Basement Wall Insulation Options

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Old 04-01-15, 01:54 PM
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Basement Wall Insulation Options

Hello,
I'm hoping for input on the "best" options for temperature and moisture control as I look to finish a basement. I've heard about wood studs, metal studs, or applied furring. I've heard of bat insulation, rigid foam boards, spray foam, using no insulation, or "InSoFast" panels. There seem to be a lot of options out there and people seems to have their favorites, but I'm looking for a good long-term solution.

Here is my situation: 2 year old home with 8" thick poured concrete walls with mastic spray applied waterproofing and WatchDog insulation on the exterior of the foundation. There is exterior and interior drain tile with a sealed sump basket and passive radon venting. The rim joists have (closed cell?) spray foam to R19 and there is spray foam under the slab (which is also run for radiant heat, though it's not hooked up).

Cost is always a factor (the sky is NOT the limit), but within reason I'd rather pay a little more now to have long-term benefits of a comfortable and healthy home. So, what seems to be the best solution in this situation?
Thanks,
Guy
 
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Old 04-01-15, 02:38 PM
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Basically making the best basement is your goal. FUrring strips are out. Why drill holes in an otherwise non leaking wall? Building a free standing wall about 1" from the monolith, captured on the base plate and top plate in your existing framing is best. Minnesota may have more insulation requirements for the raw wall, so I'll let Bud address that. Some place rigid foam boards glued to the wall and taped at all intersections for a thermal break. Roxul insulation between the stud bays is an excellent choice, although a little more expensive than fiberglas. It is moisture proof, fireproof, and mold proof, and requires no vapor barrier, although in your climate you may need to apply a 6 mil barrier between your studs and the final coating (sheetrock). Hang in here for more comments.
 
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Old 04-01-15, 03:18 PM
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Tell us more about WatchDog insulation on the exterior - never heard of that.
 
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Old 04-01-15, 03:26 PM
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1 1/2" rigid foam glued to the wall then frame your stud wall in front of it with *NO* airspace. Insulate and vapour barrier then drywall. Ideally, your vapour barrier will wrap your bottom plate of the stud wall and be sealed to the foam, but not critical if it isnt. If no vapour barrier under your stud wall, be sure to use a sill gasket or some other barrier between the wood and concrete. Presure treated is rated to be in direct contact with concrete but it will still draw moisture and can lead to mold growth. Insulation under your slab will greatly reduce moiture problems, as will using the in floor heating if you ever choose to.
 
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Old 04-01-15, 04:01 PM
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As stickshift and chandler said, we need more information so I'll list some questions.
1. What zone are you in (closest large city), MN has 2 zones, although I believe they both have the same foundation insulation requirements.
2. "WatchDog" seems to be associated with a spray applied waterproofing where you are calling it a "WatchDog insulation" We need to know if there is an R-value associated with this material on the exterior.
3. Is there a protective covering over the above grade portion of the foundation?

Depending upon what is on the outside, I believe you can add that to whatever you use on the inside for your total r-value. The link below looks old, 2010 so refers to the 2009 energy codes. Your area may have moved up to the 2012 codes.
http://www.duluthmn.gov/media/122796...ormat-2010.pdf

Bud
 
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Old 04-01-15, 07:57 PM
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Many thanks for the thoughts so far. I am located near Minneapolis. I copied that information directly from my spec sheet for the home, so I'll have to reach out to my builder for more information. I did, however find a great picture I took during construction of the exterior with the three types of insulation prior to backfill and siding. As you'll see there is the yellow insulation below grade (there was a spray applied black waterproofing under that), the finished (gray in the picture) material above grave, then an insulation with embedded "studs" for siding above that.
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I did asked my builder what their standard is and it sounds like they would frame a wall up an inch out and leave it without any additional insulation. That might meet minimum code, but it seems we can do better!

On specific question is about an additional vapor barrier on the interior...doesn't that risk creating an area of moisture trapped in the insulation?

Thanks again!
Guy
 
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Old 04-01-15, 08:32 PM
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Trapping moisture against the concrete is not a problem as concrete likes moisture. But given the treatment you have on the outside I would avoid adding a plastic vapor barrier on the inside.

Now, how much insulation is needed on a foundation, ignoring codes for a minute. Above grade is the most exposed. Below grade, the first couple of feet can get rather cold. But beyond that, any heat loss is well insulated by the amount of soil it has to pass through. What that is saying is, extra insulation below 2' below grade will have almost no economic effect and absolutely no comfort effect.

