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finishsed basement no XPS?

Posted by andrelaplume2 (My Page) on
Wed, Mar 19, 08 at 14:01

A family member built his own home and just did his basement. We are on a tight budget and want to finish a portion of our basement in some fashion; if only 3 exterior walls and a dropped ceiling....nothing fancy. We have lived in this 20 year old home over a year now and there has been no water issues. The prior owner claimed there never was. It does not get overly humid in the summer (we do have a dehumnidfier running)and the temp (except on a stretch of frigidly cold days) hovers around 58 degrees in the winter. We currently have no heat down there but I hope to add a few vents when I have the home's original heat pump replaced. The ceiling is open joist but is insulated with unfaced fiberglass bats. The walls are poured concrete as is the floor.

I was shying away from the whole thing due to cost but the kids are spending more and more time down there, its a bit chilly at times, it gets dusty and I do not like the idea of those exposed bats in the ceiling. The XPS (2"?) is quite expensive. The family member feels the XPS is overkill - he did not use it in his basement in his new home. He feels we should just drop down PT 2 X 4s on the floor (an inch from the walls to provide breathability) and stud it out and add fiberglass bat insulation--faced or unfaced---not sure. We could them add the dropped ceiling and drywall or panel.

What do you think? Do I need the XPS? Is the PT lunber at the base correct?


Follow-Up Postings:

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RE: finishsed basement no XPS?

A "smart" vapour retarder, such as Membrain, may be used with fibrous insulation. Or use EPS (expanded polystyrene. You need a thicker board to match XPS performance, but it's cheaper.

Here is a link that might be useful: Smart Vapour Retarder


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RE: finishsed basement no XPS?

You could use 1" XPS...it's cheaper than 2" and would be better than fiberglass insul with not barrier against cement wall.


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RE: finishsed basement no XPS?

Well, if I simply want to bypass XPS (which I assume was done for years before it came to be) can I simply build an inche from the wall and use fiberglass bats? If so should the bats have a paper back and if so which way would the paper face?


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RE: finishsed basement no XPS?

The point they are trying to make I think is you need some sport of vapor barrier. Even though the basement is "dry" doesnt mean the concrete is perfectly dry. In fact its not unless exposed. If its underground it will absorb and transfer moisture to the basement. Without some form of vapor barrier on the walls you will get mold and/or mildew problems.

Think if a glass sitting on the warm counter (your basement) with cold liquid inside ( your walls). you get condensation on the glass. That is exactly what will happen inside your walls without a vapor barrier. Plastic sheeting is sometimes enough if it is sealed to the floor and ceiling if building offset studded, unbacked batting insulated walls. XPS with taped seams or spray foam insulation would be the best options.


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RE: finishsed basement no XPS?

....XPS is simply no in our budget. Thanks for the info. I suppose kraft baked in NOT a vapor barrier. Were does the plastic hang; in the inch of space between the foundation wall and where I stud? I asked 4 people today, all with older homes, none used XPS..it may not have even been an option back then. They have had no trouble. So, again, whats the method without using XPS. Do I sud an inck from the foundation? What kind of insulation should be used and where placed?


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RE: finishsed basement no XPS?

worthy,

have you ever used this MemBrain smart vapour retarder? After researching it a bit online, it seems in theory like it would be a really cost-effective way to prevent moisture issues. XPS is presented as the ideal, but I've spoken to more than a dozen contractors and none of them have ever used it for basements.

Is using Membrain really a viable alternative to XPS on the walls?

I live in NJ where it can get cold in the winter and humid in the summers. Would I be rolling the die with the Membrain?

thanks.


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RE: Finished basement no XPS?

I lived for up to six years each in three homes I built with basements insulated with fg, a cold side water barrier and warm side vapor barriers with no obvious trouble either. I run a dehumidifier year round. But I bet if I cut into those walls now, mold would be more abundant than I imagined. And probably in all the other homes I renoed and built, carefully following the faulty Codes mandating tight vapour barriers.

The problem of moisture accumulation in an exterior basement wall, which rises mainly from diffusion through the wall--to the outside in the winter, to the inside in the summer--can be controlled through the use of permeable insulating materials which are themselves unaffected by moisture. The principle ones are expanded polystyrene (EPS), extruded polystyrene (XPS) and sprayed foams. As mentioned above, you can also combine XPS with fibrous materials.

Membrain provides a new approach--a vapor retarder that actually changes its molecular structure with the season, allowing the wall to dry year round, thus inhibiting mold growth, decay and odours.

