kschweitzer69
New Member
Posts:64
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| 20 Oct 2010 09:22 PM |
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Had a good discussion on the forum before about my plans to place polyiso on the full exterior of my new home. We are to the point of actually putting the Polyiso on the exterior walls now and a detail that I'm struggling with deciding how to do is this..... We have 10 thick poured concrete walls, we left ourselves a 6" brick ledge. This was to allow us to place 2" of Polyiso foam from the top of the foundation wall up to the roof line and then install brick on the remaining ledge. We have a black plastic that runs from the bottom of the framed wall over the subfloor band board to protect the floor system from moisture. I'm concerned about installing the polyiso directly firm on the bottom against the plastic as the end of the polyiso board is exposed. I feel that there is a possiblity of moisture forming on the surface of the plastic and driving up through the polyiso end. I plan to tape seem the board joints, but am just not sure what do to with the detail of where the board sits on the plastic/concrete foundation wall. Maybe there is not enough moisture potental there to be concerned with. I've read that polyiso should not be used below grade, but don't know how likely water will cause a problem in this situation. Thoughts please...... |
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Dana1
Senior Member
Posts:6991
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| 21 Oct 2010 02:49 PM |
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You're worrying a bit too much, but if you're into it, lapping the plastic under then up the exterior-side facer on the iso and taping/glueing it in place would make a continuous capillary break against any wicking into the iso. Iso is only very modestly hygroscopic, you can't bury it without risk of it becoming saturated, but unless it's sitting in a puddle for weeks on end it won't be soaking up very much.
The intermittency of liquid moisture events in a masonry cavity wall make it not such a big worry- with a well vented cavity it'll dry out reliably & quickly. But I s'pose an undetected plumbing leak into the cavity could eventually damage the iso. |
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kschweitzer69
New Member
Posts:64
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| 24 Oct 2010 09:09 AM |
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Thanks for the piece of mind Dana1. I knew that polyiso was not a friendly with moisture as XPS is, but chose it for my upper level walls because of it's higher R-value and the fact I could get factory seconds very cheap. We have noticed since putting boards up... I guess because the boards are cut exactly square or the foundation wall is not exactly level that occasionally boards cannot but up tight in the seam which leaves a small gap. I'm assuming we want to do more than just tape the seam in that case. Should we just spray foam in between those seems? Another detail I'm struggling with is how to get furring srips installed so that we have a place to mount siding to in a few select places on the exterior of the house. Thanks! |
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Dana1
Senior Member
Posts:6991
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| 25 Oct 2010 11:08 AM |
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Spray foaming the gaps in the seams is the right thing to do. Single-part foam (eg Dow Great Stuff) , or anyone's 2-part polyurethane kit will do. It's sufficiently vapor retardent that you don't need to trim flush and tape over the spray foamed parts,but DO tape over any seams that aren't foam-sealed. |
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kschweitzer69
New Member
Posts:64
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| 25 Oct 2010 09:03 PM |
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Makes sense. Any thoughts on HRV unit for house? Is this something I'm going to need with my insulation practices? I've talked to several ICF homeowners who never bothered with the HRV and don't claim to have any issues. Also wondering your take on a humidifier for the house. I hate getting shocked constantly through the dry air winters we have here. Thanks again. |
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Dana1
Senior Member
Posts:6991
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| 27 Oct 2010 11:43 AM |
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Posted By kschweitzer69 on 25 Oct 2010 09:03 PM
Makes sense. Any thoughts on HRV unit for house? Is this something I'm going to need with my insulation practices? I've talked to several ICF homeowners who never bothered with the HRV and don't claim to have any issues. Also wondering your take on a humidifier for the house. I hate getting shocked constantly through the dry air winters we have here. Thanks again.
