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Engineering Calculators

CLTD Roof and Wall Numbers

Instructions:

Review the methodology to ensure it aligns with your project's requirements.

Roof:

  1. Enter the Roof Type

  2. Enter the Mass Location

  3. Enter the Insulation R-Value

  4. The CLTD Roof Number will be shown in the CLTD Roof Number box. 

Wall:

  1. Enter the Wall Material

  2. Enter the Mass Location

  3. Enter the Secondary Wall Material

  4. Enter the Insulation R-Value

  5. The CLTD Wall Number will be shown in the CLTD Wwall Number box.

Methodology:

This calculator is based on the 1997 ASHRAE Handbook, Fundamental, Table 31, page 28.42 for Roofs and Tables 33A, 33B, and 33C for Walls.

CLTD roof number

Also calculated
CLTD wall number
Wall selection note

Both numbers are read straight off the surface-type tables of the 1997 ASHRAE Handbook, Fundamentals, Table 31, page 28.42; nothing is interpolated. The roof number and the wall number are independent lookups, so the two halves of the form can be used on their own.

The two halves are read differently. A roof is classified by its deck, where the mass sits relative to the insulation, and the roof insulation R-value. A wall is classified by its principal material, where the mass sits, the secondary material on the outside face, and the total R-value of the assembly.

Not every combination is listed. The table gives roof numbers for all six mass locations only over a 2 in. heavyweight concrete deck; a 1 in. wood or steel deck is listed with the mass evenly placed, with or without a suspended ceiling, and an attic-ceiling combination only with the mass evenly placed. A pair the table does not list leaves the roof number blank, and an unlisted wall combination reports No Value, both of which mean the assembly has to be matched to a listed one rather than read off here.

One wall number is corrected against the published version. 'Wall'!O147 (4 in. wood, mass outside the insulation, steel or other lightweight siding, R 5.5 to 6.5) is typed 110 in the workbook where the table's other 922 values are all group numbers between 1 and 16, and where the same cell in the three neighbouring blocks reads 10. This page reports 10.

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