[Bull]

I am using rigid polystyrene foam insulation by Owens Corning for a project. This is the stuff you buy in 4x8 sheets, in whatever thickness suits your needs. I read on their website that the foam has a good deal of moisture resistance. Will I still need to use an 8mil plastic vapor barrier on the heated side of the wall, as I would if using unfaced fiberglass batts? I'm hoping not, but want to make sure.

Thanks in advance.

[OhMyGoat]

I used fiberglass batts between the studs and ran half inch Tough-R over the studs. It is foil faced. All seams and capped nails were sealed with foil tape. Then I drywalled over the Tough-R. The windows needed a little extra trimming but no moisture barrier was needed. If you are just using polystyrene between the studs, you will need a vapor barrier since the studs will allow moisture movement.

[RASK]

I was pondering the same question, since I'm finishing part of my basement this winter; whether to use a vapor barrier and or even insulation. I'm no expert, so I did some research and asked people, same as you. If you have a moisture problem, you have to fix it, period, before finishing the walls, floors, etc. which may entail serious work, excavating, whatever. To test for moisture, tape a piece of aluminum foil or plastic to the walls and floor for a couple of days and see if you get condensation on either side. Condensation on the back side means it's coming through wall, inside means you have high humidity inside.

If you don't have a moisture problem, the more people I talked to said not to use a vapor barrier on the wall or even the floor since you may end up creating one. Also, if you use styrofoam insulation or other, that you leave at least a 1/2" air gap between the insulation and walls.

Personally, I'm not going to use insulation but I am using the green moisture resistant drywall. I figured during the summer I want the basement cool. For the winter, since I have heat ducts, the basement is already insulated by the ground and since it is already comfortable down there, what for?

[Pearlbluebird]

No need for poly as a vapour barrier if you use rigid polystyrene. Water vapour will not pass through it. I would seal it with caulking to the 2x4's though.

[Pearlbluebird]

Originally Posted by RASK

I was pondering the same question, since I'm finishing part of my basement this winter; whether to use a vapor barrier and or even insulation. I'm no expert, so I did some research and asked people, same as you. If you have a moisture problem, you have to fix it, period, before finishing the walls, floors, etc. which may entail serious work, excavating, whatever. To test for moisture, tape a piece of aluminum foil or plastic to the walls and floor for a couple of days and see if you get condensation on either side. Condensation on the back side means it's coming through wall, inside means you have high humidity inside.

If you don't have a moisture problem, the more people I talked to said not to use a vapor barrier on the wall or even the floor since you may end up creating one. Also, if you use styrofoam insulation or other, that you leave at least a 1/2" air gap between the insulation and walls.

Personally, I'm not going to use insulation but I am using the green moisture resistant drywall. I figured during the summer I want the basement cool. For the winter, since I have heat ducts, the basement is already insulated by the ground and since it is already comfortable down there, what for?

Rask, if you have moisture coming through the walls it is recommended to fix it first. If you use regular fiberglass or roxul insulation ALWAYS use a vapour barrier. Air sealing is important since warm air can hold more moisture. If that warm moist air cools thats where the condendation happens. I think you would be suprised at how much of a difference insulation would make in your basement. Don't rule it out yet.
Here's a question for you guys.
What would give the best benifit for keeping the house warmer ?
The same house already has 4" R12 in the attic. Basement is not insulated.
a) Bump the attic insulation to R50
b) Seal header cavity and insulate foundation walls to R12.
Both will have benefits but one is the better choice.

[Bull]

Thanks for the replies, guys.

I'm not even using this stuff in my basement...I'm using it in regular 2x4 stud walls in a first floor room. I got the idea from some other people on here a while ago. It is much more expensive than fiberglass, but in my experience mice ALWAYS tear apart fiberglass and make nasty doo-doo crusted nests in the stuff. They remove so much of the insulation that it loses its value anyway. I hope to counter that with this polystyrene, and I can get an R-17 value whereas with fiberglass I think I'd be limited to R-13 or so. I'll fill any gaps with expanding spray foam, but you can wedge it pretty tight against the studs all on its own.

[stags]

Bull - no VB needed - that's a closed-cell insulation so water vapor will not pass through it, but be sure to seal the gaps. You could use caulk for this as long as it will bond to the foam. It might be easier than can foam to work with and will flex some as the lumber shrinks. Good luck.

["Me"]

Originally Posted by Pearlbluebird

Here's a question for you guys.
What would give the best benifit for keeping the house warmer ?
The same house already has 4" R12 in the attic. Basement is not insulated.
a) Bump the attic insulation to R50
b) Seal header cavity and insulate foundation walls to R12.
Both will have benefits but one is the better choice.

In a typical "tract" house neither one is all that important when compared to infiltration. Infiltration is the biggest heat loss in the USA.

I wish they would do a pressurized check of the houses built here as I have read about in Canada. Would get rid of a bunch of hack builders. In the study I read the average house in Canada has a hole the equivalent size of a basketball. The average American house has a hole the size of an 8x8 garage door!

Don't believe all the bs about R Factor, you can have all the insulation you want, makes no difference if the air is traveling around it. I have only 6" of old fiberglass in my attic and my heat bills are never over $70 in the coldest month. Think thermos.....

Bull, you need to keep mold in mind. Do sme research and make sure you are not making a mold colony. Its much easier to grow than it is to get rid of.

[Pearlbluebird]

Originally Posted by Me

In a typical "tract" house neither one is all that important when compared to infiltration. Infiltration is the biggest heat loss in the USA.

I wish they would do a pressurized check of the houses built here as I have read about in Canada. Would get rid of a bunch of hack builders. In the study I read the average house in Canada has a hole the equivalent size of a basketball. The average American house has a hole the size of an 8x8 garage door!

