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Does steel framed basement need r13 rigid insulation?

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  #1  
Old 08-11-15, 08:07 PM
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Does steel framed basement need r13 rigid insulation?

I had a contractor come by for an estimate on my basement project. He told me that if I choose steel framing I need to get r13 rigid foam for insulation. Do I really need that? It's about $10 more per sheet so it adds up real quick. Trying to save some money if I can get away with r10
 
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  #2  
Old 08-11-15, 09:36 PM
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PA has three climate zones and the link I'll add relates to the 2009 Energy codes.
https://energycode.pnl.gov/EnergyCod...e=Pennsylvania
You will need to review your code requirements and what vintage codes your local authority is following.

However, if you look at the basement wall insulation requirements they list one value for the continuous rigid and a larger value if just insulating the cavity. I believe you can use a combination of rigid against the concrete and then cavity insulation to exceed the total requirement. There is however a ratio where you don't want too much air permeable insulation in the cavities. Just as an example, if you used r-5 on the concrete and then r-19 in a 6" cavity the surface of the rigid at the top where the foundation is exposed to the elements could drop below the dew point resulting in condensation or even frost. Not good inside your walls. But r-10 with r-13 should not be a problem. There is a chart somewhere that gives you the relationship, we just need your code requirements.

Why he is increasing the r-10 to r-13 based upon using metal studs I do not know, never heard of that.

One of the difficulties with metal studs is they are not a solid box, unless they have changed. That means a standard cavity insulation will not be wide enough to fill inside the metal stud. Labor intensive, but strips of fiber insulation could be inserted to fill that space. That's assuming your metal studs are a "c" channel. BTW, I like Roxul for basement applications, very dense.

Be sure you have resolved all moisture issues before those walls go up.

Bud
 
  #3  
Old 08-11-15, 09:48 PM
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Thanks Bud. Code says r10 is minimum here. Not much of the foundation is exposed, maybe about 12 inches from the ground. Should I put one of the 8ft rigid insulation panels from the basement floor up and then finish the rest at the top with r13? I have 9 ft ceilings in the basement.

Also I didn't consider cavity insulation, is that something that's necessary? We don't have any moisture issues at all right now since we are up on a hill. Things could change in the future so I'm all for preparing for anything.
 
  #4  
Old 08-11-15, 10:11 PM
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Basements are different from the walls in your home as only the exposed portion at the top and about another foot or so below grade will experience the real cold. Before codes started requiring full floor to ceiling insulation (over kill IMO) I would recommend above grade plus one or two feet below grade was all they needed. With r-10 floor to ceiling you are ok, but the top is still a bit low on r-value. I would come up with a way to add some cavity insulation in addition to the rigid at the top.

As for finishing the top with just fiber, no, that is where you want the rigid to keep the inside surface (now the rigid and not the concrete) warm enough to not form condensation. I'll add a like that illustrates the rim joist area above the concrete walls.
Understanding Basements | Building Science Corporation

Bud
 
  #5  
Old 08-12-15, 04:12 AM
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Perhaps before you commit to anything you should check the price of having closed cell foam sprayed onto the foundation. A seamless application that is bound directly to the wall is the best scenario. You didn't say what the walls are but usually a poured concrete wall will have some variations at the form joints and where the ties go through the walls. These can present issues when trying to get sheet material to lie flat and without an air gap between the wall and foam.

By spraying the foam directly to the wall you can surmount those issues and have a truly continuous surface.

I, too, have never heard of a case where the steel studs require a higher r value than the 10 where there is continuous insulation applied to the surface.

Regarding Bud's comment on the fiberglass insulation width for steel stud applications, the manufacturers do make a special size material for that. It is a full 16" or 24" wide, depending on your situation. If you do go with a rock wool product, this too is available in a full 16" material as the standard big box store products are usually made for wood studs and will be sized to fit that type of cavity. The special sized materials are more likely to be found at a specialty drywall supply yard or a firm that deals with acoustical supplies. Commercial buildings use those types of products all the time.
 
  #6  
Old 08-12-15, 02:27 PM
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Hi Calvert thanks for replying. I have a poured concrete foundation. Code requires insulation to be r10 or above and from what I understand closed cell foam is about 6.
 
  #7  
Old 08-12-15, 03:31 PM
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The closed cell is near 7 that I have done for me. 1-1/2" gets you to where you need to be. I have had it pass at that level numerous times. Any foam you use will have to be thicker than 1".
 
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