{"product_id":"insulation-screw-dgz","title":"Double threaded screw for insulation — DGZ","description":"\u003cp\u003eDGZ is the Rothoblaas double threaded insulation screw, certified under ETA-11\/0030,\nfixing counter battens and façade battens through the insulation and holding them clear\nof the structure behind.\u003c\/p\u003e\n\n\u003cp\u003eThe screw carries the batten load back to the rafter, joist or panel through the\ninsulation, without a bracket or secondary joist crossing the layer. ETA-11\/0030 covers it\nin solid timber, glulam, CLT, solid wood panel and LVL, in hard, soft and façade\ninsulation, at 60° or 90°. Design is to EN 1995-1-1 and the UK National Annex.\u003c\/p\u003e\n\n\u003ch2\u003eKey features\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eCertified in non-pre-drilled LVL, the highest withdrawal case on the sheet, at\n      fax,k 15.0 N\/mm², ρa 500 kg\/m³, characteristic density 410 to 550 kg\/m³\u003c\/li\u003e\n  \u003cli\u003eAlso covered in solid timber, glulam, CLT and solid wood panel\u003c\/li\u003e\n  \u003cli\u003eDouble thread with a 3 THORNS tip, 100 mm point side and 60 mm head side, which is\n      what allows the tight minimum spacings below\u003c\/li\u003e\n  \u003cli\u003eThirteen lengths, Ø7 from 220 to 380 mm and Ø9 from 240 to 520 mm\u003c\/li\u003e\n  \u003cli\u003eCylindrical head, Ø9.50 mm at Ø7 and Ø11.50 mm at Ø9, seated inside the batten\u003c\/li\u003e\n  \u003cli\u003eCertified for hard, soft and façade insulation, fixed at 60° or 90°, both tabulated\n      in the ETA\u003c\/li\u003e\n  \u003cli\u003eTX30 on Ø7 and TX40 on Ø9, bit included in every box\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eThermal bridging\u003c\/h2\u003e\n\u003cp\u003eFixing the insulation continuously, rather than interrupting it with timber\ncounter-joists, was calculated to improve the U-value of the roof build-up by 10 to 15%.\nThe calculation was carried out by EURAC Research as part of the MEZeroE project, funded\nby the European Union's Horizon 2020 programme under grant agreement No 953157. It\ncompares a continuous insulation package against one interrupted by secondary joists; it\nis a calculation, not a site measurement, and the result for any specific roof depends on\nthat roof's build-up.\u003c\/p\u003e\n\n\u003cp\u003eThat benefit depends on restraint. The datasheet is explicit that excessive anchoring\nor incorrect arrangements should be avoided in order not to compromise the thermal\nperformance of the package. More fixings than the design calls for works against the\nreason for choosing this detail.\u003c\/p\u003e\n\n\u003ch2\u003eMinimum spacings\u003c\/h2\u003e\n\u003cp\u003eThe 3 THORNS tip is what buys the tight spacings. They are independent of insertion\nangle and of grain angle.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eBetween screws, a1 and a2: 5·d, so 35 mm at Ø7 and 45 mm at Ø9\u003c\/li\u003e\n  \u003cli\u003eTo end grain, a1,CG: 10·d, so 70 mm at Ø7 and 90 mm at Ø9\u003c\/li\u003e\n  \u003cli\u003eTo the edge, a2,CG: 4·d, so 28 mm at Ø7 and 36 mm at Ø9\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eThese hold only in members of at least 12·d thickness, 84 mm at Ø7 and 108 mm at Ø9,\nand at least 8·d width or 60 mm, whichever is greater. The datasheet does not print that\nprecondition next to the spacings, so check the member before you rely on them.\u003c\/p\u003e\n\n\u003ch2\u003eBefore you fix\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eCheck the tip cannot break through the underside of the member. This is the most\n      common error on long insulation screws\u003c\/li\u003e\n  \u003cli\u003eBatten minimums are not optional: 50\/30 mm base and height at Ø7, 60\/40 mm at Ø9\u003c\/li\u003e\n  \u003cli\u003ePre-drilling is required above 550 kg\/m³ characteristic density. Note that\n      pre-drilling LVL puts you outside the 15.0 N\/mm² case above\u003c\/li\u003e\n  \u003cli\u003eElectrogalvanised zinc at minimum 5 µm, so service class 1 and 2 only, C2\n      atmospheric and T2 wood corrosivity. Not for exterior or coastal exposure\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eThe same screw, two code ranges.