How to Write a Better Historic Window Restoration Specification
Scope, Allowances, Unit Prices, and the Details That Prevent Bid-Day Confusion
A historic window restoration specification can be technically correct and still produce three very different bids. We see it more often than you might expect.
One contractor assumes every sash will be removed, stripped, reglazed, repaired, painted, weatherstripped, and returned to operation. Another assumes deteriorated glazing will be addressed only where visibly failing. A third carries a general allowance for repairs because the documents don't define how much deterioration is included.
All three may believe they priced the drawings and specifications correctly. That is the problem.
Historic window restoration contains enough variables that broad language such as "restore existing windows" leaves too much open to interpretation. When that happens, the apparent low bidder may simply be carrying less scope. For architects and consultants, the goal shouldn't be to write a 40-page specification that attempts to predict every defect hidden beneath 100 years of paint. That's probably impossible.
The goal is to establish enough common ground that qualified restoration contractors are pricing substantially the same work. Here is where we believe the biggest opportunities lie.
Start by Defining What "Restore" Means on This Project
This sounds basic, but it is probably the most important step.
"Restore existing wood windows" is an objective. It isn't yet a scope of work.
Does restoration include removing the sash? Are all coatings being removed, or only loose and failing paint? Is all glazing putty being replaced, or only failed sections? Are sash cords included? Is the hardware restored? Are the windows expected to operate at completion? Is weatherstripping included? How much wood repair is included before it becomes additional work?
See how many questions remain unanswered with a vague scope like that? Those questions materially affect labor.
A better specification tells bidders what the finished assembly is expected to be and establishes the major steps required to get there. For a full wood-window restoration, that might include removal and identification of sash, paint removal, repairs, glass and glazing work, hardware rehabilitation, finish coatings, weatherstripping, reinstallation, adjustment, and confirmation of operation. For another project, the owner may intentionally choose a less invasive treatment.
That's perfectly legitimate.
The important thing is that everyone knows which treatment they're pricing. For a deeper discussion of defining restoration scope, see our guide, How Architects Should Specify Historic Window Restoration.
Don't Make the Contractor Guess the Window Inventory
A window schedule that identifies 200 openings is useful. A schedule that tells us what those 200 openings actually are is much more useful.
At a minimum, restoration bidders benefit from knowing:
window type
approximate dimensions
sash configuration
lite configuration
material
operation
location
known special conditions
Lite count deserves particular attention. A 6-over-6 double-hung window and a one-over-one window can have nearly identical overall dimensions while requiring substantially different amounts of glazing and detail work. Each individual lite has to be dealt with, and true divided-light muntins add considerably more surface area and detail.
If the drawings contain elevations and window types, make sure those types can be reconciled with the window schedule. If they can't, bidders start making assumptions.
Separate Base Restoration From Unknown Conditions
This is where specifications can become much more useful without pretending the architect has X-ray vision. Historic buildings contain concealed conditions. Everyone involved in preservation understands that. The answer is not to bury every possible repair inside the base bid. It's also not to leave every repair undefined.
Instead, establish what constitutes normal restoration and identify repairs that fall outside that baseline. For example, a base restoration scope might reasonably include minor localized deterioration associated with normal historic-window repair.
More significant conditions might be handled separately:
complete rail replacement
complete stile replacement
extensive muntin replacement
major sill reconstruction
replicated sash
missing hardware
substantial steel section repair
That distinction makes the base bid more meaningful. It also gives the GC and owner a clearer mechanism for dealing with actual conditions once the work is underway.
The National Park Service takes a condition-based approach in Preservation Brief 9: The Repair of Historic Wooden Windows, which provides a useful technical framework for evaluating deterioration and developing appropriate repair treatments.
Use Unit Prices for Work You Know Might Occur
Unit prices can be extremely useful in historic restoration when they're tied to clearly defined work. Suppose everyone expects some sash to require new rails, but nobody can determine the exact quantity until the paint is removed and the sash is disassembled.
