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Insulation specs for Proposed house

Post in 'The Green Room' started by northwinds, Feb 5, 2007.

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  1. northwinds

    northwinds Minister of Fire

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    G-rott offered to take a look at the insulation being proposed for my house to be built sometime after spring of 2008. Anyone else is encourage to comment with thoughts also.

    The architect specializes in "green" design, so I'm anticipating that the insulation is being done right, but I'm also curious what people here might think.

    "Insulation: At basement walls: 3-inch thick EPS foam interior or exterior as shown in drawings. At frame construction: Cellulose, R-50 at ceiling, R-20 at exterior frame walls with Tu-Tuff3 vapor barrier, 1" EPS rigid insulation at interior side of vapor barrier. Electrical boxes and wiring kept to interior side of vapor barrier whenever possible."

    Thanks in advance for opinions.

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  2. sgcsalsero

    sgcsalsero Feeling the Heat

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    Did Garett come back to you on this, maybe via PM, interested in his response
  3. northwinds

    northwinds Minister of Fire

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    Not yet. If anyone else has suggestions or criticisms, let me know. I had a builder friend take a look at the complete spec list, and have already incorporated those changes during the last meeting with the architect, but none of those related to the insulation specs.
  4. TMonter

    TMonter Minister of Fire

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    Have them use expanding foam around each of the electrical boxes once they've been installed before they drywall. This should help for air infiltration.

    Consider a staggered stud wall for outside walls or at least upstairs outside walls. This prevents conduction of heat to outside walls by a large margin.

    Plan for an attic fan and/or a whole house fan for cooling.
  5. sgcsalsero

    sgcsalsero Feeling the Heat

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  6. Rhone

    Rhone Minister of Fire

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    Alright, I'll bite.

    Why the use of EPS instead of XPS particularly the basement? XPS has more R-Value/inch, is water proof, allows water vapor to travel through it (so things can still "breathe"), and has a higher pressure rating. EPS is the white styrofoam made up of little "balls", which can create space for water to "whick" through it, and it does. Once the EPS gets saturated with water, it's thermal performance drops. If it saturates with 30% water (it can absorb over 50% over years, XPS is only 1%) you're heating load will increase 3 fold, and EPS only has half the compressive strength of XPS. Given that it's only slightly cheaper, maybe there's another reason for choosing EPS? XPS is just far superior and doesn't cost all that much more.

    When insulating the foundation, insulate the exterior. That puts the mass of the foundation inside the thermal envelope buffering against heat & cool spikes. With XPS on the basements exterior, it should take care of any moisture problems in your basement and stop you from needing a dehumidifier. It also increases your space inside, and won't get in the way of any wires/plumbing. However, if you're in a termite prone area they like warm, moist, easily tunnel materials while being disguised and find tunneling inside the insulation a great highway. If you're in a termite prone area, you need to cover it with termite proof materials and put an aluminum shield on the top of it to force them out of it, into view. It doesn't have any nutritional value to them, but putting it on the inside in termite prone areas may be a wiser and in some places, and keep wood and things that can attract termites away from your foundation. I covered the exterior of my XPS with 1/2" cement or you can get those concrete forms with XPS in the middle.

    As for framing insulation, the exterior of the house should be covered in the foam insulation, it sounded like they were planning on doing the inside. Most houses use Polyiso (double faced foil board) because it has the most R-Value/inch (and $$$) but using it you get high insulation and not as thick walls. Polyiso is not as environmentally friendly. I've not heard of EPS on the exterior but XPS certainly. The reason it should be placed on the outside is because it stops air leaks, water, and short circuiting of cold through framing members. Think of it like a winter jacket. Why do winter jackets have the wind & water proof material on the outside, and the warm fuzzy fluff on the inside? Because keeping water and air movement out on the exterior keeps the fuzzy stuff inside working better. By having the walls filled with fluffy cellulose and the foam on the interior of your house it's backwards, and in winter is like wearing your winter jack inside out. You won't notice it much on those still sunny days but there should be a difference on those cold wet and foggy days. The barrier does help so maybe that's not a good example but certainly not up to the level of XPS on the exterior and cellulose in the framing members. Also, cellulose & fiberglass work best the less temperature difference there is. The more temperature difference, the less the effective R-Value Fiberglass being much worse in that regards. By having the foam on the exterior you're reducing the temperature difference in the wall letting the cellulose work more effectively. By having the foam on the inside and cellulose on the outside, you're exposing the cellulose to vast temperature differences and its effective R-Value will be less. For the inside, I'd insulate the framed walls with wet blown cellulose since it will never settle and holds its shape. But, you have to let it dry for like weeks before covering it. The other alternative is to pressure it with high density dry cellulose so it avoids settling.

    I do like the attic choice, cellulose is the best choice and at R50 that's a lot! Make sure the attic is air sealed first, it provides the biggest impact on reducing drafts in the main living area because of what's known as the stack effect. Followed by the basement, then the main living area.
  7. northwinds

    northwinds Minister of Fire

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    Thanks for the comments so far.

    sgc: I've reserved the book through my local library system. Hopefully, I'll have it in a few days and can upgrade my knowledge base about insulation.

