the clinic was open the owner compared the heating bill to the old location which was only 900 sq ft and wood framed. the heating bill for the new space 4x the size was 1/3 the cost
    fire up the saw and make some dust

  3. #3
    Join Date
    Feb 2011
    Posts
    2

    Default Re: Whats the best insulation???

    Thanks jkirk,
    But the addition is built and dried in. The furnace and duct work is done. The only things I need to do is complete rough plumbing, rough eletrical, insulation, and drywall. I installed the best windows pella had to offer. The contractor talked me out of alot of things I wanted to do. Such as ICF and foam sheathing on outside walls. He said that since I was finishing the basement all I need to do was batt the framed walls and for the outside walls, all he did was plywood, tyvek, and vinyl side them. He said that was all I needed but he wanted me to use cellulose.

  4. #4
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: Whats the best insulation???

    hmm, interesting, foaming the outside walls makes the walls perform far better for insulation value. its been done up here for years on the r-2000 homes and now its slowly becoming the norm on all renovations and 1/2 of new construction
    fire up the saw and make some dust

  5. #5
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Whats the best insulation???

    Quote Originally Posted by Disciple View Post
    Hello all,
    I am new to the forum here so please bare with me. I have a major dilemma and would love some input. I live in Michigan and just added a 25x40 addition with a full basement and a 15x25 bonus room on top. I am trying to make this addition as energy efficient as possible. The walls are 2x6 and the trusses are 2x6 as well. So here is the question. What type of insulation should I use? I have been trying to research this and it seems that it really depends on who you ask as to whether one is really better than the other. I will tell you that cellulose is definitely out. I am really considering spray foam and would like to hear what others have to say about it, I have had 2 contractors out but it seems like they wanted to push the foam because they made more money selling it.

    Foam insulation ranks in the premium class for insulation including price -- far better than batt insulation though. Generally speaking with spray foam insulation-- the 2 lb. closed cell will offer a higher R value per inch --- 1/2 lb open cell will be about the same R value as batt insulation. What both types do best is they will be a continous layer filling the majority of nooks and crannys as well around any imperfections or obsticles -- compared with batt insulation which can't do as well of a job with those issues. They both offer superior air sealing over batt insulation which is advantageous .

    In attics spray foam ( 2 lb closed cell in particular ) about an 1-1/2 inch thick sprayed on the attic side of the ceiling drywall ( and the tops of the wall framing ) covered with about 12 inches of cellulose will give you a well insulated and sealed insulated area. By the way , cellulose in the attic gives you the biggest bang for the buck.
    The closed cell foam will seal all penetrations, provide the vapour barrier, add an R value --- the cellulose will provide the rest of the R value for a reasonable cost.


    Regardless which type of insulation material is placed in the stud cavities still doesn't give you a uniform R value for the wall structure. The weak link , with an *interupted* method of placing insulation in the stud bays , are the studs themselves. Wood has an approximate R value of 1 per inch of thickness. Even though you have 2x6 studs you may think you will have about R19 insulated walls. Actually you will end up somwhere around R14 ( or less ) based on the entire assembly. The studs only offer 5- 1/2 x R1 per inch = ~ R5.5 ----- which will subtract from the insulation between the studs. Since the studs are directly coupled to the exterior and interior wall surfaces and only offer ~ R5.5 they can transfer heat far easier than the insulation within the stud bays ---- known as *thermal bridging*.

    As jkirk mentioned this is a main reason rigid foam is used on the exterior walls along with ICF -- eliminates thermal bridging and increasing the overall insulation performance of the wall assembly.



    Some other questions I have on the issue of foam is in the trusses and walls.

    I was told that the best, is to do what they call a hot roof (I was told) and spray the foam directly on the sheathing under the shingles that way there is no need for roof vents and the shingles would actually last longer.


    The method is only effective if all exterior surfaces within the attic are insulated --- the underside of the roof and the gable end walls ( if they exist ). It's a realitively newer concept and it does have merit buy creating a semi-conditioned space instead of opening the attic to the outside temperatures. It's simply based on the fact --- the greater the temperature difference ( Delta T ) between the living and attic spaces ( T1 and T2 ) --- the greater the heat gain/loss.
    It's also no different to the considerations placed on insulating walls.


    There is considerable debate as to how much effect insulating under the shingles has on their life span. Independant research has shown little to no effect on shingles --- worst case was a 10% shortened life span with a * hot roof * compared to a *vented* roof.
    I've never seen or heard anything saying a *hot* roof will last longer --- personally can't see how it could extend the life.
    However , shingle manufacturers state for warranty on their product a vented roof is still required -- although they can be used on SIP roof assemblies which would be considered *hot roofs* by definition.


    The main reason for * vented * attics in cold weather zones is to supposedly remove moisture ( condensation ) from water vapour migrating into the attic from the living space. This came about decades ago when building science was in it's infancy. Back in the day there was little regard for closely looking at the building dynamics after or during construction. The most common problem is air leakage between the attic and the living space -- always has been and continues to be. Any perforations from plumbing stacks or electrical or gaps in the structure allow warm moist air ( in the winter ) to migrate into the ice cold attic and condense --- as well as loss of heat from this. Many homes have little regard for air sealing any of these perforations --- instead the focus is mainly on adding insulation which is only half the equation.
    The questionable thoughts behind venting during the cold season is the colder the air the less moisture it can hold. The other issue if warm moist air enters a cold enough attic there will be condensation -- period --- venting or not. However, once the temperature raises enough to change that moisture back into a vapour is when it can be removed *if* there is enough venting for air exchange.

    The other questionable issue, if you have common fiberglass insulation in the attic it's performance is greatly reduced ( up to 40% )within moving air. So , if your attic is vented then your insulated attic performance will be reduced.

    For warmer seasons , the venting is used to relieve the extreme temperature buildup within the attic space which really doesn't occur till night time or when the sun isn't shinning -- in other words , the temperature will be at the same temperature as out doors.



    The other is in the walls since I have 2x6 studs should I fill the cavity or just 3.5 inches? Also should I use closed or open cell? Or should I just go the way of bat insulation? Any advice will be greatly appreciated. Thanks in advance
    Both have advantanges over batt insulation. Closed cell ( 2 lb. ) has generally more R value per inch compared to 1/2 lb open cell. The closed cell usually meets the requirement for a vapour barrier. Open cell may or may not meet the vapour barrier requirement --- depends on the local code. Generally open cell is a little cheaper than it's closed cell cousin.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  6. #6
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Whats the best insulation???

    Quote Originally Posted by Disciple View Post
    Thanks jkirk,
    But the addition is built and dried in. The furnace and duct work is done. The only things I need to do is complete rough plumbing, rough eletrical, insulation, and drywall. I installed the best windows pella had to offer. The contractor talked me out of alot of things I wanted to do. Such as ICF and foam sheathing on outside walls. He said that since I was finishing the basement all I need to do was batt the framed walls and for the outside walls, all he did was plywood, tyvek, and vinyl side them. He said that was all I needed but he wanted me to use cellulose.
    Hmm -- perhaps your contractor isn't up to or willing to try new methods.

    Personally, I wouldn't do the traditional frame and and batt insulation for the basement. Think about covering the basement foundation walls with rigid foam then build the wall framing in front -- far better method giving you the thermal break from the foundation.
    Or --- if it's in the budget --- frame the walls about an inch or two from the foundation -- have spray in foam applied in behind the studs as well as the stud bays -- this would be the premium way.
    "" an ounce of perception -- a pound of obscure "
    - Rush

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •