Insulation

[sluciani]

I am nearly ready to insulate my new 24'X24' extension. Any opinions or insights regarding insulation types , amounts and vapor barriers would be appreciated.
The outside walls are 2x4, the attic will be fully accessable from drop down stairs, the floor is 2X8 joists above uninsulated 8' basement. The house has already been sided so insulated sheathing is out.
The existing 1000sq.ft. house has R11 walls , R19 ceiling and R13 floor (above crawl). Adding additional to walls or ceiling is not practical at this time, but the floor will be redone when the extension is done (it's falling out).
I am thinking of using unfaced fiberglass in interior walls for sound proofing.

[Wgoodrich]

Key point of vapor barrier is not to create a trap concerning moisture inside the walls etc. If you have no sealing of vapor on the outside under the outside siding then I would install friction batt style fiberglass with no paper on the insulation designed to fit exactly between the studs from bottom plate to top plate of the wall within the stud spaces, then install a solid sheet of bisquine plastic alond all outside walls creating your vapor barrier just before you drywall your walls.

If you want sound barrier again the friction batt fiberglass without paper backing would be your best choice between the studs in your inside walls with no bisquine installed on these inside wall but just the friction batt style stud insulation.

The basement floor should have been prepared with a vapor barrier below the concrete normally being tar paper layed out covering the ground or bisquine layed out covering the ground then pea gravel or pit run for leveling then the concrete poured to form the floor. Then the basement walls should have what is called blue board insulation installed allong the entire outside concrete walls with no further vapor barrier anywhere in the basement. Then above the blue board between the floor joists paper back fiber glass insulation should be installed against the band board at the end of the floor joists sealing that area. This insulating design keeps moisture from from entering the home from rising out of the earth and insulates and seals the walls from vapor and cold convection and seals out drafts and cold convection through your band board at the ends of the floor joists. Crawl space areas should be done in the same manner minus the concrete floor in a crawl space using the pea gravel to cover the bisquine and hold it in place as a vapor barrier between the earth and that crawl space.

Many times insulation is installed in the floor joists above a basement or crawl space. 99% of the time that insulation will fall and hang down like sway back horses all over the basement and / or crawl spaces. This fiberglass insulation will draw moisture from the earth and over time become heavy and fall out making quite a mess. The above insulating design of crawl spaces and basements in the prior paragraph is the best advice that I have for you.

YOu attic must breath. If you install bisquine on the bottom of your ceiling joists before you drywall as a vapor barrier again you would be trapping moisture in the room but allowing the moisture to rise into the attic area from between the ceiling joists allowing that area to breath. Then you should have installed soffitt vents to allow air to flow into the low part of your attic then you should have installed roof or gable vents to allow the air to flow from the soffitt vents up and out through the roof or gable vents allowing the attic to remain dry and to discharge any moisture present in that attic. Then you should insall what is called a bridge at the end of each ceiling joist to contain the flow of blown in insulation to avoid blocking of the air flow between the roof deck and the top plate flowing from the soffit area vents into the attic then out through the roof vents. Then you should blow in either celulose fiber of fiberglass insulation to fill the areas between the ceiling joists to a point about 4" above the top of the ceiling joists.

You may further seal your home by using a table knife and small pieces of fiber insulation to be stuffed around outside windows and doors to seal off leakage in that area.

You may buy what is a rubber flat gasket to be placed behind the receptacle and switch plates to stop air leakage from entering through the drywall from outside as the walls breathe yet maintain the required cubic inch area inside the receptacle and switch boxes to promote cooling of hte wires within those boxes. The rubber switch and receptacle boxes would be sandwiched between the drywall and the receptacle and switch plates behind the switch and receptacle plates to remain unseen.

The above designs will allow your home to breathe to avoid rot and mildew from building up in the home and create a seal to contain heat and cool inside to home at a comfort range.

Hope this helps

Wg