Outsulation, Persist Walls and attached garages
Me and my fiance recently put an offer in on our first home. It is a small modular rectangular rancher built in 1991 and quoted to be an “energy star” model. Full basement (original owner who was there during construction confirmed no sub slab insulation or exterior wall insulation). Unfortunately it is not oriented due south (it is roughly 30 degrees off of due south) but after looking for about a year it was the best compromise we could find in our price range, lot size, location and school system.
After reading the original hard back Passivhaus book, reading through the cchrc Remote Wall website and doing various searches I have arrived here to ask the follow:
If I choose to go with an outsulation system such as PERSIST, is there any way of building an attached garage located outside the home’s vapor and insulation barriers? The township only allows one secondary structure and if we plan to make this our long term home, I would like both an unheated garage and a detached but heated wood working shop out back. In order to accomplish this I would like to build an attached garage on the west side of the home to help buffer the home from the strong western sun during the summer months (considering the disadvantaged orientation to begin with).
I would probably be employing the full PERSIST method vs remote wall system due to my need to include the attic space within the envelope to house the HRV and probably a forced air system of some sort for heating/cooling. The home already has an AC blower unit and duct work ran(I realize the duct work would need to be modified or replaced).
I figured a heat pump may be the way to go considering the house is electric resistive baseboard with no natural gas at the street.
To sum up: Is there a way to retrofit a home with the PERSIST system and smoothly integrate an attached garage that is outside of the home’s insulation and vapor barriers? I am hoping I can plane the exterior poliso insulation for stick framed walls even with maybe ROXUL drainboard for the above and below grade exterior basement insulation? I get hung up on the meeting plane between the garage slab, the garages above grade CMU’s (to match the above grade height of the exsisting basement CMU wall) and the stick framed garage that abutts the west side of the home.
I suppose the other stipulation would be that I would not want to voluntarily frame over the exterior insulation of the house’s wall that abuts the garage for insect inspection purposes.
I am choosing to use an ousulation method as it appears to be the easiest method for me (an electrician)to comprehend in order to achieve an air tight, continuously insulated installation with the skillset that I have.
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Replies
Lance,
Q. "If I choose to go with an outsulation system such as PERSIST, is there any way of building an attached garage located outside the home's vapor and insulation barriers?"
A. Sure. But you have to do the work in the right order. First, you would want to do most of the retrofit work on the west wall of the existing house (strip the existing siding, remove the windows, install new rigid foam or mineral wool insulation, install vertical furring strips). Then you would want to build your attached garage. If the roof of the new garage intersects the wall of your existing house, the intersection would have to be carefully flashed. Once the flashing details are figured out, you can install the siding.
Lance, if you haven't seen this manual from Cold Climate Housing Research Center, you may find it valuable. http://www.cchrc.org/docs/best_practices/REMOTE_Manual.pdf
On page 23 of this document, there is a picture of a similar situation to what Martin describes, where the control layers are all installed before the adjacent unconditioned garage roof is framed (using REMOTE, not PERSIST.) If you want to avoid this specific order of operations, try to verify how your township defines attached/detached, because maybe there's an easier way to build an "attached" garage, like connecting the house to a separate garage with a breezeway for example.