# Insulate floor on above grade addition



## fothrof4 (Dec 21, 2011)

I bought a home in Crownsville, MD that has an above grade addition. Half of the addition is the back portion of my master bedroom and the other half is the master bath. The addition is supported with 6x6's and is roughly four feet above the ground. Our home has forced air heating and our primary heat source is heating oil. Currently I have to run a space heater in the bathroom and bedroom to warm them. I thought of running duct work to the addition but the duct work will be exposed outside and the air would cool before entering the rooms (located about 30 feet (outside) from the heat source). I would like to insulate the underside but was told I risk mold issues because the cool air from inside trying to seep out below the insulation would cause moisture. Is there a vapor barrier I could use? I currently do not have funds to replace the floor and install radiant floor heating. 

Are there any options available to me?

Thanks, 
Bill


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## Windows on Wash (Aug 30, 2011)

Bill,

There are several options to your scenario that do not create a mold issue or require the removal of the floor for radiant heat.

Warm air carries more moisture than cold air and will likely being trying to diffuse to the top side of the home.

The easiest solution to your issue is spray foam. You could do rigid foam but that is more time intensive for a more questionable seal if not done perfectly.


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## AGWhitehouse (Jul 1, 2011)

I agree with WOW that spray foam installed from the exterior beneath the floor is the best option.

As for heating: They do make retrofit radiant floor systems that can be applied to the underside of floor sheathing. Though not as efficient as a system applied directly below the floor finish, it still does help. I wouldn't recommend radiant floor heat for rooms with carpeting though, as the padding acts as an insulator and blocks the heat transmissions.

An electric retrofit system: http://www.warmzone.com/retrofit-radiant-heat.asp

A hydronic retrofit system: http://www.radiantheatreviewer.com/images/AluminumPlates200185.jpg

I couldn't find an actual product for the hydronic, but the pic is what you would want. You'll need the aluminum channels to help distribute the heat energy across the floor system.

If you have a large area to heat, I would highly suggest the hydronic system. It is much more efficient than electrical. If you do not have a hydronic boiler, you can add an on-demand heater just to serve this loop.


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## AndyGump (Sep 26, 2010)

You mean that your floor has NO insulation whatsoever?

Andy.


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## Windows on Wash (Aug 30, 2011)




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## fothrof4 (Dec 21, 2011)

Andy,

NONE.....the floor is very cold and the room is extremely cold after a nice hot shower.

WOW and Washington,

Thank you for the great information. I will do more research on your posts and hopefully get something going soon.

Thanks again,
Bill


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## AndyGump (Sep 26, 2010)

Well if the floor is over a vented crawl space why not just install non-faced, R19 batt insulation?

It is fairly inexpensive and can be done DIY.

Andy.


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## fothrof4 (Dec 21, 2011)

*attached a picture of the underside of addition*

Andy, 

The space below is not a crawl space. It is elevated about four feet above ground. My basement door actually exits under the addition. the stairwell goes about halfway and then once at the top of the stairwell you have about short distance before you are out from under the addition. I just stuck some old insulation between the floor joists for now until I find the right way to do it.


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## AndyGump (Sep 26, 2010)

Oh yeah, get some fiberglass insulation under that thing.

Not likely to have any condensation problems under there.

I would say un-faced and wire it in there. You can probably find individual lengths of wire for this purpose at a building store near you.

Andy.


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## AGWhitehouse (Jul 1, 2011)

If you are going the fiberglass route be sure to cover it with an air barrier of some kind. Plywood would be best, but tyvek is minimum. Air currents through an un-faced batt will negate almost all of its R-value.


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## AndyGump (Sep 26, 2010)

AG is probably right, as open as the area is you would be better off with kraft faced or another barrier of some sort as he suggested.

Andy.


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## fothrof4 (Dec 21, 2011)

Thank you both very much


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## AGWhitehouse (Jul 1, 2011)

I wouldn't do the kraft faced as that is a Class II vapor retarder and those should only go on the warm side in this application.


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## Windows on Wash (Aug 30, 2011)

+1

unfaced batts with tyvek or housewrap barrier.

Make sure they are installed tight to the underside and slight over compression on them will ensure they maintain contact with the floor above.


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## Gary in WA (Mar 11, 2009)

Faced batts for your area. Housewrap (not a vapor retarder or barrier) on the joist bottoms would still leave you with a floor that insects/rodents could get in, is exposed to the cold ground (radiation factor) and outdoor temperatures with a lot of moisture from the Bay less than two miles away, and could still condense on your framing. 


Treat the floor as a wall. I would:
1. air seal any holes going through to the rooms above (to stop the natural stack effect);
2. foam board (2") the rim joists and air seal with canned foam; 
3. insulate any HVAC or plumbing pipes;
4. use cellulose or f.g. with a facing vapor retarder, paper, not plastic, held up with wire stays as said;
5. 1-1/2" foam board to the joist bottoms- taped at seams;
6. plywood on foam board with proper length fasteners.
http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11480


Find your Zone below the map; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec001_par001.htm
Find your floor insulation: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec002.htm

R-19= 6-1/4” thick
Or stop the ground temp. radiation with foil-faced foam board and f.g. insulation (not held up tight to the floor- figs.6,7). Except where the vinyl bathroom floor is: http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

http://www.buildingscience.com/documents/information-sheets/critical-seal-spray-foam-at-rim-joist/

Gary


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## AGWhitehouse (Jul 1, 2011)

Be carefull following GBR's advice...he has given you a system with a double barrier. 1-1/2" foil faced foam is a class I vapor retarder. Couple that with his recommendation for using the kraft-faced batts and you've got a double barrier system. Being that you are in zone 4, the code may allow that a continuous layer of foam at an R-10 value will allow you to negate the vapor retarder at the floor level. I know that is the case for CT and zone 5.


