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Insulating basements properly

bighouse1's picture
Hello, I'm currently in the design stage of building out my basement. My house is 12 year old colonial. The basement foot print is ~1300 sq ft. To date, there has never been water in the basement; even in the worst of storms. To check the walls and floors for moisture, I've taken 4ml thick plastic and duct taped it to the wall and floor. No moisture / condensation has ever accumulated on the plastic sheet. All good, so Im ready to now insulate the interior basement walls, and now i find myself lost in hos to insulate properly. Let me preface, that I've researched this topic. Ive gone to the building inspector, National Insulation societies and watched numerous videos on the proper way to insulate. What I have found from my research, the building industry lacks any consensus on the right approach. This is extremely frustrating and quite frankly unbelievable. First question: the builder wrapped the interior wall with a blanket insulation wrap with an aluminum/foil face. Can I leave this insulation om the walls and frame in front of this insulation? If yes, can I then insulate the framing? My thoughts are I'm doubling my insulation and certainly increasing my R-Value. Second question: if I tear down the foil face, stud the walls and insulate, do I use paper faced insulation. I was told by the building inspector that after I install the paper-faced insulation, cut holes into the paper to allow for airflow??? This would eliminate moisture buildup? Third question: the use of a vapor barrier over the insulation. After watching numerous television shows. I've noticed they install insulation on the studded walls and then they Apply a 4-8ml of plastic over the insulation and then they tape and seal the plastic. This is done in basements and most shows are filmed in Canada. Are they using this vapor technique because of the cold environment? Or is this a proper technique. My confusion with this stems from the building inspector telling me to cutt the paper to allow the insulation to breath and this technique is totally opposite. The plastic is sealing everything air tight but with walls that have no known condensation this seems like a viable below grade technique. Last 2" pink foam board. This seems logical, but I cannot find any answers on how best to use it. Do I use it by itself without insulating BW the studs? Or do you glue this to the foundation, frame, then insulate with R13 paper-faced insulation? Please if anyone can shed light on my questions. I'm want to do it right the first time and never have to worry about using the wrong resouces and building techniques. Thanks in advance!

Insulating basement properly (post #205916, reply #1 of 4)

The best way to insulate a basement is use 2" rigid foam glued to the wall with the proper adhesive.  Glue spots every 12 inches and leave a quarter inch gap all the way around the perimeter of each board and fill it with spray foam to seal the boards together. Then tuck tape all seams. You want no air movement.  This way you've created a thermal break on the inside which means you don't need vapour barrier. After that you can then stud the walls.

I'm going to float some ideas (post #205916, reply #2 of 4)

I'm going to float some ideas here, thoughts that are quite different from the'conventional wisdom.'

Look at electrical boxes. They don't attempt to keep ALL water out. Instead, they try to reduce the amount that enters - then make sure there's a place for the water to drain out.  I think this is the approach you should take in a basement.

Where does basement water come from? From the air, through the walls, and under the door. Don't say 'there's never been water.' Plan like there is. You must attack each source of water.

Water in the air can be exhausted through proper ventilation. This works both for humid outside air that might try to condense on the cooler walls, and for any moisture that might seep through the walls. Indeed, proper ventilation is the most important element of your 'anti-mold' plan.

Water that comes through the walls ought NOT be stopped. Basement walls are simply not designed to stand up to water pressure. While I have no objection to parging and shielding the outside face of basement walls, please note that these systems rely very heavily on the perimiter drain to divert water around the house. Successfully diverting water means all you have is minor amounts seeping through the concrete.

Let it seep through. Leave a space between the nasement wall and your insulation / finished walls for the moisture to drain.

Both this drip water, and any water that comes in under the door, will need to get pumped out. Basement floors are not nearly as flat as they should be. Step #1 in any basement remodel is to level the floor, then make sure it drains to the sump. Even a small, forever damp spot will become an odor factory.

Again, that's why I am in favor of leaving the floor and outer walls porous. Let water travel both ways. Let them 'breathe.'

I favor spacing the finished walls off the foundation wall by using "hat" channels. These will give you a 3/4" space. I also favor stopping the walls several inches above the floor (filling/ masking the space under them with plastic trim boards). I favor either throw rugs laid directly on the concrete floor, or a platform floor made by laying down foamboard and covering that with T&G plywood subflooring. (Make sure to leave a gap at the outside walls for drainage). It's critical that this platform be laid over a dead-flat floor that drains to the sump. Do not use the platform as a way to deal with floor irregularities; those little dips will trap water and become fungus farms.

Likewise, I would avoid any sort of fiber insulation or ordinary gypsum drywall, at least for the lower two feet. I've seen water quickly 'wick' up drywall 6" and fiberglass insulation 12". I reccomend foan, faced with cement board.

Always do it under (post #205916, reply #3 of 4)

Always do it under professional, otherwise it can be disaster.




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(No subject) (post #205916, reply #4 of 4)

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

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