Should basements be insulated from the outside or inside? New construction

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doss
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Should basements be insulated from the outside or inside? New construction

Post by doss » Mon Mar 25, 2019 12:34 pm

Hi all,
We are looking at possibly buying new construction and I just met with a builder's agent. When I asked about how they insulate the basement, they said that they don't do ANY exterior insulation other than interior rim joists and interior walls that are exposed above grade (e,g, sloping terrain).

However, I have read the following:

"There is a growing body of research and field experience that shows that applying insulation to
the exterior of the foundation during new home construction and implementing proper bulk
water management strategies can greatly reduce the risks related to water/vapor flow and
foundation wall temperature differential. The results are a more comfortable, durable basement
environment along with energy efficiency gains. "
--- US Department of Energy publication, 2013. PDF link: https://www.nrel.gov/docs/fy13osti/56163.pdf

Does anyone think that i should demand they do exterior insulation or is this really not that big of a deal? I thought it was standard that new construction does exterior rigid foam board insulation.

For those that purchased new construction from a builder, was your foundation insulation from the outside?

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F150HD
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Re: Should basements be insulated from the outside or inside? New construction

Post by F150HD » Mon Mar 25, 2019 1:26 pm

might want to state the area of the country you live in in your post. different areas have different needs.
-

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Marlago35
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Re: Should basements be insulated from the outside or inside? New construction

Post by Marlago35 » Mon Mar 25, 2019 1:28 pm

I'm in the northeast, and have a new construction home < 5 years old and work with home builders.

In this market, insulated concrete forms are not the norm for new residential construction. Exterior basement walls will have a below-grade dampproofing agent applied before fill gets pushed back in, and any interior above-grade area will have sprayed foam insulation at the rim joists like you said. Interior walls and ceilings in the basement will sometimes also have sprayed foam insualteion, but mostly just fiberglass.

It certainly is smart to have a well-engineered stormwater plan before you build that specifies the grade so it slopes away from the house as well as any french drains or other systems you need if you think you're in a possible problem area for water collection/runoff.

jasc15
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Re: Should basements be insulated from the outside or inside? New construction

Post by jasc15 » Mon Mar 25, 2019 2:02 pm

Insulating the exterior not only provides a moisture barrier, but keeps the concrete as part of the interior thermal envelope, preventing humid interior air from condensing on the interior surfaces of the concrete. I did a lot of reading on the Building Science Corporation's website prior to renovating my basement. I applied XPS foam to the inside since it was already built, but I think I would insist on foam on the exterior and under the slab if I were to build new.

https://www.buildingscience.com/documen ... insulation

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lthenderson
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Re: Should basements be insulated from the outside or inside? New construction

Post by lthenderson » Mon Mar 25, 2019 2:35 pm

I live in the Midwest where insulating of basements is not the norm either. But if I were going to insulate my basement, I think it is better for a variety of reasons to insulate the exterior so that the concrete becomes part of the thermal envelope as the rest of the house. One can successfully insulate from the interior but if done incorrectly, can cause lots of unintended moisture issues. Also insulating the interior makes it more difficult to finish the interior walls later but there are lots of solutions to make this possible.

I'm guessing the contractor doesn't do exterior insulation so demanding them to do so may not get you anywhere. At best case, if exterior insulation is what you want, you may have to hire another third party contractor to work with the original contractor's schedule to get it insulated.

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elcadarj
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Re: Should basements be insulated from the outside or inside? New construction

Post by elcadarj » Mon Mar 25, 2019 2:49 pm

When I asked about how they insulate the basement, they said that they don't do ANY exterior insulation other than interior rim joists and interior walls that are exposed above grade (e,g, sloping terrain).
Translation: "We don't do anything above building code minimums."

https://www.engext.ksu.edu/files/engext ... rguide.pdf

Chadnudj
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Re: Should basements be insulated from the outside or inside? New construction

Post by Chadnudj » Mon Mar 25, 2019 2:55 pm

Related to this: is there any benefit to having the ceiling of your basement (a.k.a. below your 1st floor floors) insulated? And what about insulating ducts in the basement carrying heat/air conditioning to other parts of the house from the basement located furnace/blower?

I'm in the Midwest, a new home owner, and we have some insulation around the rim joists (I think), but otherwise nothing else in our basement. House is 30+ years old, so wondering if I should be considering some revamped insulation down the line (probably have other higher priorities, like replacing the original to the house furnace and A/C units -- yes, they still work 30+ years later, thanks to owners who were really good at maintenance -- and replacing 30+ year old windows, but want to plan ahead regardless....)

