Short answer
Usually yes, because the flashing at each window and the water resistive barrier behind the siding are one water management system that can only be built as a unit while the siding is off. Combining also removes a second mobilization, a second staging setup and a second round of trim and caulking. The honest reason to split them is budget, since the two jobs together are a far larger number than either one alone.
On this page
If you are replacing siding and you know the windows are also near the end, do them together. The reason is not scheduling convenience. It is that the flashing around each window and the water resistive barrier behind the siding are a single assembly, and the only time that assembly can be built correctly from scratch is when the walls are stripped.
This post is about the combined project specifically: what it changes technically, what it actually saves, and when splitting the two is the better financial decision. We have written separately about doing windows in phases versus all at once, which is a different question.
The physical reason the two jobs belong together
Water that gets past siding is normal. Siding is a rain screen, not a seal. The layer that actually keeps the wall dry is the house wrap or felt behind it, plus the flashing that ties every opening into that layer.
At a window, the correct sequence is specific: sill pan or sill flashing first, window set and fastened, jamb flashing lapped over the window nailing fin, head flashing lapped over the jambs, and the house wrap lapped so every piece sheds down and out. Each layer overlaps the one below it like shingles. Get the order wrong and water that reaches the barrier travels behind it instead of back out.
You cannot build that correctly through a hole in finished siding. So when windows come after siding, one of two things happens. Either the installer uses an insert window that sits inside the existing frame and leaves the original flashing alone, or the installer cuts back the new siding and trim to reach the barrier, then patches it.
What this means for full frame replacement
The distinction that drives everything is insert versus full frame. An insert window keeps the old frame and sill, and does not disturb the flashing. A full frame replacement removes the old window down to the rough opening, which is the only way to deal with a rotted sill, out of square openings, or a frame that has been leaking for years. We cover the trade-off in detail in insert versus full frame window replacement.
Full frame work is the case where combining is close to mandatory. If you are going down to the rough opening anyway, doing it while the siding is off costs almost nothing extra in labor and produces a properly flashed opening. Doing it later, through new siding, costs real money and leaves seams in a wall you just paid to make continuous.
Where the money actually moves
Homeowners expect a bundled job to come in dramatically cheaper. It does not. Materials cost what they cost, and the labor to hang siding is the same labor whether or not the windows are new. What combining removes is duplicated overhead.
| Cost item | Separate projects | Combined project |
|---|---|---|
| Cost itemMobilization and setup | Separate projectsTwice | Combined projectOnce |
| Cost itemStaging, ladders, fall protection | Separate projectsTwice | Combined projectOnce |
| Cost itemDumpster and disposal | Separate projectsTwo cycles | Combined projectOne cycle |
| Cost itemWindow trim and capping | Separate projectsTrimmed, then re-trimmed or capped | Combined projectDetailed once |
| Cost itemCaulking and finish work | Separate projectsTwo rounds | Combined projectOne round |
| Cost itemLandscaping protection and cleanup | Separate projectsTwice | Combined projectOnce |
For reference on the scale of the numbers, Connecticut siding generally runs $8,000 to $35,000 for vinyl and $18,000 to $80,000 or more for James Hardie fiber cement, depending heavily on wall area and trim complexity. Standard vinyl replacement windows run roughly $300 to $700 per window installed, premium wood and fiberglass units $800 to $1,500 or more, and a full house of 10 to 15 windows commonly lands between $5,000 and $20,000 or more. Those are general ranges for Connecticut homes, not a quote. Larger or custom units, common in Greenwich and Westport, run higher.
The trim detail is the real saving
The line item people underestimate is exterior window trim. When siding goes on around old windows, the existing trim either stays, gets replaced, or gets capped in aluminum. When new windows come later, that trim gets disturbed again. Doing both at once means the trim is cut, flashed and finished once, to the new windows, with nothing patched.
The case against doing both at once
There is one, and it is mostly about cash.
- The combined number is large. Two projects that each felt manageable become one invoice in the mid five figures. If financing that means stretching, splitting is reasonable.
- The windows may not be the problem. If the existing windows are sound double pane units with intact seals and good operation, replacing them to match a siding job is spending money on appearance. Check the glass for fogging, check operation, and check the NFRC label if one survives.
- Inserts make the delay cheap. If the frames and sills are solid and you expect to use insert windows later, waiting costs you a second mobilization but not a compromised wall.
- One long disruption versus two short ones. A combined job keeps crews on the house longer, with more of the exterior open at once.
If you do split them, say so before the siding is ordered. The installer can detail the openings so a later window job does not require opening whole walls, and can leave matching material behind for patching.
Permits, egress and code numbers
Most Connecticut towns do not require a permit for a straightforward like-for-like replacement of either siding or windows. A permit is generally required once the scope grows: exterior insulation, sheathing replacement, resized openings, altered headers, or structural repair found after demolition. Combined projects reach that threshold more often, because stripping the walls is exactly when bad sheathing turns up. The details are in our post on siding and window permits in Connecticut.
Two code items to verify regardless of permits:
- Egress. Every bedroom needs at least one window meeting egress dimensions. An insert window reduces the clear opening, so a room that barely complied can stop complying. Full frame replacement, which a combined project makes practical, is the usual fix.
- Energy performance. All of Connecticut is in the ENERGY STAR Northern climate zone. Under version 7.0, effective October 2023, a qualifying window needs a U-factor of 0.22 or lower and a solar heat gain coefficient of at least 0.17. The SHGC figure is a minimum, not a maximum, because in a heating climate a window that blocks too much sun gives away free winter heat.
What to ask for in the quote
Ask for the two scopes priced as separate sections within one contract. You want to see what the siding costs, what the windows cost, and what the combined pricing removes. That structure also lets you cut one section if the total comes back higher than you expected.
Specific lines worth seeing in writing:
- Whether the windows are insert or full frame, stated per opening.
- House wrap product, and how it is lapped at window heads, jambs and sills.
- Sill pan flashing at each opening, named as a product rather than implied.
- A per sheet price for sheathing replacement, agreed before demolition.
- Trim treatment at each window: new trim, existing trim retained, or aluminum capping.
- The U-factor and SHGC of the specific window being quoted.
When you are ready, request a written estimate through our estimate page. Someone comes to the house, measures the openings and the wall area, looks at the condition of the existing trim and sills, and gives you a written, itemized price for the work.
