Tender weather allowance
A tender weather allowance worked out from the record.
Most tender weather allowances are a percentage on the programme or a line in the preliminaries carried over from the last job. Construction Metric works the allowance out from the long-term record for the site: how many days each month, for each trade, the weather makes the work unsuitable. The 1-in-10 return values sit beside it, separately, because an average and a return period are different numbers that answer different questions.
In development with early customers · Per trade, per calendar month · Averages and return periods shown apart
Two different numbers
An average is not a return period
The average
How many days will an ordinary year cost?
Take every recorded year for the site, count the days in each month that breached the threshold for the trade, and average them. That is the allowance: the days a contractor should expect to lose in an ordinary year, and price for in the programme and the preliminaries.
The 1-in-10 return value
Where does the exceptional year begin?
Take the same recorded years and find the level the record shows is exceeded, on average, less than once in ten years. That is a return period. It is the comparison NEC clause 60.1(13) makes, and it is not the average of the last ten years. The allowance covers the ordinary year. The return value marks where the contract, rather than the allowance, starts to matter.
What you get
What goes into the allowance
The record for the site, not the region
The long-term record is taken for the location of the site, with the gauge and the data source named. A regional figure hides the difference between an exposed site and a sheltered one.
Unsuitable days per calendar month
For each month, the average number of days the weather made the work unsuitable: frost days, days with rain over 5 mm, days with wind above the crane limit. Averaged over the recorded years, and the years are stated.
Per trade, using each trade’s limits
A bricklayer, a roofer and a crane crew stop for different weather. The allowance is built per trade from that trade’s own thresholds, so the earthworks allowance is not the cladding allowance.
Priced into the programme and the prelims
The unsuitable days go into the programme as a non-working allowance per month and into the preliminaries as time-related cost, with the working shown, so the estimator and the planner are using the same number.
The 1-in-10 return values, shown separately
Beside every average sits the 1-in-10 return value for the same measure. The average is what you price. The return value is the line beyond which the contract, not the allowance, is likely to carry the risk. The two are never merged.
The working, ready for the tender file
The years used, the thresholds applied, the gauge and the source, exported with the figures. If the allowance is questioned at tender clarification or later on a claim, the basis is already written down.
How it works
From the record to the tender
Name the site and the trades
A postcode or coordinates, the trades on the job, and the months the programme covers.
Set the thresholds
Frost, rain over 5 mm, wind over the crane limit, or your own. Each trade gets its own set, and the set is recorded with the result.
Read the allowance
Average unsuitable days per trade per calendar month, with the years used, and the 1-in-10 return values shown beside them, separately.
Carry it into the price
Non-working days into the programme, time-related cost into the preliminaries, the working into the tender file.
An allowance describes the ordinary year, and this page describes the design. The weather record and the site diary are live in Construction Metric today. The rest of what this page describes is being built with early customers, and the design will follow what they need. The long-term record says what an ordinary year looked like at that site. It does not promise the next one. The allowance is a basis for pricing, not a prediction, and the years it rests on are stated so anyone can see how much history sits behind it. Once the job starts, the same site record keeps the actual weather day by day against the allowance, so the month that turns out exceptional is recognised while it is happening rather than argued about afterwards. Whether that month is a Relevant Event or a compensation event is decided by the executed contract and the people administering it, not by the allowance.
Price the weather from the record.
Start on one site and the long-term record, the allowance and the actual weather live in the same place, from tender to final account.