Membrain has been used in Europe for seven years and since 2004 in the US. I confess I've only recently come across it when it was approved for use in Canada this February. Certainteed, the manufacturer, says a study at the University of Minnesota proved its value. I haven't seen the study and can't find it on-line, so will contact Certainteed for further info.

It certainly sounds effective and likely much cheaper--both in materials and labour--than installing XPS. Until I learn more, I have reservations about going back to fg: water can still enter the wall through minor flooding, settling and poor installation can quickly deteriorate R values. Where the customer wants the best, nothing beats sprayed closed cell foam (at least on the rims) or XPS.

Building a stud wall a few inches from the exterior wall and using a vapour barrier on the warm side doesn't eliminate the vapour drive in the summer. So water will be accumulating in the wall, dripping to the floor and looking for an exit. And within that wall space, the air currents render the fg virtually useless as insulation.

Here is a link that might be useful: Basement Insulation Systems


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RE: finishsed basement no XPS?

....am I to understand that all finished basements prior to XPS are filled with mold? An inch of airspace is going to let moisture build up and run down the concrete or wet the fiberglass bats? Just want to be sure I understand....

What is EPS? How muc is it, where do I get it? Isaw what appeared to be white styrofoan at HD..is that EPS?


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RE: Finished basement no XPS?

am I to understand that all finished basements prior to XPS are filled with mold?

No such thing as all!

But basements with the biggest problem are those in mixed climates--cold in winter, hot and humid in summer--AND which have warm side vapour barriers, or worse yet, vapour barriers on both sides. Homes built in that manner have failures within as little as a year from completion.

But I've personally taken apart literally dozens of finished basements not built in that manner that also had rampant mould from water leakage, capillary action and floods.

Mould prevention should be a concern for every builder and homeowner.

Expanded polystyrene board
Expanded polystyrene insulation Raylite brand

EPS is expanded polystyrene, the white stuff, which is also acceptable and recommended for basement use by Building Science.

Mechanical dehumification is absolutely essential in keeping basement humidity levels low.

Here is a link that might be useful: Mold (EPA)


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RE: finishsed basement no XPS?

OK, well, the dude who was going to do it said 'its your money', so maybe I should wait and get it. I see the 3/4 XPS is the same price as the white styrofoam stuff...maybe I will use that. I hope 3/4 is enough. If I dig down and see that this stuff is on the outside of the home, is it still necesary? (The home is 20 years old--not even sure if this XPS stuff was around back then)


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RE: finishsed basement no XPS?

3/4" EPS has a lower R factor than 3/4" XPS. 3/4" XPS may be all you need when combined with fg to the interior without a vapour barrier. Depends on your climate. It would be exceptionally rare to find XPS on a foundation exterior; and if it were there, you'd likely see it without digging, as it would continue above grade to insulate the sill and rim joist area.


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RE: finishsed basement no XPS?

If you used 1" XPS with no fiber glass, your increased costs are minimal when you factor in your savings from not having to buy the fiber glass insulation. Just a thought.


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RE: finishsed basement no XPS (follow up)?

Just did some quick numbers and a roll of kraft faced R-19 is going to run you about $32...this is enough to cover 10 linear feet of wall. $32 will buy enough 1" XPS to cover 12 linear feet of wall. Your R-value will be less with the XPS, but more than likely sufficient for a basement.


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RE: finishsed basement no XPS?

I was just at HD. I see 1" R5 XPS, 2 X 8 sheet (2 linear feet?) is $8.50. 12 linear feet = $51.

I see R13 fg bats, 40 sq ft for $10 (about 5 linear feet). 12 linear feet = $24.

The fg appears waaaaaaay cheaper and offers almost 3X the R value...though I likely do not need it. I was at an Easter party, I found no one who used XPS in their basements. Homes ranged from new to 40 years old. The one new home owner insisted he had it on the outside of his basement. We all live in Eastern PA...if that makes a difference in so far as whether or not it is necesary. I wonder if it is required by code?


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RE: finishsed basement no XPS?

The HD's near me have 1" 4x8 XPS for $10 a sheet. Are the fg bats you referring to faced? The faced fg is what you would want to use and that is more expensive. I was also quoting 6.5 inch thick fg insul, not the 3.5 inch stuff. I have a Menards flyer in front of me and they have R19 Faced, 6.5 inches at $17.38 for 49 sqft or $30 for 87 sqft. I personally would use the 6.5 inch fg and if you look at the cost comparisons your right in line with XPS.

