Metal roof butyl tape sealant is a non-curing, 100 percent solids gasket that only works under compression, and its position at a panel endlap is measured, not eyeballed. Metal Sales dimensions the endlap tape three inches down from the high side of the lower panel, adds a row above and below it, and drives the endlap screws through the middle row. Put the tape somewhere else and the lap leaks even though the butyl looks perfect from the ridge.
That is the practitioner gap in most sealant guides: they tell you butyl belongs in the lap and stop. Panel manufacturers publish exact dimensions, exact tape sizes, and exact fastener relationships, and those numbers differ by profile. Below is what four published installation manuals actually say, why the common field errors leak, and how to pick tape width, thickness, and install temperature for the joint in front of you.
Where butyl tape goes on a metal roof, joint by joint
Butyl tape belongs in every concealed metal-to-metal joint that gets squeezed by a fastener or a seam: panel endlaps, panel sidelaps, closure strips at ridge and eave, and trim laps. It does not belong anywhere sunlight touches it. McElroy Metal states that prolonged exposure to UV light degrades the sealant, so butyls are not intended for applications that leave the sealant exposed.
| Joint | Butyl form | Published detail |
|---|---|---|
| Exposed fastener panel endlap | Tape, 3/32 in. to 1/8 in. thick | Metal Sales: three rows, screws through the middle row |
| Exposed fastener panel sidelap | Single bead tape on the underlap rib | Metal Sales: stitch fastener 12 in. on center through the sealant and the underlap rib |
| Standing seam sidelap | Roll tape inside the seam leg | McElroy MasterLok-FS: 3/32 in. by 1 in. roll tape along the panel leg, eave to ridge |
| Standing seam endlap | Pre-cut roll tape plus a tube bead | McElroy MasterLok-FS: 1/8 in. by 1-1/2 in. tape, plus tube sealant 1 in. uphill of it |
| Ridge and eave closures | Tape top and bottom of the closure | McElroy: 1 in. butyl line above the fasteners, closure seated in it, second line on top |
| Trim and flashing laps | 3/32 in. by 3/8 in. butyl tape | McElroy: trim pieces lap 2 in., butyl in the lap, then pop rivet |
| Exposed trim joints and penetrations | Not butyl | Use a urethane, tripolymer, or hybrid rated for UV |
The closure joints are their own trap, because a foam or metal closure needs butyl on both faces to seal to the panel profile and to the trim above it. Our guide to foam closure strips for metal roofing covers inside versus outside closures and where each one lands.
Endlap placement: where the tape sits relative to the fastener line
At an endlap, the butyl band is positioned so the endlap fastener row passes through it, and manufacturers dimension that band from the upslope end of the lower panel rather than from the lap edge. Metal Sales measures three inches down from the high side of the lower panel. McElroy Metal measures 5-3/4 in. down from the end of the lower R-panel. Fabral places its endlap tape just below the centerline of the purlin.
| Manual | Panel | Minimum endlap | Tape size | Published position |
|---|---|---|---|---|
| Metal Sales PBR-Panel Installation Manual | PBR / R-panel | 6 in. | Single bead tape | Row 3 in. down from the high side of the lower panel, plus one row just above and one just below; fasteners driven through the middle row |
| Metal Sales Post Frame Installation Guide (7/24) | Post frame panels | 6 in. | Tape sealant, full panel width | About 3 in. from the panel end, across and over the ribs; fasteners must penetrate sealant |
| McElroy Metal Multi-Rib / R-Panel Manual (9/25) | Multi-Rib / R-panel | Lower panel extends 6 in. past the structural member web | 1 in. roll tape | Continuous run 5-3/4 in. down from the end of the lower panel |
| McElroy Metal MasterLok-FS Manual | Field seamed standing seam | Backup plate and cinch strap joint | 1/8 in. by 1-1/2 in. roll tape | Exactly 3 in. from the end of the panel, never past the notch; tube sealant about 1 in. uphill of the tape |
| Fabral Standard Details for Metal Roofing and Siding | StrongRib, GrandRib 3, 5V Crimp | 12 in. total lap | 3/32 in. by 1/2 in. butyl | Continuous bead on the lower panel just below the purlin centerline |
Two things fall out of that table. First, the tape is always on the lower (downslope) panel, laid before the upper panel drops on it, because the upper panel and the screws are what compress it. Second, the endlap has to land on structure. UL Construction No. 161, reproduced in the Metal Sales PBR manual for its Class 90 uplift rating, requires end laps to occur over purlins with panels overlapped a minimum of 4 in. and the lap centered over the purlin web.