Instead of guessing a quantity or negotiating every repair during construction, the bid form could request a unit price for:
Replace one deteriorated bottom rail, including fabrication to match the existing profile, joinery, preparation, installation, and finishing.
Now the team has a common pricing mechanism.
Depending on the project, useful unit prices might include:
rail replacement
stile replacement
muntin repair or replacement
sill repair
additional glass replacement by lite
replicated sash
missing or nonrepairable hardware
significant steel repair
The key is specificity.
"Wood repair – $___" isn't particularly helpful because nobody knows what one unit of "wood repair" means.
A unit price should describe a measurable event.
Don't Confuse Unit Prices With Allowances
They solve different problems. An allowance establishes a pool of money for work or material that cannot yet be fully defined. A unit price establishes the agreed price for a defined unit of work if that work is required.
Those aren't interchangeable.
On historic projects, a combination can work well. For example, the contract could carry an owner-controlled allowance for concealed deterioration while the bid schedule establishes unit prices for the most likely repair categories. If ten rails ultimately need replacement, the team doesn't have to negotiate ten new prices. The actual quantity can be documented and reconciled against the agreed unit cost.
That is far cleaner than discovering the condition first and figuring out the commercial terms afterward.
Be Careful With "Replace in Kind"
This phrase appears frequently in preservation specifications. It sounds clear. Sometimes it isn't.
If an original sash must be replicated, what exactly must match? Material? Dimensions? Muntin profile? Meeting rail? Joinery? Glass configuration? Sightlines? Operation?
"In kind" should not become shorthand for "make something that looks approximately like the original."
The Secretary of the Interior's Standards provide a much better framework. Where deterioration requires replacement of a distinctive historic feature, the new feature should match the old in design, color, texture and, where possible, materials. The National Park Service's rehabilitation guidance also specifically identifies sash, muntins, glazing configuration, sills, casings, operation, and related features as potentially important to a building's historic character.
If replication may be required, identify the characteristics that matter. For projects where existing assemblies cannot reasonably be repaired, Austin Historical also performs historically accurate replication as part of our Commercial Window & Door Restoration services.
Address Glass Before Bidding
Glass is another area where a few words in the specification can have large consequences.
The documents should clarify the intended approach to:
existing historic glass
broken panes
nonhistoric replacement glass
safety glazing locations
new glass required for replicated sash
specialty glazing
If historic glass is to be retained wherever possible, say so. If all broken glass is to be replaced with a particular product, identify it. If the intent is to salvage historic glass from nonrepairable sash for reuse elsewhere, make that clear too. Otherwise, one bidder may assume widespread glass replacement while another assumes nearly complete retention.
Again, the bids may look comparable even though the scopes aren't.
Hardware Needs Its Own Direction
"Restore hardware" can be almost as ambiguous as "restore windows."
Historic window hardware may include:
sash locks
lifts
pulleys
sash chains or cords
hinges
operators
stays
fasteners
Specify whether hardware is to be cleaned, repaired, refinished, reused as-is, or replaced where missing or nonfunctional.
If replacement hardware must visually match the original, say so. If exact reproduction is required, identify that expectation before bid day. Small hardware decisions multiplied across hundreds of windows can become significant project costs.
Define the Required End Condition
This is one of the simplest improvements an architect can make. What does acceptance look like?
If the windows are intended to operate, state it. If sash should travel through their normal operating range, locks engage, hardware function, and weatherstripping make continuous contact, those are useful expectations.
Similarly, finish expectations should be understood. Historic restoration is handwork performed on old material. It should be professional and consistent, but it is not the same thing as installing a factory-finished product. The mockup is an excellent place to establish that standard.
Our article Historic Window Mockups: Why They Matter explains why a representative completed assembly can become the project's practical quality benchmark.
Make the Mockup Part of the Specification
Don't simply write "provide mockup." Define what the team needs to learn from it.
A useful mockup may establish:
paint-removal expectations
acceptable wood-repair techniques
glazing appearance
hardware treatment
finish quality
weatherstripping
operation
replication details
final acceptance standard
Most importantly, identify who approves it. Architect? Owner? Preservation consultant? All three?