HRVs are always a good idea, and you don't need to run them at a 100% duty cycle to get good results. Running it on dehumidistat control in winter set to keep the relative humidity down to 30-35% will use less power and deliver far better air quality than dehumidifiers & filters. In a reasonably (not even super) tight house you'll NEVER need a humidifier in your climate zone (and I mean NEVER!). If the natural ventilation rate is high enough that your humidity drops below 30% RH it's an indication that your ventilation rate is way too high- the place is a veritable sieve. Blower door test the place a soon as the shell is up and windows/doors installed, find & fix all of the air leaks before the cavity insulation is installed. (You may need to sheet-rock the upper floor ceiling if the house will have a vented attic- then don't punch any holes for plumbing/electrical etc. in that without foam-sealing it as you go.) It's not all that tough to hit below one air exchange per hour at 50 pascals pressure on new construction, which is way better than most existing homes. Air sealing is by far the cheapest most cost effective efficiency boost you can build into a place, but you have to have some religion about it- don't let the various trades mess it up as they go. Even as retrofit it's usually possible to air-seal an existing home sufficiently to keep the humidity pretty much above 30% all winter, and it'll be good for heating & cooling efficiency as well. The biggest untreated air leaks are typically the foundation sill & rim joist, and undampered (or poorly sealed dampers on) flues/vents, followed by recessed lighting cans. Fix the big holes first, then worry about the smaller stuff like window weatherstripping & sash-weight cavities, etc. Plumbing & electrical chases that extend from basement to attic (or balloon framing & partition framing with out top plates) have huge stack-effect forces in effect. An unsealed foundation sill (or vented crawlspace) combined with a swarm of recessed can lighting on the upper floor is also huge. When you fix both the top & bottom of the "stack", the relative importance of air leaks in-between falls dramatically (but fix 'em anyway.) |
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kschweitzer69
New Member
Posts:64
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| 28 Oct 2010 10:35 PM |
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I'm not sure I understand your reasoning for us to not need a humidifier. In our climate during the winter the air is very cold and dry. I hate nothing more than getting shocked all over the house everytime I get up off the couch. This is something also experienced in the winter getting in and out of the car. Are you saying proper air sealing and a HRV will provide more humidity? Does a HRV just complicate the house mechanicals more? Will I have problems if I don't install one? I get concerned because I read all the time if not done right a HRV can actually hurt more than help and I'm finding it difficult in my area to find professionals familar with all the things I've thrown at them energy efficency wise. I'm confident my HVAC guy could install the HRV, but probably not having done it before may not know what to look for in a proper installation. I don't have the $$ to bring in energy consoltants from the city to guide me through process, so I"m trying to educate myself best that I can to try to avoid future problems. I know raising the humidity in the house also helps to make the air feel warmer and seems to help hold temperature better causing the HVAC to cycle less. In regards to air sealing, if I understand you correctly more effort needs to be put towards air sealing holes in the floor that extend through the ceiling as well due to stack effect, correct? We are running a double wall flue pipe for a wood furnace in the basement. This will extend through the middle of the house. Do I want that pipe to be insulated double wall from the basement through the roof or do I want to gain heat from the pipe in the upper level and just use the double wall in the attic and upper chimmney space? Should this be foam seal insulated at the floor and ceiling connections in the house? I know its a cardnal sin for energy efficiency, but do plan to use can lights in the kitchen for sure and perhaps the living room. Should those be foamed around the ceiling hole? We are addressing the rim joist concerns by foaming the full exterior of home from top of foundation wall to roofline with 2" polyiso. This should really cut down on air infiltration for this problem area of the house. Once again I appreaicate your professional analysis. Thanks. |
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JohnyH
Basic Member
Posts:114
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| 29 Oct 2010 08:22 AM |
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I'll just put in my two cents, you should reread Dana1's comment on the HRV! If it is a well to excellent sealed home you will need an HRV, you may be surprised at how much humidiity is created by doing meals, dishes, showers/baths, having plants and just by having people in the house will create. Without it you will notice severe condensation on all of the windows on very cold nights and this will hold true for any cold spots on the walls. For the first while your house will also be drying out itself from all of the construction material used.
You DO need fresh air brought in just to make the air in the house breathable and comfortable, an HRV will do it with some energy savings!
I wanted to make a comment when you typed about some ICF homeowners that did not have an HRV, I honestly find that statement ironic. An ICF home should be extremly air tight and an HRV I would have thought to be an essential component to the HVAC system!
Where are these homes, your location? Are they built on grade/slab without a basement?