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lthenderson
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Re: Should basements be insulated from the outside or inside? New construction

Post by lthenderson » Mon Mar 25, 2019 3:08 pm

Chadnudj wrote:
Mon Mar 25, 2019 2:55 pm
Related to this: is there any benefit to having the ceiling of your basement (a.k.a. below your 1st floor floors) insulated? And what about insulating ducts in the basement carrying heat/air conditioning to other parts of the house from the basement located furnace/blower?
You can but it needs to be unfaced insulation or you can induce condensation problems between the bottom of the first floor and the insulation. Also, you will be making the basement colder by not allowing heat transfer to occur so depending on how cold your basement will now get, you may now have to be concerned with insulating pipes to keep from freezing and exposed duct work to prevent more condensation problems.

Topic Author
doss
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Re: Should basements be insulated from the outside or inside? New construction

Post by doss » Mon Mar 25, 2019 3:09 pm

F150HD wrote:
Mon Mar 25, 2019 1:26 pm
might want to state the area of the country you live in in your post. different areas have different needs.
-
Good point -- STL area.

Chadnudj
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Re: Should basements be insulated from the outside or inside? New construction

Post by Chadnudj » Mon Mar 25, 2019 3:11 pm

lthenderson wrote:
Mon Mar 25, 2019 3:08 pm
Chadnudj wrote:
Mon Mar 25, 2019 2:55 pm
Related to this: is there any benefit to having the ceiling of your basement (a.k.a. below your 1st floor floors) insulated? And what about insulating ducts in the basement carrying heat/air conditioning to other parts of the house from the basement located furnace/blower?
You can but it needs to be unfaced insulation or you can induce condensation problems between the bottom of the first floor and the insulation. Also, you will be making the basement colder by not allowing heat transfer to occur so depending on how cold your basement will now get, you may now have to be concerned with insulating pipes to keep from freezing and exposed duct work to prevent more condensation problems.
Thanks. Like I said, we have bigger fish to fry in terms of improving energy efficiency, but it sounds like I don't need to be thinking about basement insulation regardless.

runner3081
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Re: Should basements be insulated from the outside or inside? New construction

Post by runner3081 » Mon Mar 25, 2019 4:34 pm

elcadarj wrote:
Mon Mar 25, 2019 2:49 pm
When I asked about how they insulate the basement, they said that they don't do ANY exterior insulation other than interior rim joists and interior walls that are exposed above grade (e,g, sloping terrain).
Translation: "We don't do anything above building code minimums."

https://www.engext.ksu.edu/files/engext ... rguide.pdf
...unless you want to pay for it.

ralph124cf
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Re: Should basements be insulated from the outside or inside? New construction

Post by ralph124cf » Mon Mar 25, 2019 5:36 pm

doss wrote:
Mon Mar 25, 2019 3:09 pm
F150HD wrote:
Mon Mar 25, 2019 1:26 pm
might want to state the area of the country you live in in your post. different areas have different needs.
-
Good point -- STL area.
In the STL area the benefits of exterior basement insulation would be marginal. In the Chicago area or north I would definitely want it. Good waterproofing on the outside is still needed, along with a drainage plan, probably including sump pumps with a backup. Keep in mind that sump pumps do not just remove water from a basement, they relieve hydrostatic pressure from the basement walls and floor, which would tend to crack the walls and foundation, or force water thru the pores of the concrete.

Ralph

Topic Author
doss
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Re: Should basements be insulated from the outside or inside? New construction

Post by doss » Fri Mar 29, 2019 7:09 am

So I've been looking around at a few new construction homes (and some yet to be built) and have not seen a case where anyone has actually placed exterior insulation on the below grade foundation. So, it seems to me that the STL area may not be an area where insulating the exterior foundation of basements is common. Must be a upper Midwest thing (Minnesota/Wisconsin/etc).

WWV
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Re: Should basements be insulated from the outside or inside? New construction

Post by WWV » Fri Mar 29, 2019 7:24 am

My experience

Worked with a custom home builder building our home in 1993. He was doing energy efficiency upgrades at a fairly high level (blower door testing, etc). Was working with a consulting professor out of Minn. I asked about insulation of the basement. He said the consultant "ran the numbers" and said that it didn't make sense to do it in the Chicago area.

Wish we had a ranked order list of all the residential energy efficiency options tailored to each area.....
"The average investor has only 11,000 more genes than a worm"-New York Times

Topic Author
doss
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Re: Should basements be insulated from the outside or inside? New construction

Post by doss » Fri Mar 29, 2019 7:43 am

WWV wrote:
Fri Mar 29, 2019 7:24 am
My experience

Worked with a custom home builder building our home in 1993. He was doing energy efficiency upgrades at a fairly high level (blower door testing, etc). Was working with a consulting professor out of Minn. I asked about insulation of the basement. He said the consultant "ran the numbers" and said that it didn't make sense to do it in the Chicago area.

