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Insulating the sill plate when you have a brick veener wall with no weep holes
Last Post 07 Feb 2011 07:23 PM by FBBP. 16 Replies. |
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Partner24
New Member
Posts:31
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| 21 Jan 2011 10:16 AM |
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I have to insulate the sill plate better because there is mold on it (because of existing fiberglass batts). I had a recommandation to apply sprayed urethane foam on it by a specialist. It basicaly make sense, because it's an air and vapor barrier and will prevent condensation on it. But here is the catch:
My exterior walls are covered with brick veeners with NO weep holes. If water get behind the brick, ultimately it ends on the sill plate. Since sprayed urethane foam is an air and vapor barrier, the sill plate would then have to dry from the outside only if it gets moisted. So I fear that by resolving an actual problem by using sprayed urethane foam, I could create another problem that could become very significant over time. Am I right? If so, what would you recommand to get the best of both worlds (preventing problems from the inside AND the outside)? Thank you very much! |
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arkie6
Veteran Member
Posts:1453
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| 21 Jan 2011 01:07 PM |
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Drill some weep holes in the brick veneer. |
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Alton
Veteran Member
Posts:2157
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| 21 Jan 2011 02:15 PM |
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In my part of the country, weep holes are drilled into the vertical mortar joint about every 2' apart. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Dana1
Senior Member
Posts:6991
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| 21 Jan 2011 02:15 PM |
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You fears about the foam are (mostly) unfound. Closed cell foam at less than 2" thickness' isn't a vapor barrier, but at 2" or more it's moderately vapor-retardent. At 1" it's still semi-permeable, and will allow considerable inward drying capacity (~5x more than a kraft facer on a fiberglass batt would), but you really need to treat the masonry wall properly as well. At 1" you're only looking at ~ R6, but it's waterproof to liquid water/condensation, so you can still fatten up the interior-R in a vapor permeable way with unfaced fiberglass batting, using a vapor permeable air barrer (such as a high-perm housewrap, eg. Tyvek) on the interior side. The air-barrier is necessary to limit convection currents from depositing large amounts of condensation/frost on the surface of foam when it's really cold out, as well as to keep the same currents from robbing the batting of it's R value at the temperature extremes. Both the foam and fiberglass are condensation tolerant, and any condensation events that might occur, while temporarily reducing the R of the fiberglass, won't wick into the foam to the wood. Give it an inch of (closed cell only) foam, but not two if you feel it needs maximal interior drying capacity.
The brick veneer needs 3 things: A semi-permeable silane or acrylic masonry sealer (usually not at box stores- see a masonry supply distrubutors) on the exterior to keep it from wicking rainwater & dew into the wall, while still letting it dry via vapor-diffusion to the exterior when conditions allow. Be sure to read the specs- some are design to be true vapor barriers. Then, what arkie6 said- drill weep holes at intervals on the bottom course to release any liquid condensation that might run down the wall. But you also want to drill corresponding vent holes at the top course to allow the cavity to slowly convection-dry, purging any moisture buildup that might occur in the cavity from either inward OR outward vapor drives. With top & bottom holes to allow a slow convection, the cavity behind the masonry becomes a "rainscreen", limiting rainwater intrusion while enhancing the overall outward drying capacity of the assembly. Without the vents the cavity still helps protect the inner structural wall, but it's an order of magnitude less. |
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Partner24
New Member
Posts:31
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| 21 Jan 2011 02:57 PM |
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Thank you Dana! That make sense and I appreciate this wise advice.
That being said, regarding the retrofit weep holes, it's not something that is usually recommended. I've red a lot about drilling holes in the bottom masonry veener to creat retrofit weep holes, but a lot of people say to never do that, because you might end up far worse. Why? Because you can drill and come through the "flashing" behind the brick wall, and if you do, you'll end up far worse than to do nothing because now water will come in your house easier than before if it gets behind the brick.
So I guess that 85% of my dilemma is now resolved because of you and thank you very much!
