What Happens to Exterior Insulation When Siding Is Replaced?

JR Girskis: Siding Replacement Is an Opportunity to Inspect the Wall

Brian “JR” Girskis, President and Owner of Suburban Construction, joined the family business full-time in 2002 and became President in 2007.

After decades of exterior remodeling experience in the Quad Cities, JR's approach is to look beyond the new siding panel and evaluate the wall system underneath it.

That does not mean every material underneath old siding needs to be replaced. It means the materials should be evaluated before they are covered again.

Meet JR Girskis & the Suburban Construction Ownership Team

What Might Be Under Your Existing Siding?

Quad Cities homes have been built and remodeled across many decades, so there is no single wall assembly you should expect to find.

After removing the exterior siding, a contractor might find:

• Housewrap directly over structural sheathing
• Thin fan-fold foam
• Rigid foam insulation board
• Older foam products
• Existing insulated siding
• Wood fiberboard or other older sheathing products
• Previous siding layers
• Areas that were repaired differently from the original wall

This is one reason siding replacement projects should not be planned as though every house is constructed exactly the same way.

Step One: Remove the Existing Siding

A full siding tear-off gives the contractor access to the materials underneath.

Suburban Construction's siding installation process includes removing the old siding so the underlying wall can be inspected before the new exterior is installed.

This can reveal conditions that were impossible to see during the original estimate.

See the Suburban Construction Siding Installation Process

Step Two: Inspect the Sheathing

Before worrying about whether an existing foam board should stay, evaluate the wall behind it.

The sheathing may show evidence of:

• Water staining
• Rot
• Swelling
• Delamination
• Previous repairs
• Damage around windows and doors
• Problems near roof-to-wall intersections

If deterioration is discovered, the cause should be identified and the damaged material addressed before the wall is covered again.

New siding should not be used to hide an existing wall problem.

Step Three: Evaluate the Existing Exterior Insulation

Once the wall is exposed, the existing insulation can be evaluated directly.

A contractor should consider several questions.

Can Existing Foam Insulation Stay Under New Siding?

Potentially, yes.

Existing exterior foam does not automatically need to go into the dumpster just because the siding is being replaced.

If it is in good condition and the planned siding installation is compatible with it, keeping usable material may make sense.

However, the decision needs to consider more than whether the foam “looks okay.”

The contractor still needs to account for:

• Fastener requirements
• Wall flatness
• Window and door depths
• Flashing
• Trim details
• Water management
• The siding manufacturer's installation requirements

Reusable insulation needs to work with the new siding system—not simply exist underneath it.

When Should Existing Exterior Insulation Be Replaced?

Replacement may be appropriate when the existing insulation is:

• Water damaged
• Crushed
• Broken
• Missing in significant areas
• Badly deteriorated
• Creating an uneven wall
• Improperly installed
• Interfering with proper flashing
• Not compatible with the new siding installation

In those situations, keeping old insulation solely to save a small amount during the project may create unnecessary compromises in the new installation.

What if the Exterior Foam Is Wet?

Do not simply cover it with new siding.

First determine why moisture reached the wall.

Potential sources can include:

• Improper window flashing
• Door flashing problems
• Roof-to-wall intersections
• Damaged housewrap
• Exterior penetrations
• Failed trim details
• Previous installation problems

The underlying wall materials should also be evaluated for moisture damage before the new siding installation continues.

Learn About Hidden Water Damage Behind Vinyl Siding

Is Exterior Insulation the Same Thing as Housewrap?

No.

This is an important distinction.

Exterior insulation is primarily intended to improve the thermal characteristics of the wall assembly.

Housewrap or another properly installed water-resistive barrier is part of the wall's water-management strategy.

Depending on the wall system and products being used, these layers need to be integrated correctly with windows, doors, flashing, and other exterior penetrations.

Do not assume that foam insulation automatically replaces the water-management function of properly detailed housewrap or another approved water-resistive barrier.

Read: Does House Wrap Matter Under Vinyl Siding?

Can You Add Exterior Insulation During Siding Replacement?

Yes, depending on the house and the siding system being installed.

Siding replacement can be a logical time to consider exterior insulation because the exterior wall is already being worked on.

Instead of removing good siding later just to access the wall, insulation decisions can be considered as part of the siding project.

However, adding insulation affects other parts of the installation.

The contractor may need to account for:

• Fastener length
• Window projection
• Door projection
• Corner details
• Mounting blocks
• Utility penetrations
• Flashing
• Trim depth

Adding exterior insulation is a wall-system decision, not simply a matter of putting foam behind the siding.

What Is Continuous Exterior Insulation?

Traditional wall insulation is usually installed between the wall studs.

The studs themselves still create pathways where heat can move through the wall more readily. This is commonly called thermal bridging.

Continuous exterior insulation places insulating material across a larger portion of the exterior wall, including over the framing.

Depending on the product and wall assembly, this can add thermal resistance and help reduce thermal bridging.

How much benefit a particular house receives depends on the insulation product, thickness, existing wall construction, installation details, and the rest of the home's thermal envelope.

What About Insulated Vinyl Siding?

Another option is insulated vinyl siding.

Insulated siding combines a vinyl siding panel with contoured foam backing.

