Whether a Sunroom Leaks Is Decided at the Drawing Stage
Sunroom leaks are rarely caused by careless fitting — they are designed in. Slope, drainage paths and sealing hierarchy decide the outcome. Here are the four structural conditions of a watertight sunroom.
Crews who service sunrooms learn the same lesson repeatedly: nine out of ten leaks are not in the sealant — they are in the structure. Sealant buys time; it cannot fix a design error. This article reverses the usual order and asks: what four conditions must a sunroom satisfy on paper to stay dry?
First, slope. A 'flat' glass roof is never flat: the code minimum is about 3°, and we design to 5° or more. Too shallow, and heavy rain builds a water layer above the joints — water under pressure finds its way through perfect sealant. Joint directions must follow the drainage plan on the drawing, not improvisation on site.
Second, a complete drainage path. Water from the glass should enter the frame's gutter channel, travel through the column's drainage cavity and exit at the base — outdoors. If any link is missing, water reroutes into the room. Many budget sunrooms have no gutter or cavity at all and rely purely on surface sealant; they stay dry until the sealant ages. Ask any bidder: where does the roof water go? If they cannot draw the path, they have never built one properly.
Third, sealing hierarchy. A watertight roof has three independent lines of defence: an inner air-seal, a structural middle layer and an outer weather seal. Each is applied separately; when one ages, the others hold. A single bead of sealant is a single point of failure. Use neutral structural or weather silicone on roofs — cheap acidic sealant corrodes coatings and is incompatible with some profiles.
Fourth, span versus section. Over-spanned glass deflects under water and self-weight, working the joints until they fatigue. Wide roofs need closer rafters, or a different build-up — polycarbonate or laminated glass on steel flats. When a four-metre span is quoted with only four rafters 'to save money', joint fatigue shows up in year two or three. Compare rafter spacing alongside price.
Finally, maintenance: clean the roof and drainage outlets twice a year, inspect the main joints for blisters, and clear heavy snow in northern winters. A correctly designed sunroom with simple annual care stays dry for a decade; a badly designed one is simply on a countdown, no matter how often it is resealed.