How to Dry In and Tarp a Roof Overnight Without Letting Rain or Wind In
Every roof opened in the morning must be watertight by evening. Underlayment first, tarps where you have to, and wind plans for both.
- Advanced
- 1 to 3 hours per section
- Updated
The short answer
Dry in an open roof by covering bare deck before nightfall with self-adhered membrane or properly lapped underlayment, taped and capped at the edges, or with heavy tarps over the ridge and fastened to lumber strips, not through the tarp alone. Overlap tarps from the ridge down, weigh and batten them against wind, close off open edges and penetrations, and check the forecast before stripping any section.
A tear-off leaves a house open to the sky. Even a light shower soaks insulation, stains ceilings and starts mold within days, and in the Fraser Valley a clear afternoon can turn to heavy rain at dusk. Drying in is the routine of making every part of the roof that was opened today watertight by tonight, so that whatever happens overnight, the inside of the house stays dry.
The best way to dry in is to install the new underlayment and ice and water shield as you go, so the roof is covered by the work itself. Tarps are for what cannot be covered: a section that is waiting on decking repairs, a roof where materials did not arrive, or a sudden weather change. A poorly secured tarp can do more harm than none, because it flaps, tears and channels water under itself.
Plan for this before the job starts. See how to plan a roof tear-off. For the permanent layers, see how to install ice and water shield and how to install synthetic underlayment. For an existing leak rather than an open roof, see how to tarp a leaking roof.
Tools
- Hammer or cap nailer
- Utility knife
- Staple gun or hammer tacker
- Cordless drill and screws
- Tape measure
- Ladder and roof anchors
- Headlamp for evening work
Materials
- Heavy-duty poly or canvas tarps, 6 mil or thicker, 10 by 12 feet or larger
- 1 by 3 or 2 by 4 lumber strips for battens
- Deck screws or 2-1/2 inch nails
- Underlayment and ice and water shield
- Sandbags or weights
- Rope or ratchet straps
- Roofing tape or tarp tape
Safety first
- Do not tarp in wind or rain if you can avoid it. A tarp in a gust can pull a worker off a roof. Stay tied off throughout.
- Tarps and wet poly are very slippery, and so is a wet roof. Do not step on a wet tarp.
- Work in daylight when possible. If you must finish at dusk, use lights and keep the crew together.
- Stay away from power lines and keep the ladder stable as you carry tarps and lumber up.
Step by Step
Step 1: Check the forecast and size the day's work
Check a reliable forecast the night before and again in the morning, and watch for wind as well as rain. Decide the stripping area by how much the crew can finish covering by evening, not by how much they can tear off. If a front is coming, strip smaller sections or wait.
Keep a reserve of tarps and lumber on site and on the roof's access side, so there is material available if the weather changes.
Step 2: Dry in with underlayment as each section is finished
A properly lapped underlayment sheds water well for a day or two, particularly with self-adhered membrane at the eaves and valleys. Install it in the usual order from the eave up, with laps, cap nails and tape at the ridge and open edges. See how to install synthetic underlayment.
Underlayment alone is not watertight at its edges and at penetrations. Where the next section is still open, cover the open top edge with a tarp lapped up and over it.
Step 3: Close off the ridge, open edges and penetrations
Water gets in where layers end. Lap underlayment over the ridge to the other slope, or tarp over the ridge if one side is still open. Cover the tops of chimneys and cut vent openings with poly. Tape the top edge of the dry-in to the deck with tape that works on wet wood, or lap a tarp over it.
Check that there is no water path from a stripped area down behind the new underlayment. Always shingle upslope layers over downslope ones.
Step 4: Lay tarps from the ridge down
Start with the tarp at the top so it covers the ridge and extends at least 4 feet down the other side, and lay lower tarps to overlap by at least 3 feet, with the upper layer over the lower. Use one large tarp where possible instead of several small ones. Keep the tarp taut but do not stretch it so tightly that wind can lift it like a sail.
Fold the edges at rakes and eaves under themselves to reduce flapping. Do not leave folds that hold water or channel it toward a wall.
Step 5: Secure the tarp with battens, not just nails
Roll the tarp edge around a 1 by 3 or 2 by 4 strip and fasten the strip to the deck, or lay a strip over the tarp edge and fasten through it, spacing fasteners at about 12 to 16 inches. This spreads the load and keeps wind from getting under the edge. Plain nails through a tarp punch holes that leak and tear out in gusts.
