Technical Papers

Insulation & Air Sealing - Different Methods to Treating a Walk Up Attic

Thursday, March 1st, 2018 by Hal Smith

This article was written by Halco owner, Hal Smith, and published in ACCA's newsletter, IE3. Please click here to visit the original publication. 

StockWalk up attics have to be dealt with differently than a normal attic with a hatch. They are different because the interior attic door, the back of the stairs, and the three walls surrounding the stairs are typically outside and all need to be dealt with in some manner. In my opinion it is not effective to try to insulate & airseal these areas. Our company has tried many times with minimal success. You think you do alright with it until you check afterward, with a blower door running and while using a thermal imaging camera. All that hard work with disappointing results! It's pretty difficult to put foam on the back of an interior attic door, seal it well and still have it operate.

Things to consider before deciding how to solve this puzzle!

  • Are there any future plans of finishing the attic space?
  • Is there an air handler and or ductwork in the space?
  • How is the space being used?
  • Is the space used for cold storage with just occasional entry?
  • Are there windows in the gable ends that need to be considered?

If there are future plans of finishing the space:

  • Typically spray foaming the attic slopes and gable ends is usually the best treatment
  • Our company cuts sheets of 1” foam board into 3”x8’ furring strips. These foam furring strips when fastened to the rafters and gable ends walls prevent thermobridging and help to level out the surface to later screw drywall to. We install these foam furring strips before we spray foam. We then lace the foam on the side of the rafters then spray down to the back of the foam board. This provides a great seal!
  • When doing this method, it is very important to pay close attention to the outside top plates. Make sure you are able to spray to the back side of the top plate other wise cold air can come in and warp the ceiling below.
  • If you are going to ventilate this attic it is very important to staple ventilation shutes from the soffits up the rafters to the ridge vent before spraying.
  • Plan on how you are going to treat the windows in the gable ends. In some cases, the homeowner will have us replace these windows because they have immediate plans of finishing the space. Other times we will install foam board plugs over the windows that can easily be cut out later. We typically find the existing windows to be in very poor condition
  • Our company recommends to spray a minimum of 4” of closed cell foam on the slopes and 3” of closed cell foam on the gable ends.
  • When we are able to treat a walk up attic using these methods we have excellent results and the homeowner gains a lot of space in their home.
  • The down side to this method is that it is not inexpensive, we would typically see $8,000 dollars plus! for a job like this depending on the size.

If the attic is used as cold storage with a minimal amount of access needed, we suggest the following:

  • We close off the walk up opening at the attic flat by installing a prebuilt 2’x6’ attic hatch and framing in the rest of the opening, we then cover it with foam board. This method works well in both attics with straight stairs and attics with “L” shaped stairs. It is not as convenient as a walk up attic but much more energy efficient.
  • We would typically dense pack the floored attic flat and then offer to also add 2” foam board sandwiched with 7/16” OSB board on top. This goes right on top of the existing floored attic. Sometimes when we are dealing with a low income program we are only able to dense pack the existing floored attic because of budget constraints.
  • When using this method, it is very important to spray foam the top plates just as it is when insulating the slopes & gables.
  • When we use this method, it takes the attic door stairs and wall out of the picture because you have extended the thermal and pressure boundary completely to the attic flat.
  • This method is much less expensive and works extremely well when the attic is only used for storage with limited entry.

How to treat an attic with an air handler and/or duct work:

  • Remember that the air handler and duct work is outside the thermal boundary in this scenario.
  • If it is possible to spray foam the attic slopes and gables as suggested above that would be the preferred method. This will bring the air handler and duct work inside the thermal and pressure boundary.
  • If you are using the attic flat method then it is important to build an insulated doghouse with access panels out of foam board around the air handler and then spray foam all of the ductwork. This takes considerable labor to properly do but still ends up less expensive than spray foaming the slopes and gables. Make sure you follow all local codes as they pertain to thermal and ignition barriers.

I hope this helps. We have a lot of old homes with walk up attics in our area. I realize some areas of the country do not have any. If there are any questions, please don’t hesitate to contact me.

CLICK HERE to see a recent walk up attic job completed in Rochester, NY!

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