\u003c\/strong\u003e DGZ and DWZ are the same Rothoblaas\nscrew under two codes: DGZ is the designation used in ETA-11\/0030, DWZ is the Holz Technic\ncode. Same manufacturer, same geometry, same approvals. The range here is the wider one,\nrunning to 520 mm at Ø9 where \u003ca href=\"\/products\/insulation-screw-dwz\"\u003eDWZ\u003c\/a\u003e stops at\n400 mm, and the DWZ selection table is this same table narrowed to the stocked lengths, so\nsome deeper cells are blank there. For deeper build-ups, this is the page. The screw is\nalso certified in flange-head (DGT) and countersunk-head (DGS) versions, which we do not\nstock. An EVO version with a Zn-Al flake coating is available on request for service class\n3 applications.\u003c\/p\u003e\n\n\u003ch2\u003eDesign and specification support\u003c\/h2\u003e\n\u003cp\u003eRothoblaas MyProject is a free calculation tool that produces a fastening calculation\nreport for this screw. It is a design aid for the specifier. It does not replace the\nstructural design of the roof, and the connection must still be checked and signed off by\nthe project's structural engineer. See also our\n\u003ca href=\"\/blogs\/insights\/eurocode-5-explained-timber-design-uk\"\u003eguide to Eurocode 5 timber\ndesign\u003c\/a\u003e, our \u003ca href=\"\/pages\/services\"\u003estructural engineering support\u003c\/a\u003e, and the full\n\u003ca href=\"\/collections\/screws-for-timber\"\u003estructural timber screw range\u003c\/a\u003e.\u003c\/p\u003e\n\n\u003ch2\u003eCommon questions\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eDoes a larger diameter mean fewer fixings?\u003c\/strong\u003e\nRothoblaas's own worked example on the datasheet runs both diameters over the same roof:\nGL24h 120x160 joists at 0.70 m centres, 20 mm planking, 160 mm soft insulation at σ(10%)\n0.03 N\/mm², C24 60x40 battens, 30% pitch, 1.70 kN\/m² snow. It resolves to 324 screws at\nØ7 or 252 at Ø9. That is an illustration from one build-up, not a sizing rule. The number\nfor your roof is your engineer's.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eWhy does the ETA give two different fax,k values?\u003c\/strong\u003e\nBecause withdrawal depends on the timber. In solid timber, glulam, CLT and solid wood\npanel, fax,k is 11.7 N\/mm² at ρa 350 kg\/m³ with characteristic density up to 440 kg\/m³.\nIn non-pre-drilled LVL at ρa 500 kg\/m³ and characteristic density 410 to 550 kg\/m³ it\nrises to 15.0 N\/mm². Pre-drill the LVL and the higher figure no longer applies.\u003c\/p\u003e\n\n\u003cp\u003e\u003cem\u003ePrice shown is per box of 50 pieces. See the table below for codes, lengths and\npack prices.\u003c\/em\u003e\u003c\/p\u003e","brand":"Rothoblaas","offers":[{"title":"7 mm · min. batten 50\/30 mm \/ 220 mm","offer_id":54916833640790,"sku":"DGZ7220","price":57.6,"currency_code":"GBP","in_stock":true},{"title":"7 mm · min. batten 50\/30 mm \/ 260 mm","offer_id":54916833673558,"sku":"DGZ7260","price":76.0,"currency_code":"GBP","in_stock":true},{"title":"7 mm · min. batten 50\/30 mm \/ 300 mm","offer_id":54916833706326,"sku":"DGZ7300","price":84.54,"currency_code":"GBP","in_stock":true},{"title":"7 mm · min. batten 50\/30 mm \/ 340 mm","offer_id":54916833739094,"sku":"DGZ7340","price":98.14,"currency_code":"GBP","in_stock":true},{"title":"7 mm · min. batten 50\/30 mm \/ 380 mm","offer_id":54916833771862,"sku":"DGZ7380","price":110.94,"currency_code":"GBP","in_stock":true},{"title":"9 mm · min. batten 60\/40 mm \/ 240 mm","offer_id":54916833804630,"sku":"DGZ9240","price":88.26,"currency_code":"GBP","in_stock":true},{"title":"9 mm · min. batten 60\/40 mm \/ 280 mm","offer_id":54916833837398,"sku":"DGZ9280","price":112.26,"currency_code":"GBP","in_stock":true},{"title":"9 mm · min. batten 60\/40 mm \/ 320 mm","offer_id":54916833870166,"sku":"DGZ9320","price":122.4,"currency_code":"GBP","in_stock":true},{"title":"9 mm · min. batten 60\/40 mm \/ 360 mm","offer_id":54916833902934,"sku":"DGZ9360","price":141.6,"currency_code":"GBP","in_stock":true},{"title":"9 mm · min. batten 60\/40 mm \/ 400 mm","offer_id":54916833935702,"sku":"DGZ9400","price":163.47,"currency_code":"GBP","in_stock":true},{"title":"9 mm · min. batten 60\/40 mm \/ 440 mm","offer_id":54916833968470,"sku":"DGZ9440","price":203.46,"currency_code":"GBP","in_stock":true},{"title":"9 mm · min. batten 60\/40 mm \/ 480 mm","offer_id":54916834001238,"sku":"DGZ9480","price":244.0,"currency_code":"GBP","in_stock":true},{"title":"9 mm · min. batten 60\/40 mm \/ 520 mm","offer_id":54916834034006,"sku":"DGZ9520","price":278.4,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1025\/7383\/4582\/files\/DWZ_RP_42b2e7a8-298b-4412-b53d-e1ad4112a12d.jpg?v=1786179797","url":"https:\/\/timbasystems.com\/products\/insulation-screw-dgz","provider":"TimbA Systems","version":"1.0","type":"link"}