Wish we had a ranked order list of all the residential energy efficiency options tailored to each area.....
I can't find it now, but I read the new energy studies for housing in cold climates...and I think you saw the same "professor out of Minn" that I did...forget his name, but they took common stock upper Midwest homes and retrofitted them with exterior insulation foam and did all the other basics like rim joists insulation, etc ...and yes, it did make the home more energy efficient, however, there was honestly not much a difference when you look at the before/after charts vs a fully insulated new construction home with exterior foam boards. It seems that the key point was to insulate the exposed part of the foundation and just get some foam a few feet into the ground. No need to insulate the entire side all the way to the footing with backhoes and tearing up the landscape (too much $$). The study showed how you just need to get a water pressure machine and make a slot down a few feet below grade, fill it up with spray foam and regrade it. Cost was like 3k for labor, foam, high water pressure rental.

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hand
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Re: Should basements be insulated from the outside or inside? New construction

Post by hand » Fri Mar 29, 2019 7:58 am

jasc15 wrote:
Mon Mar 25, 2019 2:02 pm
Insulating the exterior not only provides a moisture barrier, but keeps the concrete as part of the interior thermal envelope, preventing humid interior air from condensing on the interior surfaces of the concrete. I did a lot of reading on the Building Science Corporation's website prior to renovating my basement. I applied XPS foam to the inside since it was already built, but I think I would insist on foam on the exterior and under the slab if I were to build new.

https://www.buildingscience.com/documen ... insulation
This aligns with my thinking, but with a couple of caveats:
1) There is some risk of pests with exterior rigid foam, specifically ants and termites, so management of this issue is important
2) There is a difference between best practice and what your builder is able to reliably and economically deliver - if the *right* solution is one the builder has never delivered before, it is quite possible the extra cost and reduced quality if you force your builder into it make the *right* technical solution the wrong one for your specific situation.

I'm incredibly happy with the 2 inch foam + spray foamed rim joists interior to my basement which improved temperatures (and presumably HVAC costs), but more importantly addressed the condensation / dampness / mustiness, but I ultimately had to do it myself because it wasn't a project local contractors were used to doing the right way.

jasc15
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Re: Should basements be insulated from the outside or inside? New construction

Post by jasc15 » Fri Mar 29, 2019 8:31 am

hand wrote:
Fri Mar 29, 2019 7:58 am
jasc15 wrote:
Mon Mar 25, 2019 2:02 pm
Insulating the exterior not only provides a moisture barrier, but keeps the concrete as part of the interior thermal envelope, preventing humid interior air from condensing on the interior surfaces of the concrete. I did a lot of reading on the Building Science Corporation's website prior to renovating my basement. I applied XPS foam to the inside since it was already built, but I think I would insist on foam on the exterior and under the slab if I were to build new.

https://www.buildingscience.com/documen ... insulation
This aligns with my thinking, but with a couple of caveats:
1) There is some risk of pests with exterior rigid foam, specifically ants and termites, so management of this issue is important
2) There is a difference between best practice and what your builder is able to reliably and economically deliver - if the *right* solution is one the builder has never delivered before, it is quite possible the extra cost and reduced quality if you force your builder into it make the *right* technical solution the wrong one for your specific situation.

I'm incredibly happy with the 2 inch foam + spray foamed rim joists interior to my basement which improved temperatures (and presumably HVAC costs), but more importantly addressed the condensation / dampness / mustiness, but I ultimately had to do it myself because it wasn't a project local contractors were used to doing the right way.
We hired out the finish work of our basement, but I did all the insulation myself. The contractor advised against what I was planning regarding insulation, saying it would "trap moisture in" the basement, never mind the fact that source of that moisture is through the concrete from outside... So your point about the best solution being outside a builders capability/experience is well taken. Like most other industries, the building trades are very slow to change. Most customers don't know/care, and builders will just do what they've always done.

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ElJay
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Re: Should basements be insulated from the outside or inside? New construction

Post by ElJay » Sat Mar 30, 2019 8:35 am

Chadnudj wrote:
Mon Mar 25, 2019 2:55 pm
Related to this: is there any benefit to having the ceiling of your basement (a.k.a. below your 1st floor floors) insulated?
When I had an energy audit done on my home, I was told this wasn't very effective. (The former owners of my house had done it.) I think the problem is that it doesn't help much to mitigate the "stack effect" because the cold air is now already inside the building through the basement walls. Insulating the top of my house helped incredibly with energy efficiency and comfort, so I never had anybody come back and do the basement walls. It was hard to expect a similar return on investment for that project.

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