# Crawlspace Wall Insulation



## Earnie (Jan 24, 2008)

What's the story on adding rigid foam board to the crawlspace block walls?

I'm looking into sealing my crawlspace. Currently there is 6 mil plastic on the ground and the vents are closed. I want to add plastic up to about six inches from the top of the blocks. Before I do that, I'm thinking about adding rigid foam board to the blocks.

Will check the county building code for requirements. 

Is adding the foam boad a good idea before adding the plastic over the blocks?

Is foil covered better than straight foam? If so, which direction for the foil?

Recommended foam board thickness?

Termite treatment company is on-board with the idea.


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## jklingel (Dec 21, 2008)

sounds like you are generally in control. greenbuildingadvisor.com has several articles on this. j


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## ConcreteTreat (Dec 5, 2010)

Earnie, here's what I would recommend:

1. Seal the crawl space vents and doors with airtight covers.
2. Install rigid foam board on the crawl space floor.
3. Install a 10+mil vapor barrier on the floor and 1' up the walls.
4. Install spray foam insulation on the walls.
5. (Optional) Install a self-draining dehumidifier in the space to keep it dry so pests won't be an issue.


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## stadry (Jun 20, 2009)

*6mil vapor barrier's only good IF its never walked on again imo,,, we like 15mil stego,,, i wouldn't worry about insulation of the floor so much as the walls depending on your geographical location - ambient earth temp's usually about 67f as i recall.*


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## ConcreteTreat (Dec 5, 2010)

Conc, I've heard the ambient earth temp is about 50... am I wrong?

Personally, I use a 20mil vapor barrier and encourage the homeowner to use the crawl space as storage, but few people are willing to bid on the extra expense of that kind of material nowadays.


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## ConcreteTreat (Dec 5, 2010)

Here, I found a source that says it's about 50-60F year-round. See page 2 of this PDF:

http://www.santa-fe-products.com/pdf/MaxDry_sell.pdf


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## Earnie (Jan 24, 2008)

Many thanks for the replies and information.

After doing a bit more reading and calling the County building department, here is a tentative plan.

- Cover the existing 6mil poly with a 12 - 15 mil reinforced poly.

- Install Dow Thermax White Finish polyisocyanurate board on block walls up to six inches from the top of the blocks. Allows termite company to inspect for activity.

- Possibly upgrade existing house dehumidifier that is in the crawlspace with a commercial unit.

Questions:

- What should be installed first, the poly or the foam board? Install poly one foot up the wall then install the foam board, or install foam board and lap the poly one foot over the foam board?

- What about Radon gas? I am in a low (zone 3) area but it's still a concern. Will the complete sealing of the ground help to keep radon out of the crawlspace?


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## ConcreteTreat (Dec 5, 2010)

Anytime, Earnie. 

That Dow Thermax White Finish polyisocyanurate board sounds like a pretty good plan. Just be sure that you install a continuous, unbroken sheet of insulation along the walls-- any gaps will significantly affect its insular value. That's why I usually recommend spray foam instead. 

The poly sounds great as well. I'm also very on board with the commercial dehumidifier -- I recommend the SaniDry or a Santa Fe model.

One word of warning -- if you have crawl space vents, it's extremely important that you seal them. Check with local building codes, of course, but you're trapping outside moisture, rain, and wet air inside your crawl space if you don't -- and the insulation won't be much help either if you have open vents. Also install a plastic airtight door. I can't emphasize enough how important that step is.

I would personally install the foam board first, then the poly.

As far as radon gas goes, a test kit costs $15-25 at your local hardware store. Now, before you seal your crawl space, is the time to find out if that's going to be an issue -- you never know. That said, crawl space encapsulation will create a passive radon mitigation system in your home that will hold the gas back and help things out significantly.

