Large openings are a popular inclusion in the modern home, but loading and structural movements that cause few problems with regular sized door openings can have very significant consequences in a bigger opening. Your structural engineer will generally be able to ensure your building complies with all statutory regulations and does not fall down, but the movement of and around large openings can often cause unnecessary problems for the builder or the homeowner.
Here, Centor explores three of the most common problems that can arise with large openings and shows how all of them are avoidable if planned for in advance.
Problem 1: Deflection
The header beam on a big opening deflects progressively as a construction material is added during the building program. Finish flooring, interior and exterior wall sheeting above the opening are added after the doors are installed. The deflection can be enough to make the doors inoperable. This causes concern for the architect and frustration for the builder who has to perform costly and time-consuming rework.
Have a professional engineer calculate the final building load and specify a beam with tighter deflection limits. 2 to 3mm (1/16” to 1/8”) across an opening is ideal.
Problem 2. Creep
The load sitting on a wood header beam will cause “creep.” As a general rule of thumb, the deflection that occurs when a wooden beam is first loaded will be doubled within the first year. The change is gradual but eventually, there can be enough movement to make doors inoperable. The homeowner will call the builder to get it fixed, but in most instances, there is an insufficient adjustment and the real fix is major and expensive.
Use steel structures for openings more than 3.65m (12 feet) wide. Steel has zero creep.
Problem 3: Twisting Loads
Several years after completion, gaps can appear, and cracks may show in the drywall (plasterwork) near the top corners of the door opening. The builder will be called back, and while a simple fix may work, frequently the problem reappears. The cause is often a poor connection between the header beam and the posts. Twisting loads from windloads or door operation cause the beam to move inside the wall.
Run the posts full height, from floor structure to ceiling diaphragm, firmly securing the header beam to the post at both top and bottom edges. Do not simply rest the beam on jacking studs as the beam will roll. If a steel header is used, then use steel posts that run full height.
All of these solutions are simple and inexpensive if implemented during the construction phase. Find more details in Centor’s Engineering Design Guide.