Another benefit of 1" of spray foam is that I still can see if there is a moisture problem in the sill plate. Even if I'll can't visually, at least I'll be able to remove the fiber glass over the spray foam and use a moisture meter (with pins).
Another question. I live in a cold climate. What R value would you recommend for a foundation? My first tought was to go with 3.5 inches (long terme R value factor of approximately 20), but since foam at this thickness is a vapor barrier (that's what the manufacturer told me), the foundation will not be able to dry from interior and moisture will climb by capillarity and then evaporate to the outside (I have approximately 3 feets of the foundation that is above grade). Would you think that it might create a problem or not? If so, would you recommand to use 2 inches or so instead?
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Partner24
New Member
Posts:31
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| 21 Jan 2011 03:02 PM |
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And lastly, a highly insulated basement wall from the interior keep the warm inside and the foundation will logically frost more because it gets less exposed to the interior warm. Do you guys think it might create a problem over the long term? |
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Dana1
Senior Member
Posts:6991
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| 21 Jan 2011 04:26 PM |
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"Cold climate" means different things to different people- what's your location (or zip code, if USA)??
And what is the approximate R-value of the first-floor walls?
If instead of weep holes, you go with ventilation slits cut into the vertical mortar on the 2nd course of bricks every couple of feet you still get 90% of the benefit, at low risk of damaging the flashing. It should be cut/drilled at an angle sloping outward, to redirect any splash or rainwater running down the exterior outward rather than funneling it into the cavity.
Foundations run below freezing without damage, as long as they're dry enough. If there's too much moisture in the foundation you can get spalling on the above-grade sections from freeze/thaw, but most situations like that can be mitigated with a sacrificial parge. (It's better to dig down and fix the drainage issues though.) This is just one other reason to keep the interior insulation at least semi-permeable, but air-tight. Unfaced EPS allows a higher R than XPS without becoming too vapor retardent (4", or ~ R15-R16). Combined with a studwall and unfaced batting (DO NOT USE KRAFT OR FOIL FACERS ON FOUNDATIONS) you can get reasonably high interior-R, but for truly high-R (R40+), it's much better if at least some of the insulation (preferably the bulk of it) is on the exterior. (Not practical as a retrofit, in most instances.) The stackup & total R needs to be designed for the specific climate though- the R value of the foam sets an upper bound on the R-value of the fiber, but that boundary will vary by climate.
At 3.5" closed cell polyurethane is pretty much a vapor barrier- more vapor retardent than kraft-facers on batts, but still not as vapor retardent as 6-mil poly or foil facers. |
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Dana1
Senior Member
Posts:6991
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| 21 Jan 2011 05:06 PM |
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Posted By Partner24 on 21 Jan 2011 03:02 PM
And lastly, a highly insulated basement wall from the interior keep the warm inside and the foundation will logically frost more because it gets less exposed to the interior warm. Do you guys think it might create a problem over the long term?
It occurs to me that maybe you meant "frost heave", rather than simply freeze, and yes, that can be an issue in VERY cold climates. The solution is to apply some insulation to the the exterior of the foundation wall, and bury insulation on the perimeter of the exterior of the foundation (sloping slightly away from the building, to direct sub-surface rain moisture away) to keep the adjacent soil warmer by earth-coupling it to the deeper subsoil, in much the same way that shallow foundations are frost-protected: http://oikos.com/esb/43/foundation.gif How far out this insulation needs to extend and it's R-value depends on the climate specifics, as well as site-specifics for average soil moisture, etc. (The drier the soil the less likely you are to encounter a problem.) In MN state code even specifies a hard limit of R10 (R13, if fiberglass) to the amount of insulation you can apply to a basement wall, but exceeding that can be safe with some analysis and moderate precaution. All insulated concrete form foundations would be non-compliant, were the letter of the law applied, yet they're being built there every day (well, every day that it's above 20F, anyway.  ) Drainage, and backfill material make a difference. |
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greentree
Advanced Member
Posts:587
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| 22 Jan 2011 12:03 AM |
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Posted By Partner24 on 21 Jan 2011 02:57 PM
That being said, regarding the retrofit weep holes, it's not something that is usually recommended. I've red a lot about drilling holes in the bottom masonry veener to creat retrofit weep holes, but a lot of people say to never do that, because you might end up far worse. Why? Because you can drill and come through the "flashing" behind the brick wall, and if you do, you'll end up far worse than to do nothing because now water will come in your house easier than before if it gets behind the brick.
