How to Compare Siding Estimates That Are Thousands of Dollars Apart

Three companies walked your house. Three numbers came back. The spread between highest and lowest is several thousand dollars, and nothing in the documents explains where it went.

That gap is usually not a pricing difference. It is a scope difference. An estimate is a written description of work, and the price is what that description costs. One document can include a full tear-off, a new water-resistive barrier, kick-out flashing at every roof-wall intersection and a dumpster. Another leaves all four unsaid. Compare the documents, not the totals.

What a complete estimate contains

A complete estimate names things. An incomplete one describes an outcome. You should be able to put a finger on a line for each of these:

• Product by manufacturer and line, not “premium siding.” HardiePlank lap at a stated exposure, ColorPlus or primed. For vinyl, brand, profile and panel.
• Square footage, and how it was measured.
• Trim: material, width and location. Corners, casing, rakes, frieze.
• Soffit and fascia, or a statement that they stay.
• The water-resistive barrier, by name.
• Flashing, by type and location.
• Tear-off scope, and where the debris goes.
• Permit, disposal and site protection.
• Approximate start and completion dates.
• Total price, deposit and payment schedule.
• The workmanship warranty term, separate from the manufacturer warranty.
• The Pennsylvania registration number.

A missing line is rarely free work. It means nobody has decided yet, and undecided resolves one of two ways later: a change order you pay for, or a shortcut you never find out about.

The barrier behind the siding is not the siding

Siding is cladding. It sheds most of the water most of the time. What keeps water out of the wall is the water-resistive barrier behind it, and both manufacturers say so.

James Hardie requires a water-resistive barrier per local building code, installed with penetration and junction flashing per that code, then states flatly that James Hardie will assume no responsibility for water infiltration. The Vinyl Siding Institute is just as direct: vinyl siding, insulated vinyl siding and polypropylene siding are exterior claddings, not water-resistive barriers, and must be installed over one to comply with current building codes.

So look for the barrier by name. Not “house wrap.” The product. If the estimate is silent, ask whether it is a new barrier or the one already on the wall, cut open by every window replacement since. Tyvek HomeWrap may be left exposed 120 days, so the crew has a real window between tear-off and siding, and it is vapor-open at 56 perms, which is why the wall behind it can dry. More in choosing siding materials.

Flashing and trim, checked from the driveway

Flashing is where two bids that read alike stop being alike. It is also the part you can verify without a ladder. Every ZIP code in Pennsylvania sits in James Hardie’s HZ5 zone, and James Hardie publishes HZ5 clearances in inches:

• Siding to ground: minimum 6 in.
• Siding to slabs, paths and steps: minimum 2 in.
• Siding to deck: minimum 2 in, with Z-flashing.
• Roof to wall: minimum 2 in.
• Siding to gutter: 1 in.
• Sheltered areas: minimum 1/4 in.
• Mortar and masonry: minimum 1/4 in, with L-flashing and Z-flashing.

James Hardie requires kick-out flashing at a minimum of 4 in by 4 in, as required by IRC code. It throws roof runoff into the gutter instead of behind the siding. From the driveway of a house in Mechanicsburg or Lititz, count the places a roof edge dies into a wall. Each one needs a kickout. Then see whether the word appears in your estimates.

James Hardie also requires flashing gaps left open, not sealed. Horizontal Z-flashing carries a minimum 1/4 in gap with an explicit instruction not to caulk, and the same holds at block penetrations and field-joint flashing. Caulking a gap meant to drain traps the water the flashing was installed to release.

Trim diverges the same quiet way. Material, width and location are the specification; “trim included” is not. Wrapping existing trim in coil is different work from replacing it.

None of this is only a leak question. Improper installation is an explicit exclusion in James Hardie’s warranties, and the instructions say in capitals that failure to install and finish per applicable building codes and James Hardie written application instructions may void the product-only warranty. The 30-year substrate warranty pays no labor at all, as we set out in the ColorPlus warranty breakdown, so the installer carries more of your risk than the manufacturer does.

