# Wisconsin - crawl space insulating project



## JoshInWi (Oct 10, 2018)

Hello,

I have been putting off addressing the lack of insulation in the crawl space below our addition, but now that addition is our office/homeschooling setup and I can no longer put it off.

The addition was added a few years after home construction in 1963. 

It is approx 24" in height and 12'x14'. Poured concrete for a floor in crawl space.

No vents to the outside, it is sealed with 1 hvac vent running across the length of the room. The opening for "access" into the crawl space is small, approx 18"x18" square.

Here is my tentative plan that I would love feedback on(2 layers of R10 foamboard):
-sweep, clean concrete floor in crawl
-buy 4'x8' sheets of scored R10 insulation board, cut into 16"x8' strips
-place first layer
-place second layer, finishing it off using seam tape for optimal increased R value.
-buy roll of R30 batt, and stuff exterior joist cavities
-buy/use hvac duct insulation for the run of duct

Questions:
Is it true that the "score" line when unused truly lessen the R value? That seems like a bit of a nuanced take but I have read some reviews say they don't like scored board for this reason.

Is it worth my time to also mount insulation board to the exterior walls of the crawl?

Once all insulation is complete, what about a 2nd small hvac duct that runs off the nearby furnace and it blow warm air into crawl at the 18"x18" opening?

When using the 2" board with 1" scores every 8", can you just snap it at every 16" without additional cutting? Or will I be cutting foam board no matter what?

As always I really appreciate the insight from everyone.

Josh


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## Bud9051 (Nov 11, 2015)

Hi Josh, how much of this addition foundation is above grade?
Exterior wall is probably more important than covering that floor, along with the joist cavity.
Not a fan of fiberglass but mice are. Many detail those cavities with rigid.
Consider Dow Thermax.
A foil faced rigid foam board could provide the thermal covering for the foam and provide a radiant barrier which adds to the insulation performance. If available in your area Dow Thermax is the best but a bit expensive. Benefit is it provides an approved foil face AND when you tape the seams the tape sticks to the foil.

Note, not sure if or how much insulation you need on the floor. The soil below adds a lot of insulation value.

Bud


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## JoshInWi (Oct 10, 2018)

Thanks, Bud.

The entire addition is above ground and I would estimate that maybe 6"of the crawl is below grade. It is bone dry, pitch away from home is strong too so that 6" varies. But that is my rough estimate. Based on where old sump line that used to pass through the crawl and exit just a few inches under ground outside (have since re-routed that sump discharge due to patio project.).

Josh


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## 3onthetree (Dec 7, 2018)

If I am reading right, you have a 24" high crawl and are lining, assuming concrete or CMU wall, with (2) layers 16" rigid stacked aligned. So you'll have 8" wall exposure at the bottom, which may occur partially above grade. Why not 24" sheets, an 18x18 hole fits 25" diagonally according to Mr Pythagorus.


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## JoshInWi (Oct 10, 2018)

3onthetree said:


> If I am reading right, you have a 24" high crawl and are lining, assuming concrete or CMU wall, with (2) layers 16" rigid stacked aligned. So you'll have 8" wall exposure at the bottom, which may occur partially above grade. Why not 24" sheets, an 18x18 hole fits 25" diagonally according to Mr Pythagorus.


The floor of crawl is poured concrete. I was thinking of doing two - 2" layers of R10. The sidewalls are in fact CMU. I hadn't considered putting foamboard over those until Bud suggested it. 

And yes, great point, I can likely fit 24" on an angle through the opening so that will save time.

Do you think it's worth putting a layer of insulation board on the floor? Or are you in Buds camp and think the primary concern is the joist cavities and walls? Would the floor just be a bonus? I was thinking about doing the floor primarily because in winter the slab gets to be as cold as 30F.


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## Chris616 (Dec 31, 2019)

One of our federal gov’t departments has some good info on insulating basements and crawlspaces in cold climates.
https://www.nrcan.gc.ca/energy-effi...heat-chapter-6-basement-insulation/15639#a6-3


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## 3onthetree (Dec 7, 2018)

JoshInWi said:


> Do you think it's worth putting a layer of insulation board on the floor? Or are you in Buds camp and think the primary concern is the joist cavities and walls? Would the floor just be a bonus? I was thinking about doing the floor primarily because in winter the slab gets to be as cold as 30F.


Didn't even register with me you were doing the floor, and initially I even read it twice :sad: I had wondered what all the floor cleaning was for.
Yeah, I don't understand why you'd be insulating on top of the floor vs the walls. Air seal/insulate rim board area, insulate walls, extra insulation in the main field of floor joists is possible, but you minimize heat transfer from the space above (if the perimeter is now tight).

If your floor, in the middle of the space, is getting way below a typical 50-55F into the 30Fs, then I'd ask if the foundation walls go down to frost depth. Also, if the 18x18 opening (does it have a cover?) is through CMU of the main house and is that the only pass-thru for heat (like the old rim board wasn't removed so the addition joists could bear on the old foundation wall).