    I'll be the first to admit that I am not a builder; this is not an area where I have skills or knowledge. I don't know eps from xps. The architect warned me that insulating on the interior was a controversial technique, but asserted that it was a better way to achieve an energy efficient design. It sounds like Rhonemas disagrees, and I'm going to email a copy of his comments to my architect for comment.

    I did find an article discussing use of xps on the interior:

    http://www.xpsa.com/news/index.html

    This is a walkout ranch. I took a photo one of the computer drawings that we were provided with recently.

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  8. Rhone

    Rhone Minister of Fire

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    The reason that article states that XPS was used on the interior in that application is because it was applied to a masonry building. Think of a log cabin, you wouldn't cover the exterior with XPS foam boards you'll cover the beauty that is a log cabin. Same with masonry buildings, so I think they did the right thing in that article for the situation. But, houses with siding the XPS can go on the exterior and it won't make a difference to the looks. They also mentioned insulating the interior of the basement with it, which makes sense if you're retrofitting or live in a termite infested area but if your house is being built from scratch insulating the exterior is the best method, putting the mass inside the envelope and should prevent any moisture issues in the basement. You can look online about insulating basements and the benefits of choosing inside vs. outside.

    That house is sweet! I love the extra windows on the roof line, looks like they face south! Walk-out basements are tough for heating/cooling, as concrete has nearly no R-Value. Even 10" concrete has a worse R-Value than a single pane of glass. It looks like they tried to bunker as much of your walkout as possible, an excellent job. You may want to think of paying for extra insulation on just the walk-out wall to compensate for concrete being nearly useless for R-Value but you won't hear any complaints from me, I only put R10 on mine... it being a retrofit the walls of my house weren't built out for more. I'll be putting some on the interior as well. If you want to know a trick about insulating walkouts (exterior) I included a picture of the newest thing going, it's how I did the walkout side of my basement. Bury a piece of XPS graded away from the foundation. That prevents water from sneaking down the exterior and wicking into the footer. It also raises the frost line so helps keep your basement warmer, and keeps the footer warmer in winter prevent potential damage. Just make sure it's deep enough so it doesn't interfere with any plants & their roots you may want in the area.

    If I were building a house I'd make sure the window in the basement you have on the right, is big enough for Egress to allow that room to be a bedroom. You never know if you'll turn it into a guest area complete with bedroom or one or both of your parents/inlaws falls ill/old and they're moving in with you. You certainly wouldn't want them on the same floor, and with a ranch that means they can only move into the basement. Likewise, make sure when your house is built you at least include drainage for plumbing a full bathroom in the basement even if you decide not to frame or get the fixtures for it when built. Adding the drainage to a concrete foundation is a groan and you're almost garunteed pitch issues. The previous homeowners in my house installed an in-law apartment complete with bathroom, bedroom, and kitchen after the fact. They had to get a concrete cutter and make a window big enough to meet egress codes in one of the rooms and a bathroom installed in a basement after the fact is almost garunteed pitch issues, and a groan because you have to smash away the concrete. The toilet we had there failed to flush properly much of the time so we replaced it with another which also had the same problem. Bringing in a plumber, they politely informed us there's nothing that can be done about that, we need a power flush toilet because the drain pipe does an immediate 90 instead of giving the toilet some room to work properly. He told us, the bathroom was probably added after the fact and they had to do that to make as much pitch. The tub in the basement also has similar pitch issues and about 4x a year I have to use a snake to pull out clogs in the line (currently it's our only working tub/shower). That is a nice looking house! I love those windows on the top. Are you putting in a Cathedral ceiling? I'm also curious what your architect says... he's probably going to ask why you're asking advice about insulation from a wood burning forum and whose credentials do you trust :) Here's my pics.

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  9. northwinds

    northwinds Minister of Fire

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    Tell my architect that I'm asking advice about insulation from a wood burning forum? I may not know anything about insulation, but I'm not nuts. :)

    Actually, the guy has been fairly open to suggestions so-far. He agreed to beef up the exterior sheathing even though a tree or two more might be sacrificed in the process (1/2" osb instead of 1/2" fibreboard). A friend with building experience gave that recommendation. I'll be curious to see what the architect says too. I won't hear for awhile as he's out of the office for a couple of weeks.

    The pic that I posted does show the house facing south, so there will be passive solar gain. We will need to take some trees out in front, as this entire acreage is heavily wooded.

    The design is being changed so that the lower bedroom window is large enough for ingress/egress. My wife badly wants to put a bedroom, bathroom and family room in the lower level. It will at least be roughed in; I think it's unnecessary living space that will add to the size of the mortgage, but I'll probably lose that argument (she doesn't read the forum). The great room ceiling won't be cathedral but will be vaulted. I don't have the height number. The next step is that we are supposed to get a set of preliminary plans that we can take to select a builder and obtain initial pricing estimates, so this is still a good time to make changes.

    I'm posting a pic of the building site. It's my happy place that I go to de-stress. About half the time, I'll go out there to cut wood and end up just sitting on a stump listening to the sound of the wind and the birds.

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