Guild of Project Controls: Compendium | Roles | Assessment | Certifications | Membership

Tips on using this forum..

(1) Explain your problem, don't simply post "This isn't working". What were you doing when you faced the problem? What have you tried to resolve - did you look for a solution using "Search" ? Has it happened just once or several times?

(2) It's also good to get feedback when a solution is found, return to the original post to explain how it was resolved so that more people can also use the results.

Advise - Estimating Down Time

3 replies [Last post]
Chris Wilson
User offline. Last seen 14 weeks 4 days ago. Offline
Joined: 21 Oct 2016
Posts: 22
Groups: None


I have seen a couple of spreashsheets created that estimated days /month or days/activity that a project is likley to lose from different weather conditions such as below.


Both of these do a job but I am wanting to create something that has a bit more jsutification behind it, for example the first picture shows recommended delay days but what is the justification for these and for what area is this relevant.  wherease the second has a bit more justification in that it looks at wind speeds which can be amended for areas and environments  taken from eurocodes but theres no justification as to why this is used.  

Im wanting to create something that I can generate days per month estimated down time for different locations and activities with jsutification behind it. 

Does anyone have any examples or advice, they can share? Or is the best bet pulling historical weahter data for a number of years and then compring against max operational speeds for cranes and lowest temp say concrete can be pour at , lowest temp bricks can be layed etc to see how many days/hours would be lost to each every month.




Peter Holroyd
User offline. Last seen 3 days 19 hours ago. Offline
Joined: 6 Jun 2005
Posts: 132

Chris, as you rightly observe this is a very complicated subject if you tackle it from the detail end. I have always made subjective order of magnitude allowances from the weather data provided by the Client and the project location along the lines of

1 Wind - 15 days per year totally winded (non working calendar days) off a 3 year coastal location project where tower cranes were critical to production

2 Sea swell - on Marine / Foreshore works - 10 days down time over tidal working height data

3 Weather windows in SEA countries (rain period lasts 6 months) - 2/3 rds production rate, but labour required to clean up daily.

4 High Temperature - above 50 / 60 degrees drop rates to 30 min / hr (UK indise working  - additional breaks allowed, in/out barrier change time etc)

5 Low Temperature - below - 10 / - 30 degrees - never allowed for this as site methods to over come are in place (but obviously reflected in unit rate)

All factors declared in Basis of Schedule and submitted in bid to Clients.

Do you have any rule of thumbs?

Rafael Davila
User offline. Last seen 30 min 32 sec ago. Offline
Joined: 1 Mar 2004
Posts: 5149

That there is high wind does not always mean a work stoppage but usually a reduction in production rates and an increase in activity duration. Similar to rain, wind is usually seasonal. The seasonal impact of reduced production rate cannot be overlooked. 

Your deterministic and statistical models shall consider not only days lost to bad weather but also its seasonal impact on work hours, resource assignments, productivity and resulting changes in activity durations as the schedule moves and thigs do not go as planned.

If an activity is delayed by client from a high productivity season to a lower productivity season it may justify an extension of time as well as the associated cost increase; it should be easier to justify if the baseline model includes the calculation logic.

                                     ↑  open the options menu for a better view as desired

Good Luck.

Patrick Weaver
User offline. Last seen 3 days 6 hours ago. Offline
Joined: 18 Jan 2001
Posts: 307
Groups: None

Hi Chris,

If you want justificatin, you need data but there are challenges!

1. Climate seems to be changeing and becoming more severe (as well as generally warmer), this needs factoring in.

2. If you measure two or three factors, like wind, rain and temprature, you cant just add up the days.....  some days will be too windy or too cold, other days you will find it is too wet, too windy and too cold (but only lose the one day). There may be a degree of correlation but generally you need to use a probabalistic modelling process.  The 'portfolio effect' suggests the total allownace needed will be less then the sum of the individual risks.

3. Corrrelation between work and the event is lso an issue:
   - Wind on a day (or at night) when you don;t need to lift has no effect on the crane
   - Cold tempartures at night after a concrete pour may still be an issue although this can be mitigated by heating or 'blankets'

There's more basic infomraiton on risk at: BUT... this is an area where buying in an expert for a few hours really pays dividends - most of the cost is in gathering the data.