The fastener pattern at the lap is not the field pattern either. Endlap rows are denser, and the screw count changes at the lap line. Our metal roofing screw pattern guide lays out the row-by-row spacing that the endlap tape has to line up with.
Why metal panel seams leak when the butyl is wrong
A leaking endlap almost never means the butyl failed chemically. Butyl does not cure, does not shrink, and stays flexible for the life of a concealed joint. The failures are geometric and procedural, and these eight cover most of them.
- The fastener row missed the tape. If the screws land uphill or downhill of the band instead of through it, every screw hole in the lower panel sits outside the gasket. Metal Sales and McElroy both state the fastener must penetrate the sealant.
- The tape was stretched off the roll. Mule-Hide’s product data sheet for Butyl Seal Tape says it plainly: apply without stretching the tape, allow tape to lay naturally, DO NOT STRETCH TAPE. Stretched butyl thins below its sealing thickness and slowly recovers, pulling back from the ends of the lap.
- One row where the manual calls for three. The PBR endlap detail is a three-row detail. A single row leaves the screw hole sealed but gives no redundancy if the row is off position.
- The tape was pressed too hard, not evenly. McElroy’s MasterLok-FS endlap note tells installers to press sealant into the corners of the panel configuration without excessive pressure. Crushing butyl out of the rib corners is the same defect as stretching it.
- Oil or dirt on the panel. McElroy’s general notes require sealant to be field applied on a clean, dry surface. American Buildings goes further on coated stock: all areas on aluminum coated panels that require mastic should be wiped clean with a mild all purpose detergent cleaner before mastic application.
- Installed below the tape’s application temperature. Butyl seals by wetting out the substrate on contact. Cold tape stays hard and bridges the rib profile instead of filling it.
- Tape run past a stop point. The MasterLok-FS manual warns not to position the tape strip past the panel notch. Tape in the wrong place can hold a seam open as easily as it can seal it.
- The endlap floats between purlins. Without structure under the lap, the panels flex apart under load and the compression that makes butyl work disappears.
Butyl tape width and thickness by application
Thickness governs how much irregularity the tape can fill; width governs how long the water path across the joint is. Published sizes cluster at 3/32 in. and 1/8 in. thick, in widths from 3/8 in. to 1-1/2 in. Marco Industries lists its Mastix butyl tape at 3/32 in. thick in 3/8, 1/2, 3/4, and 1 in. widths on 45 ft rolls, which is the standard shelf range.
| Size | Typical application | Source |
|---|---|---|
| 3/32 in. by 3/8 in. | Trim and flashing laps, riveted joints | McElroy Metal installation manuals |
| 3/32 in. by 1/2 in. | Exposed fastener panel endlaps | Fabral standard details |
| 3/32 in. by 1 in. | Standing seam legs, closures, R-panel endlaps | McElroy Metal installation manuals |
| 1/8 in. by 3/4 in. | General metal lap and repair tape | Mule-Hide Butyl Seal Tape, 50 ft rolls |
| 1/8 in. by 1-1/2 in. | Standing seam endlap over a backup plate | McElroy MasterLok-FS manual |
| 3/16 in. by 7/8 in. double bead | Bottom and sides of outside closures at the ridge | McElroy MasterLok-FS manual |
| 3/8 in. by 3/32 in. single bead, 50 ft | Catalog stock size for panel laps | Metal Sales post frame accessories |
Double bead tape exists for a reason: at ridge closures the tape has to seal a foam or metal closure to a ribbed panel below and a trim above, so the extra bulk fills the profile. The closure and cap assembly is detailed in our guide to the metal roof ridge cap.
Sidelap butyl: required below 3:12, recommended everywhere
Sidelap tape is a slope question. Metal Sales sets the minimum recommended slope for R and PBR panels at 1:12 and requires sidelap sealant and stitch screws below 3:12, while recommending sealant on sidelaps in all roof applications. The tape goes on the underlap rib of the panel already installed, and the stitch fastener goes through the tape at 12 in. on center.
Fabral takes the same line for its exposed fastener profiles: use sealant tape or butyl caulking at all sidelaps and endlaps, and use sealant tape in all sidelaps when weather-tightness is critical. On a low slope panel roof, water sits in the sidelap channel longer and moves up the lap under wind pressure, which is exactly the condition a compressed butyl bead is built for. Panel choice matters here too, since rib height and anti-siphon grooves change how much the lap relies on the tape. See our breakdown of R-panel roofing dimensions and gauge.
