Basement is too cold, need help in insulation
Hi,
I live on the border or CT and MA. My basement is around 47 degrees. I have my basement roof insulated with R30 batt insulation. When I measured the temperature of my basement walls, above grade part is coming around 35-40 degrees and below grade is about 40-45 degrees, my basement floor is around 45-50 degrees. I put durashield paint on the basement walls to prevent from moisture ( I did not have too much moisture but I still wanted to avoid any future issues), similarly I painted my floor with two part epoxy.
Still the basement is really cold. I had the guy come and check perform thermal inspection, he is suggesting to put the rigid board around the basement walls and I am doing lot of research regarding the same, many people are saying that use XPS instead of polyiso etc. I am kind of confused on what to use for the walls and what to use for the floor.
My plan is to put finish the basement at later point.
Thanks
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Replies
Amit,
Any of the three common types of rigid foam insulation -- XPS, EPS, or polyiso -- can be used to insulate the interior side of a basement wall. However, EPS and polyisocyanurate are more environmentally friendly than XPS.
For all the information you need to do this work, see How to Insulate a Basement Wall.
Thanks for the quick reply. I did read that link before I posted here. It has great information. I was going towards polyiso, but then I was told that it's R-value reduces over time, also it should not be installed where you have any moisture, someone was recommending XPS, because it has more durability and R-value does not change. Then I looked at this link and read few posts and then people are recommending EPS. Now I am totally confused, which one for which application, and which one has most economical and still have good value.
I also want to insulate my rim joists, currently the rim joists have batt insulation along with the entire roof. Which material to use in this case?
I read many forums regarding the framing for basement and many people say that even though you are insulating the basement walls with rigid foam, I should put batt insulation between the 2x4.
Another school of thought is that insulate the concrete walls with 1" XPS and then attach 1X3 to the wall.
https://www.youtube.com/watch?v=oKQdo88Ne74
Which option is better?
I have a source giving me polyiso for $16 for 2" board and $12 for 1". For EPS P2000, I have the cost of 1" around $25 and 2" around $44. I still need to find the cost of XPS. Another issue is that if I use EPS, then I may have issues in certain areas, like in front of stairs and many other areas where I do not have 3-4" of space for insulation and then 2x4 dry wall.
Amit,
I stand by my advice -- any of the three common types of rigid foam will work. I also stand by the advice in my article.
For information on insulating rim joists, see Insulating Rim Joists.
Polyiso is fine on a basement wall, as long as the cut edge at the bottom isn't in contact with a slab that doesn't have a vapor barrier under it.
Polyiso doesn't lose R-value over time, but doesn't perform well when the mean temp through the foam is below 40F. In your climate 3" of polyiso will deliver a performance north of R15 in this type of application, but if it were on the outside of a fiber-insulated studwall wall it can be lower than that (depending on the R-value of the fiber, which affects the average temp at the warm side of the polyiso.) Foil-faced polyiso may have a higher intial R than decades later as the pentane blowing agent leaks out, but fiber-faced roofing iso is going to be the fully depleted R5.5-R6/inch within the first year. From a design point of view, just treat it as R5/inch and you'll not be disappointed, unless you insulate further to the interior side of it.
XPS loses about 15% of its R-value over a handful of decades, as it's climate-damaging HFC blowing agents leak out, eventually stabilizing at the same R-value of EPS of equal density. It's a bit more rugged than EPS from a handling & damage point of view, but I wouldn't pay extra for it (YMMV), and from a dew-point/stackup-design point of view, treat it as if it were the fully depleted R4.2/inch. Samja?
In the MA/CT border region there are several vendors of reclaimed & factory-seconds foam, at a huge discount from virgin-stock goods, which makes all-foam basement insulation solutions affordable. Sounds like you've hooked up with one of those.(?) Nationwide Foam in Framingham, MA can sometimes beat those prices, as can Green Insulation Group in Oxford, MA, but it depends on what's in stock. There are several smaller operators out there too, sometimes much cheaper, but those two sources will usually have are reasonable selection at some price.
Even though you are not planning to finish the basement until later, from a fire safety & code point of view you still need to install a thermal barrier on the interior side, such as half-inch wallboard. From a fire-risk point of view polyiso is a bit safer than EPS/XPS, since it's kindling temperature is a bit higher, and it doesn't melt into a flaming pool of liquid spreading the flame when burning, but instead chars in place, much like a piece of wood does.
