Find a roof leak by tracing the water upslope from the stain inside, catch the drip in a container, and cover the entry point from outside only if it is safe, with a tarp tied to the framing and battened down, because stones or logs slide off any roof steeper than about 17 to 27 degrees. Leave the permanent repair for dry weather, and fix or cover the leak within 24 hours, before the damage cascades.
Part of Building Maintenance Schedules
Emergency patching is the temporary stopping of a roof or wall leak in wet weather so that a building stays dry until a proper repair can be made.
The Water Enters Higher Up Than It Drips
The maintenance guide’s emergency steps for an active roof leak are four: place containers under the leak inside; if safe, cover the leak area from outside with a tarp weighted down with stones or logs; do not attempt a permanent repair in wet conditions; mark the leak location for repair in dry weather. The roof guide adds the urgency: a leak left more than 24 hours in wet weather starts damage that cascades, and even a temporary patch of bark or hide buys time (Roof Systems).
One instruction needs correcting. A tarp “weighted down with stones or logs” works only on a nearly flat roof. On a steep one the weights slide, and a stone falling from an eave onto a person below is an injury the repair has caused.
Worked Example: Why Weights Slide, And How Fast A Bucket Fills
Weights. A stone of 20 kg on a slope of angle θ. The force along the slope is m × g × sin θ; the friction that can hold it is μ × m × g × cos θ. It slides if tan θ is greater than μ. The friction coefficient of wet plastic tarp on wood or thatch is not given in this corpus; 0.3 to 0.5 is assumed for the example.
- At 45 degrees, the pitch at which thatch is laid: force along the slope = 20 × 9.81 × 0.707 = 139 N. Friction available = μ × 139 N = 42 N (μ = 0.3) to 69 N (μ = 0.5). The stone slides.
- A stone stays only if tan θ is below μ: arctan 0.3 = 17 degrees and arctan 0.5 = 27 degrees. Above those angles, weights alone do not hold.
- At 45 degrees, tan 45° = 1, so μ would have to be 1 or more.
Bucket. A leak that drains a catchment of area C in a rain of depth rate r passes C × r. Two square metres of roof draining through one hole in 10 mm/h of rain is 2 × 10 = 20 L per hour, so a 20 L bucket fills in an hour and needs emptying; a larger catchment, or a heavier rain, fills it faster.
What You Need
- Buckets, basins or pots inside, and cloths
- A tarp larger than the damaged area, with eyelets or edges that can be fixed
- Battens, nails or lashings, and rope
- A ladder and a crawl board, and a second person
- Bark, hide or sheet material for a small temporary patch
Method: Trace, Catch, Cover
Step 1: From inside, find the stain or drip and follow the wet timber upslope. Water runs along rafters and drips far from where it entered, so the entry point is higher than the drip.
Step 2: Catch the water: containers under the drip, and a cord from the drip point into a bucket to stop splashing.
Step 3: Mark the probable entry point from inside, and measure from a fixed point, such as the ridge, so it can be found outside.
Step 4: Decide whether to go out. Only in light wind, daylight, and with a second person; not in rain, ice or on a roof you cannot trust.
Step 5: Lay the tarp over the ridge if you can, or tie its upper edge to the framing, and hold the lower and side edges with battens fixed to the rafters or ropes tied to the structure. Loose weights hold only on shallow roofs.
Step 6: Check from inside that the dripping has stopped, and note the tarp’s position in the log.
Step 7: In dry weather, make the permanent repair and record it.
Common Mistakes
- Patching over the stain. It is rarely under the hole.
- Climbing in the storm to save a roof. The risk of a fall exceeds the loss.
- Loose stones on a pitched roof. They slide.
- Forgetting the log. The same place leaks again.
Safety
A wet roof in the dark is where people fall
Do not go onto a roof in rain, ice, wind or darkness. A rotten rafter or deck gives way under a person’s weight; test timber from inside before stepping on it. A sliding stone can hit someone below, so keep the area under the roof clear while working. Hot tar for permanent repairs is flammable and burns skin; heat it away from the building.
What’s Next
- Learn next: Roof Maintenance — preventing the leak
- Combine with: Thatch Repair & Re-Ridging — the permanent repair on thatch