Most small and medium projects go out to tender without a detailed envelope specification. Quotations are gathered against the line "sandwich panel, 60 mm", and the quotations that arrive cannot be compared with one another, because that same line covers very different products.

Writing a specification does not require an engineering office. Five lines are enough.

The five lines to write

  1. Core type and fire class. Such as "PIR core, B-s1-d0 to EN 13501-1". If the regulation requires A2, write rock wool or hybrid.
  2. Insulation thickness. Not the total thickness of the panel but the insulation thickness. If there is a target U-value, write that too.
  3. Steel thickness and coating. Inner and outer sheets separately; the coating as polyester, PVDF or plastisol.
  4. Cover width and panel length. The cover width is 1000 mm; if the panel is to be cut to the project, say so.
  5. Load and span. The purlin spacing and the snow load for the region; ask the bidder for the load table at that span.

Where do those five lines come from?

The fire class has already been established at the permit stage; it is read from the permit file.

Thickness and U-value are found by calculation: the U-value calculator gives the result for the section and the heat loss calculator its annual value. The second also shows in how many years going up one step in thickness pays for itself.

Load and span are read from the table; the tables are in the Library section.

The quantities come from the panel area calculator and make sure the quotations arrive against the same quantity.

Making quotations comparable

Once the five lines are written, the quotations that arrive describe the same product and the price really can be compared. Without them, what is compared is not the price but the generosity of the quotations.

Where to look:

  • Is it the insulation thickness that is written, or the total thickness
  • Which core is the fire class given for, and is there a report
  • Is the steel thickness the same on both faces
  • Does the load table belong to this product
  • Is the panel cut to the project, or bought in standard lengths and cut on site

What to do when a decision cannot be made

If there is no clear answer under one heading, leave that heading blank and ask the bidder for a proposal. A line left blank is better than a line filled in wrongly; the second one surfaces on site, and changing it at that point is expensive.

Which panel is used where, by building type, is set out building by building in the Solutions section: factories, warehouses, cold stores, agricultural buildings, modular buildings and roofs carrying a solar plant.

What a specification is really for

A specification is written not to make one product mandatory but so that no argument arises on site. When all five lines are written, the performance does not change even if the panel does; when they are not, the performance changes even if the panel stays the same.