Quick answer
On a new commercial building, the big roof choices should be settled before the roof assembly and submittals are approved. The owner, designer and builder should agree on the deck, loads, drainage, moisture control, penetrations and roof access for that building. They should pick an exact tested assembly and details, control substitutions, and plan closeout records. A warranty is not automatic. It depends on the products, installer and terms.
Why decide early
On a new building, the roof is easiest to get right on paper. Once the steel is up and units are set, changes cost more and may not be possible.
The owner, designer and builder each play a part. The owner sets goals and budget. The designer sets the assembly and details. The builder plans how it gets built. Getting them aligned before submittals are approved avoids costly fixes later.
Deck and loads
The deck is the base of the roof. It might be steel, concrete or wood. The structural engineer sizes it for the loads it must carry: the roof itself, snow, drifts, rooftop units, rain and wind.
Think ahead about future loads. Will you add solar, more units or a roof deck people can use? Tell the engineer now. Adding loads later can mean costly reinforcement.
Slope, drains and overflow
Low-slope roofs still need slope so water drains. That slope may come from the structure or from tapered insulation. Water should reach drains or scuppers without sitting for long.
Every roof that relies on drains also needs a backup path for water if the main drains clog. That might be overflow drains or scuppers set higher. The designer and plumbing engineer decide the sizes and spots under the codes that apply.
| Decision | Settle before | Usually led by |
|---|---|---|
| Deck type and loads (snow, units, wind) | Structural design is final | Structural engineer |
| Slope, drains and overflow | Roof plan is final | Roof designer and plumbing engineer |
| Vapor and air control layers | Assembly is approved | Designer or envelope consultant |
| Exact tested roof assembly and edge details | Submittals are approved | Roof designer |
| Penetrations, curbs and roof access | Trades lay out rooftop gear | Designer, builder and trades together |
| Substitutions | Any product is swapped | Designer review and owner approval |
| Closeout and warranty papers | Final payment | Builder and roof installer |
Moisture: vapor and air control
Moist air from inside can rise into the roof and condense in cold weather. A vapor retarder slows water vapor moving through materials. An air barrier stops air from leaking through gaps. One layer may do both, but they are not the same.
Whether a roof needs these, and where, depends on the climate, the building use and the assembly. Pools, kitchens and some plants make a lot of moisture. The designer should explain the plan.
Pick an exact tested assembly
Wind and fire ratings belong to a tested assembly. That means a specific deck, insulation, cover board, fasteners or adhesive, and membrane, put together as tested.
The WBDG resource on wind safety stresses careful design of the whole envelope, with special care at edges and corners. The roof designer should name the assembly and show how it meets the wind loads for this building. A rating on one product alone is not enough.
Edges, details and the load path
Roof edges, copings and corners face the most wind. Detail drawings should show how each is built and fastened. They should match tested edge systems where they apply.
The roof's hold-down chain must reach the structure. Membrane to insulation, insulation to deck, deck to frame. On metal roofs, the Metal Construction Association explains how clips and fasteners carry loads into framing. Each link should be in the drawings.
Penetrations and rooftop gear
Pipes, vents, curbs and supports pass through the roof. Each needs a proper flashing detail for that roof system. Too many, too close or too near drains and edges can cause leaks.
Plan rooftop gear with the trades before they lay it out. Group items where you can. Leave room around each one for flashing. Set gear high enough for proper flashing height.
Roof access and safety
People will need to reach the roof for years to service gear. Plan safe access: hatches, ladders, walkways and guardrails or anchors where needed.
Walk pads protect the membrane on service paths. Mark skylights and guard them. These choices are easiest to make now.
Submittals: the checkpoint
Before work starts, the installer sends submittals. These include product data, shop drawings and the proposed assembly. The designer reviews them against the plans.
This is the last easy point to catch mistakes. Check that the products, assembly and details match the design. Check that edge and penetration details are included.
Substitutions
During the job, someone may want to swap a product. Maybe it's cheaper or faster to get. A swap can change the tested assembly, the wind or fire rating, or the warranty.
The contract should set how substitutions are reviewed. The designer should check them. The owner should approve them in writing. Don't let swaps happen on the roof without review.
Inspections during the job
Many layers are hidden once the roof is done. Inspections during the work catch problems while they can still be fixed. That might be the designer, a roof consultant, the maker's rep or the local inspector.
Ask for photos of each layer as it goes on. Ask for reports from each inspection.