--------
Concrete Treat
Concrete Sealer


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## Gary in WA (Mar 11, 2009)

Microsoft Word - RE_06_64_07 

Cold concrete foundation wall must be protected from interior moisture-laden air in summer and winter
Rim joist assembly must be insulated with air impermeable insulation or insulated on the exterior
Rigid insulation completely wraps exposed concrete preventing interior air from contacting potential concrete condensing surface
Seams in rigid insulation and joints to other materials sealed to provide air barrier
 Rigid insulation is vapor semi-impermeable or vapor semi-permeable (foil facing or plastic facing not present)
Rigid insulation provides bond break between foundation wall and slab when insulation is installed before slab is poured http://www.buildingscience.com/docu...ce-insulation/?searchterm=foam board in walls
 
Cover the foam as you don’t want foil faced as previous article. 
2.1. *Continuously operated mechanical exhaust ventilation *at a rate equal to 1 cfm (0.47 L/s) for each 50 ft2 (4.7 m2) of crawlspace floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2.8;
You may get by with an ignition barrier: http://www2.iccsafe.org/cs/committeeArea/pdf_file/RE_06_64_07.pdf
Gary


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## Earnie (Jan 24, 2008)

CT - 

The Thermax board is available with a ship-lap seam. That will make sealing a bit easier. I'll proabaly go with either 1.5" or 2" thickness.

I closed off the wall vents this past spring but there are still air gaps that need sealing.


Gary -

Thanks for the BSC link. Only issues I have is that I will not be able to install the foam board down into the ground along the block wall. Also, I don't think applying the foam board all the way up an over the top of the block wall is a good idea. What prevents termites or other bugs from crawling behind the foam board up to the wood?

I still need to look at the radon issue. I noticed mitigation systems that can be installed under the vapor barrier.


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## ConcreteTreat (Dec 5, 2010)

Earnie-- try treating the wood with boric acid, or borate. That should deter pests and stop mold.


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## Rick Webb (Mar 20, 2008)

Pool liners make for great vapor barrier in the crawl space.
You can often pick them up quite reasonable form pool shops, that were made the wrong size.....or free if you catch someone tearing out a pool. Some buy and sell papers/websites will also have them.

For taping up the vapor barrier seams, house wrap sealing tape or Tuck tape works good.


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## Earnie (Jan 24, 2008)

CT - Nice idea on the borate. Just did some reading on it. I forgot about "20 Mule Team....." Might be a good idea to place some borate along the block wall and interior pillars before installing the poly. 


Rick - I'll check some local pool stores. Thanks.


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## Earnie (Jan 24, 2008)

To Gary or anyone else that knows:

I'm still stuck on the foam board installation. I've read and re-read the BSC article about installing foam board to the block walls. I still do not understand what they are recommending.


_Up to two inches of unfaced extruded polystyrene (R-10), four inches of unfaced expanded polystyrene (R-15), three inches of closed cell medium density spray polyurethane foam (R-18) and ten inches of open cell low density spray foam (R-35) meet these permeability requirements.
In crawlspaces where the insulation material will need to be covered by a fire/ignition barrier, it may be acceptable to use fire-rated foil-faced insulations. However, such requires careful attention to supplemental moisture management strategies._ _With vapor impermeable facings on interior insulation, it is possible that water may accumulate between the insulation facing and the inside surface of the foundation wall. The airtightness of the assembly is, therefore, extremely important to prevent the exchange of air between this damp interface and anywhere else in the building._


This section has me confused. Per my building code, I need the foam covered by a fire rated material. Thermax has 1.25 mil foil on one side and 0.9 mil foil on the other side. This exceeds the 0.41 mil thickness required by R314.5.4.6 (Corrosion-resistant steel having a base metal thickness of 0.016 inch (0.41 mil)).

- Is aluminum foil equal to "corrosion-resistant steel"?

- Since I also need about 5 inches of inspection area on the block wall to check for termite activity, how would this affect the air tightness or moisture accumulating behind the foam per the last sentence in above BSC quote?

- Can anyone explain what R314.6 states about an ignition barrier not being needed if the foam has been tested? This is referenced in R314.5.4


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## Rick Webb (Mar 20, 2008)

I'll give you my thoughts here Ernie, and hopefully it will be of some help.......



Earnie said:


> To Gary or anyone else that knows:
> 
> I'm still stuck on the foam board installation. I've read and re-read the BSC article about installing foam board to the block walls. I still do not understand what they are recommending.
> 
> ...