It's fine to use unfaced batts in a studwall that traps the foam to the wall, but use R5 (or higher) foam and install the interior gypsum right away (in an air tight manner) to limit the amount of condensation that would form at the foam/fiber interface during winter. Put an inch of XPS or EPS (but not polyiso) under the bottom plate of the studwall as a thermal & capillary break to limit both summertime adsorption from the room air and groundwater wicking.
Thanks Dana/Martin. I have few more questions.
1. When you mention vapor barrier should be installed between the bottom of polyiso board and the slab, what should I use there? Will a 8mm simple plastic sheet/some foil tape be good or something else?
2. The polyiso I am getting that is fiber faced, I am not able to get foil faced prices yet.
3. I am not 100% clear on the last point. When you say install the interior gypsum right away. Is the interior gypsum similar to fire rated drywall?
4. Are you suggesting that after attaching the polyiso directly to the cement basement wall, make the stud wall, put the fiberglass batts between the studs and then put the gypsum stuff on top like a drywall?
Amit,
The usual vapor barrier that is installed under a concrete slab is 6 mil polyethylene, but a thicker material is sometimes used. This recommendation has nothing to do with your plan to install wall insulation, except as an explanation for why you need to keep a small gap between the bottom of your wall polyiso and a damp slab (one without a vapor barrier).
"Interior gypsum" is a reference to drywall. Drywall is known by several terms, including Sheetrock, drywall, gypsum drywall, wallboard, and gypsum wallboard. It's all the same thing.
Thanks for the reply. I do not think that they had installed any insulation under the slab while building the house. I am asking what should I put under the polyiso board.
Amit,
You don't need to install any membrane between the rigid foam and your concrete wall. That information, and much more useful advice, can be found in the article that I suggested you read back in my first response. Here is the link again: How to Insulate a Basement Wall.
Hi Martin, I guess I was not clear enough. I am talking about Dana's comment "Polyiso is fine on a basement wall, as long as the cut edge at the bottom isn't in contact with a slab that doesn't have a vapor barrier under it."
I am talking about the bottom of the polyiso and the basement floor.
Amit,
You can either leave a little gap, or you can seal the gap with caulk.
Another approach is to install a thin (1-inch wide or 2-inch wide) strip of XPS between the bottom of the polyiso and the slab.
If your basement has a history of flooding, stop the polyiso above the high-water mark and use EPS for the lower section.
If the basement is generally dry and has never flooded, leave a half-inch gap to the concrete and fill it with 1-part expanding polyurethane foam (eg. Dow Great Stuff), which will both air seal the gap & moisture-seal the potentially susceptible exposed polyiso on the edge that has no facer.
have you had a blower door test done and the basement air sealed? This can have a huge effect on the comfort of the basement and house, although uninsulated concrete is very poor insulation and does need the foam.
Thanks to all of your responses. I tried many times to put some images, but things are not working for me.
I did have blower door test and the number was around 1200 for 3600 sq ft house. Basement is not air sealed I guess, only base plate is air sealed. I have batt insulation (R30) in my basement roof. Here is what I came up with and need expert opinion.
I am planning two sheets of either 1" PolyISO (non-foil faced) or 1 1/2" of PolyISO(non-foil faced) to get benefit of staggered seams. Then seal the top edge with the can spray, put tape against all seams etc. Spray foam (contractors are suggesting open cell) for the rim joist.
Questions: 1. Should I go for total 2" or 3" rigid foam. Will the extra inch really going to make a difference? If it is not, then I will save some money as well as an extra inch for some tight places in my basement.
2. While connecting the first Poly sheet to the concrete wall, I was planning to use the glue and then for second one, plastic anchors, is this approach good or I can do anything better way? Also should I seal the seams of both the sheets OR only the top sheet?
3. Should I put 1" XPS under the PolyISO and the base plate pressure treated 2X4? I was told by my installer that the concrete screws to nail down the 2X4 comes only up to 3". What should I do?
4. What about the top plate (pressure treated 2X4), should there also be some sort of XPS?
If there is a problem in base plate installation with XPS underneath, should I consider some smaller thickness material which they use to put on top of foundation?
Amit,
You are in Climate Zone 5, where building code require a minimum of R-15 insulation on basement walls (assuming you are using rigid foam). That means you need a minimum of 2.5 inches of polyiso.
Yes, you can attach rigid foam to the concrete wall with adhesive and plastic anchors. (That's what my article said; I hope you got a chance to read it.)
A 1 inch strip of XPS along the very bottom section of your wall polyiso, where the polyiso meets the floor, makes sense. There is no need to install rigid foam under your pressure-treated bottom plate.