There's a reason hammer drills have depth rods on them; and if yours doesn't, then there's a reason you can buy drill bit depth collars. |
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Partner24
New Member
Posts:31
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| 22 Jan 2011 06:13 AM |
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Very interesting comments from you again. Regarding the climate, I live north of the border, in Canada. I'm approximately 250 kilometers away from Vermont. It gets cold in winters and warm and moist in summers. Regarding the 1st floor walls insulation, that's the only part of my house that I don't know, but it's fiberglass and the house was built in the 70's. The ceiling is insulated with a R 54 factor (a layer of fiberglass and a layer of blown cellulose). I guess the "frost heave" issue is not a significant risk, because if it would the foundation would already show signs of troubles. But that being said, the foundation is actually insulated with a R-4 factor with EPS. I'll never use EPS or XPS on the inside part of the basement wall! Let me tell you why: The basement is actually 2/3 finished and the previous owner did a very good aesthetic job. But here's the catch: there's a lot of convection behind the EPS panels, so I have a condensation and a mold problems. I need to put all the walls down, remove the mold carefully, reinsulate and finish the walls again! There is a risk with foam boards. They have to fit very tightly to the foundation, or this convection problem will occur. A local mold removal specialist told me that my case is very typical...so typical that he told me the problem precisely before I could have the chance to end my sentence. So, as far as I know, sprayed polyurethane foam remove that mold issue for good and "forever". Same thing with these sill plates. Kraft faced fiberglass, condensation and mold. So I have to remove them, remove the mold and insulate. After having carefully reviewed documentation online, the best solutions seemed to put some foam panels on the exterior side of the foundation and/or insulate the interior with sprayed polyurethane foam. The foundations aren't coated with a damp proofing product. So I guess that anyway, I'll have to at least damp proof them to reduce the capillarity factor associated with the combination of soil in direct contact with the foundation and an overall vapor barrier insulated interior basement wall. What do you think of this idea? 2.5 inches of sprayed polyurethane foam in the inside of the foundation. 1" in the sill plate with adding R 20 fiberglass batts faced with an air barrier but not vapor barrier product like you suggested. On the exterior side, damp proofing (and maybe even water proofing for extra care) and insulating with a R 10 factor the under grade part of the basement wall with 2 layers of 1 inch each extruded polystyrene foam. On the above grade section, simply let the wall uninsulated to maximize the vapor evaporation from the outside, even if it creates a thermal loss because of the uninsulated part. I guess you can see now why I ask these questions. These things will require a lot of work and I'm trying to find the best long term substainable and safe solution to never have to do something like this again. Do you think that would make sense? Any suggestion or comments are very welcome and appreciated. |
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Matt G
New Member
Posts:93
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| 22 Jan 2011 08:55 AM |
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Partner: In order to have mold you have to have a moisture source and I'm not buying condensation as the root cause. There are exterior water leakage problems that are making the structure moist. You have already identified one - the brick veneer with no weeps. I'll bet that one is a ticking time bomb and that you would be absolutely horrified if you were able to see the bottom few feet of wall sheathing behind the veneer - not only mold but rot I'd bet. That is a major moisture source. You have been given a solution for that one though. - drill weep holes. What about your foundation? I think you are already headed in this direction. Is it waterproofed effectively on the outside? A drainage plane really helps too. Is there an effective drainage piping system to get water away from the foundation? Is the surrounding lot and pavement graded properly so as to direct water away from the house? Is the exterior grade below the floor frame level (mud sill)? Is roof runoff being handled so as to direct the water away from the foundation? Does the roof have overhangs? Is there a vapor barrier under the basement slab? Is there moisture coming up from there? Check by taping a 2'x2' piece of polyethylene plastic tightly to the concrete floor and wait several days. What about your kitchen and bath fans? Although probably not related, do they exhaust to the exterior of the home and are they used on a regular basis? Just another moisture source... I'm also not buying this stuff about the types of insulation