Plans Review with a few questions
We are getting closer to building our new home. The preliminary drawings have been completed (links to plans at the bottom). We aren’t exactly building a green house, but over the last year I’ve read an enormous amount of good information from this website and a few others to help guide me in building a more durable and energy efficient house than what is typically done around here (vented crawlspaces and ducts in a vented attic are pretty standard here). We are in a more mild part of the mixed humid climate zone 4 (The Hampton Roads area of Virginia), and that does change the cost effectiveness of some upgrades. I’d appreciate any input on my current plan. My above code goals for the house are to have a continuous air barrier with results verified by a blower door test, a conditioned crawl space, all HVAC ducts inside a conditioned space, and right sized HVAC equipment with mechanical ventilation.
The first floor HVAC ducts will be in the conditioned crawl space. For the second floor, these are the three options I’m considering:
1. Open web floor trusses for ducts (Possibly with spray foam to insulate between trusses on the exterior wall?). Attic floor 2″ oc foam + loose fill on top for R38.
2. Open web floor trusses for ducts (Possibly with spray foam to insulate between trusses on the exterior wall?). Attic floor loose fill (R38) with airtight drywall ceiling.
3. Conditioned attic: Ventilation channel under roof, then loose fill between rafter, then 1-2″ of trgid foam covered in drywall. Small supply register to condition attic air. Will require closed combustion appliances.
Exterior wall cladding will be a premium vinyl siding (cedar shake style). Wall sheathing options are:
1. OSB with taped seams +Tyvek
2. ZIP sheathing (taped) + Tyvek
3. Zip R sheathing (taped) + Tyvek.
All walls 2×4 construction with R13 cavity (Fiberglass batts are typical around here), no vapor barrier, just regular latex paint on drywall. The air barrier will be at the sheathing. Upgrading to Zip R sheathing will add more cost to my mortgage than it will save me in energy costs, at least according to modeling using this website: http://hespro.lbl.gov/pro/ Zip R (R3.6) is over 30 dollars a sheet (and I have to buy it in quantities of 30 sheets at a time). Regular Zip is about 15. OSB is about half that. I like Zip sheathing but I also don’t like trusting the tape to flash the windows and doors. If tape fails on housewrap, the seams are overlapped, giving another layer of security. Then there is the question of if I’m going to use a housewrap anyways, what’s the advantage of using regular Zip sheathing versus just taping regular OSB that’s half as expensive.
For mechanical ventilation, my options include:
1. Supply only, integrated with Central fan(s), preferably with an ECM. Possibly ultra aire ventilating dehumidifier
2. Whole house ERV with dedicated ducts (easier with floor trusses).
3. 2 or 3 spot ERV’s (ie Panasonic FV-04VE1)
Supply only will be good in the summertime, but I worry about humid indoor air in the wintertime being force through the walls. I really like the ultra aire ventilating dehumidifier, but they are expensive and with an HVAC system on both floors, I’d probably have to buy two. How much more expensive are AHU with ECM’s? I like balanced ventilation, but I’m not sure if the cost of an ERV is justified in my climate. I do plan on hiring a third party to do the HVAC design to ensure I get a proper manual J.
Windows will be Anderson 400 series with an energy star rating.
First floor plan: http://s18.postimg.org/m3c1ychmf/1st_Floor.jpg
Second floor: http://s18.postimg.org/m4lzrrjg7/2nd_Floor.jpg
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