Converting a Window to a Door
Converting a window opening to a door is a structural modification that always requires a building permit. The existing window rough opening is typically too narrow and too high (sill too far from floor) for a door, requiring enlargement of the rough opening and installation of a larger header.
Structural Requirements
A standard 32" interior door requires a rough opening of approximately 34"x82.5". An exterior door requires a wider, taller opening with weather-resistive barrier integration. The header above the enlarged opening must be sized for the new span — typically a doubled 2x10 or engineered lumber beam for spans over 5 feet, depending on load conditions and your local code edition.
Exterior Waterproofing
The transition from window to door changes how water must be managed at the threshold. Exterior door installations require: pan flashing at the sill, side flashing integrated with the building wrap, head flashing above the door, and a threshold that meets ADA slope requirements if a deck or patio is being added. Inspectors specifically check the waterproofing assembly at the door rough opening.
What the Permit Covers
Expect a structural plan review for the header, a rough-in inspection after framing and before sheathing, and a final inspection after door installation. If the conversion is to an exterior door on an accessible route, ADA compliance may be reviewed in some commercial-adjacent residential contexts.
FAQs
Yes, this is a common project. A standard 6-foot sliding glass door requires a rough opening of approximately 72.5"x80.5". The existing window opening must be enlarged and a header sized for the full 6-foot span installed. This is a permitted structural project in all jurisdictions. Some areas require tempered or safety glass for sliding doors adjacent to walking surfaces — confirm with your permit office.
In most cases, no — prescriptive header sizing tables in the IRC allow contractors and permit reviewers to specify the header size without a stamped engineering letter. However, if the wall is load-bearing and carries an unusually heavy load (multiple floors above, heavy roof loads), or if your jurisdiction requires engineering for all structural modifications, an engineer's letter may be required. Ask your permit office when you apply.