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Basement Insulation - What is the Best Method?
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ralpharch




Joined: 02 Nov 2007
Posts: 211
Location: Derwood


PostLink    Posted: Mon Nov 16, 2009 7:54 pm    Post subject: Reply with quote


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AnalogRocks wrote:
Wouldn't you also add weeping tiles at the same time you do your exterior insulation?


I'll have to look back at my reference for insulation outside the basement (trenching etc.). In my case I already have a drainage system installed under/outside the house footers - and I wouldn't be going that deep or disturbing the existing french drains. Even though I noted several times above my basement was flooded to several inches through the joint at the floor, in the cases to-date three were caused by breakage of polybutelene plastic supply pipe by Shell (corporation that ended up shelling out $2k for each of the threee houses that broke (the water travelled along the pipe trench from the other houses - even across the street to my basement) - but the payment was limited to actual events for 12 years after installation so I had to wait for the crap to break or spend the money on my own) - and once from an exterior grading situation that was then fixed.

So my tile system is working well unless it gets overwelmed as-above - which shouldn't happen again. Don't know if I would need one half height up the basement as well but I will look into it.

This would not have helped with the leak I got from the AC condensor drain pan, nor other miscellaneous leaks. And there is always some limited condensation from the colder concrete temperature to the relatively warmer basement humid air.

Bottom line for me and many others is that you are going to get mold in a basement if you insulate inside and use a vapor barrier - so why cause a worse problem than the heat you are trying to save? (My basement was insulated on the inside down to the freeze line by the builder, as are many others down here).
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ecrabb
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PostLink    Posted: Mon Nov 16, 2009 8:24 pm    Post subject: Reply with quote

Ralph,

Why did the builder only insulate to your frost line? Why not just stick a whole 4x8 sheet in and go as deep as possible? It's not like it still isn't damn cold below the frost line! A 40-degree wall may not be freezing, but it's still a giant 40-degree heat sink! Also, how do you treat the exposed exterior XPS above-grade? That's something I've always wondered.

Since I didn't figure this whole basement insulation thing out before my foundation was backfilled, I couldn't exactly dig out the entire foundation of the house, so I had to insulate on the interior and let the foundation "go cold" on the exterior. So, I used 1-inch R-6.5 XPS on the interior facing the concrete, then framed in front of it and lightly filled the wall cavity with un-faced R-13 fiberglass batt. With the XPC facing the concrete, the moisture-laden interior air shouldn't ever condense anywhere, and I have a ~R-20 basement wall assembly. Since we can go several weeks in the winter here without the temp getting out of the single digits, that concrete can get COLD. I want a warm, cozy basement. Since the XPS is sealed, any water intrusion from the exterior (should it ever happen) should weep to the bottom of the wall assembly and run onto the floor. Since my floor covering isn't directly on the concrete, I'm hoping I don't ever see any mold.

SC
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CRT_Ben




Joined: 28 Aug 2006
Posts: 1684
Location: Northern Virginia


PostLink    Posted: Mon Nov 16, 2009 8:27 pm    Post subject: Reply with quote

I'm following this with great interest as I hope to finish the rest of my basement within the next 6 months or so. I have no idea what to do for insulation because there are so many conflicting opinions and real-world accounts Sad

Any thoughts from our resident builders? Joel, Ron, ?
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zaphod




Joined: 16 Jun 2006
Posts: 2002
Location: Cloverdale


PostLink    Posted: Mon Nov 16, 2009 8:41 pm    Post subject: Reply with quote

out here in BC, code has the builder insulate to frostline and so that is what they do. i just moved into a new house and that's the deal. FWIW, they also put vapour barrier on the warm side of the insulation, acoustical sealant (ooohh how i hate that stuff) and then drywall. i was told that's current code in BC.


16 years ago when i finished my basement in Ontario (London), code had me frame the walls, put in batts of fiberglass, vapour barrier the warm side (with the lovely acoustical sealant of course) - and this is the weird part - extend the vapour barrier UNDER the bottom plate and up the wall on the cold side of the insulation about 2 feet.

this protected the wall and insulation from moisture from flooding, but still let the wall breathe on the cold side. i'd never heard of this method before (and haven't since) but that's what the govt. docs aimed me at...

