Insulating a small room-closet in existing basement

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Dec 6, 2009
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I am in the process of converting a small storage room in my basement to a small closet for servers/IT equipment/telecom stuff. This closet is approx. 80sqft and is located between a family room and a mechanical room (sump pumps, hot water heater, water well pressure tank, septic tank piping, etc).

Because of its proximity to the family room, it will be heavily insulated against noise which means heat dissipation will be negligible and no openings to evacuate the heat from the servers. It will require a small AC to keep it at around 18C (65F).

In the summer the humidity in the basement can get up to 60% and around 28-30C (80-85F). The adjacent mechanical room is also pretty humid due to the foundation sumps, misc water equipment.

I wonder how to properly insulate the walls and ceiling of that little closet. I believe that I need thermal and noise insulation and also need to block off moisture from the remainder of the house/basement so I dont end up with condensation and mold issues down the road. I have already stripped the walls from within the closet. The other side still has drywall. This is now I envision doing it:

  • Walls (except the foundation wall): vapor barrier, 3 1/2" batt cavity insulation, 1-1/4 extruded polystyrene board, sonopan noise panel + resilient channels, 2x 5/8" drywall. Total R value approx. 21
  • Ceiling: vapor barrier, 8" batt cavity insulation, 1-1/4 extruded polystyrene board, sonopan noise panel + resilient channels, 2x 5/8" drywall. Total R value approx. 36
  • Foundation wall: I have no idea... Similar to the other walls? Need to spray urethane to block moisture from concrete?

  1. As far as I know usually vapor barriers are normally installed on the "hot side" of the wall, which in my case would be on the unstripped side of the walls of that closet. Unless I strip the walls down to the studs on both sides of the walls, I cannot install a vapor barrier film on the "hot side" of the walls. How do I do this?
  2. How to insulate the foundation wall?
  3. How do I do the joints/junctions between walls and ceiling?
Thanks !!
Before I did anything I'd test the walls to see if moisture is coming in through them. Tape a piece of plastic or foil to the wall sealing all for sides. If after a few days the wall is wet you have water vapor coming in through the foundation. If this is the case, I'd lean towards painting the concrete with Thoroseal or Drylock paint to seal it up. I'd skip any plastic vapor barrier in a basement as it will cause more problems than it will solve. It will hold any moisture between it and the concrete wall. Your AC will take care of the humidity level in the server room. I'd think for a basement space R36 is way more insulation than is needed. The basement is probably naturally above 55-60F. A double coat of drywall on both sides of the walls, will help with noise. Building the walls 6" thick with 2x4 studs alternating for each side of the wall will help reduce noise transmission through the wall. For the concrete wall use fiberglass insulation with craft paper facing. This will provide all the vapor barrier you want/need. The vapor barrier should go towards the conditioned space.

Here is a site that talks about staggered walls. It is in relation to home theater and noise there would include noises like music, and special effects from movies. Staggered-Stud Wall Framing

From the link above

Staggered Studs​

  1. With traditionally studded walls, both sides of the wall connect to each other via the studs between them. This connection allows sound to travel through the wall to the other side. Staggered-stud framing keeps the two sides of the wall from touching, reducing sound travel. The base and top plates of the walls should be of 2-by-6-inch boards instead of the regular 2-by-4s. Attach studs to both sides of the base and top plates in an alternating pattern. Use two 2-by-2s at the ends of the walls so you have something to nail drywall to on both sides of the wall.
Back at it after a few months dealing with other issues and life in general.

I'm almost done stripping the existing room and managed to understand how to frame the walls and insulate the foundation walls.... However, before I buy everything (> $2000 CAD rupees) I made a quick sketch showing what I will do.

Highlighted in orange is existing stuff I am keeping.

Note that the thick 3" EPS board on the foundation wall will be new because I found rot in the dividing wall to the mechanical room and the foundation wall is badly insulated. Question: is 3" excessive or 2" would be plenty sufficient?

Circled in a blue dotted box is the question I have regarding the foundation wall: Like I said I intend to put a 3" EPS board against the foundation (foil face pointing towards the inside of the house) then build the 2x4 wall and fill with batt insulation. Finally I was going to finish this wall the same way as the other walls of that computer cabinet: 1" EPS board (NO vaper barrier) sonopan soundproofing, resilient bars, then 2 layers of 5/8 drywall. Should I skip the 1" EPS board on the foundation wall?

Are you guys spotting anything wrong or incorrect in my sketch? Note that I opted to only apply vapor barrier on the poured concrete wall... My thinking is to let the AC capture the moisture making its way to the server cabinet and freely disperse in the house... Trapping in the walls would probably result in mold over time... For the foundation wall, its mandatory to prevent moisture from outside getting in ;)

I'm looking forward to hearing back from you guys and starting this soon!!!



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