Just FYI, if your 168sf crawlspace is closed up and has poly sheeting below the slab, then you MUST insulate the perimeter walls, and also have to choose one of these:
A. continuous mechanical exhaust of min. 4cfm and keep the access panel open
B. run a min. 4cfm supply duct into the space and keep the access panel open for return
C. dehumidification

The access hole is required to be 16x24, but you're grandfathered at 18x18.


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## JoshInWi (Oct 10, 2018)

Chris616 said:


> One of our federal gov’t departments has some good info on insulating basements and crawlspaces in cold climates.
> https://www.nrcan.gc.ca/energy-effi...heat-chapter-6-basement-insulation/15639#a6-3


Thanks for the link!


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## JoshInWi (Oct 10, 2018)

3onthetree said:


> JoshInWi said:
> 
> 
> > Do you think it's worth putting a layer of insulation board on the floor? Or are you in Buds camp and think the primary concern is the joist cavities and walls? Would the floor just be a bonus? I was thinking about doing the floor primarily because in winter the slab gets to be as cold as 30F.
> ...


-The opening to the crawl is NOT sealed. It is left open to a storage room. 

-So just to confirm your hypothetical approach on my project, you would: use caulk or great foam in rim board area above CMU, then fill with insulation? Would you just use batt insulation in the joist areas? 
Regarding the walls, use 2 layer of R10 insulation board. I assume using an adhesive + concrete screws is how to install? 

Leave the floor as is for now, and also I do not need to add insulation in between the floor joist the entire length, correct?

Main focus should just be air sealing rim board area above CMU exterior walls and then insulating the walls, correct?


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## 3onthetree (Dec 7, 2018)

JoshInWi said:


> Main focus should just be air sealing rim board area above CMU exterior walls and then insulating the walls, correct?


Best bang for the buck yes

Caulk vs foam watch some Youtube videos to see which method you like. Cutting a rigid insert and seal that, depends on ease of access (how far arm reach, lengthen foam nozzle, etc) insulating gurus here maybe will chime in their preferences.

The interior of the floor area should not need the insulation, theoretically, if you've done well with the rest of the encapsulation.


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## Missouri Bound (Apr 9, 2011)

Have you looked into spray foam?

Once you weigh the cost of materials and time it may not be a bad option.
There will be no infiltration once it is done and all you need to worry about is the ventilation.


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## JoshInWi (Oct 10, 2018)

Missouri Bound said:


> Have you looked into spray foam?
> 
> Once you weigh the cost of materials and time it may not be a bad option.
> There will be no infiltration once it is done and all you need to worry about is the ventilation.


The thing is, I have never done it before. Also, as I mentioned, the crawl is only about 24" in height, so its a tight area. Only I do is going to be a bummer, but I just feel like spray foam could be hard for having zero experience. 

Do you recommend any spray consumer kits i can look at?
-Josh


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## bob22 (May 28, 2008)

I've seen them at big box stores. Smaller than a gas grill propane tank. 
I'd do the rim joist area with that to block off air infiltration from outside and then insulate the joist bays under your warm in winter room's floor. Anything after that is likely money and time not well spent IMO.


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## JoshInWi (Oct 10, 2018)

.


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## JoshInWi (Oct 10, 2018)

bob22 said:


> I've seen them at big box stores. Smaller than a gas grill propane tank.
> I'd do the rim joist area with that to block off air infiltration from outside and then insulate the joist bays under your warm in winter room's floor. Anything after that is likely money and time not well spent IMO.


Oh yeah? Putting foarmboard or spray foaming the cinder blocks not worth it?

By "joist bay" I assume you are talking entire 13ft runs that are 16" wide? Just putting face batt insualtion in those?


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## bob22 (May 28, 2008)

Oh yeah? Putting foarmboard or spray foaming the cinder blocks not worth it?
To me, if you are only trying to keep the room above warm, you put insulation between it and the cold. Instead of putting it on the floor of the crawl space, I'd put that $ and effort into material between the warm room and source of cold.

By "joist bay" I assume you are talking entire 13ft runs that are 16" wide? Just putting face batt insualtion in those? 
Yes.


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## JoshInWi (Oct 10, 2018)

Just for fun I figured I would post a follow-up.

Upon advice received i went ahead and bought some R10 insulation board for the joist bays. Since working in this small crawl was going to be a pain I figured I would make the most of my efforts. 
-I crawled in once and go measurements of the joist bays.
-came out and made the cuts, but I actually made double the cuts, used adhesive to make an R20 cutout for each joist bay.
-the next day went back in armed with pre-cut R20 blocks and cans of great foam window/door seal. Installed and filled gaps.
-came out and grabbed ductwork insualtion roll, went in and wrapped ductwork.

We have had a few mornings in the 30F range already and I can feel an improvement from the work I did. Floor not a noticeable ice cube.

Will let this ride out for a bit. May go ahead and cut foamboard for the face of the CMU wall around the perimeter of the crawl, but that will just be a bonus if I ever do it.

Thank you everyone for the advice.

Josh


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