Before assembling your Therma-Dome cover, read and understand these instructions completely.

Determine which installation method will be appropriate for your application. The kit includes all material needed to assemble the cover in either configuration. All parts may not be used, depending on your installation requirements.

If the attic has floor decking, it is recommended that the cover be assembled and installed as a lift-off unit (Method A).

If the attic floor is open (especially if loose fill insulation is used on the attic floor), the cover should be assembled so that the sidewall assembly doubles as an insulation dam. (Method B), which will allow insulation to be installed to the full depth right up to the attic opening.

Make sure there is enough headroom in the space above the attic stair opening for the completed Therma-Dome cover to fit through the opening. If the opening is obstructed, the assembly must be done in the attic. Assembly is best achieved on a flat, sturdy work surface.

All Therma-Dome parts are lap-jointed for a precise fit, and should have a continuous ¼" bead of adhesive applied to the center of each joint as you assemble your Therma-Dome cover.

Part "A"
End pieces
(short, with Velcro® strap and gasket)
Part "B"
Side pieces
(long, gasket on one edge)
Part "C"
Top center piece
(long, nothed on both edges, with D-rings)
Part "D"
Top side pieces
(long, notched on one edge)
Part "E"
Top second layer
(no notches, only included in R-40 kits)

Always hold the pieces securely by the thickest part of the board to avoid breakage of the component.
Do not hold pieces by the narrow part of the board as breakage could occur.

Initial Assembly

Steps 1 and 2 apply to either assembly configuration.

After completing Step 2, complete Step 3 and on corresponding to the installation method you are using.

Step 1:

Apply adhesive to and join each end (Parts "A") and side (Parts "B") together.

Make sure all parts are tight and edges are even. Use 3- to 4-inch lengths of foil tape to secure each of the four corners while the adhesive dries.

Step 2:

Assemble the three lid components (Parts "C" and "D") together by applying a continuous bead of adhesive along the shiplap of one of the components, then firmly joining the two components together. A slight "back-and-forth" motion as you press down will help to ensure a solid bond.

Apply foil tape to the length of both sides of each joint.

Assembly Method "A" (Placement as a lift-off cover)

Follow these steps to complete the cover installation if you are placing the cover as a unit that lifts off in its entirety.
This installation configuration allows the cover to be completely removed for unobstructed access (no "trip hazard") to the attic when needed for storage or maintenance.

Step 3:

The gasketed edge should be downward facing. Apply a bead of adhesive along the top edge of the assembled side panels.

Place the assembled lid onto the top of the sides, ensuring that the edges line up to form a square box. Although they will not be used in this assembly configuration, the D-ring anchors on the lid should be facing the inside of the cover.

Use 6-inch sections of foil tape to hold the lid onto the sides while the adhesive dries.

Step 4:

Use the remaining adhesive to attache the final lid panel components (Parts "E") to the upper surface of the lid, side-by-side, gently pressing each panel into place.

Note: the second-layer of the top panel is only included with the R-40 version of the stair cover.

Step 5:

Flip the cover over onto its lid. Apply foil tape to the inside corners of each joint.


If there is not a solid attic floor to mount the cover against, cut strips of flooring material (such as plywood or OSB, which may be included in the Versa-Dome kit that you purchased). Attach these strips to the floor surrounding the attic opening. Blocking may be required to support the strips.

Center and nail the anchors to each end of the stairway opening so that the Therma-Dome cover can be secured in place over the attic opening using the Velcro® straps that are attached to each end of the inside of the cover.

Assembly Method "B" (Placement as an insulation dam with lift-off lid)

Follow these steps if you would like to install the cover in such a way that the sidewalls remain fixed to the floor of the attic (to act as an insulation dam).

Step 3:

Measure and cut the wood strips to the appropriate length to form a continuous, level surface for the sidewalls to attach to. Secure these wood strips to the framing of the attic floor around the staircase opening (blocking under the strips if necessary to support them), and caulk or seal any joints that may allow air to bypass the cover.

Step 4:

After test-fitting the cover to ensure a good fit, apply a continuous bead of adhesive to the non-gasketed edge of the assembled side panels, and gently press the assembly onto the floor surrounding the stair opening.

Apply foil tape to the seam between the floor and the side panels, and also to the inside corners of the joints between the side panels.

Step 5:

Apply the remaining adhesive to the upper surface of the lid (the side that does NOT have the D-ring anchor points), and gently press the remaining lid components (Parts "E") into place side-by-side.

These seams do not need to be taped, since the air seal was accomplished with the taping of the seams on the first layer.

8- to 10-inch pieces of tape may be used to hold the second layer panels in place while the adhesive dries.

Note: the second layer of the lid is only included with R-40 versions of the cover.

Step 6:

Set the lid in place and use the Velcro™ straps and D-ring anchors to secure the lid in place over the attic staircase.