Historic Window Repair or Replacement in California

Original windows are a large part of what makes an old house look the way it does: the wavy glass, the thin muntins, the depth of the sash in the wall. They are also drafty when neglected, painted shut more often than not, and coated in lead paint. Both things are true, and the right course is rarely to replace everything or to touch nothing.

This page is part of our California window guide. It is written for owners of older houses, whether formally designated or not.

First, work out what you have

Three questions shape everything else.

1. Is the building designated? A local landmark, a contributing building in a local historic district, or a property on the California or National Register is treated very differently from a house that is simply old.
2. Are the windows original? Many old houses have already had some windows replaced, often with aluminum in the 1960s or vinyl later. Replacing a non-original window is usually much easier to get approved than replacing an original one, and it can be a chance to put back what was there.
3. Which elevations are visible from the street? Preservation review concentrates on what the public sees.

Repair or replace: judging condition

The National Park Service's Preservation Brief 9, the standard reference on historic wood windows, sorts repair into three classes of increasing effort.

• Routine maintenance. Removing paint build-up, freeing sashes, replacing broken glass and failed putty, renewing sash cords, adding weatherstripping, repainting. Most windows that "need replacing" need this.
• Stabilization. Treating and consolidating wood that has begun to decay, filling, and repainting, where the piece is still structurally sound.
• Splices and parts replacement. Cutting out a rotted section, such as the end of a sill or the bottom rail of a sash, and fitting new wood to match, or making a new sash for an existing frame.

The brief's position is that retaining and repairing original windows is desirable wherever possible, and that there is a point at which condition clearly indicates replacement. When it does, it advises starting not with a catalog of replacement products but with the window being replaced: the pattern and size of the openings, the proportions of frame and sash, the configuration of panes, the muntin profiles, the type of wood, and the characteristics of the glass.

San Francisco's Planning Department makes the practical case. Deterioration usually starts on horizontal surfaces and at joints where water collects. Many wood windows from the late nineteenth and early twentieth centuries still perform well because they were made of dense heartwood. And an owner should survey all the windows before deciding, because often only some need replacing. The department notes that windows on east and north elevations often last longer than those facing south or west.

Signs replacement is reasonable

• Sash joints have opened and the sash is racked out of square.
• Rot runs through several members of the sash or into the frame and the framing around it.
• The window is a later, poor-quality replacement with no historic value.
• The cost of repair, honestly quoted, exceeds a faithful replacement.

Improving comfort without replacing

Most of the heat lost through an old window goes through gaps, not glass. Sacramento's historic district standards say so directly: most heat loss related to older windows is the result of air leakage through gaps that have developed because of a lack of maintenance, and they recommend repairing single-pane windows so they are tight fitting and considering weatherstripping or glazing film instead of replacing them with double-pane units.

The options, roughly in order of cost:

• Weatherstripping the sash and frame.
• Window film on the existing glass. Sacramento's exemption form lists clear insulating film. See window film versus window replacement.
• Interior storm panels. San Francisco's standards note that an interior storm window does not require a building permit there, and Sacramento lists interior storm systems among exempt work. See storm windows.
• Reglazing the existing sash. Where the sash is thick enough, single glass can sometimes be replaced with laminated or thin insulated glass. San Francisco notes that changing glass types requires a building permit.

Under the 2025 Energy Code, glass replaced in an existing sash and frame, or sashes replaced in an existing frame, are treated as repairs, provided the replacement is at least equivalent to the original in performance. That is helpful for owners who want to keep the frames and improve the glass.

The California Historical Building Code

The California Historical Building Code is Part 8 of Title 24. It exists so that historic buildings can be repaired and altered using alternatives to the regular code where strict compliance would damage what makes them significant.

It applies to a qualified historical building or structure, which Health and Safety Code section 18955 defines as any structure or property deemed of importance to the history, architecture or culture of an area by an appropriate local or state governmental jurisdiction, including buildings on existing or future national, state or local historical registers or official inventories. City and county registers and designated historic districts count.

For a private owner dealing with a city building department, Section 8-102 of the code provides that the agency applies it to permitted repairs and alterations when the owner elects to use it. So you may need to ask for it by name.

For windows, two consequences matter.

• Energy. The 2025 Energy Code excepts qualified historic buildings, as regulated by the Historical Building Code, from its general scope. An owner of a qualified building is therefore not automatically held to the U-factor and SHGC figures that apply to an ordinary house, though the building department makes the determination.
• Life safety still counts. The Historical Building Code offers alternatives, not a blanket waiver. Bedrooms still need a way out, and glass in hazardous locations is still a hazard. Discuss escape openings and safety glazing with the building official early. The ordinary rules are in Sections R319 and R324 of the 2025 California Residential Code, formerly R310 and R308.

