What the scope document settles
A replacement goes wrong in the gap between what you thought you were buying and what the crew was told to build. The scope closes that gap. It fixes the assembly, fixes the details, names the exclusions and prices the unknowns, and once you have approved it, changes to it require your signature rather than a conversation on the roof.
It also does something quieter. It makes the bids comparable. Send the same document to three contractors and a difference in price means a difference in approach, which you can act on. Send a description of the building instead and you get three different roofs at three different prices, and no way to tell which one assumed the least.
What we will not agree to
We will not recommend an overlay without knowing whether the existing insulation is dry. An overlay over wet insulation seals the water in, the decay continues where nobody can see it, and the eventual tear off takes everything anyway. The evidence for that decision costs a fraction of the roof.
We will not open more roof in a day than the crew can close before it leaves. That rule sets the pace of the whole job, and a schedule that ignores it is a schedule with water damage priced into it somewhere.
We will not price the deck as a lump sum. Anyone who does is either carrying a large contingency you are paying for or planning to come back to you once the roof is open.
When the timing works and when it does not
The best version of this project starts a year before the roof has to come off. That is enough time to survey it, test it, write a specification, compare real bids and take a slot early in the season rather than the leftovers.
The worst version starts the week a tenant reports water. There is no time to test, no time to compare and no leverage, and the roof gets replaced on someone else’s schedule at someone else’s price.
Occupied buildings change the sequence rather than the decision. Work happens above the deck, tenants stay in place, and what they need is notice: the dates, the daily hours, which section is open this week and who to call if water appears. Laboratories, kitchens, data rooms and medical suites need more than notice, because adhesive fumes and torch work sit directly above their air intakes. Raise those at the bid stage so the method reflects them.
Common questions
What has to be in the specification before anyone prices the job?
Enough detail that two contractors reading it would build the same roof, plus an exclusions list and unit rates for the unknowns.
- Insulation type and thickness, cover board, attachment method and fastening pattern all named
- Membrane named by product and mils, with flashing details drawn rather than summarized
- Edge metal, drain bowls, walkway pads and terminations at every wall and curb
- Exclusions name where deck replacement, equipment disconnection, interior repairs and permits live
- Unit rates turn the unknowns into arithmetic rather than a negotiation on site
Write the specification before you invite prices, or have a consultant write it. A specification written after the bids is shaped by whoever bid lowest, and that scope is the one you will receive.
Can a replacement be split across two budget years?
Often, and a moisture survey is what tells you whether it is sensible.
- One section saturated and the rest dry is the case for phasing
- Wetness spread thinly across the roof buys two mobilizations instead of one
- You set up twice, buy smaller quantities, and the second phase price is not fixed
- The join between new and old needs a proper termination rather than a lap
- Two phases can mean two warranties with different start dates and terms
Manufacturers warrant the roof they inspected, so ask what will actually be issued for each phase, and get it in writing before you commit to the split.
What happens to the rooftop units while the roof is replaced?
They are lifted, supported or disconnected so the new assembly can be flashed underneath and around them, and that work usually belongs to a mechanical contractor rather than the roofer.
- It is the commonest reason a replacement schedule slips
- Book the mechanical trade before tear off, not when the crew reaches the unit
- Cooling, ventilation or process air may be down for part of a day
- Kitchen exhaust and laboratory extract need shutdown agreements rather than notice
The curb under a rooftop unit is one of the places commercial roofs leak most, because it is hand built and sits under a machine that vibrates. Replacement is the one chance to rebuild that detail, and it is wasted if the unit never moves.
Who decides how much deck gets replaced?
You do, on the contractor's recommendation, and the mechanism should be in the contract before the first sheet comes off.
- Nobody can price the deck in advance, so ask for a rate per unit
- A photograph of every area called out as failed, taken before it is covered
- A named person on your side who approves the quantity before the work happens
- A definition of failed, since corroded steel is not surface rust on a sound sheet
Expect some deck work rather than none. Old roofs that have leaked usually have damage at drains, under ponding areas and along the perimeter, so a bid carrying no allowance is not cheaper, it is unfinished.
Will the new roof sit higher than the old one?
Usually yes. Insulation is generally brought up to current standards rather than matched to what was there, and tapered boards to correct drainage add more.
- Flashing heights at parapets and walls must stay adequate above the new surface
- Counterflashings, coping and door thresholds onto the roof may need reworking
- Curbs under equipment may need extensions so flashing still turns up far enough
- Drain bowls reset to the new level, or the roof ponds around them
- Edge metal, scupper openings and equipment supports all follow
None of this is a problem when it is priced and drawn at the start. Ask how much the assembly will grow and what has to be adjusted, and expect the answer in the scope rather than on site.