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## Windows on Wash (Aug 30, 2011)

Kraft faced batts are not a vapor barrier (1.0 perm and Class II or III vapor retarder).

An exterior foam layer of sufficient thickness would eliminate the necessity of any vapor control layer at the warm side beyond normal materials (i.e. sub floor etc).

Double vapor barriers would be in question in situation such as vinyl tile/floor coverings as mentioned by GBR previously.


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## Gary in WA (Mar 11, 2009)

Well put, WW. That is why I said paper facing- not plastic, which could trap condensation. Where plastic is a vapor barrier and asphalt-coated paper facing is not (it is more vapor-open (hygroscopic) the wetter it gets as is plywood). http://www.buildingscience.com/documents/reports/rr-0004-air-barriers-vs-vapor-barriers

AGW, with un-faced foamboard, as I said in the numbered steps, you could use paper-faced insulation. 

(This space means a different thought than the previous)
( So does the "Or"- means a different approach)


OR, the foil-faced insulation without faced batts as the article said.

Please don’t mix the two thoughts/articles, AGW. Please read it again, notice the thoughts are separated by a space……I even added another entirely different thought about Zones between the two so readers would not get confused.


Gary


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## AGWhitehouse (Jul 1, 2011)

*I did read "faced batts" in your first sentence and "facing vapor retarder" in item #4 of your post.* "faced batts" are faced with kraft-paper facings and are considered to be a class II vapor retarder. This cannot be placed to the exterior of insulation envelope in zone 4. *It is a code violation.* If you are providing a continuous rigid insulation board, then you can provide a thickness that will negate the requirement for a vapor barrier on the warm side. The magic number for the foam thickness in zone 5 is R-10, not sure about zone 4.

Here is cut for kraft-faced fiberglass batts: http://www.specjm.com/files/pdf/bid0016.pdf

Notice the kraft 1.0 perm rating as determined by ASTM E96 at the bottom of the first page. That is considered a class II retarder. This is what code officials go by, not buildingscience.com.

To be clear, I wasn't trying to create confusion, but rather clear up the one you created...


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## Windows on Wash (Aug 30, 2011)

AGWhitehouse said:


> If you are providing a continuous rigid insulation board, then you can provide a thickness that will negate the requirement for a vapor barrier on the warm side. The magic number for the foam thickness in zone 5 is R-10, not sure about zone 4.


Is a vapor barrier required in zone 4 or 5?


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## Gary in WA (Mar 11, 2009)

fothrof4, here is some information to help you understand the issue. “*Figure A:* The traditional “vapor barrier” on a fiberglass batt is actually “asphalt-coated kraft paper” that varies in vapor permeance as a function of relative humidity. It pretty much is a vapor barrier only in the absence of vapor. It really functions much like a valve that opens and closes depending on available moisture. In the winter in most older homes the interior relative humidity is in the 20 percent range whereas in the summer the interior relative humidity is in the 50 percent to 60 percent range. So in the winter a kraft-faced batt has a vapor resistance of approximately 1 perm—an interior vapor retarder on the correct side of the thermal control layer—reducing outward vapor flow. And in the summer the same kraft faced batt has a vapor resistance of approximately 10 perms—allowing the same assembly to dry inwards.” http://www.buildingscience.com/documents/insights/bsi-024-vocabulary

The foam on the exterior does replace the interior vapor retarder requirements if you add in the latex paint and drywall (Class III), which you* don’t* have in your floor system. Plywood sub-floor (1 perm), [email protected]”+ (1.25 perm) and ½” plywood (1 perm) plus the f.g. insulation with paper facing (1 perm) will permit drying either way. You don’t require the paper facing per code, but are not disobeying it by having it. They dock you when not meeting minimum code, not surpassing it. If worried about it, omit the paper facing (most box stores are not carrying it), it’s not that big a deal, just ask your local inspector. 



Seattle has 4900 Heating Degree Days and 39” annual rain--- Crownsville has 4700HDD and 41” rain yearly, quite similar with both on the coast of a bay. Read this, especially the beginning and Fig. 3b; http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design

Any other concerns or questions, feel free to ask, we are all here to help.

Gary


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## AGWhitehouse (Jul 1, 2011)

Windows on Wash said:


> Is a vapor barrier required in zone 4 or 5?


Not sure about zone 4, but zone 5 requires a minimum class II retarder at the warm side in winter. This can be negated if there is continuous minimum R-10 of foam insulation provided on the exterior of the assembly. The reason being that within zone 5, an R-10 of foam will cause the dew point to fall within the foam layer and thereby eliminating the chances of condensation within the wall cavity.


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