New House: Would You Insulate Foundation?

[38Chevy454]

In process of getting a new house built. It is just at the start of foundation work, only the foundation footers have been completed to this point.

I asked builder about putting the 2-inch hard foam board insulation around the foundation, cost would be $4000 extra. Builder claims he has never done this on residential before in his 24 years doing houses. He can do it though if I agree for the increase in cost.

House is located in Cincinnati, OH area. 1770 sq ft ranch style house, full basement of which little over half is finished including a BR and full bath. So most of the foam board will be full height, only have the shorter pieces around the unexcavated garage. I already upgraded framing to be 2x6 with R-19 insulation above ground.

Now is the time to decide to put the insulation in, before backfill and after walls are poured. Would you recommend doing it for the $4K cost?

 

[TractorJeff]

With a bedroom and bath in the basement, I would!
My brother had finished his basement in a split level and it was always cold down there.
If you can swing the cost under the floor I would do this too!
Is it possible for you to install it to save cost?

 

[NUTTSGT]

You moving to Ohio ?

My parents insulated the foundation around their house with some rigid foam when it was built. It went on after the waterproofing but before back filling. I believe it's something my step-dad did ( I was like 10) over the course of the weekend when the construction crew wasn't there. I somewhat remember him buying the rigid foam second hand and we went and picked it up.

Is there the possibility that you can do it and save some cash ?

 

[jgbnm]

We'll be doing more than that when we break ground (under slab) but it's for a particular type of energy efficient home (Passive House).

I thought R-19 and 2 x 6 was the minimum? Minimizing air leakage by taping seams and tightly insulating can have a big effect as well.



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[rburke65]

jgbnm......this is for the FOUNDATION walls.....not studded walls. And back to the OP....I believe I'd insulate now. And as said maybe DIY?

 

[adam0872]

Yes insulate

 

[Falcon67]

You moving to Ohio ?

Being that my wife is from Albuquerque, that was also my first reaction.

ANYTHING you can do to insure against water penetration and to add any sort of static thermal control to a basement would be a good investment IMHO.

 

[Denwood]

Here is a guide...insulation R value is a function of your climate zone. Keep in mind that this is 8 yrs old, so your plan of R10 on the foundation walls is likely about right. The spec here is R10 to 13 on basement walls. Click the green or yellow bar top right and the specs will drop down.

https://energycode.pnl.gov/EnergyCodeReqs/?state=Ohio

Keeping your walls at conditioned temp (because you insulated outside) is better for thermal regulation, and moisture control. You should look carefully at vapor barrier suggestions with this wall system in your climate zone to ensure the foundation walls can dry to the inside, if you're sealing the outside. Building code has not necessarily kept up with building science with regard to basement insulation and vapor barrier.

 

[James-W]

I don't know, I have mixed feelings about this. On the one hand I think insulating the outside of the basement walls is a good idea, but on the other hand I would almost say that since the basement is in the ground and there will be no air infiltration from wind, etc, it would make more sense to spend the $4,000 insulating the inside walls of the basement.

Most people who finish off their basement put up a stud wall and then insulate between the studs with rigid foam insulation. Having a stud wall allows you to run wires thru the walls to run the electrical outlets and for lighting, as well as running coax cable for television, Internet cable, and surround sound system cable.

 

[ItsNemo]

I don't know, I have mixed feelings about this. On the one hand I think insulating the outside of the basement walls is a good idea, but on the other hand I would almost say that since the basement is in the ground and there will be no air infiltration from wind, etc, it would make more sense to spend the $4,000 insulating the inside walls of the basement.

Most people who finish off their basement put up a stud wall and then insulate between the studs with rigid foam insulation. Having a stud wall allows you to run wires thru the walls to run the electrical outlets and for lighting, as well as running coax cable for television, Internet cable, and surround sound system cable.

Sure, but do both. The exterior insulation will help keep the foundation at a more controlled temperature.

 

[Kaizen]

Sure, but do both. The exterior insulation will help keep the foundation at a more controlled temperature.

No expert but won't that cause water mold issues? If op had heated slab I would say insulate on outside but for that price I would waterproof outside and sprayfoam inside...I've heard both sides of srayfoam on foundation interior. Not sure who is right


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[ard]

4000 seems like a rip off.

Op- what are they doing to WATERPROOF that foundation wall on the outside???? IMO that is way more important than insulation. Waterproofing and possibly drain pipe at the base of the wall.