Fasten battens into the roof deck where the new roofing will cover them, so the fastener holes are covered later. Put battens along the eave, the rakes and across the tarp at intervals on larger slopes. Use ratchet straps or ropes over the ridge only when they do not chafe.
Watch out: A tarp fastened only at the top with nothing at the eave and rakes flaps, tears and can cause as much damage as open roof.
Step 6: Weight and brace against wind
Wind under a tarp acts like a sail. Close every edge, and add intermediate battens every 4 to 6 feet on a wide slope. Sandbags at eaves help, but never put heavy weights where they could slide off a steep roof. In the Fraser Valley, outflow winds can rise in the evening, so check the tarps before leaving.
If strong wind is forecast overnight, plan for extra fastening or keep the section small.
Step 7: Check inside and leave the roof safe
Check the attic for daylight and water. Clear nails and debris from the roof and the ground, and remove tools that could blow off. Tie off loose materials and remove or fasten stacks of shingles so they cannot slide. Check the tarp again after the first rain or wind, and in the morning before any work starts.
If Rain Arrives Suddenly
- Stop stripping and cover the open area first, before any tools or materials.
- Use tarps lapped from the ridge down, not small patches.
- Secure the edges with battens as quickly as you can, and do not go onto a wet or steep roof unsafely to do it.
- If conditions are too dangerous, protect the inside of the house instead: move belongings, cover ceilings and catch water.
- Call the homeowner and the insurer if water has entered.
Tarp, Underlayment or Both
Underlayment is a good short-term dry-in for a day or two if it is lapped and sealed. A tarp is a good short-term cover for a section that is open or damaged. For more than a few days, or for storm conditions, use both, with tarps over underlayment and sealed edges. Neither replaces the roof.
Common Mistakes
- Stripping more than you can cover. Uncovered deck at dusk is how ceilings get soaked.
- Nailing through the tarp with no batten. The nails tear out in wind and leave leak holes.
- Laying tarps with the wrong lap. A lower tarp over an upper one runs water under the seam.
- Leaving edges loose. A flapping edge lets wind under the tarp and peels it off.
- Ignoring the ridge. Water runs in at an uncovered ridge and behind the tarp.
- Not checking in the morning. A tarp that shifted overnight can leave a section open for the next storm.
When to Call a Professional
If the roof is steep, wet, windy, or high, leave the tarping to a roofer with fall protection and experience, particularly in a storm. A tarp in wind is one of the most dangerous jobs in roofing.
If a tear-off has been interrupted by weather and rain is coming, a roofing contractor can get the roof covered safely and assess damage to the decking and the house.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Replacement service or the towns we cover.
How to Dry In and Tarp a Roof Overnight: Questions
How do you tarp a roof without nails?
Wrap the tarp edge around a wood strip and fasten the strip to the roof deck, or fasten a strip over the edge, so the fasteners go through wood instead of the tarp. On a stripped roof the screws go into the deck and are covered by roofing later. Sandbags and ratchet straps can hold a tarp temporarily, but fastened battens are more secure.
Can you leave a roof with only underlayment overnight?
Properly lapped, fastened underlayment sheds water for a day or two, especially with self-adhered membrane at the eaves and valleys. It is not a finished roof. Edges, penetrations and any open area should be covered. If heavy rain or wind is forecast, cover the roof with tarps as well.
What if it rains during a roof replacement?
Stop stripping and cover the open deck with underlayment or tarps immediately, working from the ridge down and securing the edges with battens. Do not work on a wet or steep roof in unsafe conditions. Protect the inside of the house if water is getting in, and check the attic and ceilings afterward.
How do you keep a roof tarp from blowing off?
Close every edge with battens fastened into the deck, run the tarp over the ridge, add intermediate battens across a wide slope, and keep the tarp taut but not stretched. Sandbags help at the eaves. Any edge left loose lets wind get underneath and lift the tarp like a sail.
How long can a roof be covered by a tarp?
A well-secured heavy tarp can protect a roof for days to weeks, but sun, wind and flapping wear it out, and trapped moisture can damage the deck. It is a temporary measure. Permanent roofing should follow as soon as possible, and tarps should be checked after every wind or rain event.
Related Guides
All Tear-Off, Decking and Underlayment guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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