How to seal bay joints on a modular building
Where two modules meet, the roof has a joint, and that joint is one of the most common places for water to get in. Whether you're closing up a new modular building on site or fixing a leak on a cabin that's been moved, sealing the bay joint properly is what keeps the building dry.
Supraseal® is widely used by modular building manufacturers and installers for exactly this job. It's butyl based and bitumen free, so it bonds to single-ply membranes and coated steel without staining plastisol-coated panels.
What you'll need
- Supraseal® Weatherproofing Tape. 200mm is the standard width for bay joints, and 300mm suits wider joints or roof-to-roof junctions (see our width guide)
- A silicone seam roller
- Clean cloths and a suitable cleaner for the roof surface
- A sharp knife or scissors
Step 1: Check the joint is closed and dry
Make sure the modules are fully pulled together and fixed. Tape bridges a joint; it isn't designed to fill a large gap. Wait for a dry spell, as the surface must be completely dry for the tape to bond.
Step 2: Clean both sides
Clean a strip at least as wide as your tape on both sides of the joint. Remove dirt, moss, old sealant and any loose coating, then let it dry. Most tape failures come down to a dirty or damp surface.
Step 3: Lay the tape centrally
Start at one end with the tape centred over the joint, so there's an equal lap onto each module. Peel the release liner back a little at a time and press the tape down as you go, without stretching it. On long runs, work with a second pair of hands to keep the line straight.
Step 4: Roll it firmly
Roll the full length with firm, overlapping passes, paying extra attention to both edges. The roller pushes the butyl into full contact with the surface, and the bond keeps strengthening over time.
Step 5: Finish the ends and junctions
- Where the joint meets an upstand, parapet or gutter, turn the tape up or into the detail rather than stopping short.
- Where two runs of tape cross, lay the second over the first with a generous overlap and roll the crossing well.
- Round the corners of cut ends so they're less likely to catch and lift.
On the production line
For factories taping joints module after module, the 10m rolls of 200mm and 300mm tape save changeovers. Trade accounts on invoice terms, with bulk and pallet pricing, are available. Email hello@supraseal.com.