roofing & siding

Most any traditional materials can be used to clad exterior wall panels or cover SIPs roofs.

Most traditional exterior wall coverings can be used, though some, such as stucco and steel panels, require special construction techniques because of the screw holding characteristics of OSB sheathing on SIPs panels.

stucco walls
The building's exterior is first wrapped twice using 15 pound building paper. Wrapping prevents water infiltration and damage to OSB during stucco application and drying. Next, a self-furring wire mesh is thoroughly fixed with screws to support the first thin layer.

This base coat must set and dry thoroughly before any subsequent applications. This is necessary because, unlike masonry or concrete walls, which draw water out of the stucco into an absorbent wall, OSB wrapped with building paper is water tight and does not allow absorption.

The base coat must dry from the outside inward, This takes time. If applying a second coat before the elastomeric finish coat, the same is true. Applying subsequent coats without complete curing and drying causes stress cracks. Although hairline cracks are unavoidable, they are readily bridged and sealed by the final high quality, weather-sealing, elastomeric finish coat as long as the elastomeric sealer isn't applied over damp undercoats. Be very wary when hiring stucco workers who lack experience with SIPs. They won't want to expend the time and care to work according to SIPs specifications and the resulting cracked stucco will need expensive repair.

steel roofing and siding
Steel is an excellent roof and wall covering for SIPs buildings. Applying a membrane is the same: use 30 pound roofing felt or one of the new tear and aging resistant rubber/plastic membranes. Use nails or staples with plastic washer heads to prevent tear through. But do not use a fastener that will prevent the steel panels from laying flat.

The problem with installing steel panels over OSB lies with the holding power of OSB fibers and not just because the OSB is only 3/8 in (10 cm) thick. More important is that the amount of torque needed to compress rubber sealing washers against the steel panel is identical to the torque needed to strip the OSB fibers from the threads. Trials with special screws with more thread surface have had mixed results and engineers do not recommend them.

But there are work-around solutions. While one could fix 1 inch (25 mm) wood strips over the felt at regular intervals coinciding with steel panel installation requirements, eg, at 18 inch (45 cm), and then run the screws into these, the steel roof is then raised so that no one could ever walk on the roof without causing damage. Service would be very difficult. Moreover, the wood strips would still be fastened into OSB, so not much if anything is gained. Others re-sheath the entire roof with plywood. But such redundancy wastes money, time and significantly increases roof load.

best solution appears to be the most economical and robust. If specified some SIPs manufacturers will integrate wood backers into the panels at required spacing during panel production. But there must be careful coordination between SIPs and steel panel technicians in order to accomodate the standard 48 inch (122 cm) wide SIPs panels with standard narrower steel panels, which require fasteners at 9 inches (23 cms) or 18 inches (45 cms), depending on the rib profile and metal thickness. We found that we could satisfy technical requirements of both roofing manufacturer and Enercept by doing the following:

After the SIPs engineer has drawn up the numbered panel sequencing plans, divide them into 18 inch (46 cm) bands running from ridge to eave. The 18 inch band division lines represent
possible placement of blockers for the screws. Due to the fact that steel panels are not a simple multiple of 48 inches, every panel requires different block placement . Some of the blocks will be very close to integrated I-joists, and these serve as attachment lines. One sees that some panels require just one extra wood strip while others require two, but always in the same place for each panel. Good communication is necessary.

ceramic tile roof
Flash and cover the SIPs roof panels making certain that flashing extends at least 3 - 3 1/2 inches (7-8 cm) onto the roof at both rake and eave. Eave flashing goes on first, then membrane, next rake flashing and ice dam membranes and last, the wood battens to support the tile. The ice dams are 12 in wide (30 cm), self-adhering membrane strips that further seal flashing to the roof. We fabricate roof flashing, fascia and drip edge all in one piece in order to make a leak-proof single piece. This piece extends enough below the of the SIPs roof panel thickness - usually 8 1/4 inces (21 cm) - plus the thickness of sheathing (3/8 in or 10 cm), which covers the underside of roof panel overhangs. Our flashing is often about 9 inches (23 cm), depending on the thickness of the underside sheathing. The lower drip edge can either flair out at 45 degrees or fold under to cover the overhang sheathing as it would in a steel building.

Tile roofs require horizontally-placed, pressure-treated battens to lift the tile off the roof membrane and to receive the galvanized or stainless roofing nails. The 2 inch wide (5 cm) , 5/4 in thick (3 cm) battens must be screwed through the roof membrane into the SIPs roof panels, and this penetration could cause leaks in the membrane. Therefore we recommend butyl, bitumen or other synthetic roof membranes rather than 15 lb felt because synthetics resist tearing from shoes, tile and tools, and it is easier to apply a membrane-compatible sealant to the bottom of each stick before attaching it. This precaution stops any possible leaks caused by batten screw penetration. Use stainless, zinc or good quality zinc-coated nails. Leave 3/4 inch or so (2- 2.5 cm) gaps every 4-5 feet (1.2 - 1.5 m) in the horizontal batten run so that any condensation under tiles can easily escape. Stagger the gaps on subsequent runs. Lay the tile on the treated wood battens following standard tile laying procedures.