Here is what I would recommend, assuming you have a good layer of insulation the full height of the foundation on the outside. Cover the inside of the foundation walls with 1" of pink or blur rigid insulation and tape all seams. Then stud your wall against that rigid, pressure treated bottom plate with a sill gasket as Keith suggested under it. Keep your stud wall vertical even if it isn't tight against the rigid. Then add 4' batts of 3.5" Roxul in the top 4' of those stud cavities. Make sure you use a 2x4 on top and don't leave any spaces for critters to get into those walls. Add drywall and keep it 1/2" up off the floor and be sure to use treated lumber rated fasteners anywhere anything is attached to the pressure treated wood.

Bud
 
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Old 04-01-15, 08:53 PM
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Thanks, Bud! That was the conclusion I was starting to come to as well. It didn't make sense to me to add a vapor barrier as the last thing before the drywall, so I'm glad that's out. Just to check the other options... I assume adding a thicker layer of xps might help some...I guess I'm wondering if it's more cost effective to use, say 2" (or 3"?) xps, and eliminate the Roxul? But that doesn't necessarily put the most insulation where it will do the most good, as you suggested.

Another thought...frame a wall up an inch out from the foundation, then spray foam against the foundation at least 1" thick so it's coming into the stud bay. Have it applied to a thicker depth anywhere that is above grade to improve those specific areas. I'm sure that isn't as cost effective, but are there any real benefits to a spray foam option? I'm guessing that I can do the first option myself whereas I'd have to hire out the spray foam, the costs would start getting pretty steep, pretty quickly.

This is a bit off topic, but a note for a moderator: the sticky at the top of this forum section has what were probably some good links to basement insulation information, but they all appear to be dead links at this point.
Thanks,
Guy
 
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Old 04-01-15, 09:11 PM
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If you already have 2" rigid insulation on the outside (R-10), all the way down, then using 1" on the inside (R-5) plus 3.5" of Roxul (R-15) will give you an above code wall.

Installing full sheets of rigid is very easy. Use a flat grinder to quickly smooth off any form ridges and apply an adhesive with a horizontal serpentine pattern. That limits any air flow behind the right insulation. Vertical glue lines allows air to circulate top to bottom. Then build your walls.

Spray foam would be good, but $$$. I do like Roxul as it is very dense and not subject to moisture issues. Although I suspect your basement will have few moisture problems from the outside.

Be sure you have a functioning sump pit with pump as all basements are subject to broken water pipes.

Bud
 
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Old 04-01-15, 09:33 PM
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Closest thing I've had to a plan in the two years I've been thinking about this...much appreciated. I might price spray foam, but sure this will be the most cost effective solution! I'll have to price Roxul as well...any good sources?

In a previous post you mentioned about eliminating any potential areas for critters to get in. Assume you mean cracks from the outside? Also, one detail I'm wondering about...at the top of the rigid would I use canned foam to seal that to the existing foam insulation of the rim joist to create a complete system?

This is a bit off topic, but any tips on sound insulation between the floors?
Thanks again for all the input!
 
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Old 04-02-15, 04:57 AM
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Google Roxul and locate closest source. They also make a "safe and sound" material you might want to look at for noise control. Several threads here on stopping noise between floors.

Mice are almost impossible to keep out and once in they set up house keeping. Wall cavities they can get into from the inside may not be close to where they actually got into the house, but I have found many in basements where my infrared camera would show massive networks of trails and potty spots. Attics are bat as well. Can foam would be better than an open crack, but some inexpensive metal flashing caulked in place would be better. I can't see the detail needed so can't offer more specifics.

Setting mouse traps of some sort sounds silly with a new well made home, but in the fall when temps drop the critters will find the holes by following the heat and they can squeeze through a very small opening. Waiting to go find where they GOT IN can leave you wondering where they have been. If you set traps for a few years and never find one, perfect, then you can omit the traps.

Bud
 
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Old 04-02-15, 05:00 AM
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Then add 4' batts of 3.5" Roxul in the top 4' of those stud cavities. Make sure you use a 2x4 on top and don't leave any spaces for critters to get into those walls. Add drywall and keep it 1/2" up off the floor
What do you do below the top 4'? Leave it empty?
 
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Old 04-02-15, 05:44 AM
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Yes, not a problem that far below grade if there is already substantial insulation on the outside of the foundation. I'm guessing r-10 outside, plus the r-5 inside would meet current code minimums. My personal opinion is that below 2' below grade the soil temp outside doesn't require as much insulation. But codes always trump any opinions.

