§ 16

Covering: strips and rolls for edge coverage

How many rolls does it take to cover along the edge?

Answer: Along a crown of wall, a stern or a façade, roof felt must be led up in an edge covering. The edge covering height above finished roof surface is as main rule at least 150 mm and is normally done in two layers with under- and over-strip. The calculator works out strip width (up the edge, onto the roof surface and over the top), how many strips you can cut from one roll across and how many rolls go to the whole edge per layer when strips overlap.

Formula

Strimmelbredde = højde + ind på tagfladen + over toppen

Strimlerne skæres på tværs af rullen, så hver strimmel er rullebredden lang. Strimler af én rulle = nedrund(rullelængde ÷ strimmelbredde)

Hver strimmel dækker rullebredde − overlæg langs opkanten. Strimler pr. lag = oprund(opkantens længde ÷ (rullebredde − overlæg))

Ruller pr. lag = oprund(strimler pr. lag ÷ strimler af én rulle)

PTM guideline: underlap heights generally at least 150 mm (can be reduced with slope at least 1:5 away from or parallel to the underlap), welded overlap at least 80 mm, with mechanically fastened felt at least 100 mm

Symbols and units in the formula
Symbol	Meaning	Unit
laengde	Top edge length	m
hoejde	Coverage height above finished roof surface	mm
ind_paa_tag	Onto the roof surface	mm
top	Over the top / under the underlap profile	mm
rulle_l	Roller length	m
rulle_b	Coil width	m
overlaeg	Overlap between the strips	mm
=	Rollers per layer	ruller
=	Strip width	mm
=	Strips per layer	stk
=	Strips from one roll	stk
=	Coverage area per layer	m²

Validity and source

Source: PTM guideline 8 Roof Details (5th edition 2023): underlap height min. 150 mm, welded overlap min. 80 mm

Does not apply when

Calculate under and over strip each separately: they are two different products (under strip at least same quality as underlay over strip as overlay) and under strip is often narrower. Corners skylights and hoods need extra pieces not included here.

Worked example

The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.

Substituted

Top edge length24 m
Coverage height above finished roof surface150 mm
Onto the roof surface150 mm
Over the top / under the underlap profile100 mm
Roller length5 m
Coil width1 m
Overlap between the strips100 mm

Giver

Rollers per layer3 ruller
Strip width400 mm
Strips per layer27 stk
Strips from one roll12 stk
Coverage area per layer9.6 m²

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Sådan bruger du den

Opkanter langs mure, sterne og facader skal have inddækning, og strimlerne skæres af ruller. Beregneren giver strimmelbredden, hvor mange strimler en rulle giver, og hvor mange ruller der går pr. lag. PTM-anvisningen kræver som hovedregel mindst 150 mm inddækningshøjde over færdig tagflade.

Step by step

Mål opkantens længde og den højde, inddækningen skal op.
Bestem hvor langt strimlen føres ind på tagfladen og over toppen eller under profilet.
Skriv rullens mål og overlægget mellem strimlerne, mindst 80 mm ved svejsning.
Regn under- og overstrimlen hver for sig, fordi de er forskellige produkter.

Typical errors

At glemme overlægget mellem strimlerne. Så mangler du ca. 10 %.
At måle inddækningshøjden fra den rå konstruktion i stedet for den færdige tagflade.
At bruge samme rulle til under- og overstrimmel. De skal have samme kvalitet som henholdsvis underpap og overpap.

Examples from everyday life

Murkrone langs et fladt tag

En opkant er 24 m lang. Inddækningen skal 150 mm op, 150 mm ind på tagfladen og 100 mm over murkronen. Rullerne er 1 × 5 m, og du bruger 100 mm overlæg.

Top edge length: 24 m
Coverage height above finished roof surface: 150 mm
Onto the roof surface: 150 mm
Over the top / under the underlap profile: 100 mm
Roller length: 5 m
Coil width: 1 m
Overlap between the strips: 100 mm

It means: Strimlerne bliver 400 mm brede, og en rulle giver 12 pcs. Du skal bruge 27 pcs og dermed 3 rolls pr. lag. Inddækningen dækker 9.6 m² pr. lag.

Høj facadeopkant ved tagterrasse

Langs en facade på 36 m skal inddækningen 300 mm op, 150 mm ind og 150 mm under facadeprofilet. Rullerne er 7,5 m.

Top edge length: 36 m
Coverage height above finished roof surface: 300 mm
Onto the roof surface: 150 mm
Over the top / under the underlap profile: 150 mm
Roller length: 7.5 m
Coil width: 1 m
Overlap between the strips: 100 mm

It means: Strimlerne er 600 mm brede, en rulle giver 12 pcs, og du skal bruge 40 pcs, altså 4 rolls pr. lag.

Rule of thumb

Med 400 mm strimler giver en 5 m rulle 12 strimler, nok til ca. 10 m opkant pr. lag.

How to check the answer

Strimler af én rulle gange strimmelbredden må ikke være mere end rullens længde: 12 × 400 mm = 4,8 m.