Both do the same job: they lift the roof sheet off the purlin so the blanket keeps its thickness. What decides a job is pitch, height and paperwork. Bradford Ashgrid is limited to roofs of 10 degrees or less and comes in five heights up to 150 mm. Roof Razor works up to 30 degrees in three heights up to 115 mm. Check the pitch first, then the blanket.
In short
- Pitch settles a lot of jobs on its own. Ashgrid stops at 10 degrees. Roof Razor goes to 30.
- Ashgrid comes in 60, 80, 110, 120 and 150 mm for blanket from 80 to 175 mm. Roof Razor comes in 60, 85 and 115 mm for blanket from 75 to 145 mm.
- For 175 mm blanket only Ashgrid lists a height. Neither lists one for 55 or 60 mm blanket.
- Both need at least a 1.2 mm BMT purlin, or 1.5 mm for the cyclonic versions.
- A pack of Ashgrid covers 14.4 lineal metres of purlin. A pack of Roof Razor covers 7.2.
What both of them do
A roof spacer screws down to the purlin and holds the roof sheet a set height above it. Without one, the sheet clamps the roofing blanket flat at every purlin, and the blanket only reaches its rated thickness in the gaps between. Both manufacturers describe their product in the same terms: it lets the blanket keep its position and its full nominal thickness, which is what the NCC asks of roof insulation.
They also go on in the same order. Safety mesh and blanket are laid first, the spacer is fixed through the blanket to the purlin, and the roof sheet is fixed to the spacer. Why spacers matter, and how they work with mesh, is covered in our guide to stopping insulation sag under a metal roof. This article is only about choosing between the two systems we stock.
Side by side
Everything below comes from the two manufacturers' own documents: Bradford's Product Technical Statement for Ashgrid and Fletcher's technical data sheet for Roof Razor.
| Bradford Ashgrid | Roof Razor | |
|---|---|---|
| Made by | CSR Bradford | Fletcher Insulation |
| How it comes | 1200 mm bars with brackets, 12 bars per pack | 1200 mm spacers, 6 per pack |
| Lineal metres per pack | 14.4 m | 7.2 m |
| Heights | 60, 80, 110, 120 and 150 mm | 60, 85 and 115 mm |
| Blanket thickness covered | 80 to 175 mm | 75 to 145 mm |
| Maximum roof pitch | 10 degrees | 30 degrees |
| Screws | Pre-loaded in the brackets | Six pre-loaded, at 38 mm centres |
| Minimum purlin | 1.2 mm BMT, 1.5 mm cyclonic. Bearing area at least the size of the bracket | 1.2 mm BMT, 1.5 mm cyclonic. A full 50 mm flat surface |
| Cyclonic version | Four brackets per bar instead of two, plus a ridge strap | Extra batten insert and heavier screws, for wind regions C and D |
| Timber | Load tables for timber purlins on request | A version without pre-loaded screws for timber battens, 85 and 115 mm |
| Steel | Bar 1.25 mm BMT, bracket 1.6 mm BMT, EPDM pad under the bracket foot | 1.15 mm BMT G550, Z275 coating |
| Weight | 1.21 to 1.34 kg per lineal metre, cyclonic 1.40 to 1.47 | 2 kg per spacer, cyclonic 3 kg |
| Structural data published | Wind load table in kPa by purlin spacing and bracket centres | Dead load of 205 kg between the legs, and the screw capacity the roof sheet fixings need |
BMT is base metal thickness, the steel without its coating.
Roof pitch comes first
Start here, because it can rule one system out before anything else is looked at. Bradford's statement sets a maximum roof pitch of 10 degrees for Ashgrid, and its load table is only valid up to that pitch. Fletcher rates Roof Razor for pitches up to and including 30 degrees.
Under 10 degrees, both are available. Over it, only Roof Razor is. A shed, carport or skillion pitched at 15 degrees sits outside the Ashgrid statement and inside the Roof Razor sheet. There is no site fix for that. Bradford's document says the product must not be modified, and that compliance only holds for the product and configuration it lists.
