What a snow-damaged roof usually shows
A ridge or rafter that has dropped, cracked sheathing across a span and doors that stick at the top. Each is a framing question as well as a covering question.
A dip in the ridge or a rafter line that bows along its length is the sign the framing has taken more than it was sized for. Cracked sheathing across a long span shows the same strain in the deck. Doors and windows that stick at the top after a winter point to a roof that has moved under the load.
A roofer checks the framing before the covering, because a covering laid over a sagging frame carries the same strain into the new work.
- A dropped ridge or rafter line
- Cracked sheathing across a span
- Doors and windows that stick at the top
When an engineer is needed
Where the framing is short, where the design is unclear or where a strengthening is large, the roofer names an engineer's review in the scope.
An engineer checks the calculation where the framing is short or the design is in doubt, and the review is quoted as its own line. The roofer does not assume the framing is sound when the measurements say otherwise.
The engineer's written review, with its date, goes into the file before the covering is ordered.
- Short framing or unclear design
- A large strengthening
- The review written and dated before the covering
Repairing before the covering goes on
Strengthen the framing to the stated load first, then the decking, then the covering, in that order.
The order is the safe one. Framing is strengthened to the stated load, the decking is repaired or replaced where it has cracked, and only then is the covering laid. Each stage is checked before the next, and the readings are recorded at each.
A roof covered before its framing is sound is a roof that will sag under the next heavy winter, and the homeowner should refuse that order.
- Framing strengthened to the stated load
- Decking repaired before the covering
- Each stage checked before the next
The attic readings the crew takes
The attic shows the load path before the covering is lifted.
Before any shingle is lifted, the attic is read end to end. The crew looks at the ridge board, the rafter tails at the wall plate and any collar ties or braces that have been added over the years. A brace that is cracked at its joint or a ridge that has dropped in the middle is a sign that the load has moved onto a part of the frame that cannot carry it.
The readings are written as measurements at fixed points, not as general impressions. The distance from the ridge to a string line, the gap at the wall plate and the spacing of the rafters are recorded so the next visit can compare the same points.
- Ridge board checked along its length
- Rafter tails at the wall plate measured
- Braces and collar ties checked at their joints
When sag means the framing must change
A sag that is still moving after the snow is off needs the frame changed, not only the roof covered.
Some sags settle back once the snow is cleared. A sag that stays, or that grows after the snow has gone, shows the rafters are overloaded or undersized for the span. A new shingle laid over that roof will simply sag under the next winter.
In that case the crew says so and sets out the framing work that the county snow figure requires: sistering rafters, adding a purlin or a brace, or setting a new ridge. The owner is shown the measurements and the choice is made with the full record in hand.
- Sag that stays after snow is cleared
- Sistered rafters or added purlin
- Owner shown the measurements before work
