Boontucky-girl
Basic Member
Posts:250
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| 17 May 2010 03:01 PM |
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We're building a house on our own, one thing at a time as we save up money for it. The plan is to move into the basement (which is ICF) and live there for a few years, but b/c of budget, we can't afford to install the heating for the main floor this year like we planned, nor the insulation in the walls just to keep it from freezing, or to keep the heat in the basement.
So we've considered closing off the stairwell, covering the subfloor on the main floor with plastic, caulking it to the bottom plates of exterior walls and taping seams, and unrolling r-38 rolls of fiberglass on the main floor turning it into a sort of attic to get us through the winter. The basement level is heated with radiant in-floor heat. But we're wondering if that will create moisture problems in the main floor from heat from the basement if we do it this way? I know that technically we won't have hot air rising to the main floor, but we'll still have infiltration issues since that would not be airtight. The HRV would be hooked on providing ventilation for the basement, but not sure if moisture will be an issue in the basement as well?
So I'd like opinions or suggestions as to how we might make this work? Thanks.
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Dana1
Senior Member
Posts:6991
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| 17 May 2010 03:56 PM |
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If you're laying the fiberglass atop the subfloor of an unfinished first-floor that should work just fine. The sub-floor will be on the warm side of the insulation, and the plastic sheeting will keep moisture from the heated basement from infiltrating to condense/frost in the fiberglass. Air leaks at the access doors & plumbing/electric penetrations should be attended to, but you needn't go crazy on it. Even if you had some minor air leak & condensation issues it would be near-impossible to be so bad as to create serious mold or rot issues in a single heating season, after which you tookl up the insulation & plastic giving it all plenty of drying exposure.
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Boontucky-girl
Basic Member
Posts:250
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| 25 May 2010 08:24 AM |
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Thanks Dana1. That is what I had thought, but we had a contractor say that moisture buildup in the main floor was going to be so bad we'd be rotting out our subfloor, and that's what got us wondering if that would happen or not.
It shouldn't be too hard to seal up since most of the plumbing penetrations already have been foamed, and there's really not much done for electrical, and we do plan to roll up the insulation in the spring so we can work upstairs again.
Again, thanks. |
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Boontucky-girl
Basic Member
Posts:250
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| 01 Sep 2010 10:36 AM |
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The basement is heated with radiant heat, and we don't have A/C yet, so no blower unit in there yet and not in the budget to install until next year. We do have the ductwork already installed, since we're doing things in stages. My question is how to provide proper ventilation for just the basement since it is ICF, rim joist will be spray foamed and as mentioned before plastic will cover the main floor. O plan on doing a decent job of sealing that plastic I think the basement will be tight enough that we'll need ventilation to bring in fresh air, since opening windows is not really much of an option in below zero temps.
I was thinking that we can have an HRV installed, but will that be possible without having a blower unit? Also, since there is no forced air heat, would we need something to warm up the incoming cold air during the winter? What about humidity? Do HRV's deal with humidity? I know winter season is typically dry around here in Iowa, but I'm wondering if the basement will be tight enough that humidity might be a problem? I'd like a whole house humidity control someday, but not in the budget right now.
So if I needed to run a portable dehumidifier (or two) what would be the best way to control them so they keep moisture at decent levels?
Thanks for any comments or insight!
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Dana1
Senior Member
Posts:6991
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| 01 Sep 2010 11:55 AM |
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HRVs purge humidity, and don't add any to the incoming ventilation air. But for a temporary situation a simple low-volume bathroom exhaust fan either running constantly (or under dehumidistat control set to 30% RH in winter) could provide sufficient ventilation air in a mostly air-tight ICF house/basement.
During the muggy summer when the dew points are in the 60s or higher dehumidistat control won't get you there since the humidity in the outside air will often be higher than you want, and more ventilation would only add to the load on the dehumidifier, but duty-cycle-timer or occupancy sensor control works.
HRV systems for the whole house really need to be fully balanced, with all of the ductwork in place. Putting it in now just to serve the basement would add more expense to the project than the savings would justify.
A single portable dehumidifier set up to drain into a sink or sump would keep up as long as you don't over-ventilate during periods of high outdoor dew points. Their front-panel dehumidistats are notoriously inaccurate & have long term drift issues- get a cheap humidity monitor, and tweak the controls to where it keeps the place under 60% RH in summer and you won't run into mold issues. If you have dust-mite allergies, try to limit it to ~50% RH.