Local review: the city decides

Preservation is administered locally, and the rules differ in every city. Two examples from where we work show the range. Both describe the position in 2026. A state law that takes effect on 1 January 2027, covered in the next section, limits local review of like-for-like window replacement on buildings that are not designated historic resources.

San Francisco

The Planning Department's Standards and Recommendations for Window Replacement, dated May 2025, begins with a rule that surprises people: all window replacement projects in San Francisco require a building permit, wherever the window is on the building.

Every property falls into one of four categories:

The material rule for Categories B and C comes from Planning Code Section 136.2, passed in May 2025, which provides that the Planning Department shall impose no restrictions related to the replacement material of any window frame or sash that replaces an existing one. The document states that the legislation does not apply to historic buildings in Category A or A*, or to enlarging openings or adding new ones.

For Category A buildings the standards include a matrix. In outline: an original wood double-hung is replaced with a wood double-hung or single-hung, or aluminum-clad wood if the original has already been replaced; an original wood casement with a wood or aluminum-clad wood casement; and original thin-profiled aluminum with aluminum, or in some cases fiberglass. Windows not visible from a public right-of-way can be of any material and operation. The standards also say that existing wood windows with ogee lugs, the small curved horns at the bottom of the upper sash, must be replaced with integral lugs, not snap-on ones.

The department is clear about one thing: talk to it before you buy. It may be unable to approve windows that have already been purchased or installed.

Sacramento

Sacramento reviews work on Landmarks and on Contributing Resources in its historic districts, including Midtown and the older central city neighborhoods and, since 2024, the South Land Park Hills Eichler district. The city's standards are based on the Secretary of the Interior's Standards for the Treatment of Historic Properties.

The city's form for windows and doors on historic properties, CDD-0033, states that proposals to replace, as opposed to repair or retrofit, existing original windows on a Landmark or Contributing structure require a Preservation Application. It lists work that is exempt from site plan and design review where openings, trim and sills are unchanged, including:

• replacing only missing or non-original windows with new ones that match the original historic windows in kind, where new glazing may be dual pane even if the original was single pane, and new sashes may be single-hung even if the originals were double-hung;
• replacing clear glass within the original sashes, including retrofitting with insulated glass if the sashes are wide enough;
• adding clear insulating film or an interior storm system;
• repairing cords, weights and hardware to match;
• caulking, weatherstripping, patching and repainting.

The form defines matching in kind as matching design, dimensions, placement, materials and finishes. The citywide historic district standards add two blunt instructions: avoid the use of vinyl windows and false divided lites, and where non-original aluminum or vinyl windows replaced wooden hung windows, it is appropriate to put the wood ones back.

Other California cities run their own programs with their own forms. The pattern is consistent: repair is preferred, visible replacements must match, and you ask before you order.

A new state law: Government Code 65850.73

Senate Bill 908, signed in September 2026, adds Government Code section 65850.73, operative 1 January 2027. It changes local review of window replacement across the state, and its historic exclusions decide which side of the line your house is on.

What it does

The section covers a residential window replacement project: one that only replaces existing windows in a single-family or multifamily residential building with windows of the same size and in the same location, involves no physical alterations beyond those necessary to install them, and complies with all applicable provisions of Title 24, including the Residential Code, Building Code, Fire Code, Wildland-Urban Interface Code and Energy Code.

For such a project, a city or county:

• must approve the application administratively;
• may not require discretionary review or a hearing;
• may not deny it unless it makes written findings, based on substantial evidence in the record, that the project would have a specific, adverse impact on public health or safety and that there is no feasible way to mitigate or avoid it;
• may impose only objective conditions necessary to mitigate such an impact.

The Legislature declared the subject a matter of statewide concern, so the section applies to charter cities too. A separate subdivision addresses a local government that is both a city and a county, which in practice means San Francisco, and windows proposed in housing development projects there.

What it leaves alone

The section does not apply to:

• a residential building individually designated on the California Register of Historical Resources, if it was designated before the window application was submitted;
• a residential building individually designated on a local register of historical resources, or designated as a contributor to a multicomponent resource on a local register, again if designated before the application.

There is an exception to the second exclusion: it does not cover a building designated on a local register based primarily on its age.

