Which screw should I use for roofing sheets?
Which screw should I use for roofing sheets?
A hex-head screw with a bonded EPDM washer, driven until the washer just spreads — no further.
Every fixing through a roof sheet is a deliberate hole, and the washer is the roof at that point. Under-driving leaves the washer uncompressed and it leaks immediately; over-driving dishes the sheet, squeezes the rubber out sideways and cracks the coating — and both faults look almost identical from the ground until it rains. The correct setting is when the washer has just spread to the edge of the metal cap. Roof sheets also expand and contract along their length with temperature by a surprising amount, so oversized holes and the manufacturer's fixing pattern matter, and the fixing should never pin the sheet so rigidly that thermal movement tears the hole open.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Hex head with bonded EPDM washer | The rubber-to-steel bonded washer seals the hole, and EPDM survives ultraviolet where cheaper rubber perishes. | The seal depends entirely on driving depth, which a clutch or a depth-sensing driver controls better than a hand. |
| Stainless with EPDM washer | For coastal exposure and for anything expected to last decades. | Cost, and it must be compatible with the sheet material. |
| Screw into the crown of the profile | The high point stays out of running water, which is why most manufacturers specify it for roofing. | Requires a longer screw, and the sheet can dimple if it is not supported. |
| Screw into the valley | Pulls the sheet tight to the purlin and is used on some wall cladding. | Sits where water runs, so any seal failure leaks; follow the sheet manufacturer's instruction. |
Technique that changes the outcome
- Set the driver clutch and test on an offcut before working on the roof
- Follow the sheet maker's pattern for crown or valley fixing and for spacing
- Drive perpendicular to the sheet; an angled screw never seals
- Replace, do not re-drive, any screw that has been over-tightened
What goes wrong
- Over-driving, which dishes the sheet and destroys the seal
- Reusing old screws and washers on a re-sheet
- Walking on a fragile roof sheet — use crawl boards; fragile roof falls are a leading cause of construction deaths
Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.
Other screw questions
| For | Use |
|---|---|
| Wood | A pilot hole matching the screw's core diameter in the lower piece and a clearance hole in the upper one — that is what makes a joint tight. |
| Decking | Stainless steel — 304 inland, 316 near the coast — or a screw specifically rated for modern treated timber, which eats ordinary zinc plating. |
| Masonry | A concrete screw into a precisely sized hole, or a plug and screw — and hollow block needs a different anchor entirely. |
| Plasterboard | Coarse-thread bugle-head drywall screws into timber studs, fine-thread into metal studs — and never use them for anything structural. |
| MDF | A straight-shank MDF screw with a parallel thread, always into a pilot hole — the edge splits without one. |
| Sheet metal | A self-drilling (Tek) screw with a drill point matched to the material thickness, or a self-tapping screw into a correctly sized pilot hole. |
| Chipboard | A twin-thread chipboard screw with an unthreaded shank under the head, so it pulls the joint together instead of bursting the board. |
| Plastic | A thread-forming screw designed for plastic, or a heat-set threaded insert where the joint will be undone more than once. |
| Brass hardware | Cut the thread with a steel screw of the same size first, wax the brass one, and use a driver that fits the slot exactly. |
Common questions
- Which screw should I use for roofing sheets?
- A hex-head screw with a bonded EPDM washer, driven until the washer just spreads — no further.
- What should I avoid?
- Over-driving, which dishes the sheet and destroys the seal Reusing old screws and washers on a re-sheet Walking on a fragile roof sheet — use crawl boards; fragile roof falls are a leading cause of construction deaths
Related pages
- Which screw and pilot hole should I use for wood? A pilot hole matching the screw's core diameter in the lower piece and a clearance hole in the upper one — that is what makes a joint tight.
- Which screw should I use for decking? Stainless steel — 304 inland, 316 near the coast — or a screw specifically rated for modern treated timber, which eats ordinary zinc plating.
- Which screw should I use in masonry? A concrete screw into a precisely sized hole, or a plug and screw — and hollow block needs a different anchor entirely.
- Which screw should I use for plasterboard? Coarse-thread bugle-head drywall screws into timber studs, fine-thread into metal studs — and never use them for anything structural.
- Which screw should I use in MDF? A straight-shank MDF screw with a parallel thread, always into a pilot hole — the edge splits without one.
- Which screw should I use for sheet metal? A self-drilling (Tek) screw with a drill point matched to the material thickness, or a self-tapping screw into a correctly sized pilot hole.
- Which screw should I use in chipboard? A twin-thread chipboard screw with an unthreaded shank under the head, so it pulls the joint together instead of bursting the board.
- Which screw should I use in plastic? A thread-forming screw designed for plastic, or a heat-set threaded insert where the joint will be undone more than once.
- How do I drive brass screws without snapping them? Cut the thread with a steel screw of the same size first, wax the brass one, and use a driver that fits the slot exactly.
Sources
- Typical range compiled from manufacturer specifications — At One Place