Temperature limits at install and in service
Application temperature and service temperature are different numbers, and only one of them is about the day you are on the roof. Tremco lists an application range of 20 to 120 degrees F for its 440 butyl tape and a service range of -40 to 158 degrees F. Mule-Hide lists a service range of -40 to 250 degrees F for its butyl seal tape. Fastener Systems advises installing between 40 and 100 degrees F.
| Product | Application temp | Service temp | Notes |
|---|---|---|---|
| Tremco 440 Tape | 20 to 120 degrees F | -40 to 158 degrees F | 100 percent solids polyisobutylene cross-linked butyl; meets AAMA 800-92 specifications 804.3 and 807.3; not for joints above 158 degrees F |
| Mule-Hide Butyl Seal Tape | Not published; instant tack, full cure in 24 hours | -40 to 250 degrees F | 100 percent solids, 54 percent elongation, no shrinkage |
| Marco Industries Mastix | Not published | Not published | Isobutylene and butyl mixture, flash point above 400 degrees F |
| Fastener Systems general guidance | 40 to 100 degrees F | Not stated | Below 40 degrees F the material stiffens and may not conform |
The 54 percent elongation figure on the Mule-Hide sheet is the one worth remembering on a cold morning. Butyl tape has real but limited stretch, and once you use it up pulling the roll tight along a rib, there is nothing left to accommodate the panel’s thermal movement across the joint.
Butyl vs silicone vs urethane for panel laps
Butyl, silicone, and urethane are not interchangeable at a metal panel lap. Butyl is the only one of the three designed to be squeezed between two sheets of steel and stay soft forever. Silicone and urethane are cure-in-place sealants for exposed joints where UV, movement, and appearance drive the choice.
| Chemistry | Right job on a metal roof | Behavior | Limit |
|---|---|---|---|
| Butyl tape | Concealed panel endlaps, sidelaps, closures, trim laps | Never cures, 100 percent solids, seals under compression | Degrades under prolonged UV; not for exposed joints |
| Butyl tube sealant | Voids around closures, panel notches, gaps tape cannot fill | Same chemistry, gunnable | Same UV limit as tape |
| Urethane or hybrid | Exposed trim joints, penetrations, color matched work | Cures, flexes, paintable, UV resistant | Needs a real joint, not a compressed lap |
| Silicone | Exposed penetrations and flashing where nothing will be coated later | Longest exposed UV life | Nothing bonds over cured silicone |
Titebond’s WeatherMaster metal roof sealant, one of the hybrids carried in exposed fastener installation manuals, publishes an application temperature above 0 degrees F and meets ASTM C920 Type S Grade NS Class 50, which is a movement class butyl tape does not attempt. Different job, different product. Our full comparison of metal roofing sealant types and where each one goes covers the chemistries side by side.
Panel profiles and warranty: when butyl is not optional
Every exposed fastener profile with a lapped endlap requires sealant somewhere in that lap, and manufacturers write it as a requirement, not a suggestion. Fabral states that all end laps require sealant. Metal Sales requires sidelap sealant and stitch screws below 3:12 slope. UL Class 90 uplift construction No. 161 assumes a lap centered over the purlin web.
On the warranty side, the relevant condition is usually procedural rather than product-specific. MBCI’s weathertightness warranty program, for example, requires a certified installer on the job with a photo identification card at all times and a minimum of three inspections by inspectors selected by the manufacturer, with any deficiencies corrected before the warranty is issued. Sealant placement at endlaps and closures is exactly what those inspections look at, and substituting an unapproved tape or skipping a specified row can be recorded as a deficiency. Requirements vary by manufacturer, warranty tier, and project, so confirm the sealant schedule against the shop drawings for your specific system before the first panel goes down.
How to install butyl tape at a metal panel endlap
The sequence below follows the published Metal Sales PBR endlap procedure, with the surface preparation step that most manuals put in their general notes. Do the whole lap on the ground plane of the lower panel before the upper panel is set, because once the top sheet is down you cannot correct tape position.
- Confirm the lap lands on structure. The endlap must sit over a purlin or a solid support, with the lap centered over the member. Do not lap panels in a bay.
- Clean and dry the lap area. Wipe mill oil, dust, and filings off the lower panel. On coated aluminum, wash with a mild all purpose detergent cleaner as American Buildings specifies, then let it dry.
- Mark the tape line. Measure down from the high side of the lower panel to the dimension in your manufacturer’s manual: three inches for Metal Sales PBR, 5-3/4 in. for McElroy Multi-Rib and R-panel.