Fastening, the spec that rarely reaches paper

Almost no estimate will contain a fastening schedule. Ask anyway. The answer tells you who you are talking to.

For HardiePlank, blind nailing is the preferred method. Where no nail line is present, fasteners go between 3/4 in and 1 in from the top of the plank, no closer than 3/8 in from the edge, with a minimum 1-1/4 in overlap so the course above covers them. Face nailing should only be used where code requires it for high wind areas, and never combined with blind nailing. For fastener selection and design wind loads James Hardie points to ICC-ES reports ESR-1844 and ESR-2290. A contractor who can name the report behind their fasteners has read it.

For vinyl the failure runs the other way, because vinyl moves. Leave about 1/32 in between fastener head and panel, the thickness of a dime. Center fasteners in the slots. Do not force panels up tight. Maximum 16 in spacing on horizontal panels, screws no less than 1-1/4 in into framing or furring. Tight nailing buckles the wall with temperature, and that shows up on the first hot afternoon after the crew leaves.

Two more questions for the contractor. Where material sits between delivery and installation: James Hardie says store flat, dry and covered, and saturated planks shrink and open butt joints. And how butt joints are treated: code requires a treatment, James Hardie recommends joint flashing, and caulking is specifically not recommended on ColorPlus for aesthetic reasons. Cold-weather installation covers which temperature rules are real.

Tear-off, and everything that follows from it

This is the largest legitimate reason two honest bids land thousands apart.

For vinyl, the VSI manual expressly contemplates re-siding over existing siding, with conditions. Nail down loose boards. Replace rotten ones. Never install over rotting wood. Scrape and re-caulk around openings, remove protrusions, and check walls for evenness, adding furring strips for a smooth continuous surface. Done that way it is a real option and a real saving.

For fiber cement, we will be straight about what we can document. James Hardie’s instructions name the substrates the product accepts: braced wood or steel studs at 24 in on center maximum, or directly to minimum 7/16 in OSB sheathing, on flat vertical walls only. Technical Bulletin 19, dated February 2025, covers non-nailable substrates and defines those as continuous insulation and exterior gypsum. It does not address existing siding. We will not tell you the manufacturer permits or prohibits it, because we could not confirm either from a primary source. We can tell you that irregularities in framing and sheathing mirror through the finished wall, and that we tear off.

Tear-off also buys the one thing nobody can price in advance: a look at the sheathing. The estimate should carry a unit price per sheet, because a contractor who promises none will be needed is guessing at a wall they have not opened.

What follows belongs on the page too. Dumpster and haul-away. The permit, and who pulls it. Protection for landscaping, the condenser, and a magnet sweep before the crew leaves. And for older stock, of which Columbia, Steelton and the older rows in Reading and York have plenty: asbestos siding is a regulated material, and VSI directs that the appropriate environmental agency or local code official be contacted before re-siding over it. The walkthrough has the rest.

Allowances and exclusions are change orders you have not met yet

An allowance is a placeholder amount for something not yet chosen. An exclusion is named work that is not in the price. Both are legitimate. Both are how a low bid becomes a middle bid after work starts.

Pennsylvania hands you a lever. Under the Home Improvement Consumer Protection Act it is a prohibited act to deviate from plans or specifications in any material respect without a written change order, dated and signed by both contractor and owner, containing the price change for each deviation. Verbal change orders are not a gray area here. And under a time-and-materials provision, the contractor must give you a written initial cost estimate before work starts, and the cost may not exceed 10 percent above it without a signed change order.

So turn every allowance into a question whose answer contains a number. Ask the per-foot price if the trim runs past its allowance. And read the exclusions, because an estimate with no exclusions section is not an estimate without exclusions.

The deposit, and what Pennsylvania actually caps

Two hard rules, and most homeowners have heard neither. First, it is a prohibited act to demand or receive any payment for a home improvement before the contract is signed. A check written at the kitchen table before signing is not a deposit.