Potential benefits can include:

• Additional thermal resistance
• Reduced thermal bridging
• Greater panel rigidity
• A more solid feel
• Potential reduction in some exterior noise

The improvement is incremental rather than magical. Insulated siding should be evaluated as one component of the home's overall wall and insulation system.

Explore Insulated Vinyl Siding from Suburban Construction

Standard Vinyl Siding vs. Insulated Vinyl Siding

Does More Insulation Always Mean a Better Siding Project?

Not automatically.

More insulation can be beneficial, but it still needs to be installed as part of a properly designed wall system.

Homeowners should consider:

• The existing wall construction
• Current insulation levels
• The condition of the sheathing
• Water-management details
• The new siding product
• Manufacturer installation requirements
• Cost versus expected benefit

Insulation should improve the project without compromising flashing, drainage, fastening, or siding installation.

Don't Confuse Insulation With Water Management

A wall can be well insulated and still have a water problem.

A wall can also have excellent housewrap and flashing but still have relatively modest insulation.

These systems perform different jobs.

Why Window and Door Details Matter When Adding Insulation

Adding insulation changes the thickness of the exterior wall assembly.

That can affect how the siding and trim meet:

• Windows
• Entry doors
• Patio doors
• Garage doors
• Electrical boxes
• Light fixtures
• Faucets
• Vents

Those transitions need to remain properly flashed and finished.

The insulation cannot be evaluated separately from the windows, doors, trim, and flashing around it.

What if You Find No Exterior Insulation?

Do not panic.

Many existing homes were built without continuous exterior insulation.

Its absence does not automatically mean the wall is defective.

Siding replacement simply creates an opportunity to discuss whether adding an exterior insulation strategy makes sense for your particular home and budget.

What if You Find Old Fan-Fold Foam?

Thin fan-fold foam has been used behind siding on many remodeling projects.

Its presence does not necessarily mean the house has a high-performance continuous insulation system.

Depending on the product, thin foam may have been installed primarily to help create a smoother surface, with only modest insulating value.

If old fan-fold material is discovered, evaluate its condition and purpose before deciding whether to reuse, repair, or replace it.

Can Siding Be Installed Directly Over Exterior Foam?

It depends on the siding product, foam thickness, substrate, fasteners, and manufacturer installation requirements.

The siding still needs to be properly secured to an approved substrate according to the siding manufacturer's instructions.

Fastener length and penetration become particularly important as the thickness of exterior insulation increases.

Never assume that a fastening method appropriate for siding directly over sheathing is automatically appropriate over a thicker exterior insulation system.

What if Hidden Water Damage Is Found?

This is one of the most important advantages of exposing the wall during siding replacement.

If water damage is discovered, determine:

1. Where the water entered.
2. How far the damage extends.
3. Which materials need repair or replacement.
4. What flashing or water-management detail failed.
5. How the new wall system will prevent the problem from recurring.

Simply replacing wet insulation without fixing the source of the moisture is not enough.

How Can You Identify Hidden Water Damage Behind Siding?

Should Housewrap Be Replaced at the Same Time?

The existing water-resistive barrier should be evaluated once the old siding is removed.

If it is missing, torn, improperly integrated, badly deteriorated, or unable to provide the water-management strategy required for the new installation, corrective work may be appropriate.

Pay particular attention around:

• Windows
• Doors
• Roof intersections
• Utility penetrations
• Exterior vents

Learn More About Housewrap Under Vinyl Siding

Exterior Insulation Can Affect Your Siding Estimate

This is another reason two siding estimates can be very different.

One contractor may be quoting:

• Standard vinyl siding
• Minimal wall preparation
• Reuse of existing insulation

Another may include:

• Full tear-off
• Wall inspection
• New water-resistive barrier
• Exterior insulation
• Additional flashing and trim work
• Insulated siding

Those proposals represent different scopes of work.

Compare Suburban Construction Siding Options

Questions to Ask Your Siding Contractor About Exterior Insulation

Compare These Options in the Suburban Construction Showroom

Exterior insulation is difficult to understand from a photograph or a line item on an estimate.

The Suburban Construction showroom at 3602 North Harrison Street in Davenport, Iowa gives homeowners an opportunity to compare siding systems and discuss how the different layers of the exterior work together.

You can compare:

• Standard vinyl siding
• Insulated vinyl siding
• Composite siding
• Profiles and textures
• Colors
• Trim systems
• Soffit and fascia
• Exterior insulation considerations

This is also a good time to bring another siding estimate and ask exactly what the contractor intends to do with the existing insulation underneath your house.

Visit the Suburban Construction Davenport Showroom

The Bottom Line: What Happens to Exterior Insulation When Siding Is Replaced?

It depends on what is found after the old siding is removed.

Good existing insulation may sometimes remain.

Damaged or incompatible insulation may need to be replaced.

Homes without exterior insulation may have an opportunity to add it, and homeowners looking for additional thermal performance can also consider insulated siding.

But insulation is only one piece of the project.

The sheathing, housewrap, flashing, windows, doors, trim, fasteners, and siding all need to function together.

As JR Girskis' approach emphasizes, siding replacement is one of the few times you get a good look at the exterior wall. Use that opportunity to inspect it before covering it for the next several decades.