Saddle washers are used where a profiled roofing or cladding sheet does not provide a suitable flat seating surface for the fastener. Their job is to match the local profile, support the sealing arrangement and spread the fixing load over a more stable area.
A saddle washer should fit the local sheet geometry without forcing the sheet into a different shape. Screw diameter matters, but profile shape and fixing location usually decide whether the washer is suitable.
Why a profiled sheet changes the fixing condition
Trapezoidal and corrugated sheets include crowns, valleys and inclined webs. A flat washer placed on one of these surfaces may contact only along an edge or over a small area. Tightening the screw can then create concentrated pressure and uneven sealing.
A correctly matched saddle washer gives the fastener a broader, more stable seating surface.
Profile compatibility comes before screw size
Two sheets with similar overall depth can still have different crown widths, radii or flank angles. A saddle washer should therefore be selected against the actual profile and intended fixing position, not only by the nominal screw diameter.
A poor match can show up as rocking, edge lifting, local indentation or uneven compression of the sealing element.
Bearing and local load distribution
The saddle washer increases the contact area around the fixing and can reduce local bearing concentration in the sheet. This helps stabilize the connection, particularly on thin profiled material.
It does not, however, define the structural resistance on its own. Pull-over still depends on sheet thickness and strength, washer geometry, fastener position, head or washer arrangement and the applied load.
Sealing on a profiled surface
In weather-exposed roofing and cladding, the saddle washer normally works with an elastomeric sealing element. By matching the profile, the saddle gives that seal a more stable surface to compress against.
A screw can look tight and still seal poorly if the saddle is rotated, tilted, mismatched to the profile or overdriven.
Fixing position matters
Crown fixing, valley fixing and fixing through other local profile features do not create the same geometry or load path. A saddle washer intended for one location should not be assumed suitable for another.
The washer should sit naturally on the sheet without bridging gaps or needing excessive screw torque to force it into contact.
Alignment during installation
The screw should be driven in the intended direction so that the saddle seats symmetrically. An inclined screw loads one side of the washer more heavily and usually produces uneven sealing pressure.
Before final seating, check that the washer is correctly oriented to the profile. A rotated saddle can look acceptable after tightening while still having poor contact underneath.
What underdriving and overdriving look like
- Underdriven: the washer remains unstable and the seal is only partly compressed.
- Correctly seated: the saddle has stable contact with the profile and the sealing element is evenly compressed.
- Overdriven: the washer distorts, the sheet indents or the sealing element is excessively squeezed.
Material and corrosion compatibility
The saddle washer, screw, coating system and sheet remain exposed together after installation. Material compatibility and coating durability should therefore be checked for the actual environment.
A good geometric fit does not solve a corrosion problem. Both issues need to be addressed separately.
How this differs from a standard EPDM washer
A flat metal washer with EPDM provides sealing and bearing on a suitable seating surface. A saddle washer adds profile matching where the sheet is curved or inclined.
In some assemblies these functions are combined, but it is still useful to check three things separately: profile fit, sealing compression and structural resistance.
Site inspection points
- Confirm that the saddle matches the specified profile and fixing position.
- Check the washer orientation before final tightening.
- Make sure the screw is not visibly inclined.
- Look for stable contact without rocking, bridging or edge lifting.
- Check that the sealing element is continuously compressed without tearing or severe extrusion.
- Inspect the surrounding sheet and coating for indentation or installation damage.
Use it as part of the fixing assembly
Saddle washer selection should be coordinated with the screw, sheet profile, support condition, sealing requirement and exposure. It is not a universal accessory that can be added to any profiled sheet without checking fit.
Where project performance depends on structural resistance or watertightness, use the documented JOPAL product configuration and the requirements of the roofing or cladding system.
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.
© JOPAL Trading LLC SOC. This technical resource is published for reference and may not be reproduced or republished in whole or substantial part without written permission. Please cite the canonical JOPAL article when referencing this material.