Second, there is a statutory cap. For a contract whose total price is more than $5,000, it is a prohibited act to receive a deposit in excess of one-third of the contract price, or one-third plus the cost of special order materials that will be ordered, as designated in the written contract. Most full James Hardie projects here run $25,000 to $45,000 depending on home size, trim detail and tear-off, so the cap applies to essentially all of them. What replacement costs here covers how that range moves.

The contract has to show its work: the amount of any down payment plus any amount advanced for special order materials, listed separately. If a proposed deposit sits above one-third, the excess should be special order material named in the contract.

The contract must also carry approximate starting and completion dates and the contractor’s name, address and telephone number, where a post office box alone is not an address. You get a completed copy free of charge when it is executed. You may rescind without penalty within three business days of signing, regardless of where it was signed, so this is not limited to door-to-door sales. Any arbitration clause must be in capital letters, in 12-point boldface type, on a separate page, with its own signature line for each party.

Registration and insurance, verified

Pennsylvania does not license home improvement contractors. It registers them. The Attorney General says so plainly: registration under HICPA is not an endorsement, recommendation or approval of the contractor’s competency or skill. It does not tell you they can flash a roof-wall intersection.

The statute is blunt. No person shall hold himself out as a contractor, nor perform any home improvement, without first registering with the Bureau of Consumer Protection in the Office of Attorney General. Home improvement means work whose total cash price exceeds $500, and the definition names siding, roofs and windows outright. The number must appear on all contracts, estimates and proposals, so it should already be on the paper in your hand. Ours is PA203681.

Verify it free, two ways: the Attorney General’s public Home Improvement Contractor Search at hicsearch.attorneygeneral.gov, searchable by number, business name, county and type of work, or the helpline at 1-888-520-6680. Numbers read as PA plus the assigned number, and leading zeroes may be dropped, so PA000372 can appear as PA372.

Insurance is where the honest answer is less satisfying. The contract must contain an agreement to maintain liability insurance covering personal injury of not less than $50,000 and property damage of not less than $50,000, and must identify the current coverage maintained at signing. That is a checkable line. For general liability we know of no public Pennsylvania lookup like the registration search, so verify it from that stated amount plus a certificate of insurance issued by the carrier, current at signing and while the work is performed.

Workers’ compensation is separate. HICPA does not require it for registration. Coverage is mandatory in Pennsylvania for any employer with at least one employee who could be injured in this state, with limited exclusions for sole proprietors, general partners and executive officers granted exclusion by the Department of Labor and Industry. The check happens at the building permit: before issuing one to a contractor, a municipality must require proof of workers’ compensation insurance, or an affidavit that the contractor does not employ other individuals. Labor and Industry runs a free public Workers’ Compensation Insurance Search Form built on Compensation Rating Bureau data.

The cheapest bid is sometimes the right one

Expensive is not a proxy for careful. A high bid can carry no flashing detail at all, while a low bid names the barrier, states the tear-off scope and publishes a per-sheet sheathing price. The document is the proxy, not the number.

Build a one-page grid, one column per bid. Rows for product and line, square footage, barrier by name, kick-out flashing, tear-off, sheathing unit price, permit, deposit, dates, warranty term and registration number. Fill every cell from the document, not from what you remember the salesperson saying. Then call about the blanks and ask all three to re-quote the same scope. The numbers move toward each other, and when they stop you are comparing like with like. If the lowest bid is still lowest and its document is complete, buy it.

Two last notes. A workmanship guarantee is separate from anything the manufacturer offers, and it is the one that pays labor in year three; ours is a 10-year workmanship guarantee on full replacements. And if the numbers came in higher than you planned, waiting is allowed. Good crews book ahead seasonally, so a decision made in a rush to hold a slot is still made in a rush. If you are weighing whether the whole wall needs to come off, repair versus full replacement settles that first, and scheduling is worth reading before it applies pressure.