Home / Guides / Other Rooms and Spaces
Mini Split for an Attic Conversion
A finished attic in Central Texas sits under a roof deck that takes full sun all day. That room picks up heat the rest of the house never sees, and the old ducts were not laid out to serve it.
Convert an attic and you put living space under a short stack of roof materials. On a bad afternoon the roof surface can run well over 100 degrees, and past 110 degrees is not unusual. That heat soaks the deck and radiates into the room from above, even when the downstairs air feels fine.
Downstairs rooms have a buffer. A vented attic sits above them, and insulation at the attic floor is meant to keep that heat out of the bedrooms. A finished attic removes the buffer. You occupy the hot zone. Knee walls, dormers, and sloped ceilings add surface that takes more of the load.
People often try to reach the new room with a long supply run and a return. That plan looks simple and usually fails in July. The air handler and the original ducts did not include this space. A mini split puts an indoor unit in the conversion so the downstairs system keeps the job it already has.
The Price on the Card
That is materials and labor for a standard single zone mini split installation. One day every week is the Joker Day at $2,200. Which day it lands on changes week to week, and the current Joker Day is revealed on the home page.
A $400 materials deposit books the date. The balance is due on completion.
Call the crew: (512) 297-7493Heat coming off the roof deck
The sun sits on asphalt shingles for hours. The deck stores that energy and radiates it down. Crawl an unfinished attic in August from Waco through Austin to New Braunfels and you know the feeling. A finished room only adds drywall and a small cavity between you and that same deck.
Radiant heat keeps arriving after you set a downstairs thermostat to 72 degrees. West facing slopes take the long afternoon. Low pitch roofs hold heat against the ceiling. Dormer glass faces the sky. This load is not the same as a first floor bedroom with a full attic above it.
- Roof deck heat is a radiant load, not just warm room air
- Sloped ceilings put you closer to the hot deck
- West slopes make late day the hard part of the afternoon
Insulation at the deck versus the floor
In a normal vented attic, insulation belongs on the floor. That line is the top of the envelope for the rooms below. The attic stays hot and vented. Finish the attic and leave that floor insulation in place, and you insulated the wrong side. The new room sits above the insulation, under the roof, on the hot side of the boundary.
For a conversion, the thermal boundary usually moves up to the roof deck or the rafter bays. Insulation at the deck, or in the rafters, puts the finished room inside the envelope. Knee walls need the same care or they dump heat and air into the space. The old attic floor can remain a floor. You live in this room now, so the roof assembly is the envelope that matters.
Why extending ductwork up there rarely works
The air handler and trunk ducts were chosen for the house as built. A finished attic adds floor area plus a roof load the original layout never counted. The blower only moves so much air. Asking that machine to cover another room in July is a second job.
A new flex run up a chase looks like a fix. Long runs, tight bends, and crushed sections add resistance. The duct often crosses leftover hot pockets, so air inside the duct gains heat before the register. Supply arrives weak. A return is often missing or stuck in a hall, so the door shuts and the room does not balance.
Send extra air upstairs and rooms below can starve. Keep the new register small and the attic room stays behind. Separate equipment for the conversion leaves the original ducts on the original rooms.
How a mini split serves the conversion
A mini split uses an indoor unit in the room and an outdoor unit, connected by a line set. Refrigerant lines and a condensate drain replace a long duct. That matters when chases are full and there is no spare trunk to tap.
A wall unit on a gable can throw air down the room. Some layouts use a tall knee wall. Ceiling units show up when wall space is gone, if the framing above allows it. Those choices need a walk through, not a floor plan alone.
Sizing starts with a general BTU rule of thumb based on area and roof load. A site visit confirms the number. Dormer glass, insulation at the deck, leaks at knee walls, and how much of the envelope is roof all change it. Do not treat a square foot shortcut as a promise.
Line set path, drain, and room layout
Attic rooms are tight. Collar ties, low eaves, and furniture against knee walls limit indoor unit placement. The crew looks for a throw that covers the slope without dumping on a bed. The same visit traces how the line set exits, how it reaches an outdoor pad, and whether condensate can fall to a drain.
Questions People Ask
Can I just add a supply vent from the system I already have?
The existing air handler and ducts were laid out for the original rooms. A finished attic adds floor area and a heavy roof load. A long flex run through a hot chase loses cooling on the way, and the blower may not have air left to spare. Downstairs rooms can starve if you tap the trunk. A dedicated indoor unit keeps the old system on the old house.
Should insulation go on the attic floor or up at the roof deck?
For rooms below a vented attic, insulation on the floor is the usual line. For a finished attic you occupy, that line is in the wrong place. The room would sit on the hot side, under the deck. Move the thermal boundary to the roof deck or the rafter bays, and treat the knee walls. Then the conversion sits inside the envelope instead of above it.
How hot does a roof deck get in a Central Texas summer?
On a bad afternoon the roof surface can run well over 100 degrees, and past 110 degrees is not unusual. The deck under the shingles stores that heat and radiates it into whatever sits below. A finished room is close to that source. Insulation at the deck and a dedicated cooling unit address that load. Treat those figures as a general picture. A site visit looks at your actual roof.
Where does the indoor unit go in a room with sloped ceilings?
Gable walls are the cleanest throw down the length of the room. Tall knee walls can work if the unit sits high enough to clear furniture. Ceiling units appear when walls are gone, only if the framing above has depth. The crew checks bed placement, collar ties, and the line set path in the same visit. Photos help, but the slope and the furniture decide it.
Do I need a site visit if I already know the square footage?
Square footage feeds a general BTU rule of thumb. It does not capture dormer glass, insulation at the deck, leaks at knee walls, or how much of the envelope is roof. A site visit confirms sizing and also traces the line set, the drain, and the outdoor pad. Do not treat a square foot shortcut as a promise. Call or text and walk the room with the crew.
Book the Job
If you are converting an attic along the I-35 corridor and the room under the roof is the problem, call or text. Walk the pitch, the insulation at the deck, and the path for a line set with the crew before anyone opens a wall.
Call or text the crew at (512) 297-7493. Tell us the room, the size and whether it is insulated, and send a photo of the wall you want the head unit on. Standard days are $2,400, materials and labor. The weekly Joker Day is $2,200, and the home page shows which day it is this week. A $400 materials deposit holds the date and the balance is due when the job is finished.
Call (512) 297-7493