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## rtoni (Jul 18, 2007)

ConcreteTreat said:


> Anytime, Earnie.
> 
> I'm also very on board with the commercial dehumidifier -- I recommend the SaniDry or a Santa Fe model.
> 
> ...


I can't offer much except to 2nd the dehumidifier - I've been running the SantaFe for going on 3 years 24/7 and it has done an amazing job with very minimal additional cost (electrical) in an 1100 sq ft sealed crawl space. Fan runs 24/7 filtering the air down there and dehu kicks in as required. No regrets on the up front cost. fwiw.....


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## Earnie (Jan 24, 2008)

Up to two inches of unfaced extruded polystyrene (R-10), four inches of unfaced expanded polystyrene (R-15), Blue or pink rigid foam boards three inches of closed cell medium density spray polyurethane foam (R-18) and ten inches of open cell low density spray foam (R-35) meet these permeability requirements.
_In crawlspaces where the insulation material will need to be covered by a fire/ignition barrier, it may be acceptable to use fire-rated foil-faced insulations. However, such requires careful attention to supplemental moisture management strategies._ _With vapor impermeable facings on interior insulation, it is possible that water may accumulate between the insulation facing and the inside surface of the foundation wall. The airtightness of the assembly is, therefore, extremely important to prevent the exchange of air between this damp interface and anywhere else in the building._


This section has me confused. Per my building code, I need the foam covered by a fire rated material. Fire rated material can also be drywall and some bat insulations. But why would I want to cover foam board insulation with drywall or more insulation in a crawlspace? Thermax has 1.25 mil foil on one side and 0.9 mil foil on the other side. This exceeds the 0.41 mil thickness required by R314.5.4.6 (Corrosion-resistant steel having a base metal thickness of 0.016 inch (0.41 mil)).

- Is aluminum foil equal to "corrosion-resistant steel"? Some is I believe, it depends on the thickness of the aluminum, but importantly what is under it - the foam board. Some foam boards are quicker to combust thus more toxic. Can you provide a code reference which states they are equal? 

- Since I also need about 5 inches of inspection area on the block wall to check for termite activity, how would this affect the air tightness or moisture accumulating behind the foam per the last sentence in above BSC quote? That's good question.....if I understand, you would need something that is removeable/replaceable to inspect. So, 8' x 5" sections of foam board taped at the seams? I have no idea. Don't you just enjoy how the government makes demands but provides no help in meeting those demands! My thought was to leave the five inch area uncovered, no foam board, for easy inspection. But would that actually affect the sealing of the crawlspace?

- Can anyone explain what R314.6 states about an ignition barrier not being needed if the foam has been tested? Some or most commercial applied spray foams has a fire retardent mixed in with the foam, while it is being applied. This is referenced in R314.5.4 Can you provide a quote from the actual code reference?

All of the information I have read shows companies installing up to 20 mil plastic sheet to the crawlspace floor and up the block walls. That is a vapor barrier. Foam board with a foil facing is a vapor barrier. What's the difference?

_In crawlspaces where the insulation material will need to be covered by a fire/ignition barrier, it may be acceptable to use fire-rated foil-faced insulations. However, such requires careful attention to supplemental moisture management strategies._ _With vapor impermeable facings on interior insulation, it is possible that water may accumulate between the insulation facing and the inside surface of the foundation wall._

_What are supplemental moisture management stratigies? Won't water accumulate on the inside of a 20 mil plastic sheet just like it will accumulate on the inside of a foil faced foam board?_


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## Rick Webb (Mar 20, 2008)

This section has me confused. Per my building code, I need the foam covered by a fire rated material. Fire rated material can also be drywall and some bat insulations. But why would I want to cover foam board insulation with drywall or more insulation in a crawlspace?
A barrier between the foam board and fire.
Thermax has 1.25 mil foil on one side and 0.9 mil foil on the other side. This exceeds the 0.41 mil thickness required by R314.5.4.6 (Corrosion-resistant steel having a base metal thickness of 0.016 inch (0.41 mil)).