Don't believe all the bs about R Factor, you can have all the insulation you want, makes no difference if the air is traveling around it. I have only 6" of old fiberglass in my attic and my heat bills are never over $70 in the coldest month. Think thermos.....

Bull, you need to keep mold in mind. Do sme research and make sure you are not making a mold colony. Its much easier to grow than it is to get rid of.

Your absolutely right about the air leakage. That's were I tell my clients to start. I then walk them through showing all the typical areas. Air will move right through all insulation but foam. Without air sealing first in most cases all the insulation is doing is filtering the air movement just like the furnace filter.
I had a high end Builder here challenge me saying how great his houses are. After getting all information needed to model his house. I noticed he had about 30 pot lights installed along with pocket doors. I wish I had a camera when I saw his face after showing how much air leakage was coming from just those areas. Thats without going through the rest of the house. People don't realize that the interior of the house leaks just as much as exterior, unless it is air sealed properly. This is cheap and easy to do. If some is building it is a first cruicial step.

[stags]

I've been doing insulation contracting for 30 yrs. and I won't even price out any old house work unless the owners have addressed air infiltration first. As Pearlbluebird said, fiberglass insulation can't stop air infiltration, however it works just fine if the leakage is addressed first. Foam insulation is great in new construction but it's about 3X the cost of F-glass and often can't be used in retrofit work. Years ago, we would get call after call about pipes freezing during cold spells. Many of these were in new homes. Since air infiltration work has become routine we get very few, if any, calls. No other significant changes to account for this.

["Me"]

When I build a home my Hilti foam gun is on the job from the sill plate up. Any air leaks are taken care of as I progress. No detail is too small to worry about. Wall to roof junctions are of particular importance as are bottom wall plate to deck connections.

I recently put an addition on a Carl Strauss/F.L Wright guest house built in the 60's. It has 24'rafters with cathedrail ceilings all the way to the top. On the old parts of the house and guest house the icicles are down to the deck already. On the two sections that I built there is not even a hint of an icicle. I only had 1/4" more space to work with but thinking a little bit and attention to detail has solved the problem.

Larry

[Bull]

Isn't it possible to build a house that is TOO airtight?

[johnsma22]

Originally Posted by Bull

Isn't it possible to build a house that is TOO airtight?

IMO, you can't build a house that is too air tight. Having said that, you need take steps to insure that you get fresh air into the house and exhaust the stale air. This is accomplished with a heat recovery ventilator (HRV). A residential heat recovery ventilator uses separate blowers to bring in fresh air and exhaust stale air. The heat-exchange core transfers heat to the fresh air without mixing the airstreams.

[Pearlbluebird]

Yes you can have a house to air tight. As long as you have .15 natural air changes per hour mininmum you can get by without the HRV. Anything less than this can start to cause problems with natural vented appliances like furnaces, hot water heaters, fireplaces, etc and of course the occupants. I still recommend to tighten up as much as possible in older construction since alot of work air sealing must be accomplished to even come close to .15 ACH. The HRV is such a great idea to introduce fresh air into the house without losing heat like opening a window. During the winter months we become house hermits and indoor air quality does affect our health.
I would like to be in control of my own ventilation not house in control of me, leaking everywhere in places that most people don't know about.

["Me"]

Most houses I build get air/air exchangers. They are not that expensive.

If you are building a tight house you need to keep these things in mind, all gas appliances should have an outside air intake.

Larry

[jaba]

After reading this I finally had to go and put insulation over my old single pane basement windows. I swear by the time I was done with all 5 it felt much warmer. I am doing a whole house window/siding replacment this summer.

[goquick]

I remember when my parents built their home in the early 70's that Mom and me put insulation in every nook and cranny we could find. Worked well because that house still has very low electric bills in winter and summer. We even was up in the attic and insulated the roof overhangs of the porch. (i remember because I was the only one small enough to get into those points! ). Their home is all electric, and remember at the time people telling Dad that we didn't need to do all that, blah blah. After we were living there, the same ones could believe the electric bills were less than half other peoples houses.

[dreamingmuscle]

Originally Posted by stags

Bull - no VB needed - that's a closed-cell insulation so water vapor will not pass through it, but be sure to seal the gaps. You could use caulk for this as long as it will bond to the foam. It might be easier than can foam to work with and will flex some as the lumber shrinks. Good luck.

I agree with Stags here, except if your going to take all that time to seal all the gaps with caulk or spray foam. Wouldn't it be easier and allmost as cheap just to cover it with plastic sheeting and be done with it?

Glen

[stags]

I really dislike poly sheeting over insulation in 99% of the applications I've seen. Also, caulking/foaming the gaps really isn't that hard and won't take much longer (if at all) than a PROPERLY installed poly VB which includes taping joints, seams and around all penetrations like outlet/switch boxes, etc. If used, the poly should be in direct contact with the insulation material - no air space between the two.

[rusty67]

Couple answers to a couple questions here.
1 yes it is possible to build a home or structure to air tight. Problems in doing so are vast but the major one is with no airflow moisture builds leading to mold and mildew.
2 No a vapor barrier is not needed on foamboard. Putting a vapor barrior over foamboard creates a place for moisture to be trapped and again causing mold and mildew.
3 Fiberglass batts are measured by density not thickness ,which traps air and stops or slows temperature transfer. Sealing all penetrations with expandable foam is recommended at all times. It helps control airflow and moisture.

Ive been in the insulation business for 20+ years and am a project manager for an insulation company. Location determains nescasary (sp?) R-values and vapor barrior requirements. Here in Nebraska residential is required no less than R-13 in walls and a Vapor Barrier of 4mil or greater and commercial is 6mil or greater. Remember mice and rats eat anything including foam.