Structural calculationPrice on requestWhat is assessed?
A dormer changes the load-bearing structure of the existing roof. The assessment covers interrupted roof members, their support, and the transfer of the dormer’s weight and wind loads.
A prefabricated dormer supplier may provide calculations for its own product. Agree who checks the connections to the existing roof so that the two commissions cover all required elements.
What data is needed?
The following information can be used to prepare the assessment. The structural engineer determines whether additional research is necessary.
| Information | What should you send? |
|---|---|
| Roof cross-section and existing beam dimensions | Include existing drawings and state which dimensions are known and which still need to be measured. |
| Dimensions and position of the dormer window | Mark the dormer on the roof and share its proposed width, height and position. |
| Supplier details | Send current supplier drawings and any calculations. State what the supplier does and does not cover. |
| Photos of the inside of the roof | Include an overview of the roof and photos around the proposed opening, where accessible. |
Not everything available yet? Describe what you have and what is missing. You do not need to calculate load capacity yourself. Any survey or additional investigation needed will be discussed for your project.
What do you receive?
Record the exact delivery in the quotation. Depending on your project and assignment, this involves:
- Assessment of the roof modification
- Calculation of supporting structures around the opening
- Required connection details
Discuss who will take care of the architectural development, supplier details and any temporary support. In this way, the components involved are coordinated.
Materials and drawings
The design determines the materials and connections. Read about structural timber and the difference between an architectural drawing and a structural drawing.
How does the process proceed?
Describe your project and share the available documents. We then agree the scope, any additional information needed and the schedule. See the complete step-by-step guide for all stages.
Price and scope: agree these points first
Ask the quotation to specify which elements will be assessed. Calculating the dormer and assessing the existing roof may be separate commissions.
What should be calculated?
Discuss the roof opening, support for interrupted rafters or purlins, and connections to the existing roof. Agree who checks the dormer supplier’s information and coordinates the two sets of calculations.
What needs a separate agreement?
A site survey, architectural drawings, permit assistance, temporary support, supply and installation are not automatically included. Ask who assesses supplier changes or a different dormer position.
What affects the schedule?
Final dimensions, location, roof build-up and supplier documents determine the information needed. Missing archive drawings or differences found during a survey may require further investigation and coordination.
Ask your quotation to identify who prepares the calculations, who provides the drawings and who answers technical questions. State your preferred date; feasibility is agreed for your commission.
Can I already order material?
Order structural parts based on the coordinated and current design data. A preliminary estimate is not a complete basis for this.
Is a site visit necessary?
That depends on the project and the available information. Sometimes drawings and photos are sufficient for the inventory; sometimes an admission or additional examination is necessary.
What happens if my plan changes?
Report changes before they are implemented. The structural engineer assesses whether calculations and drawings need to be adjusted.
From data to a detailed plan
- Describe your complete construction plan.
More daylight and space, with attention to the beams and rafters affected by the new opening.
- Discuss missing data.
The structural engineer determines which site survey or additional information is required for the agreed assessment.
- Agree the scope and deliverables.
Agree on the calculated parts, drawings, price and planning.
- Coordinate the design with the construction work.
Use the current documents and have relevant changes reviewed before they are implemented.
Frequently asked questions about dormer windows
Does the dormer supplier's calculation cover my entire roof?
That depends on the supplier's assignment. His calculation can only relate to the delivered product. Record who assesses the existing roof construction, interrupted parts and connections. This way you prevent the transition between product and building from falling outside both assignments.
Does the location of the dormer window make a difference?
Yes, the opening can interrupt or load other roof components depending on its position. Therefore, share a drawn position, dimensions and a cross-section of the existing roof. Have changes to the location or width communicated to the designer involved.
Related structural topics
Your project location
Provide the building address and share available drawings and photographs. Discuss whether a site survey is needed and which travel or investigation costs form part of the commission.