We live in a 7 year old ranch house near Raleigh, NC. There
is a 350 sq ft unfinished room over the 2 car garage and an adjacent large
unfinished second floor attic area. An open stairwell leads from the first
floor (has a door at the first floor level) to the room over the garage. The
unfinished room has plywood flooring and batt insulation separating it from the
garage. The rest of the attic has blown in cellulose insulation but is not
floored (except for a small storage area). The room over the garage is about 10’
wide and 35’ long with 5’ kneewalls and a cathedral ceiling. The ceiling rafters
are 2” x 8” and 16” apart. The rafters are connected with collar ties that are
8’ from the floor. The roof has a ridge vent and there are soffit vents on both
sides behind the kneewalls. The floor behind each kneewall is not insulated to
the garage below. One end of the room has a single window. The other end has
the stairwell on one side and a connection to the rest of the attic on the
other. The roof is plywood that is sheathed and shingled. There is no shade
over the roof. The main part of the house is heated/cooled with a heat pump and
there is no duct work in the attic (all ducts are in the crawlspace).
We would like to finish off the room over the garage for use
as an occasional guest bedroom, and playroom for grandkids. We plan on putting
a ½ bath in the main attic space that is nearest to the room over the garage. The
bath will be framed off from the rest of the attic and have an 8 ft ceiling.
The plan is to use a high SEER mini-split ductless system for heating/cooling
the new room and bath, with the indoor unit being placed above the window.
The questions I have involve insulating the new room and
Each rafter would have to be extended to be able
to accommodate the code required R30 insulation (plus a ventilation gap) if we
used batt insulation. We don’t want to lose any more head space, so the plan is
to use open cell spray foam insulation between the ceiling rafters. What is the
best way (energy cost/insulation cost) to accomplish this? Should the spray be
applied all the way from the ridge vent to the soffit vent? If so, how should
the rest of the area behind the kneewall be insulated? Should the uninsulated
floor above the garage that is behind the kneewall also be sprayed, or should
batt insulation be laid down? In either case, should there be any additional
insulation in the kneewall itself? A second option would be to spray between
the rafters from the ridge vent to only just behind the kneewall. If this is
done, how should the kneewall itself be insulated? Spray or R19 batt
insulation? Code says that there can be no plastic sheathing between the wall batt
insulation and the sheetrock (paper faced insulation is ok). Is there any value
to putting plastic sheathing on the back side of the batt insulation if the
area behind the kneewall remains uninsulated and open to the soffit vent?
Should I use spray insulation on the gable (window)
end of the room, or would it be ok to use regular R13?
What is the best way to insulate the ½ bath? One
wall of the bath is part of the gable end of the main attic space, and the
other 2 walls and the ceiling are framed off from the unheated part of the
You do really have a lengthy discussion of your problem. What I grasped was your problem with the insulation of your bath and room. I would recommend to add shutters to your windows because shutters are knows to be the best insulators to any home. you can close it or open it to stabilize the temperature inside the room.
Can you post a couple of pictures....
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