IMO loss of heat is simply a financial issue- fighting moisture in the walls, carpet, etc is an ongoing disaster. once that basement exterior wall is back filled, it is too late.

 

[jetnow1]

I would put the $$$ to work on further upgrading the wall and ceiling insulation. You lose a lot more thru there than the foundation. Rigid insulation on the outside of the walls with r19 inside makes a big difference. Remember that approx. 20% of your wall surface is framing lumber, a 2x6 is only about r-6. Air sealing also makes a big difference, esp. with fiberglass insulation. It loses a considerable amount of its r value when air flows thru it, remember that air filters are made of fiberglass as it allows air flow thru it.

 

[58Yeoman]

Our basement is finished, and has 3/4 to 1 inch of rigid insulation in the walls. In the winter, we use the wood stove to keep it warm while we're down there watching tv. In the summer, it's nice and cool, and we don't have to keep the upstairs as cool, or warm in the winter.

 

[BombShelter]

I've seen some really messy water issues happen with insulation added to the exterior foundation. It might take a few years but if the wall cracks or develops holes the insulation acts as a moat, holding moisture between the foundation and the insulation, meaning that instead of having a little localized leak, water from the entire foundation could drain into the basement. Sometimes the only way to really fix it is to excavate a large portion of the foundation and either remove the insulation or repair the whole area.

If your set on using insulation I'd use a true waterproofing barrier against the foundation, something like CETCO Swelltite or Carlisle MiraClay, and not a dimple board type product. If this is too costly, make sure the insulation is firmly attached to the foundation in all spots. I've seen larger rocks and pebbles get behind the board leaving large voids (for water to collect), this is really bad. Have the contractor take photos of the panels to verify they are flush with the walls or do an on-site inspection before he backfills. I'd also run them inches above grade so water can't easily get behind them and put a cap on the top.

Personally I'd never use it, I've seen too many major water issues with this type of construction but it is possible to keep the basement dry if you properly waterproof the foundation before you apply the insulation, but it's going to get expensive.

 

[86turbodsl]

In ohio, yes insulate. Concrete exposed to atmoshere has an R value of less than 1. Your payback will be very fast. I didn't insulate my basement in michigan until a few years after i built, and i couldn't keep the house warm until i did. After, my heating system was sufficient.

 

[joe--h]

Two things to think about.
Your contractor with 24 years of experience has never done this. He is state of the art 50s technology and the price is way out of line. 1770sq' -- call it 2000. 40x50 rectangle =46 full sheets x $15 = $690

https://www.menards.com/main/buildi...660208037208362592&ipos=4&bargainStoreId=3133

EPS with borate is what you want, ants don't eat it. The Menards link says it's for below grade but says nothing about being treated so who knows.

So, you need to do some research before you let someone who's never done it have at it. If it's not done right you wasted you money.

Joe H

 

[johnnyradiant]

Is waterproofing even optional? If for some reason it is an option then your personal specs should be modified to remove the option and make it a must. My personal specs would also include exterior insulation. I would likely be doing most of the work myself. If the inside of the foundation walls are part of your used space - insulate 'em. We have the ability and knowledge now to not have to live in damp, cool areas of homes, lets move forward with life.

 

[the_saint]

I would recommend it.

We insulated outside the whole perimeter of the 'basement', and taped and sealed all the joints between the styrofoam boards.

As well the interior walls were insulated (obviously).

FWIW I went with a structural floor as well with a heated crawl space.

Makes for a very liveable space.

 

[38Chevy454]

Thanks to all for the information

Couple answers:
1. The outside foundation walls are sealed for waterproofing. The hard foam would be extra on the outside, put in place before backfilling.

2. Interior basement walls will be studded, insulated and drywalled. The finished part of the basement will be heat and air conditioned space.

3. The builder actually uses a foundation subcontractor, and they will do the work, not the builder. The subcontractor is familiar with the extra hard foam insulation, but claims it is more common for commercial use and not residential.

 

[James-W]

Thanks to all for the information

Couple answers:
1. The outside foundation walls are sealed for waterproofing. The hard foam would be extra on the outside, put in place before backfilling.

2. Interior basement walls will be studded, insulated and drywalled. The finished part of the basement will be heat and air conditioned space.

3. The builder actually uses a foundation subcontractor, and they will do the work, not the builder. The subcontractor is familiar with the extra hard foam insulation, but claims it is more common for commercial use and not residential.