that were used causing moisture problems. At least some of those ideas came from salesmen trying to sell something. Look to salesmen for information on products - but not necessarily to find out if their product is the right one for your scenario and not necessarily to troubleshoot your problems. They have an agenda - putting food on the table. Having air circulating around is not a good thing and moisture will penetrate the assemblies under those conditions but you still need that source of moisture. Regarding possibly compromising the flashing at the bottom of the veneer when drilling weeps - yes you need to careful about that but what are the chances that there even is flashing? The installer of the brick veneer didn't seem to be too concerned about water penetration. So, in summary, identify the moisture sources and deal with those. Don't confuse symptoms with root causes.  You are headed in this direction but I just wanted to underscore the point. Patch a leaky boat from the outside and the inside will become cozy and dry. Patching a leaky boat from the inside is a stop gap measure that might be done at sea until the vessle can later be hauled out and dealt with properly. |
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Partner24
New Member
Posts:31
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| 22 Jan 2011 01:14 PM |
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Hi Matt,
Good questions.
In order to have mold you have to have a moisture source and I'm not buying condensation as the root cause.
I've hired professionals in that field and they executed an infrared camera test and opened a small fraction of the basement wall and they removed a small part of the polystyrene in the unfinished part. We saw mold on the foundation behind it and they said that it was the main cause of the mold problem. In the small opening, we saw that the 2x4 was directly on the foundation, something that would cause long term mold on the wood because you can't put 2x4 studs directly on the foundation wall in the under grade part of the foundation.
Is it waterproofed effectively on the outside?
The foundation has neither damp or waterproofing stuff on it. That being said, as far as I know, the sand drain water effectively because I've never had a water leakage in my basement since I've owned it and if it was a problem, I would realize it easily I guess because the ceramical tiles lies directly on the concrete floor.
Regarding the drainage piping system, I don't know, but I'm actually also thinking about hiring a specialist to check that out with a camera.
Is the surrounding lot and pavement graded properly so as to direct water away from the house?
Yes.
Is the exterior grade below the floor frame level (mud sill)? Is roof runoff being handled so as to direct the water away from the foundation? Does the roof have overhangs?
Yes.
Is there a vapor barrier under the basement slab?
Unfortunately, I don't know.
Is there moisture coming up from there? Check by taping a 2'x2' piece of polyethylene plastic tightly to the concrete floor and wait several days.
Thank you. I'll try that.
What about your kitchen and bath fans? Although probably not related, do they exhaust to the exterior of the home and are they used on a regular basis? Just another moisture source...
Yes. I call them bombs machines since they remove the moisture very effectively directly to the outside.
I'm also not buying this stuff about the types of insulation that were used causing moisture problems. At least some of those ideas came from salesmen trying to sell something.
They are totally independant. The only thing they have to sell is their expertise and they don't recommend any specific company product, but that was a good point.
Regarding possibly compromising the flashing at the bottom of the veneer when drilling weeps - yes you need to careful about that but what are the chances that there even is flashing? The installer of the brick veneer didn't seem to be too concerned about water penetration.
Again, that's a good point. I saw a black sheet (we call this 15 pounds paper here) behind the sill plate. But I don't know if it's an effective flashing and if there is anything else after that. Actually, when you take a look at the bricks, they are very sane. They look like new. No signs of any significant problem at all, but unfortunately I don't have any idea of what's happening behind them.
Thank you very much for your very sound questions!
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Matt G
New Member
Posts:93
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| 22 Jan 2011 04:50 PM |
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Posted By Partner24 on 22 Jan 2011 01:14 PM
Hi Matt,
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The foundation has neither damp or waterproofing stuff on it. That being said, as far as I know, the sand drain water effectively because I've never had a water leakage in my basement since I've owned it and if it was a problem, I would realize it easily I guess because the ceramical tiles lies directly on the concrete floor.
