I’m contemplating an addition/renovation to our one story 1700sf 1895 Queen Anne home (local landmark designation and also in a local historic district) in climate zone 2A. Currently the house has (from bottom to top):

1. pier and beam foundation with minimally vented dirt floor crawlspace

2. T&G pine floors (mostly a mishmash of ages due to multiple renovations etc) with no sub-floor

3. dutch lap siding with no exterior sheathing, ship-lap on the interior with a few layers of drywall

4. some walls seem to have blown in cellulose – no evidence of poor paint adhesion yet

5. some blown in insulation in attic, 2×4 rafters about 24” OC, with purlins, plywood and an asphalt shingle roof.

The addition will be a 1.5 story about 1000sf set to the side and back (for various reasons, we aren’t contemplating much change to the original house’s floorplan – the addition is for our growing family). I know that we could live happily in a designed-from-scratch 1700sf house, but that isn’t in the cards.

The new addition will be a “pretty good house” – I expect it exceed our local energy code and be on a separate HVAC system. The older part of the house is where I’m trying to balance some decisions. So far, I’ve decided to:

1. move the HVAC system & ductwork to the attic (and, although local code doesn’t require it, I feel that this entails insulating and conditioning the attic to some extent). The crawlspace is about 18”-24” high, and I really hate that the ducts are down there.

2. encapsulate the crawlspace (possibly insulating, and either condition or dehumidifying it)

3. renovate and weatherstrip the existing windows and doors

My questions mostly involve whether I’m missing some areas I should address, or whether I should do more (or less) in the direction I plan. For example:

1. By concentrating on the roof, foundation, and windows/doors in this phase am I missing some big energy savings? We are too shaded for PV, but I would love that, if we weren’t surrounded by large trees.

2. Should I remove any cellulose from the wall cavities? I think our budget won’t allow opening up all the walls on the interior or exterior (lots of trim), but I plan on doing that in the next few years – hopefully from the outside where I can properly sheathe the walls and add a WRB. I figured I would take the energy hit for a few years, and then come back and do the walls.

3. I plan to insulate as much as I can at the roofline, but does that require rigid foam above? The attic space will be connected to the living space by a hatch, but will otherwise be unoccupied.

4. How much air-sealing should I invest in for the old house (and for the new)? Current code is 5ACH @ 50pa.

We have an architect and are interviewing builders, most of whom are relatively energy conscious (one just had AeroBarrier come out to do their Passive House), and I expect some of these questions will be hashed out when we hire a builder, but I’d like to be as informed as possible beforehand.

Thanks for any questions or advice!

Matt