- Lay the first row without tension. Roll the tape out along the mark, across the flats and over the ribs, letting it lay naturally. Do not pull the roll tight. Press it into the rib corners with even hand pressure, then peel the release paper.
- Add the rows above and below. The PBR detail calls for a second and third row immediately above and below the first, so the screw row lands in the middle band.
- Set the upper panel with the specified lap. Six inches minimum for Metal Sales PBR and post frame panels, twelve inches total lap on the Fabral profiles.
- Drive the endlap fasteners through the tape. Use the endlap pattern, not the field pattern, and confirm each fastener penetrates the sealant and reaches the structure below.
- Check the ends of the lap. Butyl should be visible and slightly squeezed out at the panel edges. A clean, un-extruded line usually means the joint never reached compression.
- Clean up squeeze-out and debris. Metal Sales instructs installers to clear excess sealant and debris before moving on, because trapped butyl under the next panel throws the sidelap out of plane.
One practical note on sidelaps in the same run: the sidelap tape has to marry into the endlap tape so the sealed perimeter is continuous. Fabral’s installation sequence has the installer connect sidelap sealant to endlap sealant on every panel before the next one goes down, which is why the panel order in that manual is numbered rather than left to the crew.
Frequently asked questions
Which side of the fastener line does butyl tape go on at a metal roof endlap?
Manufacturers place butyl so the endlap fastener row passes through it, with tape also sitting uphill of the screws. Metal Sales calls for three rows on the PBR panel endlap, measured three inches down from the high side of the lower panel, and instructs installers to drive the screws through the middle row so the compressed tape gaskets every shank.
What size butyl tape do I need for metal roofing?
Size follows the joint, not the roll on the truck. McElroy Metal specifies 3/32 in. by 3/8 in. butyl in trim laps, 1 in. roll tape at R-panel endlaps and standing seam sidelaps, 3/16 in. by 7/8 in. double bead under outside closures, and 1/8 in. by 1-1/2 in. at MasterLok-FS panel endlaps. Fabral specifies 3/32 in. by 1/2 in. at exposed fastener endlaps.
Can you install butyl tape in cold weather?
It depends on the product, so read the data sheet. Tremco lists an application temperature of 20 to 120 degrees F for its 440 butyl tape, while Fastener Systems advises installing between 40 and 100 degrees F because the material stiffens and stops conforming below 40. Cold butyl still bonds eventually, but it will not wet out the panel rib on contact.
Do the screws go through the butyl tape?
At exposed fastener endlaps, yes. Metal Sales states that fasteners must penetrate the sealant at post frame panel endlaps, and its PBR instructions put the fastener through the middle of three tape rows. McElroy Metal repeats the same instruction at closures: make sure the fastener penetrates sealant. The screw compresses butyl around its own shank, which is the point.
Is butyl tape better than silicone for a metal roof?
For concealed panel laps, yes. Butyl is a 100 percent solids gasket that never cures and seals under compression, which is what a lap joint needs. McElroy Metal notes that prolonged UV exposure degrades butyl, so it is not intended for joints left exposed. Exposed trim joints and penetrations call for a urethane, tripolymer, or hybrid instead.
Why is my metal roof endlap leaking even though I used butyl tape?
The three usual causes are position, stretch, and compression. If the fastener row missed the tape, every screw hole in the lower panel sits outside the gasket. If the tape was pulled tight off the roll it thins and recovers, opening the ends of the lap. If the panel was oily or below the tape’s application temperature, it never wet out.
Does butyl tape work on a standing seam sidelap?
Standing seam systems seal the sidelap inside the seam itself. McElroy runs 3/32 in. by 1 in. roll tape sealant along the panel leg from eave to ridge before seaming. American Buildings specifies its SSCK-1 butyl lap caulk on the inner face of both male and female seams. Field applied butyl on top of a finished seam is not a substitute.
Written by The Roofing Brief Team. Last reviewed: August 2026.
Sources: Metal Sales PBR-Panel Installation Manual and Post Frame Installation Guide (7/24); McElroy Metal Multi-Rib / R-Panel Installation Manual (9/25) and MasterLok-FS Installation Manual; Fabral Standard Details for Metal Roofing and Siding; American Buildings Standing Seam II product manual; Tremco 440 Tape product data sheet; Mule-Hide Butyl Seal Tape PDS 09-6750; Marco Industries Mastix butyl tape specifications; McElroy Metal published guidance on metal roofing sealants; MBCI Weathertightness Warranties brochure; UL Construction No. 161.