Sand does drain very well. But you do have a moisture source - that is my whole point - otherwise there wouldn't be mold on the walls. Mold needs moisture. The only question is where is the moisture coming from?
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I'm also not buying this stuff about the types of insulation that were used causing moisture problems. At least some of those ideas came from salesmen trying to sell something.
They are totally independent. The only thing they have to sell is their expertise and they don't recommend any specific company product, but that was a good point.
OK - I misread the source of your information, but the IR camera did identify moisture - Right?. I wonder what it would show if it were aimed at the exterior of the house at the brick veneer floor system/foundation interface. I really think it would show moisture behind the veneer. This can be exasperated by incorrect roof, window, and door flashings too. This whole water management thing is an integral part of green sustainable building, and was recently included in the US EPA Energy Star for Homes program requirements too.
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Regarding possibly compromising the flashing at the bottom of the veneer when drilling weeps - yes you need to careful about that but what are the chances that there even is flashing? The installer of the brick veneer didn't seem to be too concerned about water penetration.
I saw a black sheet (we call this 15 pounds paper here) behind the sill plate. But I don't know if it's an effective flashing and if there is anything else after that. Actually, when you take a look at the bricks, they are very sane. They look like new. No signs of any significant problem at all, but unfortunately I don't have any idea of what's happening behind them.
A sign of moisture problems on the brick could be efflorescence. It is a white stain kind of thing and could either be barely noticeable or very obvious. 15# or 30# felt is commonly used as a protective paper over the sheathing and behind the brick - like housewrap is used. That is not the same thing as flashing though. Take a look at this web site, on the left, Note #7 figure#2. It shows the thru-wall flashing we are talking about - it is shown as black and is either black plastic or a black vinyl like material if the structure is somewhat modern. It comes in either 12" or 18" rolls. If the house is more than 40 or so years old other materials were used. What I don't like about the pic is it doesn't show very well that the flashing goes up under the black paper (actually shown in blue on the fig #2). This is shown a little clearer on fig #3. I can post a pic if you need it.
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Dana1
Senior Member
Posts:6991
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| 25 Jan 2011 04:28 PM |
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Insulating the interior with rigid EPS or XPS can (and must) be done without inducing convection currents- spray-foam sealants work well. Puting EPS between the studs and putting the studs against the concrete is a guaranteed mold-problem- the studs needed to be inside the EPS, where they would be warmer, and protected from ground moisture by the vapor retardency of the EPS.
Batts with or without facers for the sill & band joist was a bad idea, due to the convection-transported moisture issue, and the fact that it's usually impossible to adequately air-seal the facer to prevent those loops. In your climate a kraft facer isn't vapor-retardent enough to prevent wintertime moisture buildup, and the kraft facer just limits the inward drying capacity to much (~0.5perms) for moisture drives from the exterior.
Without climate data for your exact location it's uncertain if that would be enough to prevent condensation on the foam with 2.5" of polurethane with R20 of batting on the interior, but it almost certainly needs to be a higher Rfoam/Rfiber ratio to keep it dry anywhere in Quebec. We can fine-tune it based on your climate if you can find a weather station near you here: http://climate.weatheroffice.gc.ca/climate_normals/stnselect_e.html With 2.5" of SPF you're looking at R15, less than half the total R value (which would be good for most of the US, but marginal at best in many parts of Quebec.)