Ashgrid also has rules about the shape of the roof:
- It can only go on roofs pitching in a single plane, unless the project's structural engineer assesses and approves it.
- The long leg of each bar faces up the slope, towards the ridge.
- A 50 x 1 mm galvanised mild steel securing strap goes over the ridge line. The cyclonic version needs it at every pitch. The non-cyclonic version needs it between 5 and 10 degrees.
- Gables with unequal spans, and monoslope roofs, need site specific details from the engineer.
Matching the height to the blanket
Both manufacturers pick the spacer height from the blanket thickness, not from the roof. Ashgrid has five heights and Roof Razor has three. Put against the blanket thicknesses each one lists, they line up like this:
| Blanket thickness | Ashgrid height | Roof Razor height |
|---|---|---|
| 55 or 60 mm | Not listed | Not listed |
| 75 mm | Not listed | 60 mm |
| 80 mm | 60 mm | 60 mm |
| 100 or 110 mm | 80 mm | 85 mm |
| 120 mm | Not listed | 85 mm |
| 130 mm | 110 mm | 115 mm |
| 140 or 145 mm | 120 mm | 115 mm |
| 175 mm | 150 mm | Not listed |
Ashgrid's steps are not arbitrary. Every blanket thickness on Bradford's list, 80, 100, 110, 130, 140, 145 and 175 mm, is a thickness in its own Anticon Medium Duty range, which we stock. Roof Razor works the other way, with one height per band of thickness. EcoRoof at 75, 100 and 130 mm falls into those bands at 60, 85 and 115 mm.
Two gaps are worth knowing before the order goes in. For 175 mm blanket, which is R4.2 in the Anticon range, only Ashgrid lists a height. And neither manufacturer lists a height for the thinnest blankets, 55 or 60 mm. If that is your build-up, ask the manufacturer rather than guess. If you are still choosing the blanket itself, roofing blanket R-values works through it.
What the purlin has to give you
Both spacers screw into the purlin, so the purlin sets the limits.
Roof Razor needs a full 50 mm flat surface on top of the purlin, and Fletcher tells you to check the purlin maker's dimensions to be sure it is there. The minimum purlin is 1.2 mm BMT for the standard spacer and 1.5 mm for the cyclonic one.
Ashgrid needs a purlin bearing area no smaller than its bracket, with the screws landing on a flat part of the flange rather than on the radius. The minimum purlin is again 1.2 mm BMT, or 1.5 mm for the cyclonic version.
Bradford's statement is explicit about what it leaves to the engineer. Purlin design is the project structural engineer's job. The purlin and roof sheet capacities have not been assessed, no testing has been done on purlin restraint or rollover, and the mass of the Ashgrid should be added to the engineer's load calculations. Fletcher's sheet says Roof Razor is structurally engineered and certified, and sends load bearing questions to its technical team. On a commercial job your engineer will want those answers in writing either way.
Wind regions and the cyclonic versions
The two makers handle wind differently, and it changes how you order.
Roof Razor is sold by wind region. The standard spacer covers regions A and B. The cyclonic spacer covers C and D, and comes with an extra batten insert, 14 gauge 10 TPI screws and a 1.5 mm BMT minimum purlin. Fletcher also states the yield capacity the roof sheet screws need: 0.583 kN per 12 gauge 14 TPI screw on the standard spacer, and 1.43 kN per 14 gauge 10 TPI screw on the cyclonic one. Those sheet screws are not supplied.
Ashgrid is checked against a load table. Bradford publishes wind capacities in kPa, for downward load and for uplift, at purlin spacings from 0.6 to 1.5 m and bracket centres of 0.3 or 0.6 m. The non-cyclonic bar carries two brackets per 1200 mm and the cyclonic bar four. For cyclonic applications the four bracket version is the one that must be used. Your engineer compares those figures with the design wind pressure for the site.