How to read it for your house

• A designated landmark or a contributing building in a locally designated historic district is excluded. Preservation review of your windows continues as before. That covers Sacramento Landmarks and Contributing Resources, and buildings designated under local landmark ordinances generally.
• An old house that is not designated, or one flagged only because of its age, gets the benefit of the section from 2027 for a same-size, same-location, code-compliant replacement.
• A building that has been surveyed or found eligible but never formally designated is the uncertain case. The exclusions are written in terms of designation. How each city maps its own categories onto the statute is for the city to say, and at the time of writing cities have not published their procedures. Ask the planning department in writing.
• Enlarging, moving or adding openings is outside the definition in every case.

A building permit and compliance with Title 24 are still required, because compliance is part of the definition. And being entitled to approval is not a reason to throw away repairable original windows.

The same bill adds Civil Code section 4754, which limits what homeowners associations can require. See HOA window replacement approval.

Mills Act contracts

The Mills Act is the state law that lets cities and counties contract with owners of qualified historic properties: the owner agrees to restore, maintain and protect the property, and in return receives property tax relief. The California Office of Historic Preservation calls it the single most important economic incentive program in California for historic buildings in private ownership.

The points that affect window decisions:

• Contracts are for an initial 10 years, renew automatically each year, and transfer with the property, so a buyer inherits the obligations.
• The owner agrees to restore, maintain and protect the property in accordance with the specific historic preservation standards and conditions identified in the contract.
• Local officials inspect periodically, and local authorities may impose penalties for breach of contract or failure to protect the property.
• Each local government sets its own criteria and administers its own program. The state office is not a party to the contract.

If your house has a Mills Act contract, the contract is the first document to read before any exterior work. Our sibling page on window replacement and property taxes covers the tax side for ordinary houses.

If you do replace

A good replacement for a historic wood window is recognizable by a few things, drawn from the San Francisco and National Park Service guidance:

• Same material and operation as the original on visible elevations.
• Depth. San Francisco's standards say windows should ideally sit about 2 inches back from the face of the building to the sash. A replacement set flush with the wall looks flat.
• Muntins that have substance. Where simulated divided lites replace true ones, San Francisco recommends an exterior muntin that matches the original profile, commonly about 7/8 inch wide and at least 1/2 inch deep, with a dark spacer bar inside the insulated unit, and advises against snap-on grilles or grilles between the panes. Our sibling page on window grilles explains the types.
• Existing trim kept. Retain the original casings and sills wherever they are sound. See the exterior window trim guide.
• No partial mixing on one elevation. Replace by elevation so the front of the building reads consistently.

Wood and aluminum-clad wood windows are covered on wooden windows and our sibling page on wood versus vinyl windows.

Lead paint

Assume original windows in a pre-1978 house carry lead paint. The EPA's Renovation, Repair and Painting rule requires firms paid to do work that disturbs painted surfaces in homes built before 1978 to be certified and to follow lead-safe work practices. Windows are a particular concern because the sashes rub in their tracks and the sills collect the dust. This applies to repair as much as to replacement. See lead paint and window replacement in pre-1978 homes and lead-safe exterior work.

Related guides

Windows are one part of the exterior. For the walls around them, see siding solutions for historic homes. For matching windows to architecture generally, see windows for California home styles.

Sources

• San Francisco Planning Department, Standards and Recommendations for Window Replacement (version dated 2 May 2025).
• City of Sacramento, form CDD-0033, Windows/Doors: Repairs/Changes, Historic Properties (19 July 2024).
• City of Sacramento, Standards & Criteria Common to Sacramento's Historic Districts.
• Senate Bill 908 (Chapter 787, Statutes of 2026), adding Government Code section 65850.73 and Civil Code section 4754.
• California Office of Historic Preservation, Mills Act Program.
• California Health and Safety Code section 18955: definition of a qualified historical building or structure.
• 2025 California Historical Building Code (Title 24, Part 8), Section 8-102.
• California Energy Commission, 2025 Building Energy Efficiency Standards: Section 100.0(a) Exception 1 and Section 150.2(b)1B.
• National Park Service, Preservation Brief 9: The Repair of Historic Wooden Windows.
• U.S. EPA, Lead Renovation, Repair and Painting Program.
• 2025 California Residential Code, Chapter 3.

Working with Heritage Exteriors

We are a replacement contractor, not a sash restoration shop, and when your windows are repairable we will tell you so and suggest you find a restorer. When replacement is the right answer on an older house, we will help you put the product sheets together for the planning counter before anything is ordered. Licensed in California, CSLB #1055919. Call (916) 546-2991.