John |
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kschweitzer69
New Member
Posts:64
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| 29 Oct 2010 11:04 PM |
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JohnyH-
Thanks for chimming in on the conversation. I do hear the points you make and perhaps the dry house problems I currently have are because the house is not tight enough. I'm sure a humidifier could always be added fairly easily in the future should we decide we need it. I'm going to have a wood furnace in this house and I just know how dry the air can get in a house burning wood.
To answer your question the ICF homes I'm referring to and my home is in the Cincinnati, OH area. The only thing I can figure on these ICF homes and maybe why they are getting along without the HRV is that they both have a fairly basic vinyl window installed in them. Probably meets energy star ratings, but certainly nothing special. I know both of these homes also have fiberglass blown in attic insulation. Perhaps this is where all the air exchanges are taking place. I will say that both of these homes are over 2000sqft in size and both have full ICF basements under them. |
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JohnyH
Basic Member
Posts:114
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| 30 Oct 2010 12:54 PM |
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Just a question, are they jsut ICF basements, that would explain some of it?
Im in Ottawa and living in a custom built home that I had built 23 years ago, all stick built, wood foundation double wall. I took a lot of time and work to ensure a tight house, I would never even have thought of not having a HRV and just recently replaced it with a new one, I think it was three years ago. I have an air tight wood stove in the living room, ground floor (its a two story) that sometimes farts into the house until I have it figured out every fall, it can keep the house warm over night and of absolutely no use when it's sunny out even at -30C! It never drys the house out and when it gets to -30 c overnight which it will in mid to the end of January I do get some condensation on the bottom of the windows (all extruded vinyl frames from Germany, lowe, argon).
The HRV brings in fresh air and removes the stale odours, humidity and other isssues that I'm probably not aware of (radon, never tested for it)!
I will be putting one in my new house that I hope to build in the next year!
All I can think of is the homes must be bringing in fresh air somehow to not be having a condensation problem in the really cold months but the fesh air is absolutely needed! At least design the HVAC system to be able to add one at a later time.
John |
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Garth Sproule
New Member
Posts:25
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| 30 Oct 2010 07:31 PM |
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In our climate (cold windy Saskatchewan) it is not unusual to experience low RH levels in mid winter even in very well sealed homes with HRV's. One thing that has been tried, is to swap out the HRV core with an ERV core for the winter months...helps to retain some of the outgoing moisture. Have not read any reliable reports as to it's effectiveness. If you do try this, you must monitor the indoor RH with an accurate humidistat to be sure it does not exceed dangerous levels. |
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JohnyH
Basic Member
Posts:114
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| 30 Oct 2010 09:03 PM |
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The newer HRV have duty cycles, 20 minutes on 40 minutes off and adjust the speed for volume of air displaced! I have not had an issue of drying out the house but do pay more attention to the plants. (well my wife does)
John |
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ghocker1
New Member
Posts:10
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| 11 May 2012 06:24 PM |
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kschweitzer69 - We are in the same place in Cincinnati that you were 18 months ago. We are building 2x6 home in Mason and trying to get our GC to adopt some new thinking in insulation (insulated sheathing, Zip system option, etc.) I recognize that air leakage is the number one priority, but followed by R and moisture issues. I like you was very concerned about condensation with improved insulation (oc or wet spray cellulose) It generates more questions than I can answer around wall thickness requirements, vapor barriers, etc.
I've hired an energy consultant to help out, but if you have a minute I would love to connect to hear more about your journey. |
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ICFHybrid
Veteran Member
Posts:3039
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| 11 May 2012 10:47 PM |
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kschweitzer69 hasn't posted in over a year. You might try asking your questions by starting a new thread. There are a number of people here who can probably help |
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kschweitzer69
New Member
Posts:64
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| 11 May 2012 11:00 PM |
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ghocker1 - I'd be happy to share my experiences with you. Having lived in the house for nearly a year now I can offer some further perspective. We are very happy with how things have turned out on our project. I not only was about building energy efficient, but also getting the most bang for my dollar when upgrading to superior consturction methods. Please send me an email at [email protected] and we can communicate that way. Or we can exchange phone numbers if you rather do that. More than happy to share. We built our home on family farm in Winchester, OH about an hour from where you are at in Mason. |
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