Both cyclonic versions have been through low-high-low pressure testing. Whichever you choose, the wind classification on the drawings decides the version, not a guess about where the building is.
Where each one stops
Bradford's statement lists these limits for Ashgrid:
- Not under tiled roofs, and not on walls.
- Not with curved profile cladding in light gauge or soft material that could crush under an over-tightened screw.
- Installed dry, and it has to stay dry once the roof is on.
- Not for harsh environments such as livestock buildings, indoor aquatic centres or fertiliser storage without written approval from Bradford.
- Not designed for seismic actions.
- A bracket has to sit within 100 mm of the end of every bar, which means an extra bracket on the last bar in each row.
- Cut edges need a galvanising treatment.
- Loads on the roof, during and after construction, should be spread evenly, because the bar has a narrower contact area with the sheet than a wider spacer would. This is about protecting the cladding.
Fletcher's sheet for Roof Razor is shorter. It is designed for metal purlins, it suits both pierced and concealed fix cladding, and for timber battens or trusses Fletcher asks for a structural engineer at design stage. The timber version comes without pre-loaded screws, and Fletcher recommends screws 62 mm long plus the penetration depth for the 85 mm spacer, and 92 mm plus the penetration depth for the 115 mm.
A shorter list does not mean the conditions Bradford names never matter for Roof Razor. Fletcher's sheet simply does not cover them. For a livestock shed, a pool hall or a fertiliser store, ask Fletcher before you specify.
What the certifier will want to see
On a commercial roof the spacer is part of how the insulation meets Section J, so the building surveyor may ask for the evidence.
Bradford publishes a Product Technical Statement for Ashgrid, reference PTS046, issue B. It cites NCC 2022 clause by clause: J4D3(3)(a) for the insulation keeping its thickness, 13.2.2 of the Housing Provisions for the residential equivalent, B1D4(c)(ii) for the steel, and Specification 4 of Volume One for the cyclonic low-high-low testing. It names an engineering report by Cardno as the evidence of suitability.
Fletcher's technical data sheet for Roof Razor is revision 8, issued in July 2022. It states compliance with Section J clause J1.2(c), and low-high-low testing of the cyclonic version under Specification B1.2. Those are NCC 2019 clause numbers, because the sheet was issued before NCC 2022. The requirement they point to is the same one. If your surveyor wants NCC 2022 references on the file, ask Fletcher for its current documentation.
Working out quantities
Both are 1200 mm long and run along the purlins, so the order starts from the total length of purlin under the blanket. Add up every purlin run on the roof, then divide:
- Ashgrid: 14.4 lineal metres per pack of 12 bars.
- Roof Razor: 7.2 lineal metres per pack of 6 spacers.
On a roof with 600 lineal metres of purlin, that is 42 packs of Ashgrid or 84 packs of Roof Razor. For Ashgrid, allow for the extra bracket on the last bar of every row. For either, allow for cuts at the ends of runs.
The blanket, mesh and spacers all go on in the same sheeting window, so it pays to order them together. Installing a roofing blanket covers the sequence on the roof.
Which one for your roof
Work through it in this order.
- Pitch over 10 degrees: Roof Razor. Ashgrid is outside its statement.
- Blanket at 175 mm: Ashgrid at 150 mm. Roof Razor's list stops at 145 mm blanket.
- Blanket at 75 or 120 mm: Roof Razor. Ashgrid's list does not include those thicknesses.
- The engineer wants a kPa load table: Ashgrid publishes one. For Roof Razor, ask Fletcher's technical team.
- Timber battens: Roof Razor has a version for them. Ashgrid on timber purlins needs project specific load tables from Bradford.
- The drawings already name a spacer: follow the drawings. Swapping one for the other changes what the engineer assumed, so the change goes back to the engineer, not the roofer.