At 2.5" most closed cell polyurethane foam is also a bit too vapor retardent (less than 1 perm- some are less than 0.5 perms at that thickness) for below-grade use, not allowing the foundation to dry toward the interior. Most closed cell polyurethane is under 1.0 perms even at 2". The better option is probably to go with 2lb closed cell Icycnene MC-R-200 that thickness or thicker due to it's higher perm rating (1.3 perms at 3" thickness, which would be ~ 1 perm @ 4"). With that stuff you can get away with 4" before it's vapor retardency is too high, at which point it's ~ R21. R21 foam combined with R13 batts on the interior the total R-value would be about the same as 2.5" of standard closed cell polyurethane + R20 batts, but importantly, the fiber insulation would likely stay dry all winter. With less foam/more batt there may be periods in winter when the fiber is damp, and the R-value is compromised. (I'm not associated in any way with Icynene, and I actively despise some of their "...you don't need more R than..." marketing arguments, but this particular product in their lineup seems uniquely well adapted to this type of application.) In my area a 3" application of MD-R-200 costs about the same as 2" of closed cell polyurethane from other vendors, and has more R-value due to the 50% greater thickness, despite a lower R/inch. So, 4" should be roughly the same cost as 2.5" of generic closed cell SPF. (Get quotes.)
R10 below grade on the exterior is good, but the huge thermal break of not insulating the above-grade exterior limits it's effectiveness. The thermal short-circuit of the ~R1 concrete is a performance killer.
15# felt paper in a single-layer isn't always enough for unvented brick veneers, but a double layer might be. Bricks are porous, and absorb rain & dew unless they've been sealed. All else being equal, the problems in the interior walls are more likely to occur on the sides where the sun falls directly on the brick, driving it's rain/dew moisture into the cavity to re-condense later on the felt (and brick). Felt is semi-permeable to water vapor, and becomes highly permeable when wet. Unless the cavity is vented to purge that moisture, it stays highly permeable until the moisture is transferred into the wall. (And if you have an interior vapor retarder like poly, so much the worse, under those conditions. Summertime condensation on the vapor retarder is a common source of mold/rot issues in Canada, where interior poly is now prescribed by code.) Ventilating the cavity to the exterior with weeps & top vents purges this type of moisture drive fairly effectively.
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Partner24
New Member
Posts:31
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| 25 Jan 2011 11:33 PM |
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Dana, these very interesting and smart comments from you.
Regarding my specific climate condition, I've used the tool you provided and here it goes:
http://www.climate.weatheroffice.gc.ca/climate_normals/results_e.html?Province=ALL&StationName=drummondville&SearchType=BeginsWith&LocateBy=Province&Proximity=25&ProximityFrom=City&StationNumber=&IDType=MSC&CityName=&ParkName=&LatitudeDegrees=&LatitudeMinutes=&LongitudeDegrees=&LongitudeMinutes=&NormalsClass=A&SelNormals=&StnId=5348&&autofwd=1
Regarding the basement wall, 2.5" of spray foam should suffice without any need to add fiberglass I guess? That would give me a long term R 14.7 based on manufacturer technical sheet. It's product is strongly vapor retardant. At 2", it gets just slightly more than 0.5 perm see Heatlok soya at:
http://www.cufca.ca/docs/2lbFoamComparrison_2010_REVG_Press.pdf
So that's why I think that 5 feets of under grade foundation would have a capillarity factor and would need to dry to the outside at the above grade section (just slightly less than 3 feets high) But I guess it would be best to at least damp proof the under grade part of the foundation to reduce that moist from soil contact factor, so that's why I tought about adding XPS foam over the damp proofing product because it would add a little bit of thermal protection, but furthermore a layer of waterproofing to the foundation.
A recent Building science study about insulation and moisture problems provided with different kind of insulation alternatives to basement wall (see case 6 for high use of spray polyurethane foam):
http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis
They rate 3.5 " polyrethane foam on the inside part of the foundation 5 on a scale of 5 for it's durability and they say that concrete is generally not affected by high moisture content. Inspectapedia does not seems to be so sure with that (see buckled foundations: is insulation guilty?). I know that the 4 cases he talk about are extreme, but even your foundations does not buckle, it remain to be seen that it doesn't cause any long term issues...and these issues could be very costly and it could take a long time to realize them since that when your wall is insulated that way, good luck to find problems early with a visual look from the inside.
Cheers!
