Adding insulation to closed walls can help improve your home’s energy efficiency and comfort. Properly insulating closed walls requires some planning and effort, but it is a project a motivated DIYer can tackle. Here is a step-by-step guide to adding insulation to walls that are already finished and closed up.
Assess Your Walls to Determine the Best Method
The first step is to figure out what kind of walls you have and whether there is existing insulation that needs to be replaced or supplemented.
Identify Wall Type
- Wood frame walls – Most exterior walls in modern homes are wood frame walls made with studs, insulation, and drywall or plaster. Blown-in insulation works best for filling cavities in these types of walls.
- Masonry walls – Some exterior walls are made of concrete, block, or brick rather than wood framing. Rigid foam boards are usually the best way to insulate masonry walls.
- Metal frame walls – Insulated metal framing is sometimes used for exterior walls. Blown-in insulation can work for metal frame walls as long as there is space for it between the studs.
Check for Existing Insulation
- Examine electrical outlets and switch plates to see if there is insulation behind them. No insulation around the openings likely indicates open wall cavities.
- Check your attic for signs of insulation settling. This may reveal open cavities in wall tops.
- Consider an infrared scan. Thermal imaging can identify cold spots that show where walls lack insulation.
- Look for dates on existing insulation. Older materials likely need replacing.
Determine R-Value Goal
Calculate the recommended R-value for your climate zone to determine how much insulation is ideal. Most homes need an R-value of at least R-13 in walls, but adding more is better.
Choose an Insulation Method
Once you understand your wall structure and insulation needs, decide on the best installation method. Common options include:
Blown-In Insulation
- Loose-fill cellulose or fiberglass pumped into open wall cavities. Requires access holes.
- Offers flexibility to fill irregular spaces. Blown-in insulation can be added to existing.
- Professional installation recommended for best results.
Rigid Foam Insulation
- Rigid foam boards glued onto masonry walls or stud faces.
- Works well for unfinished walls and basements.
- Can reduce room space slightly. Need weather barriers.
Insulating Foam Sealant
- Foam applied within wall cavities to seal and insulate.
- Quick professional installation. No major holes to patch.
- Foam pricier than other insulation options.
Prepare the Work Area
Insulating enclosed walls takes some pre-work. Follow these steps to get set up:
- Clear furniture away from exterior walls so you have room to work.
- Cover floors and furnishings with drop cloths to protect from dust or debris.
- Gather materials and tools – you’ll need access holes, insulation, foam sealant, caulk, drywall patching compound, drills, and more.
- Turn off power before cutting into walls to avoid electrical hazards.
- Put on safety gear – goggles, N95 mask, work gloves, etc. Insulation work can be dusty and irritating.
Cut Access Openings
You need to cut or drill openings in your finished walls in order to inject new insulation. Strategize opening locations wisely:
- Prioritize exterior walls, attic knee walls, and rim joists first.
- Focus on plumbing wall cavities that lack insulation.
- For wood frame walls, remove outlets or cut holes to access between stud bays.
- Make small holes low down to inject insulation as high as you can.
- Open up the wall top plate in each cavity to allow insulation to fill top.
- Cut holes no larger than necessary – easier to patch smaller holes.
Install Insulation in Wall Cavities
Now comes the messy but rewarding task of installing insulation:
Blown-In Insulation
- Feed hose from insulation machine into the access holes.
- Pump in insulation evenly, filling the cavity without packing too densely.
- Use foam sealant around hose to optimize air sealing.
- Add insulation until it piles 4-6 inches deep.
Rigid Foam Boards
- Cut boards to fit tightly between wall studs or masonry.
- Apply construction adhesive generously on board and wall.
- Press in place firmly. Use fasteners for extra support if needed.
- Seal edges with foam or caulk for maximum air sealing.
Foam Insulation
- Insert foam nozzle into access hole. Adjust to fill cavity.
- Inject foam according to manufacturer instructions to avoid excess expansion.
- Let foam fully cure and set before trimming flush with surface.
Patch and Repair Walls
Once insulation is complete, you need to seal up the walls:
- Apply masking tape over access holes before patching to help minimize need for touch ups.
- Use drywall compound to patch and smooth gypsum wallboard openings. Let dry fully.
- Caulk and seal exterior sheathing, brick, or other penetrations. Make walls air tight.
- Prime and paint patched areas to match existing walls. Multiple coats may be needed.
- Reinstall trim, outlet covers, lighting fixtures, and anything else removed from walls during the project.
Consider Exterior Insulation for Optimal Effectiveness
While insulating enclosed walls does help, the most effective thermal envelope is achieved by adding insulation levels from both the inside and outside of the structure. Consider exterior insulation options:
- Add rigid foam insulation when residing or replacing exterior wall siding.
- Install foam boards beneath new siding installs.
- Attach rigid panels directly over existing siding, then cover with house wrap.
- Insulate basement walls on the exterior before backfilling.
Combining interior wall insulation with exterior layers gives you the best insulation for closed walls and the highest possible R-value.
Safety Tips for Insulating Enclosed Walls
- Turn off electrical circuits before cutting into walls to avoid nasty shocks or electrocution.
- Wear an N95 face mask and ventilate the area to avoid breathing in loose insulation materials.
- Use thick gloves and long sleeves when working with fiberglass insulation to minimize skin irritation.
- Inspect your work area beforehand and beware of hazards like asbestos or live wires.
- Prevent electrical fires by making sure insulation does not end up packed around light fixtures or wiring.
- Take care walking in an attic when blowing in dense insulation at ceiling level.
- Follow all manufacturer safety precautions when using spray foam insulation chemicals.
FAQs About Insulating Closed Up Walls
What R-value is recommended for exterior walls?
An insulation R-value between R-13 and R-21 is recommended for exterior walls in most U.S. climate zones. Higher R-values up to R-25 provide better efficiency.
Does blown-in insulation settle over time?
All insulation settles somewhat, but dense-pack methods minimize settlement. Topping off attic insulation over time helps maintain full insulation R-value.
How do I know if my walls already have insulation?
Checking electrical boxes, attic insulation levels, infrared scans, and wall interiors when doing renovations can all help determine if walls are insulated.
What areas should be air sealed when adding wall insulation?
Cracks around windows, doors, wires, plumbing, fans, and any other penetrations should all be sealed up for maximum insulation effectiveness.
Is it worthwhile to insulate basement foundation walls?
Yes, adding R-10 to R-15 insulation to foundation walls and rim joists can significantly improve basement warmth and energy efficiency.
Should I hire a professional for enclosed wall insulation?
Professional insulation installers have the tools and expertise to do the job thoroughly. However, some DIYers can handle their own retrofit insulation project.
How long does blown-in wall insulation take to install?
The time needed depends on factors like your home’s square footage and number of exterior walls. Expect professional installation to take 1-3 days for a typical single-family home.
Conclusion
Insulating existing finished walls takes a bit more effort than insulating an unfinished structure during new construction. But with the right planning and materials, you can add insulation to your enclosed walls and improve their energy performance. Target exterior wood frame walls first, use blown-in or foam insulation, methodically patch openings, and complement with exterior insulation for optimal thermal protection. With diligence and safety, even closed up walls can get upgraded insulation.