New house construction – Minneapolis, MN
I am getting close to finalizing the plans for our new single-family house construction on a typical urban lot in Minneapolis, MN (climate zone 6A) and would appreciate some input from the GBA community. For context, it is an East-West lot, and the house is set back from the street and neighboring houses to get good solar exposure. Passive house inspired, but not looking to get certified. We are not planning on running a gas line to the house, so everything will be electric. We would like to build an office/studio above the garage that could also be an occasional guest house. My wife and I are planning on doing a fair amount of the construction to keep the costs financially feasible, so simple is better.
I’m not an architect and have never built a house, so any general comments about the plans would be appreciated. In particular, I’m wondering about the following:
1) Ductless mini-split recommendations. We are proposing a single ductless mini-split in the downstairs living room of the house. I have seen a lot of suggestions for installing a second unit upstairs for cooling in the summer, but I’m not concerned about cooling. I’d prefer to rely on natural ventilation, and only expect to use the A/C for a week or two out of the year. I’m leaning towards a ceiling recessed model for aesthetics and freeing up the wall space for other things. Is there a significant efficiency difference between a wall mounted or ceiling recessed model? Is one more appropriate for the space?
2) Heat load calculations. I ran some quick heat loss calculations and came up with a design load of 20,600 BTUs for the house and 4,800 for the upstairs of the garage. Does this seem reasonable and should I install a 21,000 BTU head unit or go up to 24,000 to be safe? We will need to have electric baseboard backups regardless.
3) Applied roof supports. I like the idea of cutting off the rafters to reduce thermal bridging and simplify air sealing, but I am a little confused about how to support the roof overhangs. Currently, I am proposing vertical 2x’s as an applied rafter over the Zip sheathing. Is this reasonable of is there a better solution? The only other option I have seen is adding the overhang support with an applied soffit which I think would look kind of funny with the modern design of the house.
4) Are the roof and wall assemblies appropriate for the zone and climate? I know the R-value of the wall is a bit under the Pretty Good House target, but hanging more than 4″ of insulation plus the rainscreen off the side of the house seemed like a lot. Also, the minimum exterior insulation ratio requirements for foam would not apply to rock wool correct?
5) Are the HDP bearing block thermal breaks on the glulam post footings necessary? I imagine the subslab condition away from the perimeter is fairly temperate, so maybe I shouldn’t be too concerned about maintaining thermal breaks there.
Current house plans and the heat load calcs are attached. Thanks for any and all input!