Bud
 
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Old 04-02-15, 07:20 AM
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Just to follow-up, I heard back from my builder that everything on the exterior is R5.
Below Grade: Energy Board R-5
Exposed: XP R-5
Above Grade: Certi-Stud R-5

Assume that means a conversation with my building inspector when the time comes, but might call for 1.5" to 2" rigid foam on the inside, with the Roxul as discussed in the highest heat-loss areas.

One more silly question...with the pipe for radiant heat run under the slab, do I need to be worried about attaching my bottom plates to the slab? If I didn't use a sill gasket the plates could be glued down, but I understand the benefits. I guess it's a 3 1/2" slab and the tubes are at the bottom...just seems risky.
 
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Old 04-02-15, 08:46 AM
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The builder could probably get you a photo of the installation or at least the intended design location of those pipes. I doubt they are near the edges, but as you say, best to check. But you may in the future want to drill elsewhere or maybe address a leak in which case, having the design or a photo would help. Since your basement floor has a layer of rigid insulation below, I would be less concerned about just attaching/gluing the pressure treated bottom plate directly to the concrete.

Strange that your basement was built with the provisions for heat and the inspector didn't require the insulation to meet code.

Being just r-5 raises a concern. The inside surface of the above grade concrete may get cold enough to present a condensation issue with warm inside air. Just be sure your inside rigid insulation is at least r-10 and air sealed.

Bud
 
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Old 04-02-15, 09:11 AM
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Oh, I have about 1,000 pictures from construction...including some of the basement with the pipes installed before the slab was laid. Here is a good example, and you're correct that they are away from the walls a bit (due to the footer alone). Perimeter walls won't be a problem. I may consider gluing down any interior partition walls though...especially in a few areas where I know the piping exists.
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I'm pretty comfortable asking my builder, so I'll see what they say about only having R5, when it appears minimum code would be R10. I'll also talk this over with the building inspector when I pull permits to begin the project, but it does seem that applying R10 of rigid to the inside will keep me comfortable. And adding Roxul to the highest heat loss areas will hopefully make it efficient!

Ok, I got another one. Is there any DIY spray foam worth considering? I've seen kits on the Internet, but it's always seemed a little sketchy to me. I haven't priced it, but wondering if those are even worth considering.
Thanks,
Guy
 
  #17  
Old 04-02-15, 09:33 AM
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Don't fall into the trap of insulation as as much as possible, since a basement wall never sees the conditions that a lightweight frame home above grade does see. Also the fictional "frost depth" in code really applies for structural properties of the home for the worst winter in about 100 years with no snow cover that provides significant exposure. The ambient soil temperature a few feet down in MN is about 54F and does not go up significantly from season to season. I have encountered on 6" of frost after 2 months of -5 to -30 every morning, and that was over 200 miles north of MSP/MN. - The reason is because of thermal inertia for the mass of the soil and concrete and the transmission rates.

If you have a finished basement inside the structure as is very common in MN, the basement that is over-insulated can actually increase the AC load in the summer. Your heated basement floor will add to the comfort in the winter.

There has always been a problem when trying to apply a "model code" to an area with drastic weather conditions. Lucky nobody was injured in the "heated" technical arguments when the acceptance was discussed. My AC is turned on in June or so to maintain an even temperature, but most importantly to reduce the humidity, since it takes time and energy to remove the moisture from the wood framing and I turn it off in September and open the house. - Every structure is different.

Dick
 
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Old 04-02-15, 10:38 AM
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Thanks for your thoughts, Dick. I agree that more is not always better when it comes to insulation. I don't think 1-2" of rigid followed by Roxul in high heat loss areas (ie exposed, not underground) is over insulated, though. The high heat loss areas hurt you in both heating and cooling scenarios, so adding more insulation to those areas makes some sense to me. Utilizing a prudent (R10-R15) amount of insulation in the below grade sections then seems "about right" since it is an area of the country where we spend more time heating than cooling.

Would love your thoughts if you disagree or have a better solution!
Thanks,
Guy
 
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Old 04-02-15, 01:05 PM
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Since your basement is insulated on the outside already, something that is rare to see in the age of mass produced homes, you are already way ahead of the game for an optimally insulated basement. Anything you do on the inside at this point is not going to have a significant effect. I have posted a few articles below that deal with proper insulation and vapour barrier use for basements.

BASEMENT: INTERIOR OR EXTERIOR INSULATION?