It is all going to be a matter of preference...I personally would sacrafice the R-Value for the mold protection XPS offers...if I wasn't going to use XPS...I would probably be looking for a higher R-Value...which in the end makes the costs too similar for me to not go with XPS.

I don't think XPS is required in many places by code and most places are still using out dated techniques that will result in mold problems down the line.


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RE: finishsed basement no XPS?

Well, you have a hell of a deal at your HD---are you sure those are 4 X 8 and not 2 X 8s???

I was looking at R13 unfaced.

Re:
I don't think XPS is required in many places by code and most places are still using out dated techniques that will result in mold problems down the line.

To play devils advovate, if this is true are there not hundreds of thousands of homes out there then with these mold problems.

If so, why is XPS not required by code.

BTW, where are you...it may be worth a trip to your HD!


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RE: finishsed basement no XPS?

Yeah...I'm sure. I just bought 8 of them 2 weeks ago.

"To play devils advovate, if this is true are there not hundreds of thousands of homes out there then with these mold problems.

If so, why is XPS not required by code.

BTW, where are you...it may be worth a trip to your HD!"

Quite honestly...I think if opened up the walls in these homes basements, you would find evidence of mold. Others, on here in the trade could probably provide more concrete evidence. I think codes are slow to catch up with the latest and greatest building alternatives...XPS may soon become code some day. I would foresee it being required on the exterior before interior, as it is used often in new construction this way.

I'm in Michigan, so with the price of gas, probably not worth a trip to my HD. Check Menards if you have them in your area...the 3/4 inch XPS is in this weeks flyer, 4x8 for $8.95.


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RE: finishsed basement no XPS?

The "standard" basement insulation in the US and Canada is fiberglass behind tightly sealed vapour barriers. It meets Code. Only a minority of custom builders, perfectionists and informed homeowners are willing to spend the extra dollars for methods and materials advocated by building scientists.

XPS is only one of several healthy alternatives to fg, others of which are spelled out above.


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RE: finishsed basement no XPS?

well, if its half the price at other HDs I'll make a trip otherwise it a very pricey alternative where I am at.


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RE: finishsed basement no XPS?

Maybe you could talk to your local HD and ask them about the price - see link.

This is my local HD, but it would seem that HD would have standard prices across the Country. Note the 4x8 1" XPS for $9.88.

Here is a link that might be useful: 1


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RE: finishsed basement no XPS?

it would seem that HD would have standard prices across the Country.

Absolutely not! Prices vary by store. It's a way to try to stay competitive and profitable, especially in face of declining sales. Given the choice, I avoid HDs serving upscale neighbourhoods.


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RE: finishsed basement no XPS?

Well to be competitive they should offer price matching...especially among their own stores


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RE: finishsed basement no XPS?

Interesting point! I understand that they do price match "competitors" plus 10%.


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RE: finishsed basement no XPS?

Well, the are not matching. Lowes had a blue colored Dow product that is 4 X 8 that says stryfoam and is labelled at R2.9. Its either 1/2 or 3/4 inch. Its $10 a sheet. They also have 4X8 white strofoam sheet but they have foil on one side. Can either of these substitute for the pink stuff...its almost half the price....


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RE: finishsed basement no XPS?

The 3/4" Styrofoam is extruded polystyrene. The foil covered board is designed for use in an attic, not a basement.


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RE: finishsed basement no XPS?

ok, the Dow blue stuff is half the price of the pink at HD. I guess Lowes gets my business. Can I just use PL2000 or something to put it up? Is is betst to do lines of PL200 or globs (dots). How much is needed per 4 X 8 Sheet.


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RE: finishsed basement no XPS?

The blue stuff from Lowes will work fine for your application. It's funny, because the Blue Dow stuff at Lowe's around me is twice the cost of the pink stuff at HD. I think you want to use PL300, not 200 for the foamboard. I think you will want to do vertical lines about 8-10 inches apart from each other and this will take about 3/4 of a tube for each 4x8 sheet.


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RE: finishsed basement no XPS?

I am glad I asked I was thinking 5 or so blobs of glue would do it as the 2X4s would then be braced up against it. The only bad thing about hte blue stuff is that it does not interlock into each other like the pink. Oh well...


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RE: finishsed basement no XPS?

No it doesn't interlock, but you can tape the seams and you'll be fine.


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