Basement insulation questions

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  #1  
Old 03-13-17, 08:37 AM
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Basement insulation questions

Hello all

I have searched many forums and everyone has their specific questions for insulation. Well here goes mine, subgrade basement located in Eastern PA. I have already Rigid board 1.5 in. all finished exterior walls tapped and spray foamed joints. My framing required me to construct my walls app 4 in. in front of the rigid board due to a drain line on 3 walls of my basement. Im planning on batt insulation in framing, main question is do I leave an airgap or attempt to fill this 4 in. gap between rigid and framing with batt. Next question is I have 1 5/8 steel framing what size fiberglass batt will fit appropriately. Given my setup faced on unfaced?

Lastly not overly important I have an area that is unfinished (workout room) should I fill the walls that meet the finished area with batt as well.

My current plan is to leave the basement un heater as it is consistently 60deg year round, I have an elect fireplace to break the cold if needed. And after everything is said and done plan to evaluate for a dehumidifier if needed but don't believe I will need one.

Thanks for your time
 
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Old 03-13-17, 11:47 AM
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Hi Hawk,
Unfortunately I don't have a reference with specific guidance for what you have, but here is a related link.
Calculating the Minimum Thickness of Rigid Foam Sheathing | GreenBuildingAdvisor.com
This link discusses using rigid foam on the exterior of a house but the principle is the same, make sure the inside surface of your foam remains above the dew point. The temperature of that surface is a function of the outside and inside temperatures plus the ratio of foam insulation to inside fiber insulation. With your current 1.5" of rigid all you need to do is NOT install too much fiber insulation between it and the warmth of the basement. In your climate region (there are 3 zones in E PA) the max basement insulation you need is R-15, that's rigid plus fiber.

One solution would be to run your unfaced batt insulation horizontally filling the 4" gap while leaving the stud bays empty. Total r-value would far exceed the requirement while maintaining an acceptable ratio of foam to fiber. If you were to also fill the stud cavities you would risk the surface of the foam becoming too cold and collection condensation.

No gap between the new wall and foundation is best.
Insulating interior walls would only be necessary if you wanted those rooms at different temperatures or for sound reduction.
Don't let it get too cold down there and do keep the RH under control.

Bud
 
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Old 03-13-17, 05:50 PM
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What is the foundation constructed of? What are your soil conditions and do you know how the foundation was dealt with for damp proofing and drainage?
What 1-1/2" foam did you use, (R-value)?
 
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Old 03-13-17, 06:24 PM
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R7. Poured concrete walls and floor. No idea of soil there is a floating slab bout an inch spacing between slab and wall never seen moisture in 3 yrs this all connect to sump. No pump sump hole had and has always had a few inches of water never rose at all even in heavy rain. But like I said attached rigid to walls sprayers and tapped all seams.
 
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Old 03-14-17, 05:28 PM
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What about the idea of placing another layer of foam over the existing foam? I think I would forget the fiberglass idea as the difficulty in placing it either between the existing foam and the new wall or within the steel studs becomes problematic.

You could add an additional 1/2" of Thermax to increase the total to over R-10 which is code for basement walls with a continuous insulative membrane. That should be able to be applied with an appropriate contact adhesive that is compatible with your current extruded foam. Of course, you could go thicker and add an inch if you choose.

A potential issue with your current proposed scenario is that you have a space between the current foam and the steel stud wall. That space is not appropriate when addressing flammability issues of the foam. Flamable insulation materials or facings should be guarded by a suitable fire barrier that is in "substantial direct contact" with the flammable material. Thermax foam is rated for such a situation and can be left exposed or with the wall as you propose being 4" away.

Adding too much insulating value can sometimes cause an issue with frost heave against the wall in cold weather. This is a function of heat loss from the basement, soil type and moisture content, height of grade on the walls and type and design of the foundation.

As an alternate, you may consider using 1" thick fiberglass duct board panels with an FSK aluminum facing. This product gives an R-4+ value and also meets the code for an exposed installation. It can also be installed with a contact type adhesive and/or a combination of the adhesive and a mechanical fastener. This comes in 4'x10' sheets and perhaps other sizes. Check with a distributor of heating and cooling systems for the availability and pricing in your area.
 
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Old 03-14-17, 06:34 PM
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Calvert

That's for your input. First thing cost is a factor so I'm not putting an additional layer of rigid I had a hard enough time doing the 1.5 but bit the bullet Bc as I understand it's the correct approach. I do not feel laying batt insulation behind the wall stacked horizontally as mention previously will be difficult at all. I hear your concerns about fire issues in that cavity. Duck board may be an option haven priced it yet does that fixed to rigid solve these fire issues? I'm not overly concerned with getting above a few more R points as i stated it is currently comfortable so if i can get it to 10 that's plenty I feel. Talk to me more about other option to help with fire issue. Roxul is out due to cost but I am putting some up top for fireblock vertically. Let me know what other ideas you might have.
 