- Is aluminum foil equal to "corrosion-resistant steel"? Some is I believe, it depends on the thickness of the aluminum, but importantly what is under it - the foam board. Some foam boards are quicker to combust thus more toxic. Can you provide a code reference which states they are equal?
Best to check with the manufacturers and see what they say.

- Since I also need about 5 inches of inspection area on the block wall to check for termite activity, how would this affect the air tightness or moisture accumulating behind the foam per the last sentence in above BSC quote? That's good question.....if I understand, you would need something that is removeable/replaceable to inspect. So, 8' x 5" sections of foam board taped at the seams? I have no idea. Don't you just enjoy how the government makes demands but provides no help in meeting those demands! My thought was to leave the five inch area uncovered, no foam board, for easy inspection. But would that actually affect the sealing of the crawlspace?
I think it greatly would! .....warm - cold = condensation. I would think that they would want to have it at the top portion of the foundation to the sill plate, and to me that's the most important area to seal..... and when was the last time you had your 5" area inspected? 

- Can anyone explain what R314.6 states about an ignition barrier not being needed if the foam has been tested? Some or most commercial applied spray foams has a fire retardent mixed in with the foam, while it is being applied. This is referenced in R314.5.4 Can you provide a quote from the actual code reference?
Check with your local building dept. and see if they recommend an acceptable company or vise versa. Only certain types are acceptable in lieu of a (15 minute?) thermal barrier. It varies, depending on where you are located. 

All of the information I have read shows companies installing up to 20 mil plastic sheet to the crawlspace floor and up the block walls. That is a vapor barrier. Foam board with a foil facing is a vapor barrier. What's the difference?
The rigid foam board will give you an R value, as well as a vapor barrier, if properly sealed. 

_In crawlspaces where the insulation material will need to be covered by a fire/ignition barrier, it may be acceptable to use fire-rated foil-faced insulations. However, such requires careful attention to supplemental moisture management strategies._ _With vapor impermeable facings on interior insulation, it is possible that water may accumulate between the insulation facing and the inside surface of the foundation wall._

_What are supplemental moisture management stratigies?_
Sounds to me like...... if you have moisture problems, you would need a way of getting rid of the moisture, as the board will not. If heavy moisture is coming through the foundation, you may need a water proof membrane on the exterior walls to seal them up or a french drain (or similar) or even something as simple as grading the ground away from the foundation.
_Won't water accumulate on the inside of a 20 mil plastic sheet just like it will accumulate on the inside of a foil faced foam board? _
I think that's a good assumption. That's why it needs to be 'managed' so it doesn't get to that point.


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## Gary in WA (Mar 11, 2009)

The way I understand is a conditioned crawlspace- exhaust outlet fan, conditioned supply air, air tight, etc., is treated as a basement for moisture control. This will help: http://www.swinter.com/news/documents/InteriorBsmtInsulSystems.pdf with the foil faced. If completely covered, you need additional interior french drain to manage the moisture through the concrete wall, stopping and condensing on the f.f foam board, run down, remove to another collection/disposal area. 

The thicker insulation board is to limit the escaping heat through the below grade concrete wall: http://www.quadlock.com/technical_library/bulletins/R-ETRO_Value_of_Basement_Insulation.pdf

Why the R-10?: http://www.buildingfoundation.umn.edu/FinalReportWWW/Chapter-5/5-optimum-main.htm

Gary


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## Rick Webb (Mar 20, 2008)

Very interesting links Gary.
It's surprising the heat loss through the concrete walls......very informative!


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## Gary in WA (Mar 11, 2009)

I found this also, start by backing up a few pages: http://books.google.com/books?id=_p...snum=10&ved=0CDEQ6AEwCThG#v=onepage&q&f=false

You may want to tape the edges and don’t make holes in the Polyiso for water: http://docs.google.com/viewer?a=v&q...iZ9vwo&sig=AHIEtbRlhNBCWID8xGZ54EyM707m0gPdXQ

Gary


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## Earnie (Jan 24, 2008)

Gary, I was writing when you posted your last info.

Thanks for the replies guys.

Ok, just to re-clarify.

