Estimating Complex Roofs

NOTE-- Our new Goldenseal roofing estimating software replaced MacNail back in 2000. There are still quite a few MacNail users, so we keep the manuals online for their use! Goldenseal is an integrated program that also includes accounting, job costing and project management features. Goldenseal has a more advanced system of project dimensioning, so most of the adjustments mentioned here do not apply to Goldenseal construction estimates.

Complex Roof Estimates

The MacNail roofing estimator software calculates roof area based on the slope, overhang, and floor area that will be covered by new roofing. In most cases, this will be fairly accurate. However, double-check it in the following cases:

• Cantilevers (upper floor hanging over a lower floor) and setbacks (lower floor not covered by upper floor) combined on one floor will create additional area to be covered with roof. Add in whichever of the two areas is smaller.
• If there are many dormers you should add some area to cover the extra overhangs.
• Mixed roof slopes in mansards and gambrels make life difficult. In general, add the height of a mansard, multiplied by its length around the building. For a gambrel, figure the slope at an average of the two slopes, and you will come fairly close.
• Work on the existing roof in gut/rehabs, additions, and remodeling projects.

The MacNail construction estimating software does not attempt to calculate roof dimensions such as eaves, ridge, rake, hips and valleys directly--there are too many possible situations for it to be able to cover them all.

The Hyper*Estimators, BidMagic and Goldenseal all do a much better job of calculating dimensions for all but the most complex roofs. We suggest that you use them for your project dimensioning and specifying.

If you do need to enter numbers directly into MacNail, take measurements from plans or elevations, and estimate the actual project dimensions as closely as you can. Since these dimensions don't affect many items, minor errors in their size will not have a very large impact on the final price.