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Old 03-15-17, 06:22 PM
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Hawkdriver,

As Bud mentioned in his response, it can be problematic to add too much of an air permeable insulation in front of the foam as the result could be to create a condensing surface on the foam. Adding 3 to 4 more points of R would be about all I would go if you use a fibrous insulation that air (and vapor) can easily transfer through.

The duct board with the FSK or FRK facing is slightly above R-4 for a 1" thickness and that facing is a good vapor retarder and is rated for direct exposure for fire resistant facings.

If you go with fiberglass batts 3-1/2" thick and lie them horizontally you are still dealing with the issue of too much R in front of the foam even if it has a facing that you think of as a vapor retarder. The facing will still be removed from direct contact with the fire resistant drywall you would install on your steel stud wall assembly.

You might check some Craigslist listings for surplus or factory reject listings of fiberglass or foam insulation board. The foam board though would have to be the Thermax brand or another that has the fire rating you should have for such an assembly. There is also the possibility that you may find a duct board that does not have the facing I described. That would also meet the fire code as unfaced fiberglass will not provide a flammable surface.
 
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Old 03-21-17, 02:34 PM
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Ok guys thanks for all your input just wanted to run a quick idea by you all. Trying to find a cost effective method to satisfy the now potential combustible problem I created with xps and the 4 in airgap. Is it a feasible option to put a radiant barrier on top of the xps. I have seen a roll of 1000sq for a very decent price. My thought was to cover all xps with the foil radiant barrier either staple or spray adhesive and tape all joints thus preventing it from combusting Next brings me back to additional insulation I'm looking for approx an additional R5-7 of batt infront of and tight against the xps covered in radiant barrier. Does this sound like a cost effective viable option?
 
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Old 03-21-17, 03:47 PM
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No, fabricating a RB in front of the current rigid insulation would not qualify it as a thermal barrier. There are several foam products that have a foil facing but only one has undergone the testing process and been found acceptable, Dow Thermax. You could use a 1" layer of the Thermax and perhaps meet both objectives, a thermal barrier and the additional insulation.

However, I did some searching to determine if Roxul can be used as the thermal barrier and found this: "Install rigid insulation on the interior of the rim joist. ROXUL® COMFORTBOARD™ IS and ROXUL® COMFORTBATT® can be used to meet thermal barrier requirements for foamed plastics."

Page 15 this link http://www.roxul.com/files/RX-NA_EN/...%20Guide_x.pdf

So, verify your local authority will be happy but you could install the Roxul horizontally behind those studs. 4" of batt insulation (3.5 will do) will be within the guidelines shown in the link in post #2. In your case you have the r-7 plus the contribution of the concrete wall so should be sufficient r-value to the outside to keep the inside surface above the dew point.

Also, no additional RB is necessary.
Bud
 
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Old 03-21-17, 05:08 PM
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Bud.

Appreciate the input. Not trying to be argumentative just trying to decide what is sufficient. Yes I agree roxul and or tjermax would be ideal but it will cost me another 500-1000 for insulation/fire protection Mainly fire protection. The mentioned product I was referring to is considered radiant guard utilized for this purpose and will cost me about 150 or less. It is astm e84 tested so it appears it meets the fire protection requirement I'm searching for a cost I'd like to see. Please take a look at it and let me know your thoughts. Unless I'm overlooking something in regards to not tested with xps etc it seems as though the product meets the requirements albeit not conventional for this purpose seems like it will do the trick. Let me know what you think. Thanks again
 
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Old 03-21-17, 05:26 PM
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If you were considering adding cavity insulation then the Roxul serves two purposes, extra insulation and the thermal barrier, so not all that more expensive.

Where's the link to the radiant barrier you are referring to. Don't make the old guy look to hard he falls asleep. Remember, unconventional solutions will definitely need local authority approval and possibly an ok from your insurance company.

Bud
 
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Old 03-21-17, 06:15 PM
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Yes I understand all the above. Here's link https://www.radiantguard.com/. Just didn't know if I could past specific products here.
 
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Old 03-21-17, 06:52 PM
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I can only offer my opinion, but their foil radiant barrier wouldn't stand a chance at passing the thermal barrier test even if they spent the massive dollars it takes to be tested. Dow went through that process:
http://msdssearch.dow.com/PublishedL...romPage=GetDoc
and passed.

The testing requirements are beyond my interest and probably my level of understanding so I rely on other experts to pass judgement and any product sold in companion with a foil bubble foil product falls flat before they get started.
\
It won't meet the required testing and should not be approved by your local authorities.

Sorry, I just get so upset with the claims made by that industry. It probably does well up against the bottom of a roof deck, but covering rigid foam to meet the thermal requirements is all hype.

Bud
 
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