Insulating a basement

[fishhuntwork]

I'm going to start my winter project, finishing my basment. Its a 50's rambler with a block foundation. What is the best type of insulation to use on the outside walls? I wish I could afford spray foam but that isn't in the budget. Am I better using a bat insulation or a sheet type like thermomax? There is no framing complete and I've never had any water in the basement. I'm kinda worried about that scary 4 letter word, mold!

[Pinusbanksiana]

Here is what I am doing. Insulate the rim joist and the end joists with foam board followed with spraying great stuff to to plug air leaks along the boards. Glue foam board insulation to the concrete walls. Tape and seal these up with proper tape for a vapor barrier. Build a 2x4 wall along this area, leaving about an inch of air space between the wall and the foam board. Insulate the 2x4 wall with batting, no vapor barrier needed. Finish with what ever you choose.

Follow the vapor barrier information very carefully because mold and moisture is stopped by proper vapor barrier. you tube has info.

[NoWiser]

I think the best way is to us thermax insulation. First make sure you seal the joint between the block and slab. Then apply the thermax insulation making sure to use acoustical sealant to seal the thermax to both the sill plate and floor slab. Use foil tape on all seams and penetrations. I also use the foil tape on both the bottom and top edgest of the thermax to seal them up. When all that is done build your stud wall leaving a bit of a gap between it and the thermax. I would't insulate this stud wall. Just take care of your plumbing and wiring and it's ready to drywall. Don't put a vapor barrier on the stud wall.

[Pinusbanksiana]

There is a relatively new insulation out there now, called Roxul made from material that will not mold. Check it out on the Y tube or the goog. I am tempted to try it out and probably will have a look at it eventually somewhere.

[BoxMN]

I think the best way is to us thermax insulation. First make sure you seal the joint between the block and slab. Then apply the thermax insulation making sure to use acoustical sealant to seal the thermax to both the sill plate and floor slab. Use foil tape on all seams and penetrations. I also use the foil tape on both the bottom and top edgest of the thermax to seal them up. When all that is done build your stud wall leaving a bit of a gap between it and the thermax. I would't insulate this stud wall. Just take care of your plumbing and wiring and it's ready to drywall. Don't put a vapor barrier on the stud wall.

This is what our builder did on our new construction. Told me the same when I go to finish it. Used spray foam on the rim joist, and fiberglass with poly on framed walls (walkout).

[SkunkedAgain]

Here is what I am doing. Insulate the rim joist and the end joists with foam board followed with spraying great stuff to to plug air leaks along the boards. Glue foam board insulation to the concrete walls. Tape and seal these up with proper tape for a vapor barrier. Build a 2x4 wall along this area, leaving about an inch of air space between the wall and the foam board. Insulate the 2x4 wall with batting, no vapor barrier needed. Finish with what ever you choose.

This is almost exactly what I did. I had lots of air leaking in where the concrete wall and joists met. I used pink foam board for everything (about 1" thick) with PL300 in the cracks, taped and sealed, built my 2x4 frame off of that. I didn't insulate with batting and still realized a huge thermal gain. I then rocked the inside of the frame and it's great.

BTW - I have the same type of 50's rambler with no history of water in the basement. While I was doing all of that, I did add several electric baseboard heaters under the windows. That's nice too

[delcecchi]

You don't have to get too carried away with the part below grade, since it doesn't get very cold once you get down a couple feet, so the heat loss isn't bad. The most important part is the top few feet, especially the air loss at the rim joist.

[amateurfishing]

i did vapor barrier foam board along cinder block with PL 400, taped, framed wall, & rocked. also insulated between ceiling joists & bedroom walls (kids) for soundproofing. used batt for ceiling & denim for bedroom walls. basement is amazingly quieter and warmer already just with the rock & taping/mudding done.

im not a pro but do no recommend 2 difft kinds of insulation together. i wanted to go overkill as well with insulation cause figured to it best and right the first time. but if u add insulation on top of insulation along foundation wall then u r actually changing the vapor barrier "transition" line from outside the foundation to the inside meaning u want to keep the vapor barrier transition outside your basement so water does not come in. the more insulation u put inside your basement the higher the chance you change your vapor barrer (condensation point) to inside the house cause the inside will be adversely warmer than the outside creating a condensation effect inside the house. you only want just enuff insulation for energy efficiency without overkill to create condensation behind the wall.

[Pinusbanksiana]

i did vapor barrier foam board along cinder block with PL 400, taped, framed wall, & rocked. also insulated between ceiling joists & bedroom walls (kids) for soundproofing. used batt for ceiling & denim for bedroom walls. basement is amazingly quieter and warmer already just with the rock & taping/mudding done.

im not a pro but do no recommend 2 difft kinds of insulation together. i wanted to go overkill as well with insulation cause figured to it best and right the first time. but if u add insulation on top of insulation along foundation wall then u r actually changing the vapor barrier "transition" line from outside the foundation to the inside meaning u want to keep the vapor barrier transition outside your basement so water does not come in. the more insulation u put inside your basement the higher the chance you change your vapor barrer (condensation point) to inside the house cause the inside will be adversely warmer than the outside creating a condensation effect inside the house. you only want just enuff insulation for energy efficiency without overkill to create condensation behind the wall.

So are you saying that you put the xps on the exterior or interior? I assume the interior but you are not clear.