If you have access to the digging equipment and are willing to design it, setting up an earth-tempering system for the incoming air that can later be used with the HRV as well can be cost-effective if you're using high wintertime ventilation rates rather than raw-minimums. But it's a whole sub-project that has to be done right- you may have enough on your plate already. |
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Bob I
Veteran Member
Posts:1435
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| 01 Sep 2010 06:09 PM |
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Caultion: "earth-tempering system for the incoming air that can later be used with the HRV" These are touted in Passive House theory but tend to have mildew & mold issues in real life use. If you install one of these "earth tubes", be prepared to do a regular cleaning, as well as monitoring it for excessive moisture. In our Passive House classes we were cautioned against using these for these reasons.
Bob |
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| Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant |
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Dana1
Senior Member
Posts:6991
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| 02 Sep 2010 11:47 AM |
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Earth tubes have to be set up correctly to deal with summertime condensation, but the CAN be designed without inherent mold issues in climates like Boontucky-girl's. (I'd be a bit more skeptical about the success of earth-tempering in much of the SE.) A lot of earth-tubes built in the US in the '80s were a disaster from a material selection and condensation drainage POV. |
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Alton
Veteran Member
Posts:2164
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| 03 Sep 2010 09:52 AM |
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I have used earth tubes. Just be sure to slope the tubes for good drainage. I actually prefer tubes that are smooth inside so moisture will not collect. In much of the Southeast I think the earth is too warm to condense much moisture from the air. In other words, the tubes may cool the air somewhat but most of the moisture will be retained. In the future I would consider earth tubes in the Southeast as make up air only. |
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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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Boontucky-girl
Basic Member
Posts:250
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| 03 Sep 2010 10:08 AM |
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Thanks for all of the replies. I really appreciate your knowledge and insight. I was really worried that running a bath fan/kitchen vent wasn't going to be enough. And I wasn't sure if the HRV could be installed now and set to handle just the basement, since the registers for the upstairs will be sealed. Like I said, the duct work for the whole house is already in place, as well as the HRV intake and exhaust ducts, since we needed all of those things before we can drywall. The HVAC guy already did heat loads and design and stuff, and he was nice enough to work with us to do this in stages. The plan is for the heat pump and blower to be installed next year before the summer so we can have A/C. As far as earth tubes, they can go on the "neat-things-for-future-to-do-list." Right now we still have the whole upstairs to budget and finish. Maybe by 2015 all of this will be done and I can start pet projects.  Thanks |
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greencleaning
New Member
Posts:50
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| 07 Sep 2010 09:28 AM |
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Heating a basement should not be a costly matter. You only require auxulary heat because much of the space is below the frost line and the ambient temperature in a basement is generally in the 60's year around.
I agree with checking the air influx tightness around the foundation and sealing/insulating as you can. Also check the basement windows - they are generally cheap single-pane glass and don't fit tightly. Even the heat-and-shrink plastic will make a world of difference if air leaks in around them. |
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Here's to you, your health and the health of your family. <a href="http://www.cleaningcleaner.com">Eco friendly cleaning</a>
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Boontucky-girl
Basic Member
Posts:250
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| 27 Sep 2010 02:08 PM |
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Thanks greencleaning.
Our basement is new, and our problem is that we have a walk-out, so only the back wall is below grade. Also, we have good quality windows, properly flashed and sealed with foam, so we're not worried about leaks there. And we're caulking the slab perimeter (mainly for radon mitigation) and our rim joist has been spray foamed with 2-3" of 2 lb foam.
The question I have now is that we want to insulate the basement bathroom walls and ceiling mainly for noise reasons.
I've been looking to see if there is a "right" way to do it, and to decide whether we need kraft faced batts, or unfaced batts, or even if we need any poly. With all of the moisture in the tub area I want to make sure I don't do something stupid like trap moisture and end up with rot.
Since we will have poly on the main floor under the insulation to get us through this winter, I want to make sure I'm ok to get us through a winter (or two) and still be ok as far as design when the insulation uptairs is removed and the main floor is finished. Any insight I will really appreciate it.
Thanks. |
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Dana1
Senior Member
Posts:6991
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| 27 Sep 2010 03:18 PM |
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Posted By Boontucky-girl on 27 Sep 2010 02:08 PM
Thanks greencleaning.
