Saddle washers are profile-matched bearing and sealing components used with roofing and cladding fasteners where the sheet geometry does not provide a suitable flat seating surface. Their function is to improve the interface between the screw assembly and the profiled sheet while supporting controlled load distribution and sealing.
A saddle washer should match the local sheet profile sufficiently to provide stable bearing without forcing the sheet into an unintended shape. Selection is therefore governed by geometry as well as fastener size and sealing requirements.
Why profiled sheets create a different fixing condition
Trapezoidal and corrugated sheets contain crowns, valleys and inclined webs. A conventional flat washer placed on a curved or inclined region can contact only part of the surface. Tightening the screw may then concentrate bearing pressure locally instead of distributing it over a stable interface.
A correctly selected saddle washer follows the intended profile and provides a broader, more predictable seating surface for the fixing assembly.
Profile compatibility is the first selection check
Saddle washers should not be selected only by screw diameter. The profile shape, crown width, local radius or flank geometry and fixing position must be considered. Two roofing sheets with similar overall depth can still require different saddle geometries.
If the washer does not correspond sufficiently to the profile, tightening may produce rocking, edge contact, local indentation or uneven sealing pressure.
Bearing and load distribution
The saddle washer increases the effective bearing interface between the fastener assembly and the sheet. This can reduce severe local contact concentration and help stabilize the connection around the fixing point.
However, the washer does not automatically determine the structural resistance of the connection. Pull-over resistance remains dependent on the complete assembly, including sheet thickness and strength, washer geometry, screw head or washer arrangement, fastener position and loading condition.
Sealing function
Saddle washers used in weather-exposed roofing and cladding commonly incorporate or work together with an elastomeric sealing element. The profile-matched body supports the sealing material so that compression can occur over a more stable surface.
Watertightness still depends on controlled installation. An apparently tight screw can have poor sealing if the washer is tilted, mismatched to the profile, under-compressed, excessively compressed or installed over a damaged surface.
Fixing position matters
The intended fixing location should be established by the roofing or cladding system design. Crown fixing, valley fixing and fixing through other local profile features create different geometry and load paths. A saddle washer intended for one position should not be assumed suitable for another.
The washer should seat without bridging unintended gaps and without requiring excessive screw tightening to force it into contact.
Installation alignment
The screw should be driven in the intended orientation so that the saddle washer seats symmetrically on the profile. Angular installation can load one side of the washer more heavily and reduce sealing uniformity.
Before final seating, the installer should confirm that the washer is correctly oriented with the profile. A rotated or displaced saddle washer may appear secure after tightening while still producing poor contact underneath.
Underdriving and overdriving
- Underdriving: may leave the washer unstable and the sealing element insufficiently compressed.
- Overdriving: may distort the saddle washer, indent the sheet, damage coatings or excessively deform the sealing element.
- Correct seating: produces stable profile contact and controlled sealing compression without visible crushing or sheet distortion.
Material and corrosion compatibility
The washer body, screw, coating system and roofing or cladding sheet should be considered as one exposed assembly. Moisture retained around a fixing point can make incompatible materials or damaged protective coatings particularly significant.
Material selection should therefore consider the project environment and the documented compatibility of the actual components. A suitable geometric fit does not compensate for an unsuitable corrosion system.
Relationship to EPDM sealing washers
A flat metallic washer with an EPDM element and a profile-matched saddle washer solve related but different interface problems. The EPDM element provides compliant sealing contact, while the saddle geometry provides support where the sheet itself is not locally flat.
In a profile-specific assembly these functions may be combined. The engineering check should still distinguish geometric seating, sealing compression and structural resistance rather than treating them as one property.
Inspection points
- Confirm that the saddle geometry corresponds to the specified sheet profile and fixing location.
- Check that the washer orientation follows the profile correctly.
- Verify that the screw is not visibly inclined relative to the intended fixing axis.
- Check for stable contact without rocking, edge lifting or bridging.
- Inspect the sealing element for continuous compression without severe extrusion or tearing.
- Check the surrounding sheet and coating for indentation, cracking or installation damage.
Selection as part of the complete fixing system
Saddle washer selection should be coordinated with screw diameter, head or washer arrangement, sheet profile, substrate, sealing requirement and environmental exposure. The component should not be treated as a universal accessory simply because the screw passes through it.
Where structural resistance or watertight performance is required by the project, verification should be based on the documented configuration and applicable system requirements.
Product-specific verification
JOPAL saddle washer dimensions, materials and compatible fixing arrangements should be selected from the technical documentation for the actual product and application. Profile compatibility should be confirmed before installation, particularly where roofing or cladding geometry differs from the nominal profile assumed during selection.
This resource explains selection principles. Final product suitability, drilling range and resistance must be verified against the applicable JOPAL technical data for the specific fastener and project condition.
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