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ecrabb
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PostLink    Posted: Mon Nov 16, 2009 9:03 pm    Post subject: Reply with quote

zaphod wrote:
this protected the wall and insulation from moisture from flooding, but still let the wall breathe on the cold side. i'd never heard of this method before (and haven't since) but that's what the govt. docs aimed me at...


Here's the problem with the whole "breathe on the cold side" idea. Have you ever seen water evaporate when it's cold? No. It doesn't. It takes forever - and that's if it's in wide-open ambient air. Forget about it if it's in a retarded, semi-permeable "container".

It takes energy (warmth) to evaporate water. So, say you do it like code said, with the vapor barrier on the warm side. Nothing's ever perfect, so there's going to be break somewhere... Say, one of the 1,000 holes made by drywall screws. Anyway, all winter long, you've got warm humid air interior and cold, dry exterior. Thermodynamics dictates that there will be a "flow" from warm to cold. So, anywhere there's void in the vapor barrier, the warm, moisture laden are goes there. It migrates through the insulation until it hits the cold foundation, condenses and sits there. It never dries because it's cold. All winter.

OK, now comes summer. You think, "great, now any moisture that accumulated over the winter can dry. Two problems with that: Now we've got warm, humid exterior air and a cool interior, so thermodynamics says the "flow" will go from exterior to interior now, so we can't dry to the exterior... Unfortunately, we can't dry to the interior either, because we have a vapor barrier, and because it probably isn't that dry in the interior, anyway - it's a cool basement in summer.

So, basically, in a northern climate, the code for how to build a basement wall assembly is a recipe for mold growth. You're basically creating a winter-time moisture sponge that never has any way to dry. There are photos all over the internet of sub-grade wall assemblies done just like that - to code - which are all full of mold.

I don't know why the building officials (and building code) continue to insist that below-grade wall assemblies be built exactly the same as above-grade wall assemblies, when all the evidence points to the contrary. How many people have to tear apart their moldy, musty, damp basement walls (that were built to code) before the codes are updated?!?!!?

SC
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ronholm




Joined: 26 Jan 2007
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PostLink    Posted: Mon Nov 16, 2009 10:47 pm    Post subject: Reply with quote

HAHAHAHAHAHAHAHAAAAA....


I hate to laugh and join the line of thousands of other remodelers that are just to cool for codes.... But yeah... SC.. That makes me laugh...


Sorry..


Now what we need is another organization that can regulate them building code folks... Rolling Eyes

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zaphod




Joined: 16 Jun 2006
Posts: 2002
Location: Cloverdale


PostLink    Posted: Mon Nov 16, 2009 11:02 pm    Post subject: Reply with quote

slightly different topic, but Ron and SC - have you ever heard of the leaky condo stuff up here about 14 years back (and still going on).

apartment condos out here were built to code, but the code was flawed (no eaves, bad envelope issues and so on) and mold grew inside the walls. entire buildings had to be stripped down to the drywall FROM THE OUTSIDE. yep, the stucco/siding came off, then the Tyvek, then the insulation and then rebuilt back properly. cost each unit owner in the 10's of thousands of dollars. people went bankrupt, walked away from mortgages, the market crashed.

some condos that got repaired have had the same problem reappear.

here's the bad part. either code was wrong, or the developers were not building to code, or the city inspectors were corrupt, or some combination of that, but the last person who has fault in this mess is the homeowner. but who got left holding most if not all of the bag? yep. the homeowner.

there were some govt. handouts and programs but they only covered part of the cost and the programs ended a while back. we still have buildings wrapped in plastic and netting, but there's no money to pay for the repairs today except for out of the homeowners pocket.


bah.

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ronholm




Joined: 26 Jan 2007
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PostLink    Posted: Mon Nov 16, 2009 11:03 pm    Post subject: Reply with quote

CRT_Ben wrote:
I'm following this with great interest as I hope to finish the rest of my basement within the next 6 months or so. I have no idea what to do for insulation because there are so many conflicting opinions and real-world accounts Sad

Any thoughts from our resident builders? Joel, Ron, ?


Most of my basement was poured in the seventies... The original foundation for my home consists of an old footing for a grain silo from where the railroad ran through my back yard in the late 1800's early 1900's...


