Siding is a rain screen, not a seal. Water gets behind it, and it always has. The wall assembly is designed on the assumption that it will, which is why the layer underneath is what actually keeps the house dry.
That layer is invisible in a finished job and invisible in most quotes. It is also where two proposals with the same headline price stop being comparable.
The Weather Resistive Barrier
Behind the siding sits a water resistive barrier, commonly called house wrap, which sheds water that gets past the cladding and directs it back out. It also functions as an air barrier when it is taped and sealed properly, which matters for both comfort and energy use.
The failure mode is almost never the material. It is the installation. Overlaps run the wrong direction, so water is directed behind the lower course rather than over it. Tears from the framing stage go unrepaired. Seams are untaped. The wrap is not integrated with the flashing at openings.
Ask what barrier is being used and whether seams will be taped. Ask what happens at the bottom of the wall, meaning whether water reaching the base has an exit path.
Flashing at Openings
Windows and doors are the holes in the wall, and flashing is what makes them not leak. This is where most siding related water damage originates.
A correctly detailed window opening gets a sill pan or flashing at the bottom, jamb flashing lapped over it, and head flashing lapped over the jambs and under the wrap above. Each layer sheds onto the one below, shingle fashion. Reversing any lap creates a funnel.
Other flashing points worth naming in a quote:
- Where a roof meets a wall, including kick out flashing at the bottom of a roof to wall intersection. A missing kick out sends the entire roof's water into the wall cavity and it is one of the most common causes of hidden rot.
- Deck ledger connections, which are both a water and a structural detail
- Penetrations for hose bibs, dryer vents, electrical, and gas
- Horizontal transitions between cladding types or at a band board
Ask whether flashing is being replaced or reused. Reusing old flashing on a new siding job is a real cost saving and a real risk, and you should at least know which one you are buying.
Sheathing and Rot Repair
Nobody knows what is under the siding until the siding comes off. On a house with existing water intrusion, some sheathing and occasionally some framing will need replacement.
This is the single largest source of change orders on siding jobs. A quote with no provision for it is not cheaper, it is incomplete. Ask each contractor:
- What is the per sheet or per square foot price for sheathing replacement
- What is the hourly or unit rate for framing repair
- How much is included in the base price before extra charges begin
- Will you be shown the damage and given the chance to approve before work proceeds
That last point matters. How change orders work on a home project covers the mechanics, and this is the classic case of budgeting for the parts of a project you cannot see.
Signs you should expect to find something include soft spots when you press on the wall, staining below windows, peeling paint on the interior of exterior walls, and any history of a roof or gutter problem above. Signs your siding needs attention covers what to look for before the quotes start.
The Insulation Opportunity
With the siding off, the wall is more accessible than it will be again for decades. Two options come up.
Continuous exterior insulation, typically rigid foam or mineral wool board over the sheathing, adds R value across the whole wall including the framing, which is where a stud wall loses heat. It also moves the dew point outward, which has moisture implications that depend on your climate zone. It adds thickness, which means window and door trim extensions and adjusted details. It is a meaningful upgrade and it is a real added cost.
Cavity insulation in an uninsulated older wall can be blown in from outside while the siding is off, which avoids drilling from inside the house. On a house with empty stud bays this is often the higher value option per dollar.
Ask both to be priced separately so you can see what each costs rather than having it folded into a single number. If you are considering it, do not do it without a contractor who can speak to the moisture implications in your climate zone, because a wall assembly that cannot dry in the direction it needs to is worse than one with less insulation.
What Should Appear in the Quote
- The siding product, profile, thickness, and finish
- The water resistive barrier product and whether seams are taped
- Flashing scope at every opening and transition, and whether it is new
- Rot repair rates and what is included in the base
- Insulation, if any, specified separately
- Trim, soffit, fascia, and corner treatment
- Caulking and sealant type at joints
- Disposal, and whether old siding removal is included or whether they are going over it
- Permit responsibility
- Warranty terms, both material and workmanship
Going over existing siding rather than tearing off is less expensive and it means nobody inspects the wall underneath. On a house with no history of moisture problems it can be a defensible choice. On a house with soft spots, it buries the problem.
Cost Context
Siding replacement commonly runs somewhere in the $7,000 to $20,000 range for a whole house, varying widely with material, house size, number of stories, and complexity. Material prices have been moving, which we covered in fiber cement and vinyl siding prices in 2026, and material selection is compared in comparing siding materials.
Get at least three quotes and hold them to the same underlayment and flashing scope. Verify licensing and insurance using verifying a contractor's license, insurance, and references.
If you want quotes for siding installation or repair, tell us about your home and we will connect you with contractors serving your area. It is free to use, with no obligation to hire.