I am not an authority on this, but I seriously doubt you will live long enough to save $4,000 on your heat bills by insulating the outside walls since you are already planning on insulating the inside walls.

 

[rustyjames]

4000 seems like a rip off.

It certainly is. The 2" XPS goes for about $30.00 per 4x8' sheet here. It's really nothing to install, just lay it up against the foundation to install. A lot of jurisdictions require this to meet minimum energy codes.

 

[Evilunclegrimace]

Here is some info that might help.https://www.quadlock.com/technical_library/bulletins/R-ETRO_Value_of_Basement_Insulation.pdf

 

[rnscustom]

Seal the interior walls and floor also for moisture before you stud and insulate . Waterproof the exterior ( hydraulic cement in the form tie holes ) . Me I would want some sort of air circulation between the concrete walls and the insulation / stud walls , tight houses and mold are big issues today , one poster has a good point about water getting between the foam and directing toward cracks so I'm not sure if I would insulate exterior foundation . I'm still on the fence with spray foam except roof insulating . Not sure if it would be stupid or not but does anyone insulate with foam board pitched maybe a few decrees touching at top only and only 4' deep ( frost line here )

 

[rnscustom]

Thinking about it theory is good but how do you back fill ,

 

[ItsNemo]

I am not an authority on this, but I seriously doubt you will live long enough to save $4,000 on your heat bills by insulating the outside walls since you are already planning on insulating the inside walls.

It's also a matter of comfort, I would pay $4000, even if it didn't save me money in the long run, to have a more comfortable living space.

 

[B.C.Biker]

Super easy and fast to do yourself. Super cheap too if you do it with used. Just did both sides of foundation of shop with 4" thick 2'x4' pieces. Got them from a chicken barn being torn down. $2 each. Bit of an odor until they were backfilled and never to be seen or smelled again.
This is in the no brainer colum me thinks.

 

[tjpavlov]

Your quote seems high. I'd definitely insulate the walls and slab though.

Don't use fiberglass insulation below grade. If your builder recommends that look for someone else.

I'd consider ICFs if I were building new. I finished my basement recently and used insofast panels. Google them. Much better than what your builder is planning.

Also you may want to consider zip system r-sheating. If you use that you can frame with 2x4s and have a better total insulation and a continuous air barrier.

 

[B.C.Biker]

And if you are searching out used and it's not part of the inspection the insulation pieces really don't even have to match. Just get them where you find them.

 

[The Cobbler]

if the interior walls are being insulated as you mention, I don't see the need ( or recovery on your investment ) in insulating outside.

 

[eddieK]

I don't know, I have mixed feelings about this. On the one hand I think insulating the outside of the basement walls is a good idea, but on the other hand I would almost say that since the basement is in the ground and there will be no air infiltration from wind, etc, it would make more sense to spend the $4,000 insulating the inside walls of the basement.

Most people who finish off their basement put up a stud wall and then insulate between the studs with rigid foam insulation. Having a stud wall allows you to run wires thru the walls to run the electrical outlets and for lighting, as well as running coax cable for television, Internet cable, and surround sound system cable.

Anything you can do to minimize moisture is a big plus. Insulation helps here as well...I have been called as a ventilation person countless times to homes with basements that are living spaces because of the smell.

 

[cheechi]

Cinci is cold as ****. Do it.

 

[James-W]

It's also a matter of comfort, I would pay $4000, even if it didn't save me money in the long run, to have a more comfortable living space.

I am not sure I understand the comfort issue. Presumably the basement would be comfortable with or without the outside insulation. The only issue would be the cost involved in making it comfortable. My suspicion is the cost savings from having the outside walls insulated would be small but the comfort level inside the basement should be the same either way. At least that is how I see it.

 

[James-W]

Anything you can do to minimize moisture is a big plus. Insulation helps here as well...I have been called as a ventilation person countless times to homes with basements that are living spaces because of the smell.

I agree that the outside walls should be waterproofed but I would not use insulation to do it. There are much better methods for waterproofing the outside walls than using rigid foam.

 

[Dick in Wisconsin]

Spray foam in the box ends of the floor joists.

You will still probably have some of the concrete foundation exposed to the outside. So you might want to put Styrofoam the first four feet. But if you're going to do that, go all the way down to the footer.

If you're going to finish the basement its imperative that you have very ample vapor barrier UNDER the concrete floor to keep the moisture under the basement floor from migrating through the concrete. Same thing on the walls.