When I finished the "new" part of my basement I built it cheap and easy.. 2x4 walls with treated bottom plate... The wall cut short about 1/2 inch or so of the floor joist above so that the walls never carry the load above them should the concrete move around... I leave about 1 to 2 inches of airspace b/t the studs and the walls... and insulate with standard paper faced batts...

Typically when finishing basements this way there will always be some place available to make certain you have plenty of air movement to ventilate the space behind the wall... Heck... I done plenty of mitigation for flooding basements and have never seen any issues behind a wall around here constructed in such a manner... Even on a couple that had been wet for some time...

The fiberglass insulation is tough to grow mold on... and you can get mold resistant drywall....



But as SC said... if you seal that space up behind the wall TIGHT... Well... he explained it pretty well... That space must breathe just like your attic...

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ronholm




Joined: 26 Jan 2007
Posts: 12111



PostLink    Posted: Mon Nov 16, 2009 11:13 pm    Post subject: Reply with quote

zaphod wrote:


here's the bad part. either code was wrong, or the developers were not building to code, or the city inspectors were corrupt, or some combination of that,

bah.



Yeah I can take a stab at that... in order..

Yep...

Yep...


Oh yeah...



and most certainly...



So you have a code system that is very often flawed... Administered by a bunch of clowns that have never built a damn thing in their lives checking up on guys who are in it to make money... and well...


Yeah... nothing could go wrong here...




In a city not far from where I live one on my subs had to take the city to court over BS like this... The local guys who well... lets say know where to spend twenty bucks here and there were getting chit passed without the inspector even setting foot in the home... and my guy... He failed inspections everytime... Stupid chit.. like the staple was 6 and a half inches from the electrical box instead of under the required 6 inches... Every single time they would fail his inspection the first time around...

He started video taping his work... and the "comparable" work next door... even managed to get the inspector passing an inspection without entering the home on tape.....


He sued the city and won... now... well... instead of real inspections he gets the same treatment as the local guy...

problem solved right???? Rolling Eyes

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ralpharch




Joined: 02 Nov 2007
Posts: 211
Location: Derwood


PostLink    Posted: Tue Nov 17, 2009 1:04 am    Post subject: Reply with quote

ecrabb wrote:
Ralph,

Why did the builder only insulate to your frost line? Why not just stick a whole 4x8 sheet in and go as deep as possible? It's not like it still isn't damn cold below the frost line! A 40-degree wall may not be freezing, but it's still a giant 40-degree heat sink! Also, how do you treat the exposed exterior XPS above-grade? That's something I've always wondered.

..........


I may have said that wrong. What my builder did, and I have seen in many homes around here with unfinished basements, was to run 4 foot-wide aluminum foil faced fiberglass insulation around the basement interior walls at the top of the walls, so leaving the bottom 5 feet or so uninsulated.

The reference I was referringto above was the Black & Decker Complete Guide to Finishing Basements.

My son bought 3 finishing my basement books and I thought this one far better than the others.

I misquoted the specifics of what they recommend though. Looking again - they firmly recommend insulating from the outside (but give directions similar to aboveif you have a dry wall - rigid foam against the inside wall then insulate inside with a frame and fiberglass but leave a gap for air to circulate- and no vapor barrier).

The recommended approach was to dig a 24 inch wide and 18 inch deep trench at ground level, fill 2 inches sand in bottom to slope away from foundation, cover the bottom of trench with rigid foam and seal to foundation, install drip edge flashing to protect top of insulation boards, then install rigid foam boards under the flashing and seal and tape to the board on the trench bottom, then install siding or other protective layer over the rigid foam and then backfill.

This all assumed you have a good drain tile system at the footers, and the book says this realizes 70% of the energy savings of insulating the entire wall
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ronholm




Joined: 26 Jan 2007
Posts: 12111



PostLink    Posted: Tue Nov 17, 2009 3:26 am    Post subject: Reply with quote

insulating from the outside is by far the best way to go about it... The insulation not only insulates but it will protect whatever waterproofing membrane you have on the outside of your foundation from rocks and debris as the ground moves that stuff around during freeze/thaw cycles.

