A portal frame building is the most common type of steel frame construction building in the UK. They are typically used for warehouses, agricultural storage or retail because it is very good at containing large volumes.
Occasionally mistakes are made in the envelope area calculations for these buildings when they are calculated from the architectural drawings due to not understanding where the internal walls and roof start. It’s important to understand the main elements that are present in these buildings to explain how they are constructed. The example below shows a retail portal frame building where parapets are more common.
Errors that can occur in Envelope Area Calculations in Portal Frame Buildings
A common mistake is that the columns are assumed to be the walls or the rafters are assumed to be the roof. It’s very rare for the mistake to be made on both elements and the mistake is more commonly made regarding the roof and the rafters.
The correct way to calculate the envelope area
The rails are attached to the columns and are used to mount the wall cladding. The purlin are attached to the rafters and used to mount the roof. Therefore where the rails and purlin end are likely to be where the wall or roof are located.
Summary
Mistakes can be made through the interpretation of architectural drawings but dimensional checks should be undertaken on site as these will identify errors in the envelope area calculations.
