RothoblaasHolz Technic
DWZ · Double thread screw for insulation layer
DWZ is a double thread insulation screw that fixes the counter batten through the insulation layer into the rafter below, holding the batten off the roof deck across the full insulation depth.
On an over-rafter warm roof the batten has to be held down through a thick, compressible layer without crushing it and without a bracket bridging it. DWZ does that with one screw. The point-side thread bites the rafter, the head-side thread bites the batten, and because the two pull at different rates the screw clamps the sandwich tight.
Key features
- Fixes the counter batten through insulation into the rafter in one screw
- Double thread with a 3 THORNS tip, 100 mm point side and 60 mm head side
- Cylindrical head, Ø9.50 mm on Ø7 and Ø11.50 mm on Ø9, sits hidden inside the batten
- Single fixing through the layer limits thermal bridging, with no bracket or rail crossing the insulation
- Certified for hard, soft and façade insulation, fixed at 60° or 90°
- Characteristic tensile strength ftens,k 15.4 kN at Ø7 and 25.4 kN at Ø9
- TX30 drive on Ø7 and TX40 on Ø9, bit included in every box
- Suits over-rafter warm roofs on rafters, CLT and glulam, and ventilated façades
Before you fix
- The tip must not protrude from the underside of the rafter. Check your build-up depth before you order a length
- Minimum batten size is 50/30 mm base/height for Ø7 and 60/40 mm for Ø9
- No pre-drilling in normal softwood. Pre-drilling is required above 550 kg/m³ characteristic density
- Electrogalvanised zinc at minimum 5 µm, so service class 1 and 2 only, C2 atmospheric and T2 wood corrosivity. Not for exterior or coastal exposure
A note on the name. This screw is certified under ETA-11/0030 as screw type DGZ. DWZ is the Holz Technic code for the same Rothoblaas screw, same manufacturer, same geometry, same approvals. If you or your building control officer are checking the approval document, look for DGZ. If your build-up calls for a screw longer than 400 mm, the identical screw is stocked in lengths up to 520 mm as DGZ: same manufacturer, same ETA, same performance, listed under the DGZ code.
What you'll also need
DWZ passes through the breather membrane, so every penetration needs sealing. Run Traspir House breather membranes under the battens and close the fixing line with nail sealing tapes such as FILLUM or GEMINI. See the full structural timber screw range.
Common questions
How do I choose the right DWZ length for my roof build-up? Length comes off the selection table on page 2 of the datasheet, from three numbers: insulation plus planking thickness, batten thickness, and whether you fix at 60° or 90°. Read it off the table rather than adding the layers up, and check the tip will not break through the underside of the rafter.
Can DWZ fix through soft insulation, or only rigid? Both. Soft insulation is a certified case in the ETA, not a workaround. It does reduce capacity, so in practice it usually means more screws or the 60° arrangement. The number and the spacing are your engineer's call.
Price shown is per box of 50 pieces. See the table below for codes, sizes and pack prices.
All sizes in the DWZ · Double thread screw for insulation layer range
| Code | Diameter | Length | Pack | Price ex VAT | Stock | Order |
|---|---|---|---|---|---|---|
| DWZ7220 | 7 mm · min. batten 50/30 mm | 220 mm | 50 pcs | £57.60 | To order | |
| DWZ7260 | 7 mm · min. batten 50/30 mm | 260 mm | 50 pcs | £76.00 | To order | |
| DWZ7300 | 7 mm · min. batten 50/30 mm | 300 mm | 50 pcs | £84.54 | To order | |
| DWZ7340 | 7 mm · min. batten 50/30 mm | 340 mm | 50 pcs | £98.14 | To order | |
| DWZ9400 | 9 mm · min. batten 60/40 mm | 400 mm | 50 pcs | £163.47 | To order | |
| No sizes match your search. | ||||||
Often ordered together
5–7 days