To do this the right way you dig out to the footing and apply any number of waterproofing membranes... proper drainage and the insulation... that is about the only way I would guarantee with 110 percent certainty that a leaky foundation was fixed for good... but you are not looking to fix a wet basement...

. and I wouldn't think worth the expense JUST for the insulation benefits.. (even just insulating the top couple feet) but it might be...

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wowchad




Joined: 29 Oct 2009
Posts: 53
Location: Milwaukee'ish, WI


PostLink    Posted: Tue Nov 17, 2009 5:44 am    Post subject: Reply with quote

ecrabb wrote:
...Also, how do you treat the exposed exterior XPS above-grade? That's something I've always wondered.


SC


I did mine the same way ecrabb explained but with 2" on the outside, 2x4 walls with batt on the inside and all we did was buy a hot-knife off eBay for cutting hobby and construction foam then cut off the top of the foam at an angle below grade.
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CRT_Ben




Joined: 28 Aug 2006
Posts: 1684
Location: Northern Virginia


PostLink    Posted: Tue Nov 17, 2009 3:35 pm    Post subject: Reply with quote

ronholm wrote:
Most of my basement was poured in the seventies... The original foundation for my home consists of an old footing for a grain silo from where the railroad ran through my back yard in the late 1800's early 1900's...


When I finished the "new" part of my basement I built it cheap and easy.. 2x4 walls with treated bottom plate... The wall cut short about 1/2 inch or so of the floor joist above so that the walls never carry the load above them should the concrete move around... I leave about 1 to 2 inches of airspace b/t the studs and the walls... and insulate with standard paper faced batts...

Typically when finishing basements this way there will always be some place available to make certain you have plenty of air movement to ventilate the space behind the wall... Heck... I done plenty of mitigation for flooding basements and have never seen any issues behind a wall around here constructed in such a manner... Even on a couple that had been wet for some time...

The fiberglass insulation is tough to grow mold on... and you can get mold resistant drywall....



But as SC said... if you seal that space up behind the wall TIGHT... Well... he explained it pretty well... That space must breathe just like your attic...


Thanks for the info - how critical is the gap between the studs and the wall if you're insulating only with paper faced batts? I just ask because it eats up a bit more room space. Alternately I could frame with 2x2 but that might be a little flimsy. What do you think of using the XPS directly against the concrete?

SC - is the XPS fastened to the concrete or just held in place by the studs?

Knock on wood, we don't really have any moisture problems that I know of, and the basement isn't musty or damp, and we don't run a dehumidifier. It helps that it's a split-foyer so half of the basement is above ground.
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WanMan




Joined: 19 Mar 2006
Posts: 10273



PostLink    Posted: Tue Nov 17, 2009 4:20 pm    Post subject: Reply with quote

Sounds like the performance you will get in your application is more acoustical than thermal. I say this because I can. Very Happy
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ronholm




Joined: 26 Jan 2007
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PostLink    Posted: Wed Nov 18, 2009 12:49 am    Post subject: Reply with quote

The gap behind the studs is handy because the concrete guys do their best... but quite often don't build things square or plum... Moving the wall out a bit from the concrete wall allows you to build it both plum and square... as well as cutting the total wall height short of the joists allows you to build the walls on the ground and then stand them up... typically 3/4 of an inch is good.. but I can assure you that you concrete floor isn't perfectly flat... so that gap also makes the process go a bit smoother... Not to mention.. if you shoudl ever need to retrofit any wiring into the wall that gap is amazing thing to have....




rarely I will lay 2x4 flat... (most of the time they are cheaper than decent 2x2's anyway) or rip some 2x4's in half.... and I have secured them (treated) directly to the concrete.... (tapcons and or hardcut nails) in areas like a staircase... or whatever whenspace really becomes an issue... But I wouldn't ever dream of doing that anywhere it isn't required... I would give up the four inches....




Also keep in mind fire codes... Quite often I have been required to install fire blocking so that should a fire break out in the basement and penetrate the drywall it would not just have free rein in a floor joist cavity....



And if you are doing it yourself... Building "drops" and boxing out to hide the HVAC and beams is very easy if you know a couple tricks... in fact... You can make those look really cool on the cheap with very little effort..