Warranty is not automatic
Makers offer warranties, but often only for certain products, installers and assemblies. Many need an application, fees and a final inspection. Terms differ a lot.
The installer's workmanship warranty is separate. Write the warranty you expect into the contract. Ask for a sample warranty before work starts so you know the terms.
Closeout records
Collect these before final payment. Keep them for the life of the roof.
- Final roof drawings with any changes.
- Product data and the approved assembly.
- Edge, drain and penetration details as built.
- Inspection reports and photos of hidden layers.
- Maker and installer warranty papers.
- Care and maintenance guidance.
Who does what on a new roof
It helps to know each role. The owner pays and sets the goals. The designer draws the roof and writes the rules for it. The builder runs the job and hires the roof crew. The roof crew puts the roof on.
Each one should know who makes which call. If a crew finds a problem, who do they tell? Who can say yes to a change? Write it down at the start. That keeps small issues from turning into fights later.
Tell the designer how you will use the building
A roof over a quiet office is not the same as a roof over a pool, a kitchen or a cold room. Each one puts its own stress on the roof. Damp air, heat, cold and fumes all matter.
Tell the designer what will go on inside. Tell them about hours, machines and any plans to grow. The more they know, the better the roof can fit the building.
Snow and drifts
Snow can pile up deep next to taller walls, parapets and big units. That pile is called a drift. It can weigh much more than the flat snow on the rest of the roof.
The engineer looks at where drifts will form and sizes the deck for them. If you move a unit or add a wall later, drifts can move too. Ask before you change the roof layout.
Keep water off the roof during the build
A roof that gets wet while it is being built can trap water. Wet insulation can stay wet for years under a new membrane. That can rust the deck and hurt the roof's warmth.
Ask how the crew will keep stored boards dry and how they will close up each area at the end of the day. Ask what they will do if rain comes before an area is done.
Other trades on the roof
Many trades walk on a new roof. Heating crews set units. Plumbers run pipes. Electric crews run lines. Each one can poke, cut or scuff the new roof.
Plan who works on the roof and when. Put down walk pads or boards where people will cross. Have the roof crew check and fix any damage before the job ends. Keep a list of who did what.
Test before you close up
Some leaks only show up later. Some jobs test seams or check for wet spots before the roof is handed over. The right test depends on the roof type and the job.
Ask what checks the crew or the maker will do at the end. Ask for the results in writing. Fix any problems before final payment.
Budget and value
It is easy to cut roof costs on paper. A thinner layer, fewer fasteners or a cheaper edge can save money now. But they can cost more later in leaks, repairs or a shorter roof life.
Ask the designer to show what each choice changes. Ask what you give up for each dollar saved. Then decide with the full picture in mind.
Roof color and heat
A light roof reflects more sun. A dark roof soaks up more heat. The right choice depends on the building, the climate and the use inside.
Ask the designer what color and finish fit your goals. Treat any energy savings as an estimate, not a promise.
Make a plan for roof care
A new roof still needs care. Drains clog. Seams get stepped on. Units get swapped. Ask the crew or maker what care the roof needs and how often. Some warranties ask for set checks. Put a care plan in place on day one.
Questions for the design team
Bring these to an early design meeting.
- What loads did you design for, including future gear?
- How does water drain, and what is the overflow path?
- What vapor and air control does this roof need, and why?
- Which tested assembly meets our wind and fire needs?
- How will substitutions be reviewed?
- What warranty do we expect, and what does it require?
Common questions
Does a new roof come with a warranty automatically?
No. A maker's warranty depends on the products, the installer and the terms, and often needs an application and inspection. The installer's warranty is separate. Spell out what you expect in the contract.
Are the federal guides you link the local building code?
No. They explain good practice. Your designer and local building office decide which current codes apply to your building.
Can the builder swap in a similar product?
Only through a review process the contract sets. A swap can change the tested assembly, wind or fire rating, or warranty. The designer should review it and the owner should approve it in writing.
Why do penetrations matter so early?
Every pipe, curb and support is a possible leak. Planning them before trades lay out gear lets the designer group them, keep them away from drains and edges, and leave room for proper flashing.
What should we get at closeout?
Final drawings, product data, the approved assembly, warranty papers, inspection reports and photos of hidden layers. Keep them together for the life of the roof.
Related help
Sources we checked
Official and standards pages we used to check facts on this page. Rules can change, so confirm with the source.