There is no need to install rigid foam above your top plate.
Thanks a lot for your responses Martin. I did read your article multiple times. It is really a very good article.
Can you also please guide me on the sealing of the polyiso. Also should I seal the seams of both the sheets OR only the top sheet?
Amit,
Sealing the seams of the second layer of polyiso should be sufficient, as long as you have used caulk to seal between the two layers of polyiso at the perimeter of the wall, and as long as you have sealed between the first layer of polyiso and the concrete at the perimeter of the wall.
Use common sense. Think like air. You don't want any interior air to reach the cold concrete. Create a barrier to prevent that from happening.
If using 2lb density fiber faced roofing polyiso it usually takes 2.75" (not 2.5") to hit R15. Most foil faced stuff is usually 1lb density and higher R6/inch or higher. Most fiber faced polyiso is 2lb density and R5.5/inch.
Masonry screws/concrete screws suitable for anchoring stud wall bottom plates to slabs come in lengths longer than 3", but you may not find them longer than that on the shelves at the big box-store chains. If you can't find them at local hardware store there are many web-store type sources, eg: http://www.confast.com/products/tapcon-concretescrew.aspx
Seal the seams of both layers. If the fiber facers are in good shape housewrap tape will do. If you're not sure, use housewrap tape then paint over it with a thin layer of duct mastic.
There is no need to use pressure treated lumber for top plates. If there is XPS or EPS between the bottom plate and the slab, there is no need to use pressure treated lumber there either.
Thanks for your answers. I will talk all this through with my installer also.
Few more questions:
I want to know. When framing, can I use 2X4 studs in flat position to save space? My installer is saying that if we do that, the studs might bulge.
Also I came across one product as a sheet rock substitute, what do you say about that?
http://firestonebpco.com/2009/02/03/firestone-isogard-hd-cover-board/
Hi,
As I mentioned that I am planning to use PolyISO with fiber face (typically used for roofs), today I happen to call the manufacturer (FireStone), they said it should not be used inside the building, but If I use it, I should be using Fire rated sheet rock.
Is it that bad? I mean am I making a mistake by considering this product? Also do I have to go with the sheet rock right away or I can wait also?
Amit,
Most building codes require that rigid foam insulation be protected by a layer of gypsum drywall (for fire protection); ordinary 1/2-inch gypsum drywall is usually sufficient. Check with your local building inspector to make sure that you are in compliance with local codes.
Thanks a lot Martin, really appreciate the help. I completely dropped the idea of putting the sheetrock substitute. It is the cost driving all this to delay the sheetrock process. Because the framing would be little expensive etc. Are there any other ideas of attaching the sheetrock to the polyiso other than the standard framing practice?
If you use 1x4 furring through-screwed to the foundation with masonry screws every 16-24" (depending on how flat you need the wall to be) you can then mount the sheet rock to the furring.
For 3" foam and 1x furring it takes a minimum length of 4.5" on the masonry screw which isn't a length usually carried by box stores. You can find them at better hardware stores or buy them online. (It means going to a 5" x 1/4" screw like the TCH145 in TapCon's lineup, at about 70-80 cents per screw when purchased online in boxes of 100.) Use fender washer to keep the screws from splitting the furring.
Alternatively, you can use foam board construction adhesive and glue the sheet rock directly to the foam board, as long as yout then constrain the sheet-rock at both the top & bottom to keep it from falling off into the basement if the adhesive were to fail in a fire. That can be done with a 2x4 at the top and a corresponding kick board anchored to the slab at the bottom of the sheet rock.
Hi Dana, Thanks for the reply. Any picture or video for constraining the sheet-rock? Also I would go that route, where should I run my wires for the switches?
Amit,
You really need to hire a contractor instead of learning every construction trade from scratch by asking one question at a time on this forum.
Electrical wiring is run in stud walls, usually, and there are rules about how far back the wiring has to be from the drywall, and how the wires are protected, and the depth of your electrical boxes. Talk to a carpenter and an electrician.
Martin I understand that, there are rules for Electrical and code for everything. I am really asking the question if I do not do the drywall in a traditional way, as Dana suggested that I can put the drywall directly on top of polyiso, I am asking in that case what should be done.
I do have contractor and electrician, but they have not even installed polyiso anywhere and they are recommending to go with the batt insulation.
So my idea is to gather the information and explain to them, so that I can do everything according to my specification but at the same time take care of the code too.