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ecrabb
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PostLink    Posted: Wed Nov 18, 2009 2:06 am    Post subject: Reply with quote

CRT_Ben wrote:
SC - is the XPS fastened to the concrete or just held in place by the studs?

You can use a special panel adhesive. Dry fit the panel, put a few dollops of panel adhesive in few spots on the back, tilt it up, and stick it on. I have gaps of between 0" and 1/2" between the studs and XPS, depending what the foundation and studs were doing in any given spot. That gap isn't super-critical, though like Ron said - it's nice to be able to pull wire behind it without drilling through every stud.

ronholm wrote:
And if you are doing it yourself... Building "drops" and boxing out to hide the HVAC and beams is very easy if you know a couple tricks... in fact... You can make those look really cool on the cheap with very little effort..

Oooh, oooh... Do tell. I've got a giant trunk pretty much running the entire length of my basement, and I'm trying to decide the best way to "use" it so it isn't just an obnoxious gyp box. The damn thing is nearly two feet wide, and will be pretty tight at probably 6'9" or so - a big presence. To frame it, I was going to just build a simple OSB and 2x wrapper (stuffed with fiberglass to dampen the air handler noise), but I was trying to think of a cool way to finish it... Tray? Lights? Baltic birch wrap with routed pattern reveal? What's you're "make it look really cool" trick? I'm all about the "little effort" methods.

Thanks, Ron!

SC
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ronholm




Joined: 26 Jan 2007
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PostLink    Posted: Wed Nov 18, 2009 3:35 am    Post subject: Reply with quote

Yeah.. what we always do is use OSB cut like you say... that goes fast... just slam some nailers up on the cieling... and rip OSB to 12-14 inches wide and pop it up there... Then make sure to stick some 2x4's (we rip them to 2x2 some times) to the along the bottom of the OSB to keep things straight... The "trick' is to not just wrap ONLY what needs wrapped but use the lowered part of the ceiling to dived space .... and well... just a few more minutes dropping the ceiling around the perimeter... Nail all those scrap 2x4's pieces you didn't want to carry out anyway to the inside of the OSB... and a few sticks of crown later... and all the sudden it doesn't look like you are just hiding mechanicals anymore...

The last basement I just finished up is a little overdone (at customer request) with these faux vaults.. and due to the Christmas lighting work picking up (to say the least) I haven't taken shots of that one yet... so remind me to post pix in a couple weeks if I haven't by then... becuase it is a perfect example of what I am talking about...

but here... These are shots of my favorite customers basement finish. Laughing it isn't the most spectacular by any stretch of the imagination... But if you look closely at the pictures I am sure you can make out the challenges the mechanicals made for me... All that stuff was totally in the "wrong" spot... but.... I think we came up with a perfect solution for the customers needs... In that tiled area is now a bar with cabinets I built... I think it looks really pretty outstanding for a 1000sq ft finish that was completed for well under 30K

(For some reason I can't find the pix on this machine of the completed job... I only have these Rolling Eyes the rest are in my "pitch book" but aaarrggg.... )




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wowchad




Joined: 29 Oct 2009
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PostLink    Posted: Wed Nov 18, 2009 10:05 pm    Post subject: Reply with quote

That ceiling is pretty bitchin, I can't wait to see what you consider "a little overdone"
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ecrabb
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PostLink    Posted: Wed Nov 18, 2009 10:54 pm    Post subject: Reply with quote

Thanks, Ron! Very nice! I like the fluted wraps for the lallys.

I get what you're saying about the mechanical boxes and I get turning them into an architectural feature instead of just boxing them in... My problem is that I don't really have the room to get too creative - there are challenges.

You know... This is way off-topic for this thread. I really want to talk about this stuff, so I'll start a whole new "creative basement finishing" techniques thread tonight. That could be a cool resource.

SC
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ronholm




Joined: 26 Jan 2007
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PostLink    Posted: Wed Nov 18, 2009 11:56 pm    Post subject: Reply with quote

ecrabb wrote:

I get what you're saying about the mechanical boxes and I get turning them into an architectural feature instead of just boxing them in... My problem is that I don't really have the room to get too creative - there are challenges.


SC



Post some pix... we can figure it out...

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