I think there is a mismatch of terms. Leaky to me means air infiltration. It does indicate the level of insulation. Nor does adding additional insulation make the house tighter.

If you are installing Andersen and Marvin windows, then I am confident the house is tighter than the average new build. Invest in a good quality exterior patio and entrance doors and you house will be sufficiently tight for your climate.

Insulation of R30 for the attic is the minimum used in new homes. You may want to increase it to R38-40 if it the additional costs are a few hundred dollars. Otherwise don't bother since it is unlikely you will ever see a return on investment. I also recommend doing this if it blown in insulation. The insulation is installed by the number of inches, but it almost always settles. The resulting R factor is less then what is advertised.

A wall insulation of R19 is above average. No need to do anything there since it is overkill for your climate.

I don't see a need for an HRV if you plan to open the windows most of the time.

A leaky envelope, lots of outdoor air infiltration, gives you less over your indoor environment. A well-sealed envelope gives you a lot of control. If the ground temp is favorable, slab insulation can be counterproductive. Insulation amounts should be decided upon based on a cost analysis as indicated by mike_home.

Here is a report that might be of use to you.

Long-Term Monitoring of

Mini-Split Ductless Heat

Pumps in the Northeast

Building America Report - 1407

December 2014

Kohta Ueno and Honorata Loomis

I think the Title 24 requirement is <3 ACH, not sure how you would show compliance without a blower door test?

As ionized pointed out, if you build a tight house then you have control; you can decide whether or not to open the windows. If you put in an HRV that also can help with air quality -- do you get smog in Santa Monica? Times you want to keep windows closed due to allergies?

Haha, a lot of guessing from afar.

I lived in Santa Mo for many years. I'm a bit north now. I've owned several houses and have done remodels a few hundred miles to the north. But I haven't built any houses. A close friend did a massive remodel of a 3000 sq ft house on the Balboa Peninsula a couple of years ago and I talked with him a lot about what he was doing along the way. But my advice is that of a former neighbor and homeowner, not someone with firsthand experience.

I think building to code should be just fine. As for "leaky", no. I wouldn't allow your contractor (or the architect) and their work to be sloppy but I wouldn't worry too much about it. Tell him you're looking for quality work but it doesn't need to be as if it were in the Midwest or East. In the design, be sure to have enough west and east facing windows for cross ventilation. A few opening skylights can be useful to vent out hotter air. A heat recovery ventilator is overkill, you can open windows the majority of the year, even on heating days, as you know.

My friend in Newport uses his A/C pretty regularly and he's got the beach one block in one direction and the bay one block in the other. so I think you would use yours too. I don't think having a minisplit unit for 1000 feet downstairs would give you the kind of air circ you'd want to have. I'd opt for conventional heat and A/C, and make sure you have enough return air coverage upstairs, that will be your real cooling target and you need enough ducting and airflow there and back to the hardware for it to work well. Good luck.

build tight, ventilate right.

all climates.

I thought cali required blower door & duct testing.

I live in Los Angeles too. Over many years I've seen temperatures increase and more humid and warm days than ever before. The thought of not including a fully functional A/C would be wrong in my estimation. I cannot comment on leaky vs tight, but not having the option to activate the a/c would pennywise and pound foolish IMHO.