I’m building an addition to my home, which was discussed in some detail in a previous thread https://www.greenbuildingadvisor.com/community/forum/mechanicals/96906/zone-1-home-addition-dual-zone-hvac-strategy.

Current home is in Zone 2, Houston area, 2*4 walls, brick veneer, blown in (pure white) insulation in the ceiling (cellulose?)

We’ve changed the floor plan to move the new living space into the existing garage, in part so we can connect that space to the existing HVAC system. Let’s ignore for the time being whether the current 4 ton HVAC can handle the increase of the existing home from 2800 to 3250 sq feet (I’ll start a separate thread on that), and lets talk about the addition:

My previous thread’s conclusion was to use ductless mini-splits for the new shop space, which now will be a 1000 sq foot woodshop plus and an additional 700 sq foot garage/storage space, each being on a separate mini-split such as a Mitsubishi FH09 and FH06 respectively.

It is rare that I will cool or heat the garage space much, but will probably want to keep it between 50 in the winter and 90 in the summer, and get some humidity control in the summer. I will have wood and other storage there. This ‘low use’ seems to highlight an advantage of the Mitsubishi FH06/9’s which can modulate down to only 1600 btu/hour.

Considering the above plan is OK…. my questions:

1) Shall I proceed with an unconditioned attic space?

Considering there won’t be any HVAC systems or ducts in the new addition attic, based on my research it seems to make more sense to insulate the ceiling instead of the rafters (i.e. no need for conditioned attic space with no mechanicals in the attic). Also, there are some complications and additional cost of having the existing part of the home unconditioned attic and the new part conditioned, and the cost to conditioning the existing attic, even if it could be done correctly (very complicated roof line), probably wont pay back in my lifetime,…

2) What’s the best practice today for blown in ceiling insulation in Zone 2? Cellulose? How thick?

Considering the many installation screw-ups I have read about SPF, and the extra cost, and my wife’s serious asthma problems which may or may not be aggravated, and the relatively good performance (cost wise) of my current home, I’m shying away from my original plan of using any SPF in the addition, and leaning towards a ceiling with blown in insulation.

3) Should I insulate the new interior wall between the woodshop and the garage?

The woodshop are garage are two adjacent rooms that share one interior wall, ~30 feet long. I plan to keep the woodshop around 80F in the summer and the garage around 90F. Each room is on their own separate mini-split.

Thanks again everyone for your help,

Mark McFarlane