Our basement is new, and our problem is that we have a walk-out, so only the back wall is below grade. Also, we have good quality windows, properly flashed and sealed with foam, so we're not worried about leaks there. And we're caulking the slab perimeter (mainly for radon mitigation) and our rim joist has been spray foamed with 2-3" of 2 lb foam.
The question I have now is that we want to insulate the basement bathroom walls and ceiling mainly for noise reasons.
I've been looking to see if there is a "right" way to do it, and to decide whether we need kraft faced batts, or unfaced batts, or even if we need any poly. With all of the moisture in the tub area I want to make sure I don't do something stupid like trap moisture and end up with rot.
Since we will have poly on the main floor under the insulation to get us through this winter, I want to make sure I'm ok to get us through a winter (or two) and still be ok as far as design when the insulation uptairs is removed and the main floor is finished. Any insight I will really appreciate it.
Thanks.
For sound abatement in partition walls use unfaced goods only. For exterior walls use only semi-permeable foam board (up to 2" of XPS, or 4" of unfaced EPS) up against concrete, with unfaced-only batts in any studwalls between the foam & interior finish wall. In bathrooms use only vapor-permeable wall/ceiling paints, and avoid highly vapor-retardent materials like poly or barely-permeable materials like kraft facers. Assemblies dry primarily via vapor diffusion, and low-perm materials only slow that process. What you're looking for in bathrooms is interior finish materials that with low CAPILLARY DRAW, but are at least semi-permeable to water vapor 2-3perms+. Higher gloss acrylic-latex paints tend to have less capillary draw than matte finishes, but similarly moderate vapor permeance. Unless the exterior walls are super-insulated and/or the bathroom is a micro-zone for the heating system, insulating all of the partition walls & ceiling could lead to a signifcant heating/cooling imbalance for that room. Using a double 2x3 staggered stud approach with double-up wall board & R8 batts on one side or no batts at all may be a better solution than going with unfaced R11 or R13 in a single-studwall. Double-gypsum using GreenGlue or similar might be all that's called for- depends on just how much sound isolation you're looking for. |
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Boontucky-girl
Basic Member
Posts:250
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| 01 Oct 2010 10:58 AM |
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Thanks Dana!
Our basement is heated with radiant heat and I had the designer check on that. He said no problem with the additional insulation.
Also, the exterior wall in the basement is ICF, and we don' have additional wall framing at the exterior.
Would tile be considered semi-permeable? I was looking into tiling the area around the tub and have read a lot of concerns with moisture getting behind the tub and rotting the studs. Short of going with a Kerdi system on the walls, what could I do now to help keep water out of the stud cavity?
Thanks. |
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Auream
New Member
Posts:3
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| 01 Oct 2010 01:28 PM |
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If you plan to tile, you MUST have a waterproof barrier behind your tile, or you will get wet, rotted studs and mold eventually. This means either a membrane product like Kerdi between the wallboard and tile, a paint-on membrane like RedGard between backerboard and tile, or (least desirable) a poly sheet behind the backerboard. Read up on JohnBridge.com for information specific to tiling. |
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Dana1
Senior Member
Posts:6991
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| 04 Oct 2010 11:22 AM |
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Posted By Boontucky-girl on 01 Oct 2010 10:58 AM
Thanks Dana!
Our basement is heated with radiant heat and I had the designer check on that. He said no problem with the additional insulation.
Also, the exterior wall in the basement is ICF, and we don' have additional wall framing at the exterior.
Would tile be considered semi-permeable? I was looking into tiling the area around the tub and have read a lot of concerns with moisture getting behind the tub and rotting the studs. Short of going with a Kerdi system on the walls, what could I do now to help keep water out of the stud cavity?
Thanks.
Tile/grout is usually between semi permeable to highly permeable, which is fine. Depending on the tile & grout type, without a capillary break sometimes lot of water can get into the wall via capillary action. Capillary draw primary mechanism by which water gets into the walls not vapor diffusion. It gets out primarily via vapor diffusion, which is why high perm/low capillary draw is the best route. Kerdi is just over the line from semi-permeable to semi- impermeable at 0.75 perms, which is fine. Poly is highly impermeable at ~0.05 perms, and less than ideal. I've read that some people have used 1/4" fan-fold XPS as a more-permeable capillary break in bathrooms but I have no direct experience with it in that application. (XPS seems a bit like overkill, but it may be useful for additional thermal-breaking of studs on exterior walls/ceilings.) 1/4" fan-fold XPS is well over 1 perm, but still under 10 perms, and adds ~R1 to the stackup. |
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