Electrical and Mechanical estimating per square foot or per square metre
Is not a good basis to tender work, however it can be useful tool to compare the completed estimate. The risks associated with tendering on a sq ft or sq metre basis are higher where the project is pre-designed, but less on a design and build project.
Use of square metre rates on Design and build projects
Square metre rates can be used instead of estimating per square foot providing the design and build contractor provides a detailed contractors proposal accompanying their tender. This reduces the risk because the basis of the tender is stated, nerveless its still a high risk strategy.
How to create a library of square metre sq/m or square foot rates sq/ft
Mechanical and Electrical contractors should convert their mechanical estimating and electrical estimating records to costs per square metre or £/m2.
The tender summary is divided by the total square metres of the project. The square metre rates used should be the area used by the services. This then gives an elemental cost per system per metre square, which can then be converted to a cost per square metre. The electrical estimate and mechanical estimate should record the overhead and profit applied and the labour rate used along with the date of submission. The mechanical and electrical contractor can then index the square metre rate sq/m2 for future adjustment.
Elemental systems to square metre sq/m2
The contractor should also indicate which items are systems and not square metre related, e.g. utility, central panels and plant. Typically the following systems can be converted to square metre rates.
Mains distribution
General power
Fire alarm
Luminaires
Lighting installation
Lightning protection
Public address systems
LTHW Low temperature hot water
Hot and cold water services
Caution on volume related services
Some systems are more onerous if converted to square metre rates because they are volume related.
Ventilation systems
Ventilation costs per square metre are more difficult to generalise because air change rates differ for different areas in the building and those areas as a percentage of the overall gross area differs.
For example you could assume that 5% of the overall building area is toilets, and that the air change is 8, and that the ceiling height is 3.2m, but if the area was 10% that would double the cost.
Some systems are dependent on user use of the building and location and aspect of the building
Further considerations before using square metre rates £/m2
Cooling, comfort or air conditioning
The main factors affecting cooling is the aspect of the building and the gain from equipment and people, often these are not known at tender stage.
Summary
Square metre rates can be very useful, and can serve to be used as a bench mark. The bench mark can be used by contractors to compare their tender and to indicate where there maybe over design or where they may have errors in their mechanical estimate or electrical estimate.
They should not be used as a short cut to avoid estimating.
If you haven’t got the resource to estimating a project contact UK Estimating Support Ltd.