Tools and Materials
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About Attic Flooring
Adding flooring to an attic can create valuable storage space and make it easier to move around above your home. But installing an attic floor involves more than simply laying plywood or OSB over the ceiling joists. You’ll need to consider the attic’s structural capacity, air sealing, insulation and ventilation before installing the decking.
Most attics aren't originally framed to support heavy storage or regular foot traffic. Before beginning this project, have a licensed structural professional determine whether your attic framing can support the intended load and make any required upgrades.
Attic structures and local building requirements vary, especially when creating space for heavy storage or considering a future conversion to finished living or working space. Follow local codes and manufacturer instructions for all materials.
Before You Install Attic Flooring
- Start by deciding how you plan to use the attic.
- A small area for lightweight storage has different structural and material requirements than an attic intended for heavy storage. If you think the space could eventually become an office or other finished area, account for that possibility during the planning stage.
- Many attics have ceiling joists primarily intended to support the ceiling and insulation below. Depending on the existing framing, span and intended load, a structural professional may recommend reinforcement such as sistering the existing joists, installing engineered lumber or adding other structural support.
- Don't guess when modifying structural components. Follow the recommendations of a licensed structural professional and the installation requirements of the materials you're using.
What Type of Attic Flooring Should You Use?
- Your attic access and intended use can help determine the best material.
- For an attic accessed by a typical pull-down ladder, smaller boards such as 1-by-8, 1-by-10 or 1-by-12 planks may be easier to carry into the space. These can provide a platform for appropriate lightweight storage when the attic structure has been evaluated for the intended use.
- With larger access, such as a full-size door and stairs, 4-foot-by-8-foot sheets of 3/4-inch tongue-and-groove OSB subfloor can be an option for a more permanent attic floor.
- Before covering the joists, however, take care of anything that will become difficult to access after the flooring is installed.
Installing Attic Flooring
Here are some general steps for flooring an attic for storage. Your steps will may vary greatly.
Step 1: Check the Attic Structure
- Have a licensed structural professional evaluate the attic framing and determine whether it can support your planned storage and flooring.
- The appropriate solution depends on the existing joist dimensions, spans, loads and intended use of the attic. Structural reinforcement may be required before decking can be installed.
- If you might eventually convert the attic to another use, such as an office, discuss those plans during the structural evaluation. Designing for future needs now may help you avoid having to remove the attic floor later.
Step 2: Air Seal the Attic Floor
Before reinstalling insulation and covering the joists, identify openings where conditioned air from the home can leak into the attic.
Common attic air leaks can occur around:
- Electrical boxes
- Wiring penetrations
- Plumbing penetrations
- Bath fan penetrations
- Top plates
- Joints between the framing and ceiling material
The project shown in the video uses expanding foam around electrical boxes and other gaps. A quality sealant can also be used at certain joints because it remains more elastic and can be worked into the opening. Create a continuous air barrier before proceeding.
Air sealing helps reduce the movement of conditioned air into the attic. Controlling air leakage is also an important fire-safety consideration.
Use products that are appropriate for the specific application and follow the manufacturer's instructions and all applicable building and fire codes.
Step 3: Reinstall or Upgrade Attic Insulation
- After air sealing, reinstall the insulation before covering the joist bays.
- Whether your attic contains batt insulation or blown fiberglass or cellulose, maintaining continuous insulation is important. If insulation must be temporarily removed to complete the project, make sure the required insulation value is restored.
- Fit batt insulation tightly into the joist bays without leaving gaps. When wiring crosses a joist bay, split the batt so insulation fits underneath and over the wire rather than compressing the entire batt around it.
- The insulation should fit continuously around the sides and ends of the joist bay and extend to the underside of the new subfloor where appropriate for the assembly.
- Wear the personal protective equipment recommended by the insulation manufacturer. Depending on the product, this can include gloves, safety glasses and a dust mask or other respiratory protection.
Don't remove insulation simply to make room for attic flooring without accounting for the home's insulation requirements. Compressing or eliminating insulation can reduce its effectiveness.
Step 4: Protect Attic Ventilation
- Before installing decking, make sure the project won't block the attic's existing ventilation pathways.
- In a vented attic, outside air typically enters at lower vents and moves along the underside of the roof decking before warmer air exits higher in the roof system. Blocking these pathways can interfere with the attic ventilation system.
- Keep required ventilation paths clear and maintain any baffles or other ventilation components specified for your attic.
Step 5: Plan the Attic Floor Layout
- Determine where each panel or board will rest before applying adhesive or installing fasteners.
- Every panel edge that requires fastening needs adequate structural support below it. Don't assume the existing joists will align perfectly with the dimensions of a 4-foot-by-8-foot panel.
- If a panel edge doesn't land on adequate framing, additional framing may be required to provide a solid fastening surface. In the project shown, an additional framing member is installed alongside the existing framing to provide solid support for the panel connection.
- Plan the entire layout before permanently fastening the first panel.
Step 6: Apply Subfloor Adhesive
- For a permanent installation, apply subfloor adhesive to the framing according to the adhesive and subfloor manufacturers' instructions.
- Adhesive can help reduce squeaks and create a stronger connection between the subfloor panel and framing. However, it also makes the flooring considerably more difficult to remove.
- If you expect to access the joist cavities or remove the attic decking in the future, consider whether a permanent glued installation is appropriate before proceeding.
- Work one panel at a time so the adhesive is ready when you position the panel.
Step 7: Set the First Attic Flooring Panel
- Before setting the panel, identify the joist locations so you'll know exactly where the fasteners need to go.
- Carefully lower the first panel onto the joists rather than dropping it.
- Dropping a heavy sheet onto the framing can create vibration that may damage drywall or plaster on the ceiling below.
Step 8: Fasten the Panel to the Framing
- Fasten the panel according to the subfloor manufacturer's instructions and your project's structural specifications.
- The fasteners must engage the framing beneath the panel to create a secure connection.
- The project shown in the video uses a nail gun for faster installation. If you're using a nailer, wear safety glasses and follow the tool manufacturer's operating and safety instructions.
- Continue checking that every panel edge has adequate support as you work across the attic.
Step 9: Stagger the Subfloor Joints
- For the tongue-and-groove OSB installation shown, offset the end joints rather than aligning them across adjacent rows.
- Staggering the joints distributes connections across the framing instead of creating one continuous joint. In the demonstrated installation, joints are offset by at least a couple of joists.
- Continue installing panels according to the manufacturer's requirements, checking alignment, support and fastening as you go.
Step 10: Inspect the Finished Attic Floor
Once the attic decking is installed, inspect the work before loading the space with stored items.
Confirm that:
- Panels are securely attached to the framing.
- Panel edges have adequate structural support.
- Required ventilation pathways remain open.
- Insulation hasn't been unnecessarily compressed or removed.
- Required access to electrical, mechanical or other building components hasn't been blocked.
- The amount and weight of stored items stay within the capacity established for the attic structure.
With proper structural planning, air sealing, insulation, ventilation and material selection, you can create a more useful attic storage area while preserving options for how you might use the space in the future.