Full height basement insulation? An animation explaining why the answer is YES.

Basement walls -- Moisture & Vapour Barriers

BASEMENT: FULL HEIGHT OR PARTIAL HEIGHT INSULATION?

MYTH: LEAVE AN AIR SPACE BEHIND THE INSULATION IN THE BASEMENT TO AVOID CONDENSATION.

To the question about attaching the plates to the floor, since you are already insulated under the floor and on the out side wall, with a proper drainage memberane chances are slim to none that you will have moisture entering your basement floor. I would just use pressure treated plates and glue them down with a good quality construction adhisive such as LePage / LePage® Construction Adhesives / PL® 9000 Heavy Duty Construction Adhesive with no fasteners in the floor.
 
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Old 04-02-15, 09:46 PM
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Thanks, I see your point that the exterior insulation is a great head start in this game. Again, I don't think some rigid (1" is probably plenty) everywhere with additional Roxul in higher loss areas is a bad strategy. By higher loss areas, I mean areas where the exterior of the foundation is exposed, above grade. In fact, one of the links Keith provided did mention interior insulation as a compliment to exterior. But would love confirmation of this assumption...

I like the idea of gluing down the plates, but also want to ensure there aren't moisture issues. Obviously you can't use a sill gasket and glue, but are there any other solutions? Is PT the best material...could I look for PT that is ground contact rated, I suppose. I'm over thinking this, aren't I?
 
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Old 04-03-15, 12:13 AM
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Over thinking? Yes . But that's a lot better than under thinking.
It's not that the PT doesn't like the moisture, but that it wicks it up and delivers it to the studs and drywall. Since the wall you will be building is not load bearing, I don't see why some strips of ice and water shield glued on both sides wouldn't be fine. Or, as long as we are over thinking, could you rip down a length of 1" thick synthetic decking and glue that down and then perhaps skip the PT and use regular framing material and avoid all of the special screws and nails. Just glue your bottom plate to the decking.

For reference I've been in basements here in Maine that have 2" rigid on the exterior of the foundation and they are warm and toasty. Even the r-5 that is on your foundation will give you a comfortable basement. Increasing the r-value is just to reduce the cost of the heat loss. With the rim cavities above the foundation filled wit spray foam and the added 1" plus Roxul you will have a comfortable inexpensive basement. Just be sure that plan meets local code requirements.

Bud
 
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Old 04-03-15, 12:48 AM
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If you want the best you can get for basement framework, you can buy treated lumber that is mold resistant. It is usually blue in color. It may not be readily avalible in all areas but any lumber yard should be able to order it.
 
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Old 04-03-15, 10:17 AM
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Just to update, I called and spoke with a local inspector to run this all by them. He said with the exterior insulation (and he believes it would have to be R10 to have passed inspection) plus he estimates an R6 for the poured concrete itself, he would not want to see any additional insulation on the interior. His reasoning is that adding insulation moves the dew point from the exterior of the foundation to somewhere in the middle of it and that could cause problems. So as others suggested, I guess keep it simple.

He said I could use some PVC decking under the sill, but would recommend against it. He was ok simply gluing down the PT bottom plate (no mechanical fastness) and building up the wall about 1/2" off the foundation. (He actually said it could be up tight to the foundation, but was fine with 1/2" off.)

Does this all sound right? I'm fighting my urge to try to do "better" and trust that it would be fine.
 
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Old 04-03-15, 01:10 PM
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It does sound like he is trying and I do understand the energy codes are only a small part of what they have to manage, but, his numbers and concerns are off a bit.
1. I think he is correct that it should have been R10 on the outside, but if it is only R5 then that is what you will need to deal with. It is a difference between 1" and 2" added thickness so maybe you can find a place to measure, or one of your pictures.
2. R6 for the poured concrete is optimistic. The link below shows poured concrete as 0.08 per inch for a total R-value of 0.64. That is less than one. When some people try to include its thermal mass they give it more credit than they should, especially during a continuously cold winter. I've always used R-1 for poured concrete walls.
3. As for the dew point, the concern is to not allow any interior surface that is exposed to warm inside air, drop below the dew point. Heating the concrete on the inside (no additional insulation) will accomplish that albeit at a price. Adding rigid insulation reduces the heat loss and keeps the inside surface warmer and when well air sealed prevents warm moist air from reaching a colder surface.
Another link below.

BSD-103: Understanding Basements — Building Science Information

ColoradoENERGY.org - R-Value Table

I'll let you digest those links.

Bud
 
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