Are you putting Styrofoam insulation under the basement slab? Another good place for insulation.

The "comfort" mentioned by a poster comes from the temperature of the finished basement walls. The warmer you can keep the walls, the warmer you will feel.

Say the opportunity cost of the $4,000 is 8%. Will you save $320 on utilities a year? Probably not. But the basement should be warmer which means the floor above should feel warmer; which will be helped by the foam insulation in the box ends of the floor joist.

Since you're going to have a basement, here is a suggestion. Have a dedicated area for mechanicals ... furnace, water heater, water softener. in the area, recess the basement floor another 4" to 6" inches, put a floor drain in this "small floor". if something overflows, the curb created by the rest of the basement floor should contain the flood. Also put some stand pipes in for the water softener discharge and the furnace condensation line.

To the poster who thinks Cincinnati is COLD? Get with the program. Cincinnati does have some cold weather in the winter ... but nothing like all the area north of Cincinnati!

 

[eddieK]

I agree that the outside walls should be waterproofed but I would not use insulation to do it. There are much better methods for waterproofing the outside walls than using rigid foam.

Insulation is not the primary moisture barrier, by any stretch. It is a way to help keep air from becoming moisture. There is always heat movement, the insulation helps reduce the transfer.

Moldy smells are serious issues in basements. The air is stagnant to start with, any moisture build up from the air just creates more issues to deal with.

Ventilation is also critical.

 

[sammer]

All this advise and not one person mentioned the freeze thaw aspect in your foundation.
In a cold climate it will make a huge difference to the overall heating of your building to insulate your basement.
Insulate on the inside and your foundation will be subject to freeze thaw cycles which will eventually breakdown the concrete. Insulating the outside will keep your walls from freezing and keep your foundation walls at a constant temperature. The concrete will act as a heat sink to help keep temps stable.
Small cracks (concrete cracks!) will not be as vulnerable to the freeze thaw cycle and will last longer, your basement will be warmer, less musty, and your heating costs will be lowered.

sam

 

[MushCreek]

I built our house with ICF, so we have foam both inside and out. Our walk-out basement never drops below 60, or goes above 75 with no HVAC at all. As mentioned, it also reduces the HVAC load on the main floor. Our whole house is ICF- strong, quiet, and comfortable. One 12K BTU mini-split keeps the whole house comfy. I doubt it will pay off in utility bills alone, but it's still well worth it, IMHO.

I would do the foam on the outside as a minimum. Properly waterproofed, it will perform well. What is 'properly waterproofed'? Peel 'n stick membrane on the foam, dimple board over that to promote drainage, french drain at the bottom, backfill most of the way with gravel, proper grading to direct water away from the foundation, and gutters to control the water coming off of the roof. Of course, if you excavate a swamp, you're on your own.

 

[yeldogt]

A properly built foundation is not going to worry about freeze cycles or the temp outside. Proper footing with drains outside and inside if ground water is a concern -- proper Vapor Barrier under slab w/ insulation. Waterproof the exterior of the foundation -- w/proper protection.

The OP is going to insulate -- the inside. You don't need to do both -- properly built walls don't leak air and the ground will have a higher temp regardless of the outside air -- you don't need as much R value.

Make sure you have a proper thermal break at the top. I'm building mine now -- stud wall with spray foam inside.

You can always do more -- with everything.

ICF's are great --- especially on a big house and even more so when taken to the second floor and the transition is not a problem. Unless in an area where available for comparable cost -- I don't see the benefit.

Exterior insulated foundations also flow well when the whole house is done exterior -- otherwise you have to adjust when the foam stops at the top of the foundation .. it's a pain.

And trust me -- in some areas insects are an issue.

 

[38Chevy454]

Update: I decided the cost is too high so I am not going to do the exterior hard foam insulation. If I could be there in-person right now I would do it myself, but I am still here finishing work and selling the current house until early Aug. So doing the work myself now is just not an option. Talked to builder and even he agreed the cost from the subcontractor seemed high. It is so easy to let costs start to spiral upward, trying to keep that to a minimum.

Cincinnati is not that sever of winter climate, as pointed out further north gets a lot worse cold. I know it seems hard for many to believe, but I actually get more snow at my current house here in NM, at 7100 ft elevation, than Cincinnati does. The bigger difference is here we get more sun and typical winter day temps can get above freezing more often. I also lived in the Cincinnati area in the past, so I know what I am getting into.

Wanted to say thanks to all who replied, it helped in my decision process.