Make the window heat-loss numbers agree across your documents
A U-factor measures how easily heat passes through a window. A lower number means less heat passes through. The rating can appear in the window list on the drawings, the written building requirements and the energy report. Different people often update these documents. If one changes, the others can fall behind.
A reviewer may compare the window rating in the energy report with the written requirements and the window list. If the same window has a different heat-loss rating in each document, the team must check which rating is correct before sending them for approval.
One possible cause is simple: someone changes a number in one document and forgets to change it in the other two.
Five ways the numbers can stop matching
Check these five situations when you compare the documents.
1. A different window is chosen
The team chooses a different window and updates the written requirements. The window list still shows the old rating.
2. The glass rating is used for the whole window
A product sheet may give one rating for the glass alone and another for the whole window, including the frame. These measure different things. Check which rating your project requires before copying it.
3. A window is missing from the list
A small window above a door, an interior window or a window high on a wall may be added to the drawing later. Check that the window list includes it. Check doors with glass too.
4. Only one page is updated
Window ratings can also appear in wall drawings, details and summary notes. Changing one page does not update the others.
5. The energy report uses old plans
The energy report may have been prepared before the latest design changes. Its numbers can agree with each other while describing an older version of the building.
How to check the documents
Your team can do this check by hand using the current project documents.
- List every window and door with glass shown in the plans. Include small windows above doors, interior windows and high windows.
- For each item, copy its rating into three columns: the drawing list, the written requirements and the energy report.
- Mark any window with different ratings in the three columns. Mark blank spaces too. Both need checking.
- Check whether each rating covers the whole window or only the glass. Record the document and page it came from.
- Check that the energy report uses the latest plans. Compare the dates and version numbers.
- Ask the qualified reviewer to check the values against the building rules that apply to the project location and design. Local rules and editions can differ.
Use the rules for your own project
This guide does not give required rating values. They depend on local building rules, climate and the way the project proves it meets those rules. Your qualified reviewer must check the requirements for your project.
Check again when the plans change
This check covers the documents you review today. If someone changes a window rating in only one document, the other documents will still show the old rating. Repeat the check before sending a new version.
Keep a shared record of the agreed numbers and the pages where they appear. When a number changes, the team can see which documents need updating.
Where Mebbian fits
Mebbian’s drawing review checks for mistakes such as a window drawn on a plan but missing from the window list. It shows the pages for your team to check.
Mebbian does not approve a design, sign it or submit it. A qualified professional must check the results and stays responsible for the work.