This is a crawlspace, approximately three feet high. Inside of crawlspace is concrete block but the exterior is 4" decorative red brick. The dirt ground inside crawlspace is above the exterior grade. Not by much, but higher. I "see" no evidence of moisture on the inside concrete blocks.

I want/need to provide a better environment for the house and HVAC air handler and ducting which are in the crawlspace.

Currently, the crawlspace only has minimum code required 6 mil poly on the ground. I want to upgrade the poly to at least 12 mil and insulate the block walls which are visible above ground. 

How is a homeowner supposed to seal and insulate a crawlspace but still make it possible to see termite tunnels before they get to the rim joist? I don't have a concrete floor like you would in a full basement, its dirt. 

It's my understanding to keep the top 5 inches of concrete block uncovered to provide a visible band around the perimeter. Makes it very easy to check for termite activity when under the house.

So, anyone have ideas how to correctly install vapor barrier and foil faced foam board insulation up the concrete blocks?

This question will be asked at the building department too.


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## Rick Webb (Mar 20, 2008)

Another point to note.....if the attic isn't properly insulated and vented, (a good flow through the sofits up) the air that is needed for the roof vents, is being pulled up from the living area.
The stale, crawl space air is then being pulled up to replace the air in the living area.


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## Earnie (Jan 24, 2008)

Good point Rick.

I have that one covered. Attic is supplied with air from plastic soffit vents on both sides of the house. Plastic baffels are in the roof cavities to keep insulation from blocking air flow. Ridge vent all along the roof.


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## stadry (Jun 20, 2009)

*'per building code' is only the MINIMUM standards to which anything must adhere/pass,,, eg, how many plumbers would have shark's grip fittings in their home ? nor would i allow toe drain & dampproofing to ONLY Meet code in OUR home ?*


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## Rick Webb (Mar 20, 2008)

I think you have to find out what your local codes require. It's much easier to work back from there, and maybe even improve on it.
They will vary by location ...... eg. where I am, we have no need for a termite 'window'. 

Here's a few sites with a bit more info, if you haven't come accross them already.....

http://www.crawl-space.com/
http://www.crawl-space.com/PDF/USDOE_techfactsheet.pdf

Here's a paragraph from this website
http://www.ornl.gov/sci/roofs+walls/insulation/ins_06.html
When a fiberglass blanket is used to insulate the walls of an unventilated crawlspace, it is sometimes necessary to attach wood furring strips to the walls by nailing or bonding. The insulation can then be stapled or tacked into place. Alternatively, the insulation can be fastened to the sill plate and draped down the wall. You should continue the insulation over the floor of the crawl space for about two feet on top of the required ground vapor retarder. Because the insulation will be exposed, be sure to use either an unfaced product or one with the appropriate flame spread rating. When rigid foam insulation boards are used to insulate the walls of an unventilated crawlspace, they can be bonded to the wall using recommended adhesives. Because the insulation will be exposed, be sure to check the local fire codes and the flame-spread rating of the insulation product. If you live in an area prone to termite damage, check with a pest control professional to see if you need to provide for termite inspections

In the above, if you have an approved insulation blanket, it may be appropriate to be able to lift it to check for termites.


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## Earnie (Jan 24, 2008)

Rick,

Thank you for the link to crawl-space.com. That's the best site I have seen to describe how to seal the crawlspace. I'll take those .pdf files with me when I visit the building department.

From what I have looked at so far, the key may be to cover the concrete block but still leave the 5" bug inspection area. Next cover the ground and lap the vapor barrier up and over the block wall vapor barrier. Finally, install the foam board on top of the block wall vapor barrier.

All subject to the government of course.


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## a6spot (Oct 22, 2012)

Rick,

I have almost the exact same crawl space design. Can you tell me what you did exactly. The termite inspection issue is one I am particularly interested in.

Jim


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## Rick Webb (Mar 20, 2008)

Jim,

You probably need to direct your question to Ernie, and find out how he made out.

Sorry, I have no experience with the termites.

Rick



a6spot said:


> Rick,
> 
> I have almost the exact same crawl space design. Can you tell me what you did exactly. The termite inspection issue is one I am particularly interested in.
> 
> Jim


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