Three lorries delivered to roof 7 on the Monday. The first two loads went onto the slab dry and the third sat through the Thursday rain, so bundle B-7 came off the top and bundle B-9 off the bottom of a wet stack.
Nine working days later the crew had laid 1,850 m² of taper, from 180 mm at the high point down to 20 mm at four sumps. Four weeks after that, sump 3 held standing water and the fall there measured 1:80.
What the Roof Asked of the Board
Three loads on one deck
Deck 3 carried a ballast layer of 22 kg/m², maintenance traffic on the marked walkways, and a plant platform on four sleeper lines near the parapet. The boards under sleeper line 4 compressed first, and the depression in the membrane landed on exactly that line.
Sump 3 sits 6 m from the parapet. Under the platform load, the boards between sleeper line 4 and the parapet carried the point loads for four weeks before the membrane went down.
The specification asked for a declared compressive value at a defined deformation, from the standard the project uses, at the thickness the thermal and drainage design needed. The installer had ordered boards on thermal performance alone.
Slope in 20 mm steps
The taper arrived drawn in 20 mm steps, 180 mm at the highest point and 20 mm at each sump. Thickness at every step, the panel sequence and the sump detail came on the drawing.
Three faults showed up during the lay. Bundles stood flat on the wet slab for three days. Sump 3 went down to the drawing while deck 3 under it ran 12 mm out of level, which pulled the local fall under 1:60. The west apron sits 40 mm below deck level, so panels came off each lorry by hand, six to a run, with no cradle under the stack.
Where Water and Vapour Go
Wet cut edges, laid anyway
Bundles B-7 and B-9 were laid wet. Water taken in at a cut edge stays in the board. Three days at 80% humidity on an open slab put water into every cut edge of both, and nobody measured them before laying.
Roof 7 is an inverted deck, so the boards sit above the waterproofing and take rain and meltwater directly. The crew relied on the drainage layer and ballast to move water away from them. A warm-deck build-up was the alternative on this project, and it would have put the boards under the membrane with the deck’s vapour control deciding what forms inside during cold months.
Reading the declared conductivity
The thermal target came off a graphite-grade assumption. The declared conductivity should come off the board’s data sheet at the reference conditions the project’s method uses, then get checked against the service temperature the roof actually sees.
Polyiso quotes its rating long-term. Compare both materials at one temperature. Grades offered for this work include the graphite grade and the flame-retardant FSH class, and the thermal conductivity selection notes set out how that choice is framed.
What the Order and the Delivery Carry
Seven lines in the purchase order
The order on roof 7 carried board type and grade, nominal thickness with the tolerance the project accepted, taper layout and panel sequence, compressive class, graphite or flame-retardant grade where the design called for it, edge condition, and fire documentation for the authority.
Delivery and storage went into the same document. Strapping tight enough to crush a thin edge arrived on site as damage. A distributor stack standing outside in the rain arrived as those two wet bundles.
The arrival check and the fire file
The site check took the supervisor an afternoon. Board type against the order. Thickness at each taper step. Edges free of crushing. Bundles dry. Fire documentation present. A bundle of the wrong thickness turned up before laying started. Half a day saved.
The authority’s file needed the board’s declared class and the membrane certification in one pack. That pack came together four days after the inspection was booked, and the visit moved with it. Seams over sleeper line 4 were probed by hand at handover; two lifted 2 mm and were re-welded before the final walk.
The replacements for B-7 and B-9 were checked at the kerb before unloading. The graphite grade EPS product range is specified where a lower conductivity is part of the design, and delivery, storage and taper layout on a job this size sit inside the construction insulation application range.
The kerb check took ten minutes per lorry. Sump 1 and sump 2 came out at 1:64 and 1:61, both inside the design. The crew re-cut four panels at sump 3 and refitted them the next morning.
The ballast went down in two passes, 11 kg/m² each. Sleeper line 4 carries the platform leg loads, four points at 6 kN. The membrane was welded along 46 seams and probed by hand at handover, and the inspector walked the roof with the site supervisor the same afternoon.
Board deliveries arrived on a Tuesday and a Thursday, two lorries per day. Panels were cut on site with a hot wire and the offcuts went back on the lorry.
Schlussfolgerung
Roof 7 failed on 12 mm of deck level at sump 3 and two bundles that took water before they were laid. Loads come first, then the slope in the layout, then the water and vapour path, then the grade against the thermal and fire requirements. Board type, thickness, taper, compressive class and storage conditions belong in the order, and the fall gets measured at every sump before the roof closes. Grade, taper layout and delivery conditions for a job like this one can be reviewed with HUASHENG.
Häufig gestellte Fragen
Q1: What compressive strength does EPS roof insulation need?
A1: The plant platform sat on four sleeper lines. The boards under sleeper line 4 compressed first and the membrane showed a depression there. Name the declared value at a defined deformation.
Q2: Why is a taper added to a roof insulation layout?
A2: To move water to the sumps without building slope into the structure. Roof 7 was drawn in 20 mm steps and still ponded at sump 3, because deck 3 under that sump ran 12 mm out of level.
Q3: Does EPS insulation absorb water in a roof?
A3: Bundles B-7 and B-9 took water at the cut edges on a wet slab and were laid that way. Keep boards dry in store, drain and ballast an inverted deck, and control vapour on a warm deck.
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