Proudly American
Give the drawing a front
National Chimney's worksheet separates overall width and length from the distance between the hole and specific sides. Ask the person who measured the chase to identify a side in ordinary words, such as “faces the driveway.” Mark the same edge on the drawing and on a professional field photograph if one is available. Do not make rooftop measurements yourself.
Read each opening as its own item
A sheet with two penetrations needs the correct position and size for both. For an offset, oval or differently sized opening, have its shape and orientation drawn. A list of two diameters cannot establish where either belongs. The person specifying the work must also account for the installed chimney system and its required clearances.
Check what extends beyond the top view
The skirt covers an edge, a collar surrounds an opening, and a drip edge and cross-break are separate choices on the manufacturer's worksheet. Request a side view when the proposal is ambiguous. For instance, a drawing may locate the pipe correctly yet show no agreed detail for water reaching the face of the chase. Resolve that before the shop receives the final order.
Freeze the right revision
If siding, trim or the chase top changes after measurement, ask which dimensions must be taken again. Write down the revision date, material and person responsible for confirming the finished dimensions. A signature against a drawing is only useful if everyone is looking at the same version.