Unfortunately, I do not have any photos of how we installed the exterior insulation on this home. I’m going to discuss two different ways I’ve installed exterior insulation along with a new product that just hit the market that I think would work well in my area. The topic of this blog is Construction Design-Exterior Insulation. 06, on the warm in winter side of our walls, which is also very common in my area, we now have drastically diminished the drying potential of the wall. Combine that with polyethylene sheeting as the air/vapor control layer, perm rating of. XPS can be a vapor barrier if its more than 1 inch thick, two inches of XPS has a perm rating of around. Extruded Polystyrene insulation (XPS) is very common in my area, and I would bet that most builders would use this product as the continuous exterior insulation because they are familiar with it, and because it’s fairly cheap. Do I agree with the Minnesota wall insulation codes, not really, but I do get why they eliminated the exterior insulation requirement. Of course you can always build above code and add exterior insulation, but there are a few other things that need to be addressed, like the interior vapor control requirements. Apparently 2 x 4 exterior walls are not allowed in the northern half of the state. If you are building in the State of Minnesota, the only time you are required to use continuous insulation is when building a 2 x 4 exterior wall in climate zone 6. Climate Zone 6 wood frame wall R-value, 20, 13+5. Now lets look at Minnesota’s 2020 Energy Code, Table R402.1.1, the code currently in force. There is another section of the code that says R-5 on a 2 x 6 wall is not enough, but that’s a discussion for another time. So, if you live in climate zones 6, 7, or 8, you need to include continuous exterior insulation, according to the 2018 International Residential Code. If you are building a 2 x 4 wall, R-13 cavity insulation along with R-10 in exterior insulation would be the requirement. What does that mean? The first values, 20 + 5 are saying that if you build a 2 x 6 wall, R-20 cavity insulation is required along with R-5 of continuous exterior insulation. The code talks about Table N1102.1.2 which includes the requirements of climate zones 1-8, I’m just going to discuss the cold climate wall insulation requirements of climate zones 6, 7 and 8. Simply, the code wants us the add the manufacturer’s listed R-values together to determine the wall or ceiling’s R-value and not include the R-value of drywall or wall sheeting for example. The code goes on to allow an alternative to the above code, using U-values, but we’ll keep it simple here and just use the R-value requirements. Where insulated siding is used for the purpose of complying with the continuous insulation requirements of Table N1102.1.2, the manufacturer’s labeled R-value for insulated siding shall be reduced by R-0.6. Computed R-values shall not include an R-value for other building materials or air films. The manufacturer’s settled R-value shall be used for blown-in insulation. Insulation materials used in layers, such as framing cavity insulation or continuous insulation, shall be summed to compute the corresponding component R-value. There’s a reason why, albeit not a very good one, that I’ll touch on in a bit, first, lets look at what the 2018 International Residential Code (IRC) has to say on the subject. Exterior wall insulation would be a great way to improve the thermal performance along with comfort in our homes, but it is rare in my area. I have friends who are building homes in Missouri who install higher wall R-values. The majority of new homes I blower door test have the code minimum R-21 of wall cavity insulation, usually fiberglass batts, and blown fiberglass in vented attics, R-49. You would think that in my very cold climate of Northern Minnesota, we would be putting as much insulation in our walls and roofs as possible.
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