And state whether the approved mockup becomes the quality standard for subsequent work. That one sentence can eliminate a surprising amount of disagreement later.
Define the Approval Path for Unforeseen Conditions
A crew removes paint and discovers that a bottom rail has deteriorated far beyond what was visible during bidding. What happens next?
Do they stop? Photograph it? Notify the superintendent? Submit an RFI? Proceed under an established unit price? Wait for architect approval?
These procedural details may seem minor during design, but they matter tremendously once production starts.
A good specification establishes a simple workflow:
Document → notify → evaluate → authorize → proceed.
The restoration contractor shouldn't make preservation decisions unilaterally. But neither should an entire production line grind to a halt because nobody established who can approve a routine field condition.
Coordinate the Specification With the Bid Form
This is an easy place for otherwise good documents to break down.
The specification may describe:
base restoration
alternates
allowances
unit prices
replication
But the bid form asks only for:
Historic Window Restoration – Lump Sum: $________
Now the GC has no practical way to compare the assumptions behind competing numbers. If the specification establishes meaningful pricing categories, give bidders somewhere to price them.
The bid form might request:
Base Bid – Defined Restoration Scope
Allowance – Concealed Conditions
Unit Price – Rail Replacement
Unit Price – Stile Replacement
Unit Price – Replicated Sash by Type
Alternate – Weatherstripping Upgrade
The exact structure will vary by project. What matters is that the pricing document and technical specification tell the same story.
Avoid Writing Requirements That Conflict With Each Other
Historic projects frequently pull language from several specification sections. That's understandable, but it can create contradictions.
One section may require retaining historic glass. Another may specify new glazing throughout.
One may require preservation of original hardware. Another hardware schedule may show all new locks.
One may require complete paint removal. Another may call only for preparation of loose coatings.
Before issuing documents, review the window package as one complete scope rather than as isolated specification sections. The restoration subcontractor will eventually have to reconcile all of it in the field. It's much cheaper to reconcile it on paper.
Reference Preservation Guidance—But Don't Use It as the Scope
The Secretary of the Interior's Standards for Rehabilitation and the National Park Service's Preservation Briefs library are excellent references. Preservation Brief 9 specifically provides professionals with a methodology for evaluating and repairing existing wood windows.
But writing "restore windows in accordance with the Secretary's Standards" does not replace a project-specific scope. Preservation guidance establishes philosophy and technical direction. The construction documents still need to tell bidders what they're actually expected to do.
Give Qualified Bidders a Chance to Ask Questions
This may be the most human recommendation in the entire article. If an experienced restoration contractor asks a detailed question during bidding, that's usually a good thing.
It may mean they've found an ambiguity before it becomes expensive. Listen to those questions.
If one qualified bidder can't determine whether glazing is being completely replaced, chances are the other bidders are making assumptions too. An addendum issued before bid day costs very little.
Resolving the same ambiguity after award can cost considerably more.
Better Specifications Produce Better Bid Comparisons
The purpose of a good historic window specification isn't to eliminate judgment. Historic buildings will always require some judgment. It's to put qualified contractors on common footing.
When the documents clearly establish:
the base treatment
window types and lite configurations
repair expectations
allowances
unit prices
glass requirements
hardware treatment
replication criteria
mockup standards
approval procedures
final performance expectations
the GC can compare bids with considerably more confidence. And that benefits everyone.
The architect gets better alignment with the design intent. The GC gets fewer scope gaps. The owner gets a more dependable budget. The restoration contractor knows what they're being asked to deliver. Most importantly, the historic building gets a treatment that was considered deliberately rather than decided through assumptions made on bid day.
Final Thoughts
There will always be unknowns in historic restoration. A good specification doesn't pretend otherwise. It separates what is known from what isn't known yet, defines how both will be handled, and gives the project team a fair commercial mechanism for dealing with the difference.
That is really the objective. Not more paperwork. Not longer specifications. Better clarity.
Because on a historic window project, one of the best ways to reduce change orders during construction is to eliminate unnecessary assumptions before anyone submits a bid.