If none of those settles it, look at the rest of the roof. Ashgrid lines up with Bradford's Anticon thicknesses, and Roof Razor's heights were chosen around Fletcher's blankets. Either works with other blankets inside its listed thicknesses.
We supply the package, your roofer lays the blanket
AWBM supplies Ashgrid, Roof Razor, roofing blanket and safety mesh across Victoria and New South Wales. Spacers and blanket go on with the sheeting, so they are supply items and your roofer fits them. What we install is batts, wall wrap and sarking. Send the purlin layout, the roof pitch, the blanket and the wind region, and we will match the spacer, work out the packs and price the lot. Delivery is $55 in metro Melbourne and metro Sydney, $99 in the outer suburbs and $149 anywhere else in Victoria and New South Wales, set by postcode.
Or browse roofing blankets, roofing and safety mesh and accessories.
Frequently asked questions
What is the difference between Ashgrid and Roof Razor?
Both lift the roof sheet off the purlin so the blanket keeps its thickness. Bradford Ashgrid is limited to roofs of 10 degrees or less and comes in five heights from 60 to 150 mm. Fletcher's Roof Razor works on roofs up to 30 degrees and comes in three heights from 60 to 115 mm.
Can Ashgrid be used on a roof steeper than 10 degrees?
No. Bradford's technical statement sets a maximum roof pitch of 10 degrees, and its load table is only valid to that pitch. Roof Razor is rated for pitches up to and including 30 degrees.
What height Ashgrid do I need for 100 mm blanket?
The 80 mm, which Bradford lists for 100 and 110 mm blanket. The 60 mm suits 80 mm blanket, the 110 mm suits 130 mm, the 120 mm suits 140 and 145 mm, and the 150 mm suits 175 mm.
What height Roof Razor do I need for 100 mm blanket?
The 85 mm, which Fletcher lists for 100 to 120 mm blanket. The 60 mm suits 75 to 80 mm blanket and the 115 mm suits 130 to 145 mm.
Which spacer suits 175 mm roofing blanket?
Ashgrid at 150 mm. The tallest Roof Razor, 115 mm, is listed for blanket up to 145 mm thick.
Does Ashgrid need a strap over the ridge?
The cyclonic version does, at every pitch. The non-cyclonic version needs it on roofs pitched between 5 and 10 degrees. It is a 50 x 1 mm galvanised mild steel strap over the ridge line.
What purlin do Ashgrid and Roof Razor need?
Both need at least 1.2 mm BMT, or 1.5 mm for their cyclonic versions. Roof Razor also needs a full 50 mm flat surface on the purlin. Ashgrid needs a bearing area no smaller than its bracket, with the screws landing on a flat part rather than the radius.
Can either spacer be fixed to timber?
Roof Razor comes in a version without pre-loaded screws for timber battens, in 85 and 115 mm, and Fletcher asks for a structural engineer at design stage for timber. Bradford provides Ashgrid load tables for timber purlins after reviewing the project.
How many packs of spacers do I need?
Add up the length of every purlin under the blanket. A pack of Ashgrid covers 14.4 lineal metres and a pack of Roof Razor covers 7.2, so 600 metres of purlin takes 42 packs of Ashgrid or 84 packs of Roof Razor.
Sources
- CSR Bradford, Ashgrid Spacer, Product Technical Statement PTS046, issue B, for the heights, blanket thicknesses, pitch limit, installation rules, load table, materials and NCC references
- Fletcher Insulation, Roof Razor technical data sheet, revision 8, issued 5 July 2022, for the heights, blanket thicknesses, pitch limit, purlin requirements, wind regions, screws and physical properties
- Blanket thicknesses and R-values from the AWBM catalogue for Bradford Anticon Medium Duty and EcoRoof, taken from the manufacturers' product data
General information from the manufacturers' documents, current at September 2026. On a commercial roof the spacer is part of the structural and Section J design, so the project engineer's specification takes priority over anything here. Manufacturers change specifications, so check the current documents before you order.