I did an experiment before starting my project. I loosely placed some xps along my basement wall, on the coldest part of the basement where the blocks were not back filled. Right next to it I placed xps but taped and sealed it as good as I could. I left it there fore a couple of cold days, zero or less at night. Then I pulled them away. The loose xps actually had frost on the concrete but the sealed sheet was dry. This tells me that in order for the system to work, the xps needs to be sealed, taped, and otherwise made impermeable to warm moist winter air. Overkill is important. I do plan on placing xps on the exterior and backfilling this area next spring which it should have been done long ago, but the experiment opened my eyes on condensation and vapor barrier importance.

[amateurfishing]

foam board on interior outside cinderblock

builder already insulated outside below grade when house built.

in 8 years i never have had condensation/frost on inside of house. i see u r in 50's rambler so probably dont have foundation insulated outside below grade and would make a big difference. u dont want to overkill and do both...if u insulate foundation exterior of house u will only want single layer of insulation inside.....if u have no outside insulation then may wanna beef it up in the basement. if u have actually seen frost you also wanna make sure there is a way for air flow behind wall frame to evaporate moisture or have tile for drainage or something. if moisture is present back there you will need a place for it to go.

[fishhuntwork]

So I'm going to insulate my rim joist first and I was thinking about using a rigid foam closed cell. Is there any code stating what the r-value has to be? I currently have none on the rim joist and the upstairs floor is cold when you get closer to the wall. I was thought I heard it has to be an r-value of 19 is that correct? I was just going to install 1 piece of 4" rigid foam which would give me an r-value of 20. The use great stuff to hold in place around the edges.

[amateurfishing]

i have no knowledge of code related r value. what i can say is for pre-inspection (inspector comes b4 anything is started and tells u easiest way to get things done to pass) was told any additional insulation along cinderblock in basement was not recommended (because foundation already insulated below grade outside walkout)but i went ahead and added 1/2 inch or inch (sorry dont remember) and just had to make sure everything taped up properly for moisture barrier. inspector said overkill but that it was also done nicely.

actually there is a minimum R code but i think it is so low that home owners usually like to go the overkill route. i know everyone finishing the basement in my neighborhood had same scenario.....insulated below grade but everyone added rigid pink inside also

[fishhuntwork]

To update you all I decided to go with spray foam. Its .90 cents a sq ft per inch, so it really isn't that much more expensive then thermax. Plus I'm getting an r 14, instead of a 9.8 with thermax.

[amateurfishing]

that will take care of a lot in 1 shot,....nice

[Pinusbanksiana]

My basement has never been warmer, can't believe I didn't do this years ago. I would just toss more wood in the furnace. Now if I could stop the cold from radiating off the concrete floor....

[nofishfisherman]

I just got done inuslating my basement this weekend. I went with 2 inches of XPS. Glued to the wall and then all seems taped. Biggest difference maker was adding XPS between the floor joists up along the rim joist and then using Great Stuff to seal it in air tight.

My basement is so much warmer now its really unbelievable. I was originally planning to add a wall and a door near the bottom of the stairs so that I could hold the heat down there but now I'm not sure its necessary.

Once I put a thick pad and carpet down there its going to be very comfortable.

[Ballyhoo]

When I did mine, we built a stud wall inside the basement wall leaving an air space, I have a poured basement. Insulated with batting. The biggest improvement on warmth came when I insulated the ouside of the foundation, about 2' of the basement wall is above grade. Used the rock covered foam and glued it to the outside. That made a big difference.

On the floor in the living part used the dri board with the plastic feet under it so there is an air space between the cement and the subfloor. Put carpet on top of that and now have a warm floor without having to worry about any moisture that may come up as there is an air space under the floor. It is expensive so I only did it in the main room.

[drewbop]

so i'm not looking to actually finish my basement, but I am trying to make it warmer. during that last week the basement didn't get very warm with the cold temps. we basically use our basement for working out, laundry, and storage. ceilings aren't high enough to finish it off, but would like to make it warmer.

all this insulation talk has got me to thinking maybe i should just glue some 1"-2" foam board to the concrete block walls, tape the joints and seal off the joists. has anyone done this before?

i also have a small problem with water leaking in at times (another reason no to finish off the basement completely)

[SkunkedAgain]

Where are your water leaks coming from specifically?

[drewbop]

it comes from the the transition of my floor to the block. i believe i know the source of my problem and will be fixing it this spring. i currently have all the gutters off of my house and therefore when it rains all the water is going to one area and coming through. i will be landscaping around the house and adding gutters to hopefully prevent this problem...

i've also thought about just using a waterproofing paint to seal up some of the cracks and think that may help some...

[nofishfisherman]

I would handle the source of the problem first. Once you have the water moving away from the foundation then I'd look at a Drylock type waterproofing. If you really want to start on the insulation now you can start by insulating up by the rim joist. Thats where you'll lose most of your warm air.

If you are able to prevent the water from coming through I see no issue with putting up 2" xps foam insulation. That is what I used and the basement is probably 5-10 degrees warmer. I am now working on framing in new exterior walls and I'll be putting up drywall but I don't see why you couldn't just stop at the insulation if thats all you want.

[Tom7227]

but I don't see why you couldn't just stop at the insulation if thats all you want.

I think the fire code requires that the foam be covered with sheet rock.

[RoosterR]

Thermax or any foil faced can be left exposed.

[nofishfisherman]

I think the fire code requires that the foam be covered with sheet rock.

Good call. I totally spaced out that rather important fact. Foil faced would be the way to go if left exposed.

[drewbop]

I forgot about a fire barrier as well. I'll have to go with the foil faced. I'll probably start the rim joists this year and tackle the rest this summer.