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Dana1
Senior Member
Posts:6991
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| 26 Jan 2011 12:02 PM |
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I would strongly recommend holding the line at 1 perm for the foam, no lower. At 0.5 perms below grade the foundation WILL run wetter, introducing higher risk of above-grade spalling of the concrete, or rot at the foundation sill. If you KNOW to a certainty that you have a good capillary break between the concrete and foundation sill you might be protected from ground moisture, and let the exterior above-grade concrete provide the drying path. If it shows signs of spalling or efflorescence after a few winters you could then give it a sacrificial parge to protect the concrete. But 3" of mid-density Icynene rather than would be the same R value (at likely lower cost), with more than 2x the inward drying capacity of 2.5" of the Heatlock Soya SPF.
According to the mean January temp is about -11C. If you keep the conditioned space air at 20C/30% RH, the dew point of the air inside the pressure-boundary of the building will be about + 2C. As long as the average temp at the surface of the foam doesn't stay below 2C for weeks on end, the risk of moisture accumulation in the fiber-insulated layer is low. There may be condensation periods during cold-snaps, but it will generally dry before it accumulates sufficiently in mold-susceptible wood to cause a problem. With 50% of the total R in fiber you could even let the basement stagnate at 2 + (11+ 2)=15C all winter without a high risk.
R13-R15 batting is CHEAP relative to any closed cell foam (or even open cell foam), and will likely still be present-value positive despite the diminishing returns that come with the higher R. It's those very curves that Icynene and some other foam vendors use to make the "you don't need more R than..." arguments, but the non-stated truth of those statements that is really being said is "It's not cost effective to go any higher R than this when using a premium priced product like spray foam."
Thanks for the reference to the BSC document on high-R foundations! A couple of things to note regarding that document: The Westford MA prototype house has the necessary capillary breaks on the footing and foundation sill to use high-perm insulation on the interior. Retrofits (particularly but not exclusively on older construction), this should not be presumed. The modeling presumes a water table 3 meters below the slab, which also can't be presumed. In the 3.5" of polyurethane model, they show a capilllary break between the footing & wall, and XPS insulation (which is also a capillary break) under the slab and between the slab & foundation, as well as exterior damproofing on the foundation wall continous with the capillary break at the foundation. In the text they state:
"The concrete is unable to dry to the interior through closed cell spray foam, but concrete is generally not affected by a high moisture content."
The concrete isn't susceptible, but without the necessary capillary breaks, the wood DEFINITELY is. (In the deep retrofits BSC does near me they make extensive use of mid-density higher perm foams for that very reason, eg: https://www.powerofaction.com/media/pdf/DER_CaseStudy.pdf )
Stick with a higher-perm foam unless you know the rest of those factors with certainty. At over 1 perm the inward drying capacity is pretty good. With the unvented brick veneer you may also need that inward drying capacity at the foundation sill for non-winter moisture drives from the exterior as well. If it were my house in your location I'd go with 3" of MD-R-200 + R13 batts, with Tyvek as the interior air-barrier wherever it isn't covered by wallboard, for R28-R29.
In my actual circa 1923 house (and milder-climate MA location) I did semi-permeable fiber-faced iso at ~ R20, with foam sealant at all seams & edges. Since the water table is less than 1 meter below the slab, and is occasionally above the slab after epic rains (!), the foam extends only down to ~15cm above the slab. If I ever hammer out the slab to replace it I'd put ~R16 EPS + 10 mil poly under the new slab, and R20 XPS along the slab edge, extending up to the semi-permeable iso. I had to remove a small section of the iso on the N side of the house to re-route some drains a couple of years ago, and there was no evidence of mold or moisture issues on the foundation or facer- it's doing a reasonable job of drying toward the interior despite significant ground-moisture drives. |
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FBBP
Veteran Member
Posts:1215
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| 07 Feb 2011 07:23 PM |
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Posted By Partner24 on 22 Jan 2011 01:14 PM
I've hired professionals in that field and they executed an infrared camera test and opened a small fraction of the basement wall and they removed a small part of the polystyrene in the unfinished part. We saw mold on the foundation behind it and they said that it was the main cause of the mold problem.
very interesting. Assuming a concrete basement. Neither the concrete or the